Mohamed Hegazy a67587c816
security-guidance: enable LLM review on default macOS Python 3.9
Fixes anthropics/claude-plugins-official#2071 — on macOS where the
default `python3` is Apple's Command Line Tools Python 3.9.6, the
plugin's agentic commit reviewer silently does not run, even when the
user has a newer Python installed.

Three compounding factors in the bug:

1. `sg-python.sh` only checks the major version (`3`), so it always
   picks 3.9 even when 3.10+ is on PATH.
2. `claude_agent_sdk` requires Python >=3.10 — pip install on 3.9
   returns "No matching distribution" -> bootstrap returns BUILD_FAILED.
3. Even with a hand-built 3.12 venv, `llm.py` imports the SDK
   in-process into the hook's interpreter (still 3.9), which raises
   SyntaxError. The existing venv-probe in `ensure_agent_sdk.py` uses
   the venv's own Python (3.12) so it reports NOOP_VENV (healthy) while
   the consumer fails — misleading telemetry on top of silent feature
   degradation.

Per BQ telemetry, 14,073 external macOS users hit
sdk_bootstrap=BUILD_FAILED in the past 4 days (the default-macOS
cohort), out of ~86K total external installed users. Combined with
~20K other users in similar broken-bootstrap states (Windows pre-#2055,
Linux <3.10), about half the installed base has a silently-broken
agentic reviewer.

This PR implements the reporter's items #1, #3, and #4. Item #2
(running the SDK out-of-process) is deferred as a bigger refactor.

Item #1 — hooks/sg-python.sh — prefer >=3.10 binaries via 3-pass probe:

  Pass 1: python3.13 / 3.12 / 3.11 / 3.10 (>=3.10 by name, highest wins)
  Pass 2: bare python3 / python / py -3 (accept only if reported >=3.10)
  Pass 3: bare python3 / python / py -3 (any Python 3, FALLBACK so
          pattern checks still work on macOS-default 3.9 — no regression
          vs today; SDK-dependent paths detect the version mismatch
          inside Python and degrade cleanly via item #4)

Item #4 — ensure_agent_sdk.py — health-check honesty:

Added HOOK_PY_INCOMPATIBLE=6 outcome with short-circuit at top of main():

  if sys.version_info < (3, 10):
      return HOOK_PY_INCOMPATIBLE, "hook_py", f"py_{...}"

Telemetry consequences after rollout: sdk_bootstrap=6 is a new clean
bucket; some users currently miscounted in sdk_bootstrap=3 BUILD_FAILED
(wasted pip cycles) and sdk_bootstrap=1 NOOP_VENV (falsely-healthy)
move to sdk_bootstrap=6. The remaining NOOP_VENV count becomes
trustworthy.

Item #3 — ensure_agent_sdk.py — one-time user-visible notice:

When outcome == HOOK_PY_INCOMPATIBLE and a marker file at
`~/.claude/security/.agentic_unavailable_notice_v<pv>` doesn't exist,
the SessionStart response includes hookSpecificOutput.additionalContext
+ systemMessage explaining the situation. Marker file is plugin-
version-keyed so a future fix (e.g. shipping out-of-process SDK) can
bump pv and re-notify users.

BUILD_FAILED is intentionally excluded from the notice — it covers
transient causes where a permanent banner would mislead.

Verified locally on macOS Python 3.13:
  - py_compile clean on both files.
  - Existing 45-test smoke + extensibility suite: 45/45 PASS in 2.50s.
  - Unit test of simulated 3.9 path: HOOK_PY_INCOMPATIBLE returned with
    correct phase/kind; notice shown on first call, suppressed on
    second, reshown on bumped pv; BUILD_FAILED correctly does NOT
    trigger notice.

NOT verified: actual Python 3.9 behavior end-to-end (would need a 3.9
install). Worth a follow-up smoke test in a 3.9 venv before next
release. The unit test simulating 3.9 covers the logic but not the
runtime invocation through the shim.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-05-28 22:58:01 -07:00
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