Run the secret-path guard with /usr/bin/python3 - #924

Scope

• What this PR changes, in one or two sentences: the Claude settings template and the repository's project settings now start the secret-path guard with /usr/bin/python3 instead of the first python3 on PATH, so a broken or inactive interpreter shim can no longer make every guarded Bash call exit 1; the new-WSL renderer admits that one absolute path as a practice-hook command word, with tests that it still refuses every other interpreter path.
• Base commit: 22e3ef6ffd53b09f3cb335c46f7c696093521274 (main after Secret-path guard hook refuses when its script is missing #920)
• Lane: lane:foundation
• Owned paths touched: adoption/templates/claude.settings.template.json (one command), .claude/settings.json (the project guard command, folded in at the command center's request), tools/adoption/new_wsl_client_config.py (BASE_COMMAND_WORDS and its comment), tests/test_install_claude_profile.py, tests/test_new_wsl_client_config.py, docs/decisions/2026-10-08-guard-hook-fails-closed.md (append-only addendum), manifests/evidence.json (re-registration).

Successor to #920, scoped by the command center on 2026-10-09: the interpreter pin, the allowlist entry for that one path, the jq refusal and missing-script exit 2 kept, and a test with no mise shim on PATH.

SOTA sources

• Claude Code hooks: exit code 2 blocks a PreToolUse call and other non-zero codes are non-blocking (https://code.claude.com/docs/en/hooks, read 2026-10-09); onFailure: "block" added in 2.1.295 (anthropics/claude-code@602df92bf481ed904533e95c09f740f40aab5aed CHANGELOG.md line 5: "a hook that can't start, times out, or exits with an unexpected code blocks the action instead of letting it through").
• POSIX Shell Command Language, 2.8.2 Exit Status for Commands: a command that is not found exits 127 (https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html).
• jq 1.7 manual, halt_error(exit_code) (https://jqlang.org/manual/v1.7/), unchanged from Secret-path guard hook refuses when its script is missing #920.
• Python ast.parse(..., feature_version=...) (https://docs.python.org/3/library/ast.html#ast.parse), used to check the guard parses as 3.9 through 3.14.
• docs/decisions/2026-10-08-guard-hook-fails-closed.md and the Claude Code native practice record of 2026-10-09 (Claude Code native practice, 2026-10: one evidenced default per role slot #923, slot hooks).

Evidence-class table

Local commands run

$ python3 -E -s -B -m unittest tests.test_apply_claude_settings tests.test_currency_due_notice tests.test_install_claude_profile tests.test_new_wsl_client_config tests.test_observability_tool_names tests.test_observability_writer_identity tests.test_render_config tests.test_secret_path_guard tests.test_skills_manifest tests.test_token_lanes_session_start tests.test_upstream_surface_watch tests.test_windows_terminal_defaults tests.test_adoption_status tests.test_credential_status tests.test_adoption_docs_consistency
Ran 1016 tests; FAILED (failures=2, skipped=16)
  K4GuardTests.test_k4_hook_process_and_hints failed its 3-second timing assertion under load; it starts the guard with
  sys.executable, not a settings command, and passed 3 of 3 alone and in the full tests.test_secret_path_guard rerun (90 tests OK)
  the one failure is the pre-existing F10, OverlayTests.test_the_installed_client_knows_no_notification_type_without_a_decision
  (plugin_notification on the installed 2.1.295); it fails the same way on clean main and is owned by the currency floor PR #922
$ python3 -E -s -B -m unittest tests.test_new_wsl_definitive_defaults tests.test_new_wsl_profile tests.test_new_wsl_handbook tests.test_new_wsl_gateway_composition tests.test_new_wsl_mcp_conformance_lifecycle tests.test_adoption_docs_consistency tests.test_adoption_contract
Ran 314 tests; OK (skipped=4)
$ python3 -E -s -B tools/adoption/new_wsl_client_config.py --check
check passed (two pre-existing mcp-inspector warnings)
$ python3 -E -s -B scripts/validate.py
{"components": 70, "hashed_files": 10939, "profiles": 4, "receipts": 239, "status": "passed"}
$ python3 -E -s -B scripts/evidence_manifest.py --check
{"files": 10939, "status": "passed"}
$ python3 -E -s -B scripts/validate_convergence.py --all-recorded --root . --json
valid: true
$ python3 -E -s -B scripts/component_matrix.py --write && python3 -E -s -B scripts/new_host_grand_list.py --write
written; no diff in the generated reports

Decision record

docs/decisions/2026-10-08-guard-hook-fails-closed.md, new addendum "the guard runs the system interpreter": the measurement, the allowlist scope, the project hook and the limits. A host without /usr/bin/python3, or a missing script with no jq on PATH, exits 127, which onFailure: "block" turns into a block from 2.1.295 (the floor raise is the currency lane's change). After this lands, the command center aligns the host's user settings to the rendered form; until then the host keeps its own pinned form.

Host evidence

Not applicable: no file under evidence/hosts/ changes.

Checklist

• New/changed GitHub Actions are pinned to a full commit SHA with a version comment (no floating tags). (none changed)
• New/changed workflows declare top-level permissions: {} and grant each job only what it needs. (none changed)
• No secrets are printed, logged or committed; no new required secret was added without a documented owner.
• No new paid hosting, subscription or billing surface was introduced.
• Peer-owned untracked files and worktrees were preserved (not deleted, moved or overwritten).

🤖 Generated with Claude Code