Merge pull request #309 from cookiee339/feat/kotlin-ecosystem

feat(kotlin): add Kotlin/Ktor/Exposed ecosystem

.cursor/rules/kotlin-coding-style.md

@@ -0,0 +1,39 @@
+---
+description: "Kotlin coding style extending common rules"
+globs: ["**/*.kt", "**/*.kts", "**/build.gradle.kts"]
+alwaysApply: false
+---
+# Kotlin Coding Style
+
+> This file extends the common coding style rule with Kotlin-specific content.
+
+## Formatting
+
+- Auto-formatting via **ktfmt** or **ktlint** (configured in `kotlin-hooks.md`)
+- Use trailing commas in multiline declarations
+
+## Immutability
+
+The global immutability requirement is enforced in the common coding style rule.
+For Kotlin specifically:
+
+- Prefer `val` over `var`
+- Use immutable collection types (`List`, `Map`, `Set`)
+- Use `data class` with `copy()` for immutable updates
+
+## Null Safety
+
+- Avoid `!!` -- use `?.`, `?:`, `require`, or `checkNotNull`
+- Handle platform types explicitly at Java interop boundaries
+
+## Expression Bodies
+
+Prefer expression bodies for single-expression functions:
+
+```kotlin
+fun isAdult(age: Int): Boolean = age >= 18
+```
+
+## Reference
+
+See skill: `kotlin-patterns` for comprehensive Kotlin idioms and patterns.

.cursor/rules/kotlin-hooks.md

@@ -0,0 +1,16 @@
+---
+description: "Kotlin hooks extending common rules"
+globs: ["**/*.kt", "**/*.kts", "**/build.gradle.kts"]
+alwaysApply: false
+---
+# Kotlin Hooks
+
+> This file extends the common hooks rule with Kotlin-specific content.
+
+## PostToolUse Hooks
+
+Configure in `~/.claude/settings.json`:
+
+- **ktfmt/ktlint**: Auto-format `.kt` and `.kts` files after edit
+- **detekt**: Run static analysis after editing Kotlin files
+- **./gradlew build**: Verify compilation after changes

.cursor/rules/kotlin-patterns.md

@@ -0,0 +1,50 @@
+---
+description: "Kotlin patterns extending common rules"
+globs: ["**/*.kt", "**/*.kts", "**/build.gradle.kts"]
+alwaysApply: false
+---
+# Kotlin Patterns
+
+> This file extends the common patterns rule with Kotlin-specific content.
+
+## Sealed Classes
+
+Use sealed classes/interfaces for exhaustive type hierarchies:
+
+```kotlin
+sealed class Result<out T> {
+    data class Success<T>(val data: T) : Result<T>()
+    data class Failure(val error: AppError) : Result<Nothing>()
+}
+```
+
+## Extension Functions
+
+Add behavior without inheritance, scoped to where they're used:
+
+```kotlin
+fun String.toSlug(): String =
+    lowercase().replace(Regex("[^a-z0-9\\s-]"), "").replace(Regex("\\s+"), "-")
+```
+
+## Scope Functions
+
+- `let`: Transform nullable or scoped result
+- `apply`: Configure an object
+- `also`: Side effects
+- Avoid nesting scope functions
+
+## Dependency Injection
+
+Use Koin for DI in Ktor projects:
+
+```kotlin
+val appModule = module {
+    single<UserRepository> { ExposedUserRepository(get()) }
+    single { UserService(get()) }
+}
+```
+
+## Reference
+
+See skill: `kotlin-patterns` for comprehensive Kotlin patterns including coroutines, DSL builders, and delegation.

.cursor/rules/kotlin-security.md

@@ -0,0 +1,58 @@
+---
+description: "Kotlin security extending common rules"
+globs: ["**/*.kt", "**/*.kts", "**/build.gradle.kts"]
+alwaysApply: false
+---
+# Kotlin Security
+
+> This file extends the common security rule with Kotlin-specific content.
+
+## Secret Management
+
+```kotlin
+val apiKey = System.getenv("API_KEY")
+    ?: throw IllegalStateException("API_KEY not configured")
+```
+
+## SQL Injection Prevention
+
+Always use Exposed's parameterized queries:
+
+```kotlin
+// Good: Parameterized via Exposed DSL
+UsersTable.selectAll().where { UsersTable.email eq email }
+
+// Bad: String interpolation in raw SQL
+exec("SELECT * FROM users WHERE email = '$email'")
+```
+
+## Authentication
+
+Use Ktor's Auth plugin with JWT:
+
+```kotlin
+install(Authentication) {
+    jwt("jwt") {
+        verifier(
+            JWT.require(Algorithm.HMAC256(secret))
+                .withAudience(audience)
+                .withIssuer(issuer)
+                .build()
+        )
+        validate { credential ->
+            val payload = credential.payload
+            if (payload.audience.contains(audience) &&
+                payload.issuer == issuer &&
+                payload.subject != null) {
+                JWTPrincipal(payload)
+            } else {
+                null
+            }
+        }
+    }
+}
+```
+
+## Null Safety as Security
+
+Kotlin's type system prevents null-related vulnerabilities -- avoid `!!` to maintain this guarantee.

.cursor/rules/kotlin-testing.md

@@ -0,0 +1,38 @@
+---
+description: "Kotlin testing extending common rules"
+globs: ["**/*.kt", "**/*.kts", "**/build.gradle.kts"]
+alwaysApply: false
+---
+# Kotlin Testing
+
+> This file extends the common testing rule with Kotlin-specific content.
+
+## Framework
+
+Use **Kotest** with spec styles (StringSpec, FunSpec, BehaviorSpec) and **MockK** for mocking.
+
+## Coroutine Testing
+
+Use `runTest` from `kotlinx-coroutines-test`:
+
+```kotlin
+test("async operation completes") {
+    runTest {
+        val result = service.fetchData()
+        result.shouldNotBeEmpty()
+    }
+}
+```
+
+## Coverage
+
+Use **Kover** for coverage reporting:
+
+```bash
+./gradlew koverHtmlReport
+./gradlew koverVerify
+```
+
+## Reference
+
+See skill: `kotlin-testing` for detailed Kotest patterns, MockK usage, and property-based testing.

agents/kotlin-build-resolver.md

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+---
+name: kotlin-build-resolver
+description: Kotlin/Gradle build, compilation, and dependency error resolution specialist. Fixes build errors, Kotlin compiler errors, and Gradle issues with minimal changes. Use when Kotlin builds fail.
+tools: ["Read", "Write", "Edit", "Bash", "Grep", "Glob"]
+model: sonnet
+---
+
+# Kotlin Build Error Resolver
+
+You are an expert Kotlin/Gradle build error resolution specialist. Your mission is to fix Kotlin build errors, Gradle configuration issues, and dependency resolution failures with **minimal, surgical changes**.
+
+## Core Responsibilities
+
+1. Diagnose Kotlin compilation errors
+2. Fix Gradle build configuration issues
+3. Resolve dependency conflicts and version mismatches
+4. Handle Kotlin compiler errors and warnings
+5. Fix detekt and ktlint violations
+
+## Diagnostic Commands
+
+Run these in order:
+
+```bash
+./gradlew build 2>&1
+./gradlew detekt 2>&1 || echo "detekt not configured"
+./gradlew ktlintCheck 2>&1 || echo "ktlint not configured"
+./gradlew dependencies --configuration runtimeClasspath 2>&1 | head -100
+```
+
+## Resolution Workflow
+
+```text
+1. ./gradlew build        -> Parse error message
+2. Read affected file     -> Understand context
+3. Apply minimal fix      -> Only what's needed
+4. ./gradlew build        -> Verify fix
+5. ./gradlew test         -> Ensure nothing broke
+```
+
+## Common Fix Patterns
+
+| Error | Cause | Fix |
+|-------|-------|-----|
+| `Unresolved reference: X` | Missing import, typo, missing dependency | Add import or dependency |
+| `Type mismatch: Required X, Found Y` | Wrong type, missing conversion | Add conversion or fix type |
+| `None of the following candidates is applicable` | Wrong overload, wrong argument types | Fix argument types or add explicit cast |
+| `Smart cast impossible` | Mutable property or concurrent access | Use local `val` copy or `let` |
+| `'when' expression must be exhaustive` | Missing branch in sealed class `when` | Add missing branches or `else` |
+| `Suspend function can only be called from coroutine` | Missing `suspend` or coroutine scope | Add `suspend` modifier or launch coroutine |
+| `Cannot access 'X': it is internal in 'Y'` | Visibility issue | Change visibility or use public API |
+| `Conflicting declarations` | Duplicate definitions | Remove duplicate or rename |
+| `Could not resolve: group:artifact:version` | Missing repository or wrong version | Add repository or fix version |
+| `Execution failed for task ':detekt'` | Code style violations | Fix detekt findings |
+
+## Gradle Troubleshooting
+
+```bash
+# Check dependency tree for conflicts
+./gradlew dependencies --configuration runtimeClasspath
+
+# Force refresh dependencies
+./gradlew build --refresh-dependencies
+
+# Clear project-local Gradle build cache
+./gradlew clean && rm -rf .gradle/build-cache/
+
+# Check Gradle version compatibility
+./gradlew --version
+
+# Run with debug output
+./gradlew build --debug 2>&1 | tail -50
+
+# Check for dependency conflicts
+./gradlew dependencyInsight --dependency <name> --configuration runtimeClasspath
+```
+
+## Kotlin Compiler Flags
+
+```kotlin
+// build.gradle.kts - Common compiler options
+kotlin {
+    compilerOptions {
+        freeCompilerArgs.add("-Xjsr305=strict") // Strict Java null safety
+        allWarningsAsErrors = true
+    }
+}
+```
+
+## Key Principles
+
+- **Surgical fixes only** -- don't refactor, just fix the error
+- **Never** suppress warnings without explicit approval
+- **Never** change function signatures unless necessary
+- **Always** run `./gradlew build` after each fix to verify
+- Fix root cause over suppressing symptoms
+- Prefer adding missing imports over wildcard imports
+
+## Stop Conditions
+
+Stop and report if:
+- Same error persists after 3 fix attempts
+- Fix introduces more errors than it resolves
+- Error requires architectural changes beyond scope
+- Missing external dependencies that need user decision
+
+## Output Format
+
+```text
+[FIXED] src/main/kotlin/com/example/service/UserService.kt:42
+Error: Unresolved reference: UserRepository
+Fix: Added import com.example.repository.UserRepository
+Remaining errors: 2
+```
+
+Final: `Build Status: SUCCESS/FAILED | Errors Fixed: N | Files Modified: list`
+
+For detailed Kotlin patterns and code examples, see `skill: kotlin-patterns`.

commands/kotlin-build.md

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+---
+description: Fix Kotlin/Gradle build errors, compiler warnings, and dependency issues incrementally. Invokes the kotlin-build-resolver agent for minimal, surgical fixes.
+---
+
+# Kotlin Build and Fix
+
+This command invokes the **kotlin-build-resolver** agent to incrementally fix Kotlin build errors with minimal changes.
+
+## What This Command Does
+
+1. **Run Diagnostics**: Execute `./gradlew build`, `detekt`, `ktlintCheck`
+2. **Parse Errors**: Group by file and sort by severity
+3. **Fix Incrementally**: One error at a time
+4. **Verify Each Fix**: Re-run build after each change
+5. **Report Summary**: Show what was fixed and what remains
+
+## When to Use
+
+Use `/kotlin-build` when:
+- `./gradlew build` fails with errors
+- Kotlin compiler reports errors
+- `./gradlew detekt` reports violations
+- Gradle dependency resolution fails
+- After pulling changes that break the build
+
+## Diagnostic Commands Run
+
+```bash
+# Primary build check
+./gradlew build 2>&1
+
+# Static analysis
+./gradlew detekt 2>&1 || echo "detekt not configured"
+./gradlew ktlintCheck 2>&1 || echo "ktlint not configured"
+
+# Dependency issues
+./gradlew dependencies --configuration runtimeClasspath 2>&1 | head -100
+
+# Optional deep refresh when caches or dependency metadata are suspect
+./gradlew build --refresh-dependencies
+```
+
+## Example Session
+
+````text
+User: /kotlin-build
+
+Agent:
+# Kotlin Build Resolution
+
+## Initial Diagnostics
+
+```bash
+$ ./gradlew build
+e: src/main/kotlin/com/example/service/UserService.kt:25:15 Unresolved reference: UserRepository
+e: src/main/kotlin/com/example/routes/UserRoutes.kt:42:9 Type mismatch: inferred type is String but Int was expected
+e: src/main/kotlin/com/example/routes/UserRoutes.kt:58:5 'when' expression must be exhaustive
+```
+
+Errors found: 3
+
+## Fix 1: Unresolved Reference
+
+File: src/main/kotlin/com/example/service/UserService.kt:25
+Error: Unresolved reference: UserRepository
+Cause: Missing import
+
+```kotlin
+// Added import
+import com.example.repository.UserRepository
+```
+
+```bash
+$ ./gradlew build
+# 2 errors remaining
+```
+
+## Fix 2: Type Mismatch
+
+File: src/main/kotlin/com/example/routes/UserRoutes.kt:42
+Error: Type mismatch: inferred type is String but Int was expected
+
+```kotlin
+// Changed
+val count = call.parameters["count"]
+// To
+val count = call.parameters["count"]?.toIntOrNull()
+    ?: return@get call.respond(HttpStatusCode.BadRequest, "Invalid count")
+```
+
+```bash
+$ ./gradlew build
+# 1 error remaining
+```
+
+## Fix 3: Non-Exhaustive When
+
+File: src/main/kotlin/com/example/routes/UserRoutes.kt:58
+Error: 'when' expression must be exhaustive
+
+```kotlin
+// Added missing branch
+when (user.role) {
+    Role.ADMIN -> handleAdmin(user)
+    Role.USER -> handleUser(user)
+    Role.MODERATOR -> handleModerator(user) // Added
+}
+```
+
+```bash
+$ ./gradlew build
+# Build successful!
+```
+
+## Final Verification
+
+```bash
+$ ./gradlew detekt
+# No issues
+
+$ ./gradlew test
+# All tests passed
+```
+
+## Summary
+
+| Metric | Count |
+|--------|-------|
+| Build errors fixed | 3 |
+| Detekt issues fixed | 0 |
+| Files modified | 2 |
+| Remaining issues | 0 |
+
+Build Status: ✅ SUCCESS
+````
+
+## Common Errors Fixed
+
+| Error | Typical Fix |
+|-------|-------------|
+| `Unresolved reference: X` | Add import or dependency |
+| `Type mismatch` | Fix type conversion or assignment |
+| `'when' must be exhaustive` | Add missing sealed class branches |
+| `Suspend function can only be called from coroutine` | Add `suspend` modifier |
+| `Smart cast impossible` | Use local `val` or `let` |
+| `None of the following candidates is applicable` | Fix argument types |
+| `Could not resolve dependency` | Fix version or add repository |
+
+## Fix Strategy
+
+1. **Build errors first** - Code must compile
+2. **Detekt violations second** - Fix code quality issues
+3. **ktlint warnings third** - Fix formatting
+4. **One fix at a time** - Verify each change
+5. **Minimal changes** - Don't refactor, just fix
+
+## Stop Conditions
+
+The agent will stop and report if:
+- Same error persists after 3 attempts
+- Fix introduces more errors
+- Requires architectural changes
+- Missing external dependencies
+
+## Related Commands
+
+- `/kotlin-test` - Run tests after build succeeds
+- `/kotlin-review` - Review code quality
+- `/verify` - Full verification loop
+
+## Related
+
+- Agent: `agents/kotlin-build-resolver.md`
+- Skill: `skills/kotlin-patterns/`

commands/kotlin-review.md

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+---
+description: Comprehensive Kotlin code review for idiomatic patterns, null safety, coroutine safety, and security. Invokes the kotlin-reviewer agent.
+---
+
+# Kotlin Code Review
+
+This command invokes the **kotlin-reviewer** agent for comprehensive Kotlin-specific code review.
+
+## What This Command Does
+
+1. **Identify Kotlin Changes**: Find modified `.kt` and `.kts` files via `git diff`
+2. **Run Build & Static Analysis**: Execute `./gradlew build`, `detekt`, `ktlintCheck`
+3. **Security Scan**: Check for SQL injection, command injection, hardcoded secrets
+4. **Null Safety Review**: Analyze `!!` usage, platform type handling, unsafe casts
+5. **Coroutine Review**: Check structured concurrency, dispatcher usage, cancellation
+6. **Generate Report**: Categorize issues by severity
+
+## When to Use
+
+Use `/kotlin-review` when:
+- After writing or modifying Kotlin code
+- Before committing Kotlin changes
+- Reviewing pull requests with Kotlin code
+- Onboarding to a new Kotlin codebase
+- Learning idiomatic Kotlin patterns
+
+## Review Categories
+
+### CRITICAL (Must Fix)
+- SQL/Command injection vulnerabilities
+- Force-unwrap `!!` without justification
+- Platform type null safety violations
+- GlobalScope usage (structured concurrency violation)
+- Hardcoded credentials
+- Unsafe deserialization
+
+### HIGH (Should Fix)
+- Mutable state where immutable suffices
+- Blocking calls inside coroutine context
+- Missing cancellation checks in long loops
+- Non-exhaustive `when` on sealed types
+- Large functions (>50 lines)
+- Deep nesting (>4 levels)
+
+### MEDIUM (Consider)
+- Non-idiomatic Kotlin (Java-style patterns)
+- Missing trailing commas
+- Scope function misuse or nesting
+- Missing sequence for large collection chains
+- Redundant explicit types
+
+## Automated Checks Run
+
+```bash
+# Build check
+./gradlew build
+
+# Static analysis
+./gradlew detekt
+
+# Formatting check
+./gradlew ktlintCheck
+
+# Tests
+./gradlew test
+```
+
+## Example Usage
+
+````text
+User: /kotlin-review
+
+Agent:
+# Kotlin Code Review Report
+
+## Files Reviewed
+- src/main/kotlin/com/example/service/UserService.kt (modified)
+- src/main/kotlin/com/example/routes/UserRoutes.kt (modified)
+
+## Static Analysis Results
+✓ Build: Successful
+✓ detekt: No issues
+⚠ ktlint: 2 formatting warnings
+
+## Issues Found
+
+[CRITICAL] Force-Unwrap Null Safety
+File: src/main/kotlin/com/example/service/UserService.kt:28
+Issue: Using !! on nullable repository result
+```kotlin
+val user = repository.findById(id)!!  // NPE risk
+```
+Fix: Use safe call with error handling
+```kotlin
+val user = repository.findById(id)
+    ?: throw UserNotFoundException("User $id not found")
+```
+
+[HIGH] GlobalScope Usage
+File: src/main/kotlin/com/example/routes/UserRoutes.kt:45
+Issue: Using GlobalScope breaks structured concurrency
+```kotlin
+GlobalScope.launch {
+    notificationService.sendWelcome(user)
+}
+```
+Fix: Use the call's coroutine scope
+```kotlin
+launch {
+    notificationService.sendWelcome(user)
+}
+```
+
+## Summary
+- CRITICAL: 1
+- HIGH: 1
+- MEDIUM: 0
+
+Recommendation: ❌ Block merge until CRITICAL issue is fixed
+````
+
+## Approval Criteria
+
+| Status | Condition |
+|--------|-----------|
+| ✅ Approve | No CRITICAL or HIGH issues |
+| ⚠️ Warning | Only MEDIUM issues (merge with caution) |
+| ❌ Block | CRITICAL or HIGH issues found |
+
+## Integration with Other Commands
+
+- Use `/kotlin-test` first to ensure tests pass
+- Use `/kotlin-build` if build errors occur
+- Use `/kotlin-review` before committing
+- Use `/code-review` for non-Kotlin-specific concerns
+
+## Related
+
+- Agent: `agents/kotlin-reviewer.md`
+- Skills: `skills/kotlin-patterns/`, `skills/kotlin-testing/`

commands/kotlin-test.md

@@ -0,0 +1,312 @@
+---
+description: Enforce TDD workflow for Kotlin. Write Kotest tests first, then implement. Verify 80%+ coverage with Kover.
+---
+
+# Kotlin TDD Command
+
+This command enforces test-driven development methodology for Kotlin code using Kotest, MockK, and Kover.
+
+## What This Command Does
+
+1. **Define Types/Interfaces**: Scaffold function signatures first
+2. **Write Kotest Tests**: Create comprehensive test specs (RED)
+3. **Run Tests**: Verify tests fail for the right reason
+4. **Implement Code**: Write minimal code to pass (GREEN)
+5. **Refactor**: Improve while keeping tests green
+6. **Check Coverage**: Ensure 80%+ coverage with Kover
+
+## When to Use
+
+Use `/kotlin-test` when:
+- Implementing new Kotlin functions or classes
+- Adding test coverage to existing Kotlin code
+- Fixing bugs (write failing test first)
+- Building critical business logic
+- Learning TDD workflow in Kotlin
+
+## TDD Cycle
+
+```
+RED     -> Write failing Kotest test
+GREEN   -> Implement minimal code to pass
+REFACTOR -> Improve code, tests stay green
+REPEAT  -> Next test case
+```
+
+## Example Session
+
+````text
+User: /kotlin-test I need a function to validate user registration requests
+
+Agent:
+# TDD Session: Registration Validator
+
+## Step 1: Define Interface
+
+```kotlin
+// validator/RegistrationValidator.kt
+package com.example.validator
+
+data class RegistrationRequest(
+    val name: String,
+    val email: String,
+    val password: String,
+)
+
+sealed class ValidationResult {
+    data object Valid : ValidationResult()
+    data class Invalid(val errors: List<String>) : ValidationResult()
+}
+
+fun validateRegistration(request: RegistrationRequest): ValidationResult {
+    TODO("not implemented")
+}
+```
+
+## Step 2: Write Kotest Tests (RED)
+
+```kotlin
+// validator/RegistrationValidatorTest.kt
+package com.example.validator
+
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.types.shouldBeInstanceOf
+
+class RegistrationValidatorTest : FunSpec({
+    test("valid registration returns Valid") {
+        val request = RegistrationRequest(
+            name = "Alice",
+            email = "alice@example.com",
+            password = "SecureP@ss1",
+        )
+
+        val result = validateRegistration(request)
+
+        result.shouldBeInstanceOf<ValidationResult.Valid>()
+    }
+
+    test("blank name returns Invalid") {
+        val request = RegistrationRequest(
+            name = "",
+            email = "alice@example.com",
+            password = "SecureP@ss1",
+        )
+
+        val result = validateRegistration(request)
+
+        val invalid = result.shouldBeInstanceOf<ValidationResult.Invalid>()
+        invalid.errors shouldBe listOf("Name is required")
+    }
+
+    test("invalid email returns Invalid") {
+        val request = RegistrationRequest(
+            name = "Alice",
+            email = "not-an-email",
+            password = "SecureP@ss1",
+        )
+
+        val result = validateRegistration(request)
+
+        val invalid = result.shouldBeInstanceOf<ValidationResult.Invalid>()
+        invalid.errors shouldBe listOf("Invalid email format")
+    }
+
+    test("short password returns Invalid") {
+        val request = RegistrationRequest(
+            name = "Alice",
+            email = "alice@example.com",
+            password = "short",
+        )
+
+        val result = validateRegistration(request)
+
+        val invalid = result.shouldBeInstanceOf<ValidationResult.Invalid>()
+        invalid.errors shouldBe listOf("Password must be at least 8 characters")
+    }
+
+    test("multiple errors returns all errors") {
+        val request = RegistrationRequest(
+            name = "",
+            email = "bad",
+            password = "short",
+        )
+
+        val result = validateRegistration(request)
+
+        val invalid = result.shouldBeInstanceOf<ValidationResult.Invalid>()
+        invalid.errors.size shouldBe 3
+    }
+})
+```
+
+## Step 3: Run Tests - Verify FAIL
+
+```bash
+$ ./gradlew test
+
+RegistrationValidatorTest > valid registration returns Valid FAILED
+  kotlin.NotImplementedError: An operation is not implemented
+
+FAILED (5 tests, 0 passed, 5 failed)
+```
+
+✓ Tests fail as expected (NotImplementedError).
+
+## Step 4: Implement Minimal Code (GREEN)
+
+```kotlin
+// validator/RegistrationValidator.kt
+package com.example.validator
+
+private val EMAIL_REGEX = Regex("^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}$")
+private const val MIN_PASSWORD_LENGTH = 8
+
+fun validateRegistration(request: RegistrationRequest): ValidationResult {
+    val errors = buildList {
+        if (request.name.isBlank()) add("Name is required")
+        if (!EMAIL_REGEX.matches(request.email)) add("Invalid email format")
+        if (request.password.length < MIN_PASSWORD_LENGTH) add("Password must be at least $MIN_PASSWORD_LENGTH characters")
+    }
+
+    return if (errors.isEmpty()) ValidationResult.Valid
+    else ValidationResult.Invalid(errors)
+}
+```
+
+## Step 5: Run Tests - Verify PASS
+
+```bash
+$ ./gradlew test
+
+RegistrationValidatorTest > valid registration returns Valid PASSED
+RegistrationValidatorTest > blank name returns Invalid PASSED
+RegistrationValidatorTest > invalid email returns Invalid PASSED
+RegistrationValidatorTest > short password returns Invalid PASSED
+RegistrationValidatorTest > multiple errors returns all errors PASSED
+
+PASSED (5 tests, 5 passed, 0 failed)
+```
+
+✓ All tests passing!
+
+## Step 6: Check Coverage
+
+```bash
+$ ./gradlew koverHtmlReport
+
+Coverage: 100.0% of statements
+```
+
+✓ Coverage: 100%
+
+## TDD Complete!
+````
+
+## Test Patterns
+
+### StringSpec (Simplest)
+
+```kotlin
+class CalculatorTest : StringSpec({
+    "add two positive numbers" {
+        Calculator.add(2, 3) shouldBe 5
+    }
+})
+```
+
+### BehaviorSpec (BDD)
+
+```kotlin
+class OrderServiceTest : BehaviorSpec({
+    Given("a valid order") {
+        When("placed") {
+            Then("should be confirmed") { /* ... */ }
+        }
+    }
+})
+```
+
+### Data-Driven Tests
+
+```kotlin
+class ParserTest : FunSpec({
+    context("valid inputs") {
+        withData("2026-01-15", "2026-12-31", "2000-01-01") { input ->
+            parseDate(input).shouldNotBeNull()
+        }
+    }
+})
+```
+
+### Coroutine Testing
+
+```kotlin
+class AsyncServiceTest : FunSpec({
+    test("concurrent fetch completes") {
+        runTest {
+            val result = service.fetchAll()
+            result.shouldNotBeEmpty()
+        }
+    }
+})
+```
+
+## Coverage Commands
+
+```bash
+# Run tests with coverage
+./gradlew koverHtmlReport
+
+# Verify coverage thresholds
+./gradlew koverVerify
+
+# XML report for CI
+./gradlew koverXmlReport
+
+# Open HTML report
+open build/reports/kover/html/index.html
+
+# Run specific test class
+./gradlew test --tests "com.example.UserServiceTest"
+
+# Run with verbose output
+./gradlew test --info
+```
+
+## Coverage Targets
+
+| Code Type | Target |
+|-----------|--------|
+| Critical business logic | 100% |
+| Public APIs | 90%+ |
+| General code | 80%+ |
+| Generated code | Exclude |
+
+## TDD Best Practices
+
+**DO:**
+- Write test FIRST, before any implementation
+- Run tests after each change
+- Use Kotest matchers for expressive assertions
+- Use MockK's `coEvery`/`coVerify` for suspend functions
+- Test behavior, not implementation details
+- Include edge cases (empty, null, max values)
+
+**DON'T:**
+- Write implementation before tests
+- Skip the RED phase
+- Test private functions directly
+- Use `Thread.sleep()` in coroutine tests
+- Ignore flaky tests
+
+## Related Commands
+
+- `/kotlin-build` - Fix build errors
+- `/kotlin-review` - Review code after implementation
+- `/verify` - Run full verification loop
+
+## Related
+
+- Skill: `skills/kotlin-testing/`
+- Skill: `skills/tdd-workflow/`

rules/kotlin/hooks.md

@@ -0,0 +1,17 @@
+---
+paths:
+  - "**/*.kt"
+  - "**/*.kts"
+  - "**/build.gradle.kts"
+---
+# Kotlin Hooks
+
+> This file extends [common/hooks.md](../common/hooks.md) with Kotlin-specific content.
+
+## PostToolUse Hooks
+
+Configure in `~/.claude/settings.json`:
+
+- **ktfmt/ktlint**: Auto-format `.kt` and `.kts` files after edit
+- **detekt**: Run static analysis after editing Kotlin files
+- **./gradlew build**: Verify compilation after changes

skills/kotlin-exposed-patterns/SKILL.md

@@ -0,0 +1,719 @@
+---
+name: kotlin-exposed-patterns
+description: JetBrains Exposed ORM patterns including DSL queries, DAO pattern, transactions, HikariCP connection pooling, Flyway migrations, and repository pattern.
+origin: ECC
+---
+
+# Kotlin Exposed Patterns
+
+Comprehensive patterns for database access with JetBrains Exposed ORM, including DSL queries, DAO, transactions, and production-ready configuration.
+
+## When to Use
+
+- Setting up database access with Exposed
+- Writing SQL queries using Exposed DSL or DAO
+- Configuring connection pooling with HikariCP
+- Creating database migrations with Flyway
+- Implementing the repository pattern with Exposed
+- Handling JSON columns and complex queries
+
+## How It Works
+
+Exposed provides two query styles: DSL for direct SQL-like expressions and DAO for entity lifecycle management. HikariCP manages a pool of reusable database connections configured via `HikariConfig`. Flyway runs versioned SQL migration scripts at startup to keep the schema in sync. All database operations run inside `newSuspendedTransaction` blocks for coroutine safety and atomicity. The repository pattern wraps Exposed queries behind an interface so business logic stays decoupled from the data layer and tests can use an in-memory H2 database.
+
+## Examples
+
+### DSL Query
+
+```kotlin
+suspend fun findUserById(id: UUID): UserRow? =
+    newSuspendedTransaction {
+        UsersTable.selectAll()
+            .where { UsersTable.id eq id }
+            .map { it.toUser() }
+            .singleOrNull()
+    }
+```
+
+### DAO Entity Usage
+
+```kotlin
+suspend fun createUser(request: CreateUserRequest): User =
+    newSuspendedTransaction {
+        UserEntity.new {
+            name = request.name
+            email = request.email
+            role = request.role
+        }.toModel()
+    }
+```
+
+### HikariCP Configuration
+
+```kotlin
+val hikariConfig = HikariConfig().apply {
+    driverClassName = config.driver
+    jdbcUrl = config.url
+    username = config.username
+    password = config.password
+    maximumPoolSize = config.maxPoolSize
+    isAutoCommit = false
+    transactionIsolation = "TRANSACTION_READ_COMMITTED"
+    validate()
+}
+```
+
+## Database Setup
+
+### HikariCP Connection Pooling
+
+```kotlin
+// DatabaseFactory.kt
+object DatabaseFactory {
+    fun create(config: DatabaseConfig): Database {
+        val hikariConfig = HikariConfig().apply {
+            driverClassName = config.driver
+            jdbcUrl = config.url
+            username = config.username
+            password = config.password
+            maximumPoolSize = config.maxPoolSize
+            isAutoCommit = false
+            transactionIsolation = "TRANSACTION_READ_COMMITTED"
+            validate()
+        }
+
+        return Database.connect(HikariDataSource(hikariConfig))
+    }
+}
+
+data class DatabaseConfig(
+    val url: String,
+    val driver: String = "org.postgresql.Driver",
+    val username: String = "",
+    val password: String = "",
+    val maxPoolSize: Int = 10,
+)
+```
+
+### Flyway Migrations
+
+```kotlin
+// FlywayMigration.kt
+fun runMigrations(config: DatabaseConfig) {
+    Flyway.configure()
+        .dataSource(config.url, config.username, config.password)
+        .locations("classpath:db/migration")
+        .baselineOnMigrate(true)
+        .load()
+        .migrate()
+}
+
+// Application startup
+fun Application.module() {
+    val config = DatabaseConfig(
+        url = environment.config.property("database.url").getString(),
+        username = environment.config.property("database.username").getString(),
+        password = environment.config.property("database.password").getString(),
+    )
+    runMigrations(config)
+    val database = DatabaseFactory.create(config)
+    // ...
+}
+```
+
+### Migration Files
+
+```sql
+-- src/main/resources/db/migration/V1__create_users.sql
+CREATE TABLE users (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    name VARCHAR(100) NOT NULL,
+    email VARCHAR(255) NOT NULL UNIQUE,
+    role VARCHAR(20) NOT NULL DEFAULT 'USER',
+    metadata JSONB,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_users_email ON users(email);
+CREATE INDEX idx_users_role ON users(role);
+```
+
+## Table Definitions
+
+### DSL Style Tables
+
+```kotlin
+// tables/UsersTable.kt
+object UsersTable : UUIDTable("users") {
+    val name = varchar("name", 100)
+    val email = varchar("email", 255).uniqueIndex()
+    val role = enumerationByName<Role>("role", 20)
+    val metadata = jsonb<UserMetadata>("metadata", Json.Default).nullable()
+    val createdAt = timestampWithTimeZone("created_at").defaultExpression(CurrentTimestampWithTimeZone)
+    val updatedAt = timestampWithTimeZone("updated_at").defaultExpression(CurrentTimestampWithTimeZone)
+}
+
+object OrdersTable : UUIDTable("orders") {
+    val userId = uuid("user_id").references(UsersTable.id)
+    val status = enumerationByName<OrderStatus>("status", 20)
+    val totalAmount = long("total_amount")
+    val currency = varchar("currency", 3)
+    val createdAt = timestampWithTimeZone("created_at").defaultExpression(CurrentTimestampWithTimeZone)
+}
+
+object OrderItemsTable : UUIDTable("order_items") {
+    val orderId = uuid("order_id").references(OrdersTable.id, onDelete = ReferenceOption.CASCADE)
+    val productId = uuid("product_id")
+    val quantity = integer("quantity")
+    val unitPrice = long("unit_price")
+}
+```
+
+### Composite Tables
+
+```kotlin
+object UserRolesTable : Table("user_roles") {
+    val userId = uuid("user_id").references(UsersTable.id, onDelete = ReferenceOption.CASCADE)
+    val roleId = uuid("role_id").references(RolesTable.id, onDelete = ReferenceOption.CASCADE)
+    override val primaryKey = PrimaryKey(userId, roleId)
+}
+```
+
+## DSL Queries
+
+### Basic CRUD
+
+```kotlin
+// Insert
+suspend fun insertUser(name: String, email: String, role: Role): UUID =
+    newSuspendedTransaction {
+        UsersTable.insertAndGetId {
+            it[UsersTable.name] = name
+            it[UsersTable.email] = email
+            it[UsersTable.role] = role
+        }.value
+    }
+
+// Select by ID
+suspend fun findUserById(id: UUID): UserRow? =
+    newSuspendedTransaction {
+        UsersTable.selectAll()
+            .where { UsersTable.id eq id }
+            .map { it.toUser() }
+            .singleOrNull()
+    }
+
+// Select with conditions
+suspend fun findActiveAdmins(): List<UserRow> =
+    newSuspendedTransaction {
+        UsersTable.selectAll()
+            .where { (UsersTable.role eq Role.ADMIN) }
+            .orderBy(UsersTable.name)
+            .map { it.toUser() }
+    }
+
+// Update
+suspend fun updateUserEmail(id: UUID, newEmail: String): Boolean =
+    newSuspendedTransaction {
+        UsersTable.update({ UsersTable.id eq id }) {
+            it[email] = newEmail
+            it[updatedAt] = CurrentTimestampWithTimeZone
+        } > 0
+    }
+
+// Delete
+suspend fun deleteUser(id: UUID): Boolean =
+    newSuspendedTransaction {
+        UsersTable.deleteWhere { UsersTable.id eq id } > 0
+    }
+
+// Row mapping
+private fun ResultRow.toUser() = UserRow(
+    id = this[UsersTable.id].value,
+    name = this[UsersTable.name],
+    email = this[UsersTable.email],
+    role = this[UsersTable.role],
+    metadata = this[UsersTable.metadata],
+    createdAt = this[UsersTable.createdAt],
+    updatedAt = this[UsersTable.updatedAt],
+)
+```
+
+### Advanced Queries
+
+```kotlin
+// Join queries
+suspend fun findOrdersWithUser(userId: UUID): List<OrderWithUser> =
+    newSuspendedTransaction {
+        (OrdersTable innerJoin UsersTable)
+            .selectAll()
+            .where { OrdersTable.userId eq userId }
+            .orderBy(OrdersTable.createdAt, SortOrder.DESC)
+            .map { row ->
+                OrderWithUser(
+                    orderId = row[OrdersTable.id].value,
+                    status = row[OrdersTable.status],
+                    totalAmount = row[OrdersTable.totalAmount],
+                    userName = row[UsersTable.name],
+                )
+            }
+    }
+
+// Aggregation
+suspend fun countUsersByRole(): Map<Role, Long> =
+    newSuspendedTransaction {
+        UsersTable
+            .select(UsersTable.role, UsersTable.id.count())
+            .groupBy(UsersTable.role)
+            .associate { row ->
+                row[UsersTable.role] to row[UsersTable.id.count()]
+            }
+    }
+
+// Subqueries
+suspend fun findUsersWithOrders(): List<UserRow> =
+    newSuspendedTransaction {
+        UsersTable.selectAll()
+            .where {
+                UsersTable.id inSubQuery
+                    OrdersTable.select(OrdersTable.userId).withDistinct()
+            }
+            .map { it.toUser() }
+    }
+
+// LIKE and pattern matching — always escape user input to prevent wildcard injection
+private fun escapeLikePattern(input: String): String =
+    input.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")
+
+suspend fun searchUsers(query: String): List<UserRow> =
+    newSuspendedTransaction {
+        val sanitized = escapeLikePattern(query.lowercase())
+        UsersTable.selectAll()
+            .where {
+                (UsersTable.name.lowerCase() like "%${sanitized}%") or
+                    (UsersTable.email.lowerCase() like "%${sanitized}%")
+            }
+            .map { it.toUser() }
+    }
+```
+
+### Pagination
+
+```kotlin
+data class Page<T>(
+    val data: List<T>,
+    val total: Long,
+    val page: Int,
+    val limit: Int,
+) {
+    val totalPages: Int get() = ((total + limit - 1) / limit).toInt()
+    val hasNext: Boolean get() = page < totalPages
+    val hasPrevious: Boolean get() = page > 1
+}
+
+suspend fun findUsersPaginated(page: Int, limit: Int): Page<UserRow> =
+    newSuspendedTransaction {
+        val total = UsersTable.selectAll().count()
+        val data = UsersTable.selectAll()
+            .orderBy(UsersTable.createdAt, SortOrder.DESC)
+            .limit(limit)
+            .offset(((page - 1) * limit).toLong())
+            .map { it.toUser() }
+
+        Page(data = data, total = total, page = page, limit = limit)
+    }
+```
+
+### Batch Operations
+
+```kotlin
+// Batch insert
+suspend fun insertUsers(users: List<CreateUserRequest>): List<UUID> =
+    newSuspendedTransaction {
+        UsersTable.batchInsert(users) { user ->
+            this[UsersTable.name] = user.name
+            this[UsersTable.email] = user.email
+            this[UsersTable.role] = user.role
+        }.map { it[UsersTable.id].value }
+    }
+
+// Upsert (insert or update on conflict)
+suspend fun upsertUser(id: UUID, name: String, email: String) {
+    newSuspendedTransaction {
+        UsersTable.upsert(UsersTable.email) {
+            it[UsersTable.id] = EntityID(id, UsersTable)
+            it[UsersTable.name] = name
+            it[UsersTable.email] = email
+            it[updatedAt] = CurrentTimestampWithTimeZone
+        }
+    }
+}
+```
+
+## DAO Pattern
+
+### Entity Definitions
+
+```kotlin
+// entities/UserEntity.kt
+class UserEntity(id: EntityID<UUID>) : UUIDEntity(id) {
+    companion object : UUIDEntityClass<UserEntity>(UsersTable)
+
+    var name by UsersTable.name
+    var email by UsersTable.email
+    var role by UsersTable.role
+    var metadata by UsersTable.metadata
+    var createdAt by UsersTable.createdAt
+    var updatedAt by UsersTable.updatedAt
+
+    val orders by OrderEntity referrersOn OrdersTable.userId
+
+    fun toModel(): User = User(
+        id = id.value,
+        name = name,
+        email = email,
+        role = role,
+        metadata = metadata,
+        createdAt = createdAt,
+        updatedAt = updatedAt,
+    )
+}
+
+class OrderEntity(id: EntityID<UUID>) : UUIDEntity(id) {
+    companion object : UUIDEntityClass<OrderEntity>(OrdersTable)
+
+    var user by UserEntity referencedOn OrdersTable.userId
+    var status by OrdersTable.status
+    var totalAmount by OrdersTable.totalAmount
+    var currency by OrdersTable.currency
+    var createdAt by OrdersTable.createdAt
+
+    val items by OrderItemEntity referrersOn OrderItemsTable.orderId
+}
+```
+
+### DAO Operations
+
+```kotlin
+suspend fun findUserByEmail(email: String): User? =
+    newSuspendedTransaction {
+        UserEntity.find { UsersTable.email eq email }
+            .firstOrNull()
+            ?.toModel()
+    }
+
+suspend fun createUser(request: CreateUserRequest): User =
+    newSuspendedTransaction {
+        UserEntity.new {
+            name = request.name
+            email = request.email
+            role = request.role
+        }.toModel()
+    }
+
+suspend fun updateUser(id: UUID, request: UpdateUserRequest): User? =
+    newSuspendedTransaction {
+        UserEntity.findById(id)?.apply {
+            request.name?.let { name = it }
+            request.email?.let { email = it }
+            updatedAt = OffsetDateTime.now(ZoneOffset.UTC)
+        }?.toModel()
+    }
+```
+
+## Transactions
+
+### Suspend Transaction Support
+
+```kotlin
+// Good: Use newSuspendedTransaction for coroutine support
+suspend fun performDatabaseOperation(): Result<User> =
+    runCatching {
+        newSuspendedTransaction {
+            val user = UserEntity.new {
+                name = "Alice"
+                email = "alice@example.com"
+            }
+            // All operations in this block are atomic
+            user.toModel()
+        }
+    }
+
+// Good: Nested transactions with savepoints
+suspend fun transferFunds(fromId: UUID, toId: UUID, amount: Long) {
+    newSuspendedTransaction {
+        val from = UserEntity.findById(fromId) ?: throw NotFoundException("User $fromId not found")
+        val to = UserEntity.findById(toId) ?: throw NotFoundException("User $toId not found")
+
+        // Debit
+        from.balance -= amount
+        // Credit
+        to.balance += amount
+
+        // Both succeed or both fail
+    }
+}
+```
+
+### Transaction Isolation
+
+```kotlin
+suspend fun readCommittedQuery(): List<User> =
+    newSuspendedTransaction(transactionIsolation = Connection.TRANSACTION_READ_COMMITTED) {
+        UserEntity.all().map { it.toModel() }
+    }
+
+suspend fun serializableOperation() {
+    newSuspendedTransaction(transactionIsolation = Connection.TRANSACTION_SERIALIZABLE) {
+        // Strictest isolation level for critical operations
+    }
+}
+```
+
+## Repository Pattern
+
+### Interface Definition
+
+```kotlin
+interface UserRepository {
+    suspend fun findById(id: UUID): User?
+    suspend fun findByEmail(email: String): User?
+    suspend fun findAll(page: Int, limit: Int): Page<User>
+    suspend fun search(query: String): List<User>
+    suspend fun create(request: CreateUserRequest): User
+    suspend fun update(id: UUID, request: UpdateUserRequest): User?
+    suspend fun delete(id: UUID): Boolean
+    suspend fun count(): Long
+}
+```
+
+### Exposed Implementation
+
+```kotlin
+class ExposedUserRepository(
+    private val database: Database,
+) : UserRepository {
+
+    override suspend fun findById(id: UUID): User? =
+        newSuspendedTransaction(db = database) {
+            UsersTable.selectAll()
+                .where { UsersTable.id eq id }
+                .map { it.toUser() }
+                .singleOrNull()
+        }
+
+    override suspend fun findByEmail(email: String): User? =
+        newSuspendedTransaction(db = database) {
+            UsersTable.selectAll()
+                .where { UsersTable.email eq email }
+                .map { it.toUser() }
+                .singleOrNull()
+        }
+
+    override suspend fun findAll(page: Int, limit: Int): Page<User> =
+        newSuspendedTransaction(db = database) {
+            val total = UsersTable.selectAll().count()
+            val data = UsersTable.selectAll()
+                .orderBy(UsersTable.createdAt, SortOrder.DESC)
+                .limit(limit)
+                .offset(((page - 1) * limit).toLong())
+                .map { it.toUser() }
+            Page(data = data, total = total, page = page, limit = limit)
+        }
+
+    override suspend fun search(query: String): List<User> =
+        newSuspendedTransaction(db = database) {
+            val sanitized = escapeLikePattern(query.lowercase())
+            UsersTable.selectAll()
+                .where {
+                    (UsersTable.name.lowerCase() like "%${sanitized}%") or
+                        (UsersTable.email.lowerCase() like "%${sanitized}%")
+                }
+                .orderBy(UsersTable.name)
+                .map { it.toUser() }
+        }
+
+    override suspend fun create(request: CreateUserRequest): User =
+        newSuspendedTransaction(db = database) {
+            UsersTable.insert {
+                it[name] = request.name
+                it[email] = request.email
+                it[role] = request.role
+            }.resultedValues!!.first().toUser()
+        }
+
+    override suspend fun update(id: UUID, request: UpdateUserRequest): User? =
+        newSuspendedTransaction(db = database) {
+            val updated = UsersTable.update({ UsersTable.id eq id }) {
+                request.name?.let { name -> it[UsersTable.name] = name }
+                request.email?.let { email -> it[UsersTable.email] = email }
+                it[updatedAt] = CurrentTimestampWithTimeZone
+            }
+            if (updated > 0) findById(id) else null
+        }
+
+    override suspend fun delete(id: UUID): Boolean =
+        newSuspendedTransaction(db = database) {
+            UsersTable.deleteWhere { UsersTable.id eq id } > 0
+        }
+
+    override suspend fun count(): Long =
+        newSuspendedTransaction(db = database) {
+            UsersTable.selectAll().count()
+        }
+
+    private fun ResultRow.toUser() = User(
+        id = this[UsersTable.id].value,
+        name = this[UsersTable.name],
+        email = this[UsersTable.email],
+        role = this[UsersTable.role],
+        metadata = this[UsersTable.metadata],
+        createdAt = this[UsersTable.createdAt],
+        updatedAt = this[UsersTable.updatedAt],
+    )
+}
+```
+
+## JSON Columns
+
+### JSONB with kotlinx.serialization
+
+```kotlin
+// Custom column type for JSONB
+inline fun <reified T : Any> Table.jsonb(
+    name: String,
+    json: Json,
+): Column<T> = registerColumn(name, object : ColumnType<T>() {
+    override fun sqlType() = "JSONB"
+
+    override fun valueFromDB(value: Any): T = when (value) {
+        is String -> json.decodeFromString(value)
+        is PGobject -> {
+            val jsonString = value.value
+                ?: throw IllegalArgumentException("PGobject value is null for column '$name'")
+            json.decodeFromString(jsonString)
+        }
+        else -> throw IllegalArgumentException("Unexpected value: $value")
+    }
+
+    override fun notNullValueToDB(value: T): Any =
+        PGobject().apply {
+            type = "jsonb"
+            this.value = json.encodeToString(value)
+        }
+})
+
+// Usage in table
+@Serializable
+data class UserMetadata(
+    val preferences: Map<String, String> = emptyMap(),
+    val tags: List<String> = emptyList(),
+)
+
+object UsersTable : UUIDTable("users") {
+    val metadata = jsonb<UserMetadata>("metadata", Json.Default).nullable()
+}
+```
+
+## Testing with Exposed
+
+### In-Memory Database for Tests
+
+```kotlin
+class UserRepositoryTest : FunSpec({
+    lateinit var database: Database
+    lateinit var repository: UserRepository
+
+    beforeSpec {
+        database = Database.connect(
+            url = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1;MODE=PostgreSQL",
+            driver = "org.h2.Driver",
+        )
+        transaction(database) {
+            SchemaUtils.create(UsersTable)
+        }
+        repository = ExposedUserRepository(database)
+    }
+
+    beforeTest {
+        transaction(database) {
+            UsersTable.deleteAll()
+        }
+    }
+
+    test("create and find user") {
+        val user = repository.create(CreateUserRequest("Alice", "alice@example.com"))
+
+        user.name shouldBe "Alice"
+        user.email shouldBe "alice@example.com"
+
+        val found = repository.findById(user.id)
+        found shouldBe user
+    }
+
+    test("findByEmail returns null for unknown email") {
+        val result = repository.findByEmail("unknown@example.com")
+        result.shouldBeNull()
+    }
+
+    test("pagination works correctly") {
+        repeat(25) { i ->
+            repository.create(CreateUserRequest("User $i", "user$i@example.com"))
+        }
+
+        val page1 = repository.findAll(page = 1, limit = 10)
+        page1.data shouldHaveSize 10
+        page1.total shouldBe 25
+        page1.hasNext shouldBe true
+
+        val page3 = repository.findAll(page = 3, limit = 10)
+        page3.data shouldHaveSize 5
+        page3.hasNext shouldBe false
+    }
+})
+```
+
+## Gradle Dependencies
+
+```kotlin
+// build.gradle.kts
+dependencies {
+    // Exposed
+    implementation("org.jetbrains.exposed:exposed-core:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-dao:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-jdbc:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-kotlin-datetime:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-json:1.0.0")
+
+    // Database driver
+    implementation("org.postgresql:postgresql:42.7.5")
+
+    // Connection pooling
+    implementation("com.zaxxer:HikariCP:6.2.1")
+
+    // Migrations
+    implementation("org.flywaydb:flyway-core:10.22.0")
+    implementation("org.flywaydb:flyway-database-postgresql:10.22.0")
+
+    // Testing
+    testImplementation("com.h2database:h2:2.3.232")
+}
+```
+
+## Quick Reference: Exposed Patterns
+
+| Pattern | Description |
+|---------|-------------|
+| `object Table : UUIDTable("name")` | Define table with UUID primary key |
+| `newSuspendedTransaction { }` | Coroutine-safe transaction block |
+| `Table.selectAll().where { }` | Query with conditions |
+| `Table.insertAndGetId { }` | Insert and return generated ID |
+| `Table.update({ condition }) { }` | Update matching rows |
+| `Table.deleteWhere { }` | Delete matching rows |
+| `Table.batchInsert(items) { }` | Efficient bulk insert |
+| `innerJoin` / `leftJoin` | Join tables |
+| `orderBy` / `limit` / `offset` | Sort and paginate |
+| `count()` / `sum()` / `avg()` | Aggregation functions |
+
+**Remember**: Use the DSL style for simple queries and the DAO style when you need entity lifecycle management. Always use `newSuspendedTransaction` for coroutine support, and wrap database operations behind a repository interface for testability.

skills/kotlin-ktor-patterns/SKILL.md

@@ -0,0 +1,689 @@
+---
+name: kotlin-ktor-patterns
+description: Ktor server patterns including routing DSL, plugins, authentication, Koin DI, kotlinx.serialization, WebSockets, and testApplication testing.
+origin: ECC
+---
+
+# Ktor Server Patterns
+
+Comprehensive Ktor patterns for building robust, maintainable HTTP servers with Kotlin coroutines.
+
+## When to Activate
+
+- Building Ktor HTTP servers
+- Configuring Ktor plugins (Auth, CORS, ContentNegotiation, StatusPages)
+- Implementing REST APIs with Ktor
+- Setting up dependency injection with Koin
+- Writing Ktor integration tests with testApplication
+- Working with WebSockets in Ktor
+
+## Application Structure
+
+### Standard Ktor Project Layout
+
+```text
+src/main/kotlin/
+├── com/example/
+│   ├── Application.kt           # Entry point, module configuration
+│   ├── plugins/
+│   │   ├── Routing.kt           # Route definitions
+│   │   ├── Serialization.kt     # Content negotiation setup
+│   │   ├── Authentication.kt    # Auth configuration
+│   │   ├── StatusPages.kt       # Error handling
+│   │   └── CORS.kt              # CORS configuration
+│   ├── routes/
+│   │   ├── UserRoutes.kt        # /users endpoints
+│   │   ├── AuthRoutes.kt        # /auth endpoints
+│   │   └── HealthRoutes.kt      # /health endpoints
+│   ├── models/
+│   │   ├── User.kt              # Domain models
+│   │   └── ApiResponse.kt       # Response envelopes
+│   ├── services/
+│   │   ├── UserService.kt       # Business logic
+│   │   └── AuthService.kt       # Auth logic
+│   ├── repositories/
+│   │   ├── UserRepository.kt    # Data access interface
+│   │   └── ExposedUserRepository.kt
+│   └── di/
+│       └── AppModule.kt         # Koin modules
+src/test/kotlin/
+├── com/example/
+│   ├── routes/
+│   │   └── UserRoutesTest.kt
+│   └── services/
+│       └── UserServiceTest.kt
+```
+
+### Application Entry Point
+
+```kotlin
+// Application.kt
+fun main() {
+    embeddedServer(Netty, port = 8080, module = Application::module).start(wait = true)
+}
+
+fun Application.module() {
+    configureSerialization()
+    configureAuthentication()
+    configureStatusPages()
+    configureCORS()
+    configureDI()
+    configureRouting()
+}
+```
+
+## Routing DSL
+
+### Basic Routes
+
+```kotlin
+// plugins/Routing.kt
+fun Application.configureRouting() {
+    routing {
+        userRoutes()
+        authRoutes()
+        healthRoutes()
+    }
+}
+
+// routes/UserRoutes.kt
+fun Route.userRoutes() {
+    val userService by inject<UserService>()
+
+    route("/users") {
+        get {
+            val users = userService.getAll()
+            call.respond(users)
+        }
+
+        get("/{id}") {
+            val id = call.parameters["id"]
+                ?: return@get call.respond(HttpStatusCode.BadRequest, "Missing id")
+            val user = userService.getById(id)
+                ?: return@get call.respond(HttpStatusCode.NotFound)
+            call.respond(user)
+        }
+
+        post {
+            val request = call.receive<CreateUserRequest>()
+            val user = userService.create(request)
+            call.respond(HttpStatusCode.Created, user)
+        }
+
+        put("/{id}") {
+            val id = call.parameters["id"]
+                ?: return@put call.respond(HttpStatusCode.BadRequest, "Missing id")
+            val request = call.receive<UpdateUserRequest>()
+            val user = userService.update(id, request)
+                ?: return@put call.respond(HttpStatusCode.NotFound)
+            call.respond(user)
+        }
+
+        delete("/{id}") {
+            val id = call.parameters["id"]
+                ?: return@delete call.respond(HttpStatusCode.BadRequest, "Missing id")
+            val deleted = userService.delete(id)
+            if (deleted) call.respond(HttpStatusCode.NoContent)
+            else call.respond(HttpStatusCode.NotFound)
+        }
+    }
+}
+```
+
+### Route Organization with Authenticated Routes
+
+```kotlin
+fun Route.userRoutes() {
+    route("/users") {
+        // Public routes
+        get { /* list users */ }
+        get("/{id}") { /* get user */ }
+
+        // Protected routes
+        authenticate("jwt") {
+            post { /* create user - requires auth */ }
+            put("/{id}") { /* update user - requires auth */ }
+            delete("/{id}") { /* delete user - requires auth */ }
+        }
+    }
+}
+```
+
+## Content Negotiation & Serialization
+
+### kotlinx.serialization Setup
+
+```kotlin
+// plugins/Serialization.kt
+fun Application.configureSerialization() {
+    install(ContentNegotiation) {
+        json(Json {
+            prettyPrint = true
+            isLenient = false
+            ignoreUnknownKeys = true
+            encodeDefaults = true
+            explicitNulls = false
+        })
+    }
+}
+```
+
+### Serializable Models
+
+```kotlin
+@Serializable
+data class UserResponse(
+    val id: String,
+    val name: String,
+    val email: String,
+    val role: Role,
+    @Serializable(with = InstantSerializer::class)
+    val createdAt: Instant,
+)
+
+@Serializable
+data class CreateUserRequest(
+    val name: String,
+    val email: String,
+    val role: Role = Role.USER,
+)
+
+@Serializable
+data class ApiResponse<T>(
+    val success: Boolean,
+    val data: T? = null,
+    val error: String? = null,
+) {
+    companion object {
+        fun <T> ok(data: T): ApiResponse<T> = ApiResponse(success = true, data = data)
+        fun <T> error(message: String): ApiResponse<T> = ApiResponse(success = false, error = message)
+    }
+}
+
+@Serializable
+data class PaginatedResponse<T>(
+    val data: List<T>,
+    val total: Long,
+    val page: Int,
+    val limit: Int,
+)
+```
+
+### Custom Serializers
+
+```kotlin
+object InstantSerializer : KSerializer<Instant> {
+    override val descriptor = PrimitiveSerialDescriptor("Instant", PrimitiveKind.STRING)
+    override fun serialize(encoder: Encoder, value: Instant) =
+        encoder.encodeString(value.toString())
+    override fun deserialize(decoder: Decoder): Instant =
+        Instant.parse(decoder.decodeString())
+}
+```
+
+## Authentication
+
+### JWT Authentication
+
+```kotlin
+// plugins/Authentication.kt
+fun Application.configureAuthentication() {
+    val jwtSecret = environment.config.property("jwt.secret").getString()
+    val jwtIssuer = environment.config.property("jwt.issuer").getString()
+    val jwtAudience = environment.config.property("jwt.audience").getString()
+    val jwtRealm = environment.config.property("jwt.realm").getString()
+
+    install(Authentication) {
+        jwt("jwt") {
+            realm = jwtRealm
+            verifier(
+                JWT.require(Algorithm.HMAC256(jwtSecret))
+                    .withAudience(jwtAudience)
+                    .withIssuer(jwtIssuer)
+                    .build()
+            )
+            validate { credential ->
+                if (credential.payload.audience.contains(jwtAudience)) {
+                    JWTPrincipal(credential.payload)
+                } else {
+                    null
+                }
+            }
+            challenge { _, _ ->
+                call.respond(HttpStatusCode.Unauthorized, ApiResponse.error<Unit>("Invalid or expired token"))
+            }
+        }
+    }
+}
+
+// Extracting user from JWT
+fun ApplicationCall.userId(): String =
+    principal<JWTPrincipal>()
+        ?.payload
+        ?.getClaim("userId")
+        ?.asString()
+        ?: throw AuthenticationException("No userId in token")
+```
+
+### Auth Routes
+
+```kotlin
+fun Route.authRoutes() {
+    val authService by inject<AuthService>()
+
+    route("/auth") {
+        post("/login") {
+            val request = call.receive<LoginRequest>()
+            val token = authService.login(request.email, request.password)
+                ?: return@post call.respond(
+                    HttpStatusCode.Unauthorized,
+                    ApiResponse.error<Unit>("Invalid credentials"),
+                )
+            call.respond(ApiResponse.ok(TokenResponse(token)))
+        }
+
+        post("/register") {
+            val request = call.receive<RegisterRequest>()
+            val user = authService.register(request)
+            call.respond(HttpStatusCode.Created, ApiResponse.ok(user))
+        }
+
+        authenticate("jwt") {
+            get("/me") {
+                val userId = call.userId()
+                val user = authService.getProfile(userId)
+                call.respond(ApiResponse.ok(user))
+            }
+        }
+    }
+}
+```
+
+## Status Pages (Error Handling)
+
+```kotlin
+// plugins/StatusPages.kt
+fun Application.configureStatusPages() {
+    install(StatusPages) {
+        exception<ContentTransformationException> { call, cause ->
+            call.respond(
+                HttpStatusCode.BadRequest,
+                ApiResponse.error<Unit>("Invalid request body: ${cause.message}"),
+            )
+        }
+
+        exception<IllegalArgumentException> { call, cause ->
+            call.respond(
+                HttpStatusCode.BadRequest,
+                ApiResponse.error<Unit>(cause.message ?: "Bad request"),
+            )
+        }
+
+        exception<AuthenticationException> { call, _ ->
+            call.respond(
+                HttpStatusCode.Unauthorized,
+                ApiResponse.error<Unit>("Authentication required"),
+            )
+        }
+
+        exception<AuthorizationException> { call, _ ->
+            call.respond(
+                HttpStatusCode.Forbidden,
+                ApiResponse.error<Unit>("Access denied"),
+            )
+        }
+
+        exception<NotFoundException> { call, cause ->
+            call.respond(
+                HttpStatusCode.NotFound,
+                ApiResponse.error<Unit>(cause.message ?: "Resource not found"),
+            )
+        }
+
+        exception<Throwable> { call, cause ->
+            call.application.log.error("Unhandled exception", cause)
+            call.respond(
+                HttpStatusCode.InternalServerError,
+                ApiResponse.error<Unit>("Internal server error"),
+            )
+        }
+
+        status(HttpStatusCode.NotFound) { call, status ->
+            call.respond(status, ApiResponse.error<Unit>("Route not found"))
+        }
+    }
+}
+```
+
+## CORS Configuration
+
+```kotlin
+// plugins/CORS.kt
+fun Application.configureCORS() {
+    install(CORS) {
+        allowHost("localhost:3000")
+        allowHost("example.com", schemes = listOf("https"))
+        allowHeader(HttpHeaders.ContentType)
+        allowHeader(HttpHeaders.Authorization)
+        allowMethod(HttpMethod.Put)
+        allowMethod(HttpMethod.Delete)
+        allowMethod(HttpMethod.Patch)
+        allowCredentials = true
+        maxAgeInSeconds = 3600
+    }
+}
+```
+
+## Koin Dependency Injection
+
+### Module Definition
+
+```kotlin
+// di/AppModule.kt
+val appModule = module {
+    // Database
+    single<Database> { DatabaseFactory.create(get()) }
+
+    // Repositories
+    single<UserRepository> { ExposedUserRepository(get()) }
+    single<OrderRepository> { ExposedOrderRepository(get()) }
+
+    // Services
+    single { UserService(get()) }
+    single { OrderService(get(), get()) }
+    single { AuthService(get(), get()) }
+}
+
+// Application setup
+fun Application.configureDI() {
+    install(Koin) {
+        modules(appModule)
+    }
+}
+```
+
+### Using Koin in Routes
+
+```kotlin
+fun Route.userRoutes() {
+    val userService by inject<UserService>()
+
+    route("/users") {
+        get {
+            val users = userService.getAll()
+            call.respond(ApiResponse.ok(users))
+        }
+    }
+}
+```
+
+### Koin for Testing
+
+```kotlin
+class UserServiceTest : FunSpec(), KoinTest {
+    override fun extensions() = listOf(KoinExtension(testModule))
+
+    private val testModule = module {
+        single<UserRepository> { mockk() }
+        single { UserService(get()) }
+    }
+
+    private val repository by inject<UserRepository>()
+    private val service by inject<UserService>()
+
+    init {
+        test("getUser returns user") {
+            coEvery { repository.findById("1") } returns testUser
+            service.getById("1") shouldBe testUser
+        }
+    }
+}
+```
+
+## Request Validation
+
+```kotlin
+// Validate request data in routes
+fun Route.userRoutes() {
+    val userService by inject<UserService>()
+
+    post("/users") {
+        val request = call.receive<CreateUserRequest>()
+
+        // Validate
+        require(request.name.isNotBlank()) { "Name is required" }
+        require(request.name.length <= 100) { "Name must be 100 characters or less" }
+        require(request.email.matches(Regex(".+@.+\\..+"))) { "Invalid email format" }
+
+        val user = userService.create(request)
+        call.respond(HttpStatusCode.Created, ApiResponse.ok(user))
+    }
+}
+
+// Or use a validation extension
+fun CreateUserRequest.validate() {
+    require(name.isNotBlank()) { "Name is required" }
+    require(name.length <= 100) { "Name must be 100 characters or less" }
+    require(email.matches(Regex(".+@.+\\..+"))) { "Invalid email format" }
+}
+```
+
+## WebSockets
+
+```kotlin
+fun Application.configureWebSockets() {
+    install(WebSockets) {
+        pingPeriod = 15.seconds
+        timeout = 15.seconds
+        maxFrameSize = 64 * 1024 // 64 KiB — increase only if your protocol requires larger frames
+        masking = false // Server-to-client frames are unmasked per RFC 6455; client-to-server are always masked by Ktor
+    }
+}
+
+fun Route.chatRoutes() {
+    val connections = Collections.synchronizedSet<Connection>(LinkedHashSet())
+
+    webSocket("/chat") {
+        val thisConnection = Connection(this)
+        connections += thisConnection
+
+        try {
+            send("Connected! Users online: ${connections.size}")
+
+            for (frame in incoming) {
+                frame as? Frame.Text ?: continue
+                val text = frame.readText()
+                val message = ChatMessage(thisConnection.name, text)
+
+                // Snapshot under lock to avoid ConcurrentModificationException
+                val snapshot = synchronized(connections) { connections.toList() }
+                snapshot.forEach { conn ->
+                    conn.session.send(Json.encodeToString(message))
+                }
+            }
+        } catch (e: Exception) {
+            logger.error("WebSocket error", e)
+        } finally {
+            connections -= thisConnection
+        }
+    }
+}
+
+data class Connection(val session: DefaultWebSocketSession) {
+    val name: String = "User-${counter.getAndIncrement()}"
+
+    companion object {
+        private val counter = AtomicInteger(0)
+    }
+}
+```
+
+## testApplication Testing
+
+### Basic Route Testing
+
+```kotlin
+class UserRoutesTest : FunSpec({
+    test("GET /users returns list of users") {
+        testApplication {
+            application {
+                install(Koin) { modules(testModule) }
+                configureSerialization()
+                configureRouting()
+            }
+
+            val response = client.get("/users")
+
+            response.status shouldBe HttpStatusCode.OK
+            val body = response.body<ApiResponse<List<UserResponse>>>()
+            body.success shouldBe true
+            body.data.shouldNotBeNull().shouldNotBeEmpty()
+        }
+    }
+
+    test("POST /users creates a user") {
+        testApplication {
+            application {
+                install(Koin) { modules(testModule) }
+                configureSerialization()
+                configureStatusPages()
+                configureRouting()
+            }
+
+            val client = createClient {
+                install(io.ktor.client.plugins.contentnegotiation.ContentNegotiation) {
+                    json()
+                }
+            }
+
+            val response = client.post("/users") {
+                contentType(ContentType.Application.Json)
+                setBody(CreateUserRequest("Alice", "alice@example.com"))
+            }
+
+            response.status shouldBe HttpStatusCode.Created
+        }
+    }
+
+    test("GET /users/{id} returns 404 for unknown id") {
+        testApplication {
+            application {
+                install(Koin) { modules(testModule) }
+                configureSerialization()
+                configureStatusPages()
+                configureRouting()
+            }
+
+            val response = client.get("/users/unknown-id")
+
+            response.status shouldBe HttpStatusCode.NotFound
+        }
+    }
+})
+```
+
+### Testing Authenticated Routes
+
+```kotlin
+class AuthenticatedRoutesTest : FunSpec({
+    test("protected route requires JWT") {
+        testApplication {
+            application {
+                install(Koin) { modules(testModule) }
+                configureSerialization()
+                configureAuthentication()
+                configureRouting()
+            }
+
+            val response = client.post("/users") {
+                contentType(ContentType.Application.Json)
+                setBody(CreateUserRequest("Alice", "alice@example.com"))
+            }
+
+            response.status shouldBe HttpStatusCode.Unauthorized
+        }
+    }
+
+    test("protected route succeeds with valid JWT") {
+        testApplication {
+            application {
+                install(Koin) { modules(testModule) }
+                configureSerialization()
+                configureAuthentication()
+                configureRouting()
+            }
+
+            val token = generateTestJWT(userId = "test-user")
+
+            val client = createClient {
+                install(io.ktor.client.plugins.contentnegotiation.ContentNegotiation) { json() }
+            }
+
+            val response = client.post("/users") {
+                contentType(ContentType.Application.Json)
+                bearerAuth(token)
+                setBody(CreateUserRequest("Alice", "alice@example.com"))
+            }
+
+            response.status shouldBe HttpStatusCode.Created
+        }
+    }
+})
+```
+
+## Configuration
+
+### application.yaml
+
+```yaml
+ktor:
+  application:
+    modules:
+      - com.example.ApplicationKt.module
+  deployment:
+    port: 8080
+
+jwt:
+  secret: ${JWT_SECRET}
+  issuer: "https://example.com"
+  audience: "https://example.com/api"
+  realm: "example"
+
+database:
+  url: ${DATABASE_URL}
+  driver: "org.postgresql.Driver"
+  maxPoolSize: 10
+```
+
+### Reading Config
+
+```kotlin
+fun Application.configureDI() {
+    val dbUrl = environment.config.property("database.url").getString()
+    val dbDriver = environment.config.property("database.driver").getString()
+    val maxPoolSize = environment.config.property("database.maxPoolSize").getString().toInt()
+
+    install(Koin) {
+        modules(module {
+            single { DatabaseConfig(dbUrl, dbDriver, maxPoolSize) }
+            single { DatabaseFactory.create(get()) }
+        })
+    }
+}
+```
+
+## Quick Reference: Ktor Patterns
+
+| Pattern | Description |
+|---------|-------------|
+| `route("/path") { get { } }` | Route grouping with DSL |
+| `call.receive<T>()` | Deserialize request body |
+| `call.respond(status, body)` | Send response with status |
+| `call.parameters["id"]` | Read path parameters |
+| `call.request.queryParameters["q"]` | Read query parameters |
+| `install(Plugin) { }` | Install and configure plugin |
+| `authenticate("name") { }` | Protect routes with auth |
+| `by inject<T>()` | Koin dependency injection |
+| `testApplication { }` | Integration testing |
+
+**Remember**: Ktor is designed around Kotlin coroutines and DSLs. Keep routes thin, push logic to services, and use Koin for dependency injection. Test with `testApplication` for full integration coverage.

skills/kotlin-patterns/SKILL.md

@@ -0,0 +1,711 @@
+---
+name: kotlin-patterns
+description: Idiomatic Kotlin patterns, best practices, and conventions for building robust, efficient, and maintainable Kotlin applications with coroutines, null safety, and DSL builders.
+origin: ECC
+---
+
+# Kotlin Development Patterns
+
+Idiomatic Kotlin patterns and best practices for building robust, efficient, and maintainable applications.
+
+## When to Use
+
+- Writing new Kotlin code
+- Reviewing Kotlin code
+- Refactoring existing Kotlin code
+- Designing Kotlin modules or libraries
+- Configuring Gradle Kotlin DSL builds
+
+## How It Works
+
+This skill enforces idiomatic Kotlin conventions across seven key areas: null safety using the type system and safe-call operators, immutability via `val` and `copy()` on data classes, sealed classes and interfaces for exhaustive type hierarchies, structured concurrency with coroutines and `Flow`, extension functions for adding behaviour without inheritance, type-safe DSL builders using `@DslMarker` and lambda receivers, and Gradle Kotlin DSL for build configuration.
+
+## Examples
+
+**Null safety with Elvis operator:**
+```kotlin
+fun getUserEmail(userId: String): String {
+    val user = userRepository.findById(userId)
+    return user?.email ?: "unknown@example.com"
+}
+```
+
+**Sealed class for exhaustive results:**
+```kotlin
+sealed class Result<out T> {
+    data class Success<T>(val data: T) : Result<T>()
+    data class Failure(val error: AppError) : Result<Nothing>()
+    data object Loading : Result<Nothing>()
+}
+```
+
+**Structured concurrency with async/await:**
+```kotlin
+suspend fun fetchUserWithPosts(userId: String): UserProfile =
+    coroutineScope {
+        val user = async { userService.getUser(userId) }
+        val posts = async { postService.getUserPosts(userId) }
+        UserProfile(user = user.await(), posts = posts.await())
+    }
+```
+
+## Core Principles
+
+### 1. Null Safety
+
+Kotlin's type system distinguishes nullable and non-nullable types. Leverage it fully.
+
+```kotlin
+// Good: Use non-nullable types by default
+fun getUser(id: String): User {
+    return userRepository.findById(id)
+        ?: throw UserNotFoundException("User $id not found")
+}
+
+// Good: Safe calls and Elvis operator
+fun getUserEmail(userId: String): String {
+    val user = userRepository.findById(userId)
+    return user?.email ?: "unknown@example.com"
+}
+
+// Bad: Force-unwrapping nullable types
+fun getUserEmail(userId: String): String {
+    val user = userRepository.findById(userId)
+    return user!!.email // Throws NPE if null
+}
+```
+
+### 2. Immutability by Default
+
+Prefer `val` over `var`, immutable collections over mutable ones.
+
+```kotlin
+// Good: Immutable data
+data class User(
+    val id: String,
+    val name: String,
+    val email: String,
+)
+
+// Good: Transform with copy()
+fun updateEmail(user: User, newEmail: String): User =
+    user.copy(email = newEmail)
+
+// Good: Immutable collections
+val users: List<User> = listOf(user1, user2)
+val filtered = users.filter { it.email.isNotBlank() }
+
+// Bad: Mutable state
+var currentUser: User? = null // Avoid mutable global state
+val mutableUsers = mutableListOf<User>() // Avoid unless truly needed
+```
+
+### 3. Expression Bodies and Single-Expression Functions
+
+Use expression bodies for concise, readable functions.
+
+```kotlin
+// Good: Expression body
+fun isAdult(age: Int): Boolean = age >= 18
+
+fun formatFullName(first: String, last: String): String =
+    "$first $last".trim()
+
+fun User.displayName(): String =
+    name.ifBlank { email.substringBefore('@') }
+
+// Good: When as expression
+fun statusMessage(code: Int): String = when (code) {
+    200 -> "OK"
+    404 -> "Not Found"
+    500 -> "Internal Server Error"
+    else -> "Unknown status: $code"
+}
+
+// Bad: Unnecessary block body
+fun isAdult(age: Int): Boolean {
+    return age >= 18
+}
+```
+
+### 4. Data Classes for Value Objects
+
+Use data classes for types that primarily hold data.
+
+```kotlin
+// Good: Data class with copy, equals, hashCode, toString
+data class CreateUserRequest(
+    val name: String,
+    val email: String,
+    val role: Role = Role.USER,
+)
+
+// Good: Value class for type safety (zero overhead at runtime)
+@JvmInline
+value class UserId(val value: String) {
+    init {
+        require(value.isNotBlank()) { "UserId cannot be blank" }
+    }
+}
+
+@JvmInline
+value class Email(val value: String) {
+    init {
+        require('@' in value) { "Invalid email: $value" }
+    }
+}
+
+fun getUser(id: UserId): User = userRepository.findById(id)
+```
+
+## Sealed Classes and Interfaces
+
+### Modeling Restricted Hierarchies
+
+```kotlin
+// Good: Sealed class for exhaustive when
+sealed class Result<out T> {
+    data class Success<T>(val data: T) : Result<T>()
+    data class Failure(val error: AppError) : Result<Nothing>()
+    data object Loading : Result<Nothing>()
+}
+
+fun <T> Result<T>.getOrNull(): T? = when (this) {
+    is Result.Success -> data
+    is Result.Failure -> null
+    is Result.Loading -> null
+}
+
+fun <T> Result<T>.getOrThrow(): T = when (this) {
+    is Result.Success -> data
+    is Result.Failure -> throw error.toException()
+    is Result.Loading -> throw IllegalStateException("Still loading")
+}
+```
+
+### Sealed Interfaces for API Responses
+
+```kotlin
+sealed interface ApiError {
+    val message: String
+
+    data class NotFound(override val message: String) : ApiError
+    data class Unauthorized(override val message: String) : ApiError
+    data class Validation(
+        override val message: String,
+        val field: String,
+    ) : ApiError
+    data class Internal(
+        override val message: String,
+        val cause: Throwable? = null,
+    ) : ApiError
+}
+
+fun ApiError.toStatusCode(): Int = when (this) {
+    is ApiError.NotFound -> 404
+    is ApiError.Unauthorized -> 401
+    is ApiError.Validation -> 422
+    is ApiError.Internal -> 500
+}
+```
+
+## Scope Functions
+
+### When to Use Each
+
+```kotlin
+// let: Transform nullable or scoped result
+val length: Int? = name?.let { it.trim().length }
+
+// apply: Configure an object (returns the object)
+val user = User().apply {
+    name = "Alice"
+    email = "alice@example.com"
+}
+
+// also: Side effects (returns the object)
+val user = createUser(request).also { logger.info("Created user: ${it.id}") }
+
+// run: Execute a block with receiver (returns result)
+val result = connection.run {
+    prepareStatement(sql)
+    executeQuery()
+}
+
+// with: Non-extension form of run
+val csv = with(StringBuilder()) {
+    appendLine("name,email")
+    users.forEach { appendLine("${it.name},${it.email}") }
+    toString()
+}
+```
+
+### Anti-Patterns
+
+```kotlin
+// Bad: Nesting scope functions
+user?.let { u ->
+    u.address?.let { addr ->
+        addr.city?.let { city ->
+            println(city) // Hard to read
+        }
+    }
+}
+
+// Good: Chain safe calls instead
+val city = user?.address?.city
+city?.let { println(it) }
+```
+
+## Extension Functions
+
+### Adding Functionality Without Inheritance
+
+```kotlin
+// Good: Domain-specific extensions
+fun String.toSlug(): String =
+    lowercase()
+        .replace(Regex("[^a-z0-9\\s-]"), "")
+        .replace(Regex("\\s+"), "-")
+        .trim('-')
+
+fun Instant.toLocalDate(zone: ZoneId = ZoneId.systemDefault()): LocalDate =
+    atZone(zone).toLocalDate()
+
+// Good: Collection extensions
+fun <T> List<T>.second(): T = this[1]
+
+fun <T> List<T>.secondOrNull(): T? = getOrNull(1)
+
+// Good: Scoped extensions (not polluting global namespace)
+class UserService {
+    private fun User.isActive(): Boolean =
+        status == Status.ACTIVE && lastLogin.isAfter(Instant.now().minus(30, ChronoUnit.DAYS))
+
+    fun getActiveUsers(): List<User> = userRepository.findAll().filter { it.isActive() }
+}
+```
+
+## Coroutines
+
+### Structured Concurrency
+
+```kotlin
+// Good: Structured concurrency with coroutineScope
+suspend fun fetchUserWithPosts(userId: String): UserProfile =
+    coroutineScope {
+        val userDeferred = async { userService.getUser(userId) }
+        val postsDeferred = async { postService.getUserPosts(userId) }
+
+        UserProfile(
+            user = userDeferred.await(),
+            posts = postsDeferred.await(),
+        )
+    }
+
+// Good: supervisorScope when children can fail independently
+suspend fun fetchDashboard(userId: String): Dashboard =
+    supervisorScope {
+        val user = async { userService.getUser(userId) }
+        val notifications = async { notificationService.getRecent(userId) }
+        val recommendations = async { recommendationService.getFor(userId) }
+
+        Dashboard(
+            user = user.await(),
+            notifications = try {
+                notifications.await()
+            } catch (e: CancellationException) {
+                throw e
+            } catch (e: Exception) {
+                emptyList()
+            },
+            recommendations = try {
+                recommendations.await()
+            } catch (e: CancellationException) {
+                throw e
+            } catch (e: Exception) {
+                emptyList()
+            },
+        )
+    }
+```
+
+### Flow for Reactive Streams
+
+```kotlin
+// Good: Cold flow with proper error handling
+fun observeUsers(): Flow<List<User>> = flow {
+    while (currentCoroutineContext().isActive) {
+        val users = userRepository.findAll()
+        emit(users)
+        delay(5.seconds)
+    }
+}.catch { e ->
+    logger.error("Error observing users", e)
+    emit(emptyList())
+}
+
+// Good: Flow operators
+fun searchUsers(query: Flow<String>): Flow<List<User>> =
+    query
+        .debounce(300.milliseconds)
+        .distinctUntilChanged()
+        .filter { it.length >= 2 }
+        .mapLatest { q -> userRepository.search(q) }
+        .catch { emit(emptyList()) }
+```
+
+### Cancellation and Cleanup
+
+```kotlin
+// Good: Respect cancellation
+suspend fun processItems(items: List<Item>) {
+    items.forEach { item ->
+        ensureActive() // Check cancellation before expensive work
+        processItem(item)
+    }
+}
+
+// Good: Cleanup with try/finally
+suspend fun acquireAndProcess() {
+    val resource = acquireResource()
+    try {
+        resource.process()
+    } finally {
+        withContext(NonCancellable) {
+            resource.release() // Always release, even on cancellation
+        }
+    }
+}
+```
+
+## Delegation
+
+### Property Delegation
+
+```kotlin
+// Lazy initialization
+val expensiveData: List<User> by lazy {
+    userRepository.findAll()
+}
+
+// Observable property
+var name: String by Delegates.observable("initial") { _, old, new ->
+    logger.info("Name changed from '$old' to '$new'")
+}
+
+// Map-backed properties
+class Config(private val map: Map<String, Any?>) {
+    val host: String by map
+    val port: Int by map
+    val debug: Boolean by map
+}
+
+val config = Config(mapOf("host" to "localhost", "port" to 8080, "debug" to true))
+```
+
+### Interface Delegation
+
+```kotlin
+// Good: Delegate interface implementation
+class LoggingUserRepository(
+    private val delegate: UserRepository,
+    private val logger: Logger,
+) : UserRepository by delegate {
+    // Only override what you need to add logging to
+    override suspend fun findById(id: String): User? {
+        logger.info("Finding user by id: $id")
+        return delegate.findById(id).also {
+            logger.info("Found user: ${it?.name ?: "null"}")
+        }
+    }
+}
+```
+
+## DSL Builders
+
+### Type-Safe Builders
+
+```kotlin
+// Good: DSL with @DslMarker
+@DslMarker
+annotation class HtmlDsl
+
+@HtmlDsl
+class HTML {
+    private val children = mutableListOf<Element>()
+
+    fun head(init: Head.() -> Unit) {
+        children += Head().apply(init)
+    }
+
+    fun body(init: Body.() -> Unit) {
+        children += Body().apply(init)
+    }
+
+    override fun toString(): String = children.joinToString("\n")
+}
+
+fun html(init: HTML.() -> Unit): HTML = HTML().apply(init)
+
+// Usage
+val page = html {
+    head { title("My Page") }
+    body {
+        h1("Welcome")
+        p("Hello, World!")
+    }
+}
+```
+
+### Configuration DSL
+
+```kotlin
+data class ServerConfig(
+    val host: String = "0.0.0.0",
+    val port: Int = 8080,
+    val ssl: SslConfig? = null,
+    val database: DatabaseConfig? = null,
+)
+
+data class SslConfig(val certPath: String, val keyPath: String)
+data class DatabaseConfig(val url: String, val maxPoolSize: Int = 10)
+
+class ServerConfigBuilder {
+    var host: String = "0.0.0.0"
+    var port: Int = 8080
+    private var ssl: SslConfig? = null
+    private var database: DatabaseConfig? = null
+
+    fun ssl(certPath: String, keyPath: String) {
+        ssl = SslConfig(certPath, keyPath)
+    }
+
+    fun database(url: String, maxPoolSize: Int = 10) {
+        database = DatabaseConfig(url, maxPoolSize)
+    }
+
+    fun build(): ServerConfig = ServerConfig(host, port, ssl, database)
+}
+
+fun serverConfig(init: ServerConfigBuilder.() -> Unit): ServerConfig =
+    ServerConfigBuilder().apply(init).build()
+
+// Usage
+val config = serverConfig {
+    host = "0.0.0.0"
+    port = 443
+    ssl("/certs/cert.pem", "/certs/key.pem")
+    database("jdbc:postgresql://localhost:5432/mydb", maxPoolSize = 20)
+}
+```
+
+## Sequences for Lazy Evaluation
+
+```kotlin
+// Good: Use sequences for large collections with multiple operations
+val result = users.asSequence()
+    .filter { it.isActive }
+    .map { it.email }
+    .filter { it.endsWith("@company.com") }
+    .take(10)
+    .toList()
+
+// Good: Generate infinite sequences
+val fibonacci: Sequence<Long> = sequence {
+    var a = 0L
+    var b = 1L
+    while (true) {
+        yield(a)
+        val next = a + b
+        a = b
+        b = next
+    }
+}
+
+val first20 = fibonacci.take(20).toList()
+```
+
+## Gradle Kotlin DSL
+
+### build.gradle.kts Configuration
+
+```kotlin
+// Check for latest versions: https://kotlinlang.org/docs/releases.html
+plugins {
+    kotlin("jvm") version "2.3.10"
+    kotlin("plugin.serialization") version "2.3.10"
+    id("io.ktor.plugin") version "3.4.0"
+    id("org.jetbrains.kotlinx.kover") version "0.9.7"
+    id("io.gitlab.arturbosch.detekt") version "1.23.8"
+}
+
+group = "com.example"
+version = "1.0.0"
+
+kotlin {
+    jvmToolchain(21)
+}
+
+dependencies {
+    // Ktor
+    implementation("io.ktor:ktor-server-core:3.4.0")
+    implementation("io.ktor:ktor-server-netty:3.4.0")
+    implementation("io.ktor:ktor-server-content-negotiation:3.4.0")
+    implementation("io.ktor:ktor-serialization-kotlinx-json:3.4.0")
+
+    // Exposed
+    implementation("org.jetbrains.exposed:exposed-core:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-dao:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-jdbc:1.0.0")
+    implementation("org.jetbrains.exposed:exposed-kotlin-datetime:1.0.0")
+
+    // Koin
+    implementation("io.insert-koin:koin-ktor:4.2.0")
+
+    // Coroutines
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
+
+    // Testing
+    testImplementation("io.kotest:kotest-runner-junit5:6.1.4")
+    testImplementation("io.kotest:kotest-assertions-core:6.1.4")
+    testImplementation("io.kotest:kotest-property:6.1.4")
+    testImplementation("io.mockk:mockk:1.14.9")
+    testImplementation("io.ktor:ktor-server-test-host:3.4.0")
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.10.2")
+}
+
+tasks.withType<Test> {
+    useJUnitPlatform()
+}
+
+detekt {
+    config.setFrom(files("config/detekt/detekt.yml"))
+    buildUponDefaultConfig = true
+}
+```
+
+## Error Handling Patterns
+
+### Result Type for Domain Operations
+
+```kotlin
+// Good: Use Kotlin's Result or a custom sealed class
+suspend fun createUser(request: CreateUserRequest): Result<User> = runCatching {
+    require(request.name.isNotBlank()) { "Name cannot be blank" }
+    require('@' in request.email) { "Invalid email format" }
+
+    val user = User(
+        id = UserId(UUID.randomUUID().toString()),
+        name = request.name,
+        email = Email(request.email),
+    )
+    userRepository.save(user)
+    user
+}
+
+// Good: Chain results
+val displayName = createUser(request)
+    .map { it.name }
+    .getOrElse { "Unknown" }
+```
+
+### require, check, error
+
+```kotlin
+// Good: Preconditions with clear messages
+fun withdraw(account: Account, amount: Money): Account {
+    require(amount.value > 0) { "Amount must be positive: $amount" }
+    check(account.balance >= amount) { "Insufficient balance: ${account.balance} < $amount" }
+
+    return account.copy(balance = account.balance - amount)
+}
+```
+
+## Collection Operations
+
+### Idiomatic Collection Processing
+
+```kotlin
+// Good: Chained operations
+val activeAdminEmails: List<String> = users
+    .filter { it.role == Role.ADMIN && it.isActive }
+    .sortedBy { it.name }
+    .map { it.email }
+
+// Good: Grouping and aggregation
+val usersByRole: Map<Role, List<User>> = users.groupBy { it.role }
+
+val oldestByRole: Map<Role, User?> = users.groupBy { it.role }
+    .mapValues { (_, users) -> users.minByOrNull { it.createdAt } }
+
+// Good: Associate for map creation
+val usersById: Map<UserId, User> = users.associateBy { it.id }
+
+// Good: Partition for splitting
+val (active, inactive) = users.partition { it.isActive }
+```
+
+## Quick Reference: Kotlin Idioms
+
+| Idiom | Description |
+|-------|-------------|
+| `val` over `var` | Prefer immutable variables |
+| `data class` | For value objects with equals/hashCode/copy |
+| `sealed class/interface` | For restricted type hierarchies |
+| `value class` | For type-safe wrappers with zero overhead |
+| Expression `when` | Exhaustive pattern matching |
+| Safe call `?.` | Null-safe member access |
+| Elvis `?:` | Default value for nullables |
+| `let`/`apply`/`also`/`run`/`with` | Scope functions for clean code |
+| Extension functions | Add behavior without inheritance |
+| `copy()` | Immutable updates on data classes |
+| `require`/`check` | Precondition assertions |
+| Coroutine `async`/`await` | Structured concurrent execution |
+| `Flow` | Cold reactive streams |
+| `sequence` | Lazy evaluation |
+| Delegation `by` | Reuse implementation without inheritance |
+
+## Anti-Patterns to Avoid
+
+```kotlin
+// Bad: Force-unwrapping nullable types
+val name = user!!.name
+
+// Bad: Platform type leakage from Java
+fun getLength(s: String) = s.length // Safe
+fun getLength(s: String?) = s?.length ?: 0 // Handle nulls from Java
+
+// Bad: Mutable data classes
+data class MutableUser(var name: String, var email: String)
+
+// Bad: Using exceptions for control flow
+try {
+    val user = findUser(id)
+} catch (e: NotFoundException) {
+    // Don't use exceptions for expected cases
+}
+
+// Good: Use nullable return or Result
+val user: User? = findUserOrNull(id)
+
+// Bad: Ignoring coroutine scope
+GlobalScope.launch { /* Avoid GlobalScope */ }
+
+// Good: Use structured concurrency
+coroutineScope {
+    launch { /* Properly scoped */ }
+}
+
+// Bad: Deeply nested scope functions
+user?.let { u ->
+    u.address?.let { a ->
+        a.city?.let { c -> process(c) }
+    }
+}
+
+// Good: Direct null-safe chain
+user?.address?.city?.let { process(it) }
+```
+
+**Remember**: Kotlin code should be concise but readable. Leverage the type system for safety, prefer immutability, and use coroutines for concurrency. When in doubt, let the compiler help you.

skills/kotlin-testing/SKILL.md

@@ -0,0 +1,824 @@
+---
+name: kotlin-testing
+description: Kotlin testing patterns with Kotest, MockK, coroutine testing, property-based testing, and Kover coverage. Follows TDD methodology with idiomatic Kotlin practices.
+origin: ECC
+---
+
+# Kotlin Testing Patterns
+
+Comprehensive Kotlin testing patterns for writing reliable, maintainable tests following TDD methodology with Kotest and MockK.
+
+## When to Use
+
+- Writing new Kotlin functions or classes
+- Adding test coverage to existing Kotlin code
+- Implementing property-based tests
+- Following TDD workflow in Kotlin projects
+- Configuring Kover for code coverage
+
+## How It Works
+
+1. **Identify target code** — Find the function, class, or module to test
+2. **Write a Kotest spec** — Choose a spec style (StringSpec, FunSpec, BehaviorSpec) matching the test scope
+3. **Mock dependencies** — Use MockK to isolate the unit under test
+4. **Run tests (RED)** — Verify the test fails with the expected error
+5. **Implement code (GREEN)** — Write minimal code to pass the test
+6. **Refactor** — Improve the implementation while keeping tests green
+7. **Check coverage** — Run `./gradlew koverHtmlReport` and verify 80%+ coverage
+
+## Examples
+
+The following sections contain detailed, runnable examples for each testing pattern:
+
+### Quick Reference
+
+- **Kotest specs** — StringSpec, FunSpec, BehaviorSpec, DescribeSpec examples in [Kotest Spec Styles](#kotest-spec-styles)
+- **Mocking** — MockK setup, coroutine mocking, argument capture in [MockK](#mockk)
+- **TDD walkthrough** — Full RED/GREEN/REFACTOR cycle with EmailValidator in [TDD Workflow for Kotlin](#tdd-workflow-for-kotlin)
+- **Coverage** — Kover configuration and commands in [Kover Coverage](#kover-coverage)
+- **Ktor testing** — testApplication setup in [Ktor testApplication Testing](#ktor-testapplication-testing)
+
+### TDD Workflow for Kotlin
+
+#### The RED-GREEN-REFACTOR Cycle
+
+```
+RED     -> Write a failing test first
+GREEN   -> Write minimal code to pass the test
+REFACTOR -> Improve code while keeping tests green
+REPEAT  -> Continue with next requirement
+```
+
+#### Step-by-Step TDD in Kotlin
+
+```kotlin
+// Step 1: Define the interface/signature
+// EmailValidator.kt
+package com.example.validator
+
+fun validateEmail(email: String): Result<String> {
+    TODO("not implemented")
+}
+
+// Step 2: Write failing test (RED)
+// EmailValidatorTest.kt
+package com.example.validator
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.result.shouldBeFailure
+import io.kotest.matchers.result.shouldBeSuccess
+
+class EmailValidatorTest : StringSpec({
+    "valid email returns success" {
+        validateEmail("user@example.com").shouldBeSuccess("user@example.com")
+    }
+
+    "empty email returns failure" {
+        validateEmail("").shouldBeFailure()
+    }
+
+    "email without @ returns failure" {
+        validateEmail("userexample.com").shouldBeFailure()
+    }
+})
+
+// Step 3: Run tests - verify FAIL
+// $ ./gradlew test
+// EmailValidatorTest > valid email returns success FAILED
+//   kotlin.NotImplementedError: An operation is not implemented
+
+// Step 4: Implement minimal code (GREEN)
+fun validateEmail(email: String): Result<String> {
+    if (email.isBlank()) return Result.failure(IllegalArgumentException("Email cannot be blank"))
+    if ('@' !in email) return Result.failure(IllegalArgumentException("Email must contain @"))
+    val regex = Regex("^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}$")
+    if (!regex.matches(email)) return Result.failure(IllegalArgumentException("Invalid email format"))
+    return Result.success(email)
+}
+
+// Step 5: Run tests - verify PASS
+// $ ./gradlew test
+// EmailValidatorTest > valid email returns success PASSED
+// EmailValidatorTest > empty email returns failure PASSED
+// EmailValidatorTest > email without @ returns failure PASSED
+
+// Step 6: Refactor if needed, verify tests still pass
+```
+
+### Kotest Spec Styles
+
+#### StringSpec (Simplest)
+
+```kotlin
+class CalculatorTest : StringSpec({
+    "add two positive numbers" {
+        Calculator.add(2, 3) shouldBe 5
+    }
+
+    "add negative numbers" {
+        Calculator.add(-1, -2) shouldBe -3
+    }
+
+    "add zero" {
+        Calculator.add(0, 5) shouldBe 5
+    }
+})
+```
+
+#### FunSpec (JUnit-like)
+
+```kotlin
+class UserServiceTest : FunSpec({
+    val repository = mockk<UserRepository>()
+    val service = UserService(repository)
+
+    test("getUser returns user when found") {
+        val expected = User(id = "1", name = "Alice")
+        coEvery { repository.findById("1") } returns expected
+
+        val result = service.getUser("1")
+
+        result shouldBe expected
+    }
+
+    test("getUser throws when not found") {
+        coEvery { repository.findById("999") } returns null
+
+        shouldThrow<UserNotFoundException> {
+            service.getUser("999")
+        }
+    }
+})
+```
+
+#### BehaviorSpec (BDD Style)
+
+```kotlin
+class OrderServiceTest : BehaviorSpec({
+    val repository = mockk<OrderRepository>()
+    val paymentService = mockk<PaymentService>()
+    val service = OrderService(repository, paymentService)
+
+    Given("a valid order request") {
+        val request = CreateOrderRequest(
+            userId = "user-1",
+            items = listOf(OrderItem("product-1", quantity = 2)),
+        )
+
+        When("the order is placed") {
+            coEvery { paymentService.charge(any()) } returns PaymentResult.Success
+            coEvery { repository.save(any()) } answers { firstArg() }
+
+            val result = service.placeOrder(request)
+
+            Then("it should return a confirmed order") {
+                result.status shouldBe OrderStatus.CONFIRMED
+            }
+
+            Then("it should charge payment") {
+                coVerify(exactly = 1) { paymentService.charge(any()) }
+            }
+        }
+
+        When("payment fails") {
+            coEvery { paymentService.charge(any()) } returns PaymentResult.Declined
+
+            Then("it should throw PaymentException") {
+                shouldThrow<PaymentException> {
+                    service.placeOrder(request)
+                }
+            }
+        }
+    }
+})
+```
+
+#### DescribeSpec (RSpec Style)
+
+```kotlin
+class UserValidatorTest : DescribeSpec({
+    describe("validateUser") {
+        val validator = UserValidator()
+
+        context("with valid input") {
+            it("accepts a normal user") {
+                val user = CreateUserRequest("Alice", "alice@example.com")
+                validator.validate(user).shouldBeValid()
+            }
+        }
+
+        context("with invalid name") {
+            it("rejects blank name") {
+                val user = CreateUserRequest("", "alice@example.com")
+                validator.validate(user).shouldBeInvalid()
+            }
+
+            it("rejects name exceeding max length") {
+                val user = CreateUserRequest("A".repeat(256), "alice@example.com")
+                validator.validate(user).shouldBeInvalid()
+            }
+        }
+    }
+})
+```
+
+### Kotest Matchers
+
+#### Core Matchers
+
+```kotlin
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.shouldNotBe
+import io.kotest.matchers.string.*
+import io.kotest.matchers.collections.*
+import io.kotest.matchers.nulls.*
+
+// Equality
+result shouldBe expected
+result shouldNotBe unexpected
+
+// Strings
+name shouldStartWith "Al"
+name shouldEndWith "ice"
+name shouldContain "lic"
+name shouldMatch Regex("[A-Z][a-z]+")
+name.shouldBeBlank()
+
+// Collections
+list shouldContain "item"
+list shouldHaveSize 3
+list.shouldBeSorted()
+list.shouldContainAll("a", "b", "c")
+list.shouldBeEmpty()
+
+// Nulls
+result.shouldNotBeNull()
+result.shouldBeNull()
+
+// Types
+result.shouldBeInstanceOf<User>()
+
+// Numbers
+count shouldBeGreaterThan 0
+price shouldBeInRange 1.0..100.0
+
+// Exceptions
+shouldThrow<IllegalArgumentException> {
+    validateAge(-1)
+}.message shouldBe "Age must be positive"
+
+shouldNotThrow<Exception> {
+    validateAge(25)
+}
+```
+
+#### Custom Matchers
+
+```kotlin
+fun beActiveUser() = object : Matcher<User> {
+    override fun test(value: User) = MatcherResult(
+        value.isActive && value.lastLogin != null,
+        { "User ${value.id} should be active with a last login" },
+        { "User ${value.id} should not be active" },
+    )
+}
+
+// Usage
+user should beActiveUser()
+```
+
+### MockK
+
+#### Basic Mocking
+
+```kotlin
+class UserServiceTest : FunSpec({
+    val repository = mockk<UserRepository>()
+    val logger = mockk<Logger>(relaxed = true) // Relaxed: returns defaults
+    val service = UserService(repository, logger)
+
+    beforeTest {
+        clearMocks(repository, logger)
+    }
+
+    test("findUser delegates to repository") {
+        val expected = User(id = "1", name = "Alice")
+        every { repository.findById("1") } returns expected
+
+        val result = service.findUser("1")
+
+        result shouldBe expected
+        verify(exactly = 1) { repository.findById("1") }
+    }
+
+    test("findUser returns null for unknown id") {
+        every { repository.findById(any()) } returns null
+
+        val result = service.findUser("unknown")
+
+        result.shouldBeNull()
+    }
+})
+```
+
+#### Coroutine Mocking
+
+```kotlin
+class AsyncUserServiceTest : FunSpec({
+    val repository = mockk<UserRepository>()
+    val service = UserService(repository)
+
+    test("getUser suspending function") {
+        coEvery { repository.findById("1") } returns User(id = "1", name = "Alice")
+
+        val result = service.getUser("1")
+
+        result.name shouldBe "Alice"
+        coVerify { repository.findById("1") }
+    }
+
+    test("getUser with delay") {
+        coEvery { repository.findById("1") } coAnswers {
+            delay(100) // Simulate async work
+            User(id = "1", name = "Alice")
+        }
+
+        val result = service.getUser("1")
+        result.name shouldBe "Alice"
+    }
+})
+```
+
+#### Argument Capture
+
+```kotlin
+test("save captures the user argument") {
+    val slot = slot<User>()
+    coEvery { repository.save(capture(slot)) } returns Unit
+
+    service.createUser(CreateUserRequest("Alice", "alice@example.com"))
+
+    slot.captured.name shouldBe "Alice"
+    slot.captured.email shouldBe "alice@example.com"
+    slot.captured.id.shouldNotBeNull()
+}
+```
+
+#### Spy and Partial Mocking
+
+```kotlin
+test("spy on real object") {
+    val realService = UserService(repository)
+    val spy = spyk(realService)
+
+    every { spy.generateId() } returns "fixed-id"
+
+    spy.createUser(request)
+
+    verify { spy.generateId() } // Overridden
+    // Other methods use real implementation
+}
+```
+
+### Coroutine Testing
+
+#### runTest for Suspend Functions
+
+```kotlin
+import kotlinx.coroutines.test.runTest
+
+class CoroutineServiceTest : FunSpec({
+    test("concurrent fetches complete together") {
+        runTest {
+            val service = DataService(testScope = this)
+
+            val result = service.fetchAllData()
+
+            result.users.shouldNotBeEmpty()
+            result.products.shouldNotBeEmpty()
+        }
+    }
+
+    test("timeout after delay") {
+        runTest {
+            val service = SlowService()
+
+            shouldThrow<TimeoutCancellationException> {
+                withTimeout(100) {
+                    service.slowOperation() // Takes > 100ms
+                }
+            }
+        }
+    }
+})
+```
+
+#### Testing Flows
+
+```kotlin
+import io.kotest.matchers.collections.shouldContainInOrder
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.toList
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.advanceTimeBy
+import kotlinx.coroutines.test.runTest
+
+class FlowServiceTest : FunSpec({
+    test("observeUsers emits updates") {
+        runTest {
+            val service = UserFlowService()
+
+            val emissions = service.observeUsers()
+                .take(3)
+                .toList()
+
+            emissions shouldHaveSize 3
+            emissions.last().shouldNotBeEmpty()
+        }
+    }
+
+    test("searchUsers debounces input") {
+        runTest {
+            val service = SearchService()
+            val queries = MutableSharedFlow<String>()
+
+            val results = mutableListOf<List<User>>()
+            val job = launch {
+                service.searchUsers(queries).collect { results.add(it) }
+            }
+
+            queries.emit("a")
+            queries.emit("ab")
+            queries.emit("abc") // Only this should trigger search
+            advanceTimeBy(500)
+
+            results shouldHaveSize 1
+            job.cancel()
+        }
+    }
+})
+```
+
+#### TestDispatcher
+
+```kotlin
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+
+class DispatcherTest : FunSpec({
+    test("uses test dispatcher for controlled execution") {
+        val dispatcher = StandardTestDispatcher()
+
+        runTest(dispatcher) {
+            var completed = false
+
+            launch {
+                delay(1000)
+                completed = true
+            }
+
+            completed shouldBe false
+            advanceTimeBy(1000)
+            completed shouldBe true
+        }
+    }
+})
+```
+
+### Property-Based Testing
+
+#### Kotest Property Testing
+
+```kotlin
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.property.Arb
+import io.kotest.property.arbitrary.*
+import io.kotest.property.forAll
+import io.kotest.property.checkAll
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.decodeFromString
+
+// Note: The serialization roundtrip test below requires the User data class
+// to be annotated with @Serializable (from kotlinx.serialization).
+
+class PropertyTest : FunSpec({
+    test("string reverse is involutory") {
+        forAll<String> { s ->
+            s.reversed().reversed() == s
+        }
+    }
+
+    test("list sort is idempotent") {
+        forAll(Arb.list(Arb.int())) { list ->
+            list.sorted() == list.sorted().sorted()
+        }
+    }
+
+    test("serialization roundtrip preserves data") {
+        checkAll(Arb.bind(Arb.string(1..50), Arb.string(5..100)) { name, email ->
+            User(name = name, email = "$email@test.com")
+        }) { user ->
+            val json = Json.encodeToString(user)
+            val decoded = Json.decodeFromString<User>(json)
+            decoded shouldBe user
+        }
+    }
+})
+```
+
+#### Custom Generators
+
+```kotlin
+val userArb: Arb<User> = Arb.bind(
+    Arb.string(minSize = 1, maxSize = 50),
+    Arb.email(),
+    Arb.enum<Role>(),
+) { name, email, role ->
+    User(
+        id = UserId(UUID.randomUUID().toString()),
+        name = name,
+        email = Email(email),
+        role = role,
+    )
+}
+
+val moneyArb: Arb<Money> = Arb.bind(
+    Arb.long(1L..1_000_000L),
+    Arb.enum<Currency>(),
+) { amount, currency ->
+    Money(amount, currency)
+}
+```
+
+### Data-Driven Testing
+
+#### withData in Kotest
+
+```kotlin
+class ParserTest : FunSpec({
+    context("parsing valid dates") {
+        withData(
+            "2026-01-15" to LocalDate(2026, 1, 15),
+            "2026-12-31" to LocalDate(2026, 12, 31),
+            "2000-01-01" to LocalDate(2000, 1, 1),
+        ) { (input, expected) ->
+            parseDate(input) shouldBe expected
+        }
+    }
+
+    context("rejecting invalid dates") {
+        withData(
+            nameFn = { "rejects '$it'" },
+            "not-a-date",
+            "2026-13-01",
+            "2026-00-15",
+            "",
+        ) { input ->
+            shouldThrow<DateParseException> {
+                parseDate(input)
+            }
+        }
+    }
+})
+```
+
+### Test Lifecycle and Fixtures
+
+#### BeforeTest / AfterTest
+
+```kotlin
+class DatabaseTest : FunSpec({
+    lateinit var db: Database
+
+    beforeSpec {
+        db = Database.connect("jdbc:h2:mem:test;DB_CLOSE_DELAY=-1")
+        transaction(db) {
+            SchemaUtils.create(UsersTable)
+        }
+    }
+
+    afterSpec {
+        transaction(db) {
+            SchemaUtils.drop(UsersTable)
+        }
+    }
+
+    beforeTest {
+        transaction(db) {
+            UsersTable.deleteAll()
+        }
+    }
+
+    test("insert and retrieve user") {
+        transaction(db) {
+            UsersTable.insert {
+                it[name] = "Alice"
+                it[email] = "alice@example.com"
+            }
+        }
+
+        val users = transaction(db) {
+            UsersTable.selectAll().map { it[UsersTable.name] }
+        }
+
+        users shouldContain "Alice"
+    }
+})
+```
+
+#### Kotest Extensions
+
+```kotlin
+// Reusable test extension
+class DatabaseExtension : BeforeSpecListener, AfterSpecListener {
+    lateinit var db: Database
+
+    override suspend fun beforeSpec(spec: Spec) {
+        db = Database.connect("jdbc:h2:mem:test;DB_CLOSE_DELAY=-1")
+    }
+
+    override suspend fun afterSpec(spec: Spec) {
+        // cleanup
+    }
+}
+
+class UserRepositoryTest : FunSpec({
+    val dbExt = DatabaseExtension()
+    register(dbExt)
+
+    test("save and find user") {
+        val repo = UserRepository(dbExt.db)
+        // ...
+    }
+})
+```
+
+### Kover Coverage
+
+#### Gradle Configuration
+
+```kotlin
+// build.gradle.kts
+plugins {
+    id("org.jetbrains.kotlinx.kover") version "0.9.7"
+}
+
+kover {
+    reports {
+        total {
+            html { onCheck = true }
+            xml { onCheck = true }
+        }
+        filters {
+            excludes {
+                classes("*.generated.*", "*.config.*")
+            }
+        }
+        verify {
+            rule {
+                minBound(80) // Fail build below 80% coverage
+            }
+        }
+    }
+}
+```
+
+#### Coverage Commands
+
+```bash
+# Run tests with coverage
+./gradlew koverHtmlReport
+
+# Verify coverage thresholds
+./gradlew koverVerify
+
+# XML report for CI
+./gradlew koverXmlReport
+
+# View HTML report (use the command for your OS)
+# macOS:   open build/reports/kover/html/index.html
+# Linux:   xdg-open build/reports/kover/html/index.html
+# Windows: start build/reports/kover/html/index.html
+```
+
+#### Coverage Targets
+
+| Code Type | Target |
+|-----------|--------|
+| Critical business logic | 100% |
+| Public APIs | 90%+ |
+| General code | 80%+ |
+| Generated / config code | Exclude |
+
+### Ktor testApplication Testing
+
+```kotlin
+class ApiRoutesTest : FunSpec({
+    test("GET /users returns list") {
+        testApplication {
+            application {
+                configureRouting()
+                configureSerialization()
+            }
+
+            val response = client.get("/users")
+
+            response.status shouldBe HttpStatusCode.OK
+            val users = response.body<List<UserResponse>>()
+            users.shouldNotBeEmpty()
+        }
+    }
+
+    test("POST /users creates user") {
+        testApplication {
+            application {
+                configureRouting()
+                configureSerialization()
+            }
+
+            val response = client.post("/users") {
+                contentType(ContentType.Application.Json)
+                setBody(CreateUserRequest("Alice", "alice@example.com"))
+            }
+
+            response.status shouldBe HttpStatusCode.Created
+        }
+    }
+})
+```
+
+### Testing Commands
+
+```bash
+# Run all tests
+./gradlew test
+
+# Run specific test class
+./gradlew test --tests "com.example.UserServiceTest"
+
+# Run specific test
+./gradlew test --tests "com.example.UserServiceTest.getUser returns user when found"
+
+# Run with verbose output
+./gradlew test --info
+
+# Run with coverage
+./gradlew koverHtmlReport
+
+# Run detekt (static analysis)
+./gradlew detekt
+
+# Run ktlint (formatting check)
+./gradlew ktlintCheck
+
+# Continuous testing
+./gradlew test --continuous
+```
+
+### Best Practices
+
+**DO:**
+- Write tests FIRST (TDD)
+- Use Kotest's spec styles consistently across the project
+- Use MockK's `coEvery`/`coVerify` for suspend functions
+- Use `runTest` for coroutine testing
+- Test behavior, not implementation
+- Use property-based testing for pure functions
+- Use `data class` test fixtures for clarity
+
+**DON'T:**
+- Mix testing frameworks (pick Kotest and stick with it)
+- Mock data classes (use real instances)
+- Use `Thread.sleep()` in coroutine tests (use `advanceTimeBy`)
+- Skip the RED phase in TDD
+- Test private functions directly
+- Ignore flaky tests
+
+### Integration with CI/CD
+
+```yaml
+# GitHub Actions example
+test:
+  runs-on: ubuntu-latest
+  steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-java@v4
+      with:
+        distribution: 'temurin'
+        java-version: '21'
+
+    - name: Run tests with coverage
+      run: ./gradlew test koverXmlReport
+
+    - name: Verify coverage
+      run: ./gradlew koverVerify
+
+    - name: Upload coverage
+      uses: codecov/codecov-action@v5
+      with:
+        files: build/reports/kover/report.xml
+        token: ${{ secrets.CODECOV_TOKEN }}
+```
+
+**Remember**: Tests are documentation. They show how your Kotlin code is meant to be used. Use Kotest's expressive matchers to make tests readable and MockK for clean mocking of dependencies.