docs: fold stocktake rule guidance into common rules

WORKING-CONTEXT.md

@@ -141,6 +141,7 @@ Keep this file detailed for only the current sprint, blockers, and next actions.
 - 2026-04-05: Added `skills/council`, direct-ported the safe `code-tour` lane from `#1193`, and re-synced the repo to `162` skills. `code-tour` stays self-contained and only produces `.tours/*.tour` artifacts with real file/line anchors; no external runtime or extension install is assumed inside the skill.
 - 2026-04-05: Closed the latest auto-generated ECC bundle PR wave (`#1275`-`#1281`) after deploying `ECC-Tools/main` fix `f615905`, which now blocks repo-level issue-comment `/analyze` requests from opening repeated bundle PRs while still allowing PR-thread retry analysis to run against immutable head SHAs.
 - 2026-04-05: Filled the SEO gap by direct-porting `agents/seo-specialist.md` and `skills/seo/SKILL.md` into `main`, then wiring `skills/seo` into `business-content`. This resolves the stale `team-builder` reference to an SEO specialist and brings the public catalog to `39` agents and `163` skills without merging the stale PR wholesale.
+- 2026-04-05: Salvaged the useful common-rule deltas from `#1214` directly into `rules/common/coding-style.md` and `rules/common/testing.md` (KISS/DRY/YAGNI reminders, naming conventions, code-smell guidance, and AAA-style test guidance), then closed the original mixed deletion PR. The broad skill removals in that PR were intentionally not replayed.
 - 2026-04-05: Fixed the stale-row bug in `.github/workflows/monthly-metrics.yml` with `bf5961e`. The workflow now refreshes the current month row in issue `#1087` instead of early-returning when the month already exists, and the dispatched run updated the April snapshot to the current star/fork/release counts.
 - 2026-04-05: Recovered the useful cost-control workflow from the divergent Hermes branch as a small ECC-native operator skill instead of replaying the branch. `skills/ecc-tools-cost-audit/SKILL.md` is now wired into `operator-workflows` and focused on webhook -> queue -> worker tracing, burn containment, quota bypass, premium-model leakage, and retry fanout in the sibling `ECC-Tools` repo.
 - 2026-04-05: Added `skills/council/SKILL.md` in `753da37` as an ECC-native four-voice decision workflow. The useful protocol from PR `#1254` was retained, but the shadow `~/.claude/notes` write path was explicitly removed in favor of `knowledge-ops`, `/save-session`, or direct GitHub/Linear updates when a decision delta matters.

rules/common/coding-style.md

@@ -12,6 +12,26 @@ CORRECT: update(original, field, value) → returns new copy with change
 
 Rationale: Immutable data prevents hidden side effects, makes debugging easier, and enables safe concurrency.
 
+## Core Principles
+
+### KISS (Keep It Simple)
+
+- Prefer the simplest solution that actually works
+- Avoid premature optimization
+- Optimize for clarity over cleverness
+
+### DRY (Don't Repeat Yourself)
+
+- Extract repeated logic into shared functions or utilities
+- Avoid copy-paste implementation drift
+- Introduce abstractions when repetition is real, not speculative
+
+### YAGNI (You Aren't Gonna Need It)
+
+- Do not build features or abstractions before they are needed
+- Avoid speculative generality
+- Start simple, then refactor when the pressure is real
+
 ## File Organization
 
 MANY SMALL FILES > FEW LARGE FILES:
@@ -36,6 +56,28 @@ ALWAYS validate at system boundaries:
 - Fail fast with clear error messages
 - Never trust external data (API responses, user input, file content)
 
+## Naming Conventions
+
+- Variables and functions: `camelCase` with descriptive names
+- Booleans: prefer `is`, `has`, `should`, or `can` prefixes
+- Interfaces, types, and components: `PascalCase`
+- Constants: `UPPER_SNAKE_CASE`
+- Custom hooks: `camelCase` with a `use` prefix
+
+## Code Smells to Avoid
+
+### Deep Nesting
+
+Prefer early returns over nested conditionals once the logic starts stacking.
+
+### Magic Numbers
+
+Use named constants for meaningful thresholds, delays, and limits.
+
+### Long Functions
+
+Split large functions into focused pieces with clear responsibilities.
+
 ## Code Quality Checklist
 
 Before marking work complete:

rules/common/testing.md

@@ -27,3 +27,31 @@ MANDATORY workflow:
 ## Agent Support
 
 - **tdd-guide** - Use PROACTIVELY for new features, enforces write-tests-first
+
+## Test Structure (AAA Pattern)
+
+Prefer Arrange-Act-Assert structure for tests:
+
+```typescript
+test('calculates similarity correctly', () => {
+  // Arrange
+  const vector1 = [1, 0, 0]
+  const vector2 = [0, 1, 0]
+
+  // Act
+  const similarity = calculateCosineSimilarity(vector1, vector2)
+
+  // Assert
+  expect(similarity).toBe(0)
+})
+```
+
+### Test Naming
+
+Use descriptive names that explain the behavior under test:
+
+```typescript
+test('returns empty array when no markets match query', () => {})
+test('throws error when API key is missing', () => {})
+test('falls back to substring search when Redis is unavailable', () => {})
+```