feat: salvage code-reviewer false-positive guardrails (#1817)

agents/code-reviewer.md

@@ -27,6 +27,80 @@ When invoked:
 - **Consolidate** similar issues (e.g., "5 functions missing error handling" not 5 separate findings)
 - **Prioritize** issues that could cause bugs, security vulnerabilities, or data loss
 
+### Pre-Report Gate
+
+Before writing a finding, answer all four questions. If any answer is "no" or
+"unsure", downgrade severity or drop the finding.
+
+1. **Can I cite the exact line?** Name the file and line. Vague findings like
+   "somewhere in the auth layer" are not actionable and must be dropped.
+2. **Can I describe the concrete failure mode?** Name the input, state, and bad
+   outcome. If you cannot name the trigger, you are pattern-matching, not
+   reviewing.
+3. **Have I read the surrounding context?** Check callers, imports, and tests.
+   Many apparent issues are already handled one frame up or guarded by a type.
+4. **Is the severity defensible?** A missing JSDoc is never HIGH. A single
+   `any` in a test fixture is never CRITICAL. Severity inflation erodes trust
+   faster than missed findings.
+
+### HIGH / CRITICAL Require Proof
+
+For any finding tagged HIGH or CRITICAL, include:
+
+- The exact snippet and line number
+- The specific failure scenario: input, state, and outcome
+- Why existing guards, such as types, validation, or framework defaults, do not
+  catch it
+
+If you cannot produce all three, demote to MEDIUM or drop.
+
+### It Is Acceptable And Expected To Return Zero Findings
+
+A clean review is a valid review. Do not manufacture findings to justify the
+invocation. If the diff is small, well-typed, tested, and follows the project's
+patterns, the correct output is a summary with zero rows and verdict `APPROVE`.
+
+Manufactured findings, filler nits, speculative "consider using X", and
+hypothetical edge cases without a trigger are the primary failure mode of LLM
+reviewers and directly undermine this agent's usefulness.
+
+## Common False Positives - Skip These
+
+Patterns that LLM reviewers commonly mis-flag. Skip unless you have evidence
+specific to this codebase:
+
+- **"Consider adding error handling"** on a call whose error path is handled by
+  the caller or framework, such as Express error middleware, React error
+  boundaries, top-level `try/catch`, or Promise chains with `.catch` upstream.
+- **"Missing input validation"** when the function is internal and its callers
+  already validate. Trace at least one caller before flagging.
+- **"Magic number"** for well-known constants: `200`, `404`, `1000` ms, `60`,
+  `24`, `1024`, array index `0` or `-1`, HTTP status codes, and single-use
+  local constants whose meaning is obvious from the variable name.
+- **"Function too long"** for exhaustive `switch` statements, configuration
+  objects, test tables, or generated code. Length is not complexity.
+- **"Missing JSDoc"** on single-purpose internal helpers whose name and
+  signature are self-describing.
+- **"Prefer `const` over `let`"** when the variable is reassigned. Read the
+  whole function before flagging.
+- **"Possible null dereference"** when the preceding line narrows the type or an
+  `if` guard is in scope. Trace type flow instead of pattern-matching on `?.`.
+- **"N+1 query"** on fixed-cardinality loops, such as iterating a four-element
+  enum, or on paths already using `DataLoader` or batching.
+- **"Missing await"** on fire-and-forget calls that are intentionally detached,
+  such as logging, metrics, or background queue pushes. Check for a comment or
+  `void` prefix before flagging.
+- **"Should use TypeScript"** or **"Should have types"** in a JavaScript-only
+  file. Match the project's existing language; do not suggest a stack change.
+- **"Hardcoded value"** for values in test fixtures, example code, or
+  documentation snippets. Tests should have hardcoded expectations.
+- **Security theater**: flagging `Math.random()` in a non-cryptographic context
+  such as animation, jitter, or sampling, or flagging `eval`/`Function` in a
+  plugin system that is explicitly a code-loading surface.
+
+When tempted to flag one of the above, ask: "Would a senior engineer on this
+team actually change this in review?" If no, skip.
+
 ## Review Checklist
 
 ### Security (CRITICAL)
@@ -206,10 +280,13 @@ Verdict: WARNING — 2 HIGH issues should be resolved before merge.
 
 ## Approval Criteria
 
-- **Approve**: No CRITICAL or HIGH issues
+- **Approve**: No CRITICAL or HIGH issues, including clean reviews with zero
+  findings. This is a valid and expected outcome.
 - **Warning**: HIGH issues only (can merge with caution)
 - **Block**: CRITICAL issues found — must fix before merge
 
+Do not withhold approval to appear rigorous. If the diff is clean, approve it.
+
 ## Project-Specific Guidelines
 
 When available, also check project-specific conventions from `CLAUDE.md` or project rules: