[FEATURE] MCP hooks — auto-trigger scans on AI write / dep change / task end (extracted from #23)

[Wolfvin]

Summary

Add 5 auto-trigger MCP hooks so CodeLens shifts from reactive (agent must call tools explicitly) to proactive (auto-scan on AI activity). This is the highest-leverage piece extracted from the over-broad #23 (Phase 3).

Worker source

Worker	Source	Detail
Semgrep	update!/CodeLens_Upgrade_Issues_from_Semgrep.md CL-013	5 hooks modeled after Semgrep Guardian: post_tool (auto-scan file after AI writes), supply_chain (auto-run vuln-scan on dep file changes), inject_secure_defaults (pre-generate injection of helmet etc.), stop (final guard check before task ends), settings (read .codelens/hooks.json). Worker rates this P0 because it's the core AI-native differentiator.

Proposed scope (P0, 2-3 weeks)

5 hooks, each with config-driven enable/disable:

1. post_tool — After AI agent writes a file via MCP tool call, auto-run scan --incremental --file <path> + guard --post --file <path>. Surface critical findings as next-turn context.
2. supply_chain — On change to package.json / requirements.txt / Cargo.toml / go.mod / pyproject.toml, auto-run vuln-scan and surface new CVEs.
3. inject_secure_defaults — When AI creates new file matching src/server.* / app.*, pre-inject secure defaults (helmet, CORS allowlist, rate-limit middleware). Configurable template per framework.
4. stop — On MCP shutdown notification, run final check --severity high and surface any unresolved critical findings.
5. settings — Read .codelens/hooks.json for per-hook enable/disable + custom config.

Architecture

• Hook registry in scripts/mcp_server.py (new HookManager class)
• MCP notifications/progress for hook events (so agent sees "post_tool hook running...")
• Config schema at .codelens/hooks.json:

  {"hooks": {"post_tool": {"enabled": true, "commands": ["scan", "guard"]}, ...}}

• 5 hook implementations in scripts/mcp_hooks/

Acceptance criteria

• All 5 hooks fire on their trigger conditions
• Hooks are non-blocking (run in thread pool, surface results async)
• Each hook can be disabled via .codelens/hooks.json
• Performance: post_tool hook adds <500ms to file-write latency
• Tests for each hook with mock MCP transport

Relationship to #23

This issue is the first of 4 facets of #23 (Phase 3). The other 3 facets (single-tool MCP philosophy, multi-skill orchestrator, git hook system) should be filed as sibling issues. See enrichment comment on #23 for the full split rationale.