fix(gateway): bounded fail-open evidence assembly + PM decision transient-failure bypass

Evidence-assembly git legs (diff, changed-files, branch fetch, advisory
conventions run) ran unbounded inside claim_review / claim_doc_task /
claim_gate_review / evidence() / i_am_done's envelope build, so a slow
clone turned the whole verb into a silent 120s FlowVerbTimeout 504.
Each leg now runs through run_bounded_leg under a shared LegBudget
(evidence_assembly_timeout_seconds, 45s total): a timed-out leg — both
asyncio TimeoutError and git's own GitTimeoutError — degrades into an
evidence_gaps note on the envelope instead of hanging the verb, while
non-timeout git errors still propagate. The advisory conventions run
gets an inner-only timeout (conventions_validator_advisory_timeout_
seconds, 30s) threaded down to the subprocess so it is never orphaned
by an outer cancel; the fail-closed i_am_done/pr_pass conventions
gates keep their hardcoded 120s.

_ensure_pm_decision now reports a PmDecisionOutcome: a transient DB
failure recording the PM's decision journal (e.g. lock timeout under
load) no longer launders into a journal:decision gate rejection that
escalates and BLOCKS the task — the verb's own rationale satisfies the
gate with a structured warning, across all seven PM verbs.

Also: repo-wide ruff realignment to the lockfile-pinned ruff (8
format-only diffs, 14 UP038 isinstance conversions) that a transiently
newer venv ruff had masked.

Gate: 15474 passed, 459 skipped; ruff/mypy/xenon/vulture/bandit/
pip-audit/deptry/import-linter/foundation-check all green.

tests/unit/services/test_main_pm_code_guard.py

@@ -169,7 +169,6 @@ async def test_create_rejects_cell_pm_assignee_plus_code() -> None:
 
 @pytest.mark.asyncio
 async def test_create_allows_cell_pm_assignee_plus_planning() -> None:
-
     be_pm_uuid = AGENTS["be-pm"].uuid
     svc = TaskService(
         MagicMock(add=MagicMock(), flush=AsyncMock(), execute=AsyncMock())