REPORT A1207

Date: 2026-08-13 Branch: fix/869-lease-probe-timeout Starting head: 2373a5ad345fb316ad2460f6390baab1f45ba08f Base: 216cd72226cd9ee17eea461cfe7cd0e010a22f02

What changed

Added Python behavior tests using isolated temporary directories and marker-writing fake mosaic executables. They prove that the supplied PATH wins over ambient os.environ["PATH"], and that absent or empty supplied PATH values do not search ambient paths, platform defaults, or the current directory.
Bound Python override behavior with executable fakes: a valid MOSAIC_LEASE_VERSION_PROBE_COMMAND wins over supplied and ambient PATH; an invalid override returns None without PATH fallback.
Added a Python runner binding test that captures kwargs and requires timeout=10.0. Existing timeout, transport-error, and nonzero-exit checks remain fail-closed with None.
Added the optional TypeScript dependency-injection seam CapabilityProbeExecFile, defaulting to the existing real execFileSync implementation. Production callers have no behavior change.
Added TypeScript tests that capture child-process options and require exactly timeout: 10_000. Injected timeout, spawn-error, nonzero-exit, unparseable JSON, and malformed-object cases all return null.
Removed the ambient no-dependency TypeScript smoke case that could execute a built checkout's real CLI. Default resolver and supervisor behavior retain their isolated tests, while capability transport tests now use an isolated artifact or the injected transport.

No Python production code changed relative to 2373a5ad. The only production delta is the optional TypeScript child-process injection seam.

Hermeticity incident and correction

An initial ambient-lookup mutation run exposed that the pre-existing Python "not resolvable" test left ambient process PATH uncontrolled. On this host, that mutation resolved and executed the host mosaic capability probe. A post-build intermediate TypeScript run also let the pre-existing no-dependency smoke case execute the checkout's built dist/cli.js capability probe. No claude process was run. I then isolated the Python test's ambient PATH, removed the TypeScript ambient smoke case, repeated the PATH mutation using only marker-writing temporary fakes, and repeated the final suites without either real probe path.

Mutation evidence

Each mutation was applied independently, its focused suite was run, and the production source was restored before the final run.

Mutation	Result	Reddened test name(s)
`shutil.which("mosaic", path=environ.get("PATH", ""))` to ambient `shutil.which("mosaic")`	RED, three failures	`ProbeActivationCapabilityTest.test_supplied_path_wins_over_ambient_process_path`; `ProbeActivationCapabilityTest.test_absent_or_empty_supplied_path_never_falls_back_or_executes` for both absent and empty PATH subtests
Python `PROBE_TIMEOUT_SECONDS: 10.0` to `2.0`	RED, one failure	`ProbeActivationCapabilityTest.test_probe_passes_ten_second_timeout_to_runner`
TypeScript `LEASE_CAPABILITY_PROBE_TIMEOUT_MS: 10_000` to `2_000`	RED, one failure	`defaultCapabilityProbe > passes the exact ten-second timeout to the injected child-process transport`

Final test run

Dependencies were installed first with pnpm install --frozen-lockfile. Workspace dependencies were then built with pnpm --filter '@mosaicstack/mosaic...' run build so package type declarations were available.

$ cd packages/mosaic && python3 src/mutator-gate/version_coupling_unittest.py
...................
----------------------------------------------------------------------
Ran 19 tests in 0.007s

OK

$ pnpm exec vitest run src/commands/lease-activation-probe.spec.ts
✓ src/commands/lease-activation-probe.spec.ts (20 tests) 80ms
Test Files  1 passed (1)
Tests       20 passed (20)

$ pnpm exec prettier --check packages/mosaic/src/commands/lease-activation-probe.ts packages/mosaic/src/commands/lease-activation-probe.spec.ts
Checking formatting...
All matched files use Prettier code style!

$ pnpm --filter @mosaicstack/mosaic lint
> eslint src

$ pnpm --filter @mosaicstack/mosaic typecheck
> tsc --noEmit

$ python3 -m py_compile packages/mosaic/src/mutator-gate/version_coupling_unittest.py packages/mosaic/framework/tools/lease-broker/activation_version_gate.py

$ git diff --check

All commands above exited zero.

Ambiguities skipped

None.

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