feat(code-review): add pattern learning to auto-suggest CLAUDE.md rules

[kpatel513]

Summary

Every review the plugin runs produces signal that currently disappears. If the same category of issue gets flagged across multiple PRs, that's a gap in the repo's CLAUDE.md — but today nothing surfaces it.

This adds a pattern learning layer that silently tracks validated issues across reviews, detects recurring patterns (3+ occurrences in the last 5 PRs), and proposes targeted CLAUDE.md changes directly in the terminal. The system also checks whether an existing rule already covers the pattern — if so, it suggests strengthening it rather than adding a duplicate.

The result: the plugin gets smarter the more you use it. Each review makes the next one cheaper.

How it works

Storage: .claude/review-patterns.json in the repo root (automatically gitignored). Schema:

{
  "version": 1,
  "patterns": [
    {
      "id": "uuid",
      "summary": "missing error handling in async functions",
      "occurrences": [
        {
          "pr_number": 123,
          "pr_title": "feat: add OAuth",
          "files_affected": ["src/auth.ts"],
          "issue_description": "OAuth state not cleaned up in finally block",
          "reviewed_at": "2026-03-07T10:00:00Z"
        }
      ]
    }
  ]
}

Threshold: 3 or more occurrences across the last 5 distinct PRs reviewed.

Terminal output when threshold is hit:

Recurring pattern — seen in 3 of last 5 PRs

  Pattern   missing error handling in async functions
  Seen in   PR #118, PR #121, PR #123

  No existing CLAUDE.md rule covers this.
  Suggested rule: "Always wrap async functions in try/catch.
                   Do not let Promise rejections go unhandled."

  Add to .claude/CLAUDE.md? [y/n]

If an existing rule already covers the pattern but violations keep occurring, the plugin suggests strengthening it instead of adding a duplicate.

Changes

plugins/code-review/commands/code-review.md

• Step 6 (expanded): after filtering validated issues, update .claude/review-patterns.json with new occurrences, detect patterns meeting the threshold, and cross-reference existing CLAUDE.md rules
• Step 7 (expanded): after main findings, surface pattern suggestions with y/n prompts; if confirmed, write the rule directly to the appropriate CLAUDE.md file

Design decisions

• Local file, gitignored: keeps it zero-setup, no shared infrastructure needed. Team-wide pattern sharing is a natural v2.
• 3 of last 5 PRs threshold: high enough to filter noise, low enough to surface real patterns quickly. Configurable in a future PR.
• Modify/remove existing rules: the plugin doesn't just add rules — if a rule exists but the pattern persists, it suggests strengthening it. This prevents CLAUDE.md bloat.
• Always terminal-only: pattern suggestions never appear in GitHub PR comments. They're a coaching tool for the developer running the review, not reviewer feedback.

Test plan

• Review 3 PRs with the same category of issue — pattern suggestion should appear on the 3rd
• Confirm .claude/review-patterns.json is created and gitignored automatically
• Review a PR with an issue covered by an existing CLAUDE.md rule — should suggest strengthening, not adding duplicate
• Answer n to all suggestions — store should still be updated, no CLAUDE.md changes
• Answer y — CLAUDE.md should be updated with the drafted rule