perf(natives): retain exact guards while reducing reaper overhead

[snowykr]

Scope

Independent current-dev prerequisite repair for the task-after-session-move stack replacing #6240. Base bb00f4c includes externally installed owner producer#6349 and current Codex partial-call/control-event/provider-veto retry fixes. Exact head059c5ac412a4bc4d462d8d058c381f102262ce80.

• POSIX exact parent traversal opens EVERY ancestor with O_DIRECTORY|O_NOFOLLOW, consolidating the prior symlink-only pre-stat into the kernel predicate.
• Failed opens remain failed. Capture original errno before close or diagnostic. Only ENOTDIR receives a no-follow diagnostic to classify a proven symlink; no rescue/retry/permission grant.
• Exact expected parent identity, both actual file hashes/identities/link counts, no-replace quarantine, post-rename validation and restoration remain unchanged. Not a new batch capability/native writer redesign. Security/ACL identity-edge helpers remain untouched. Windows native implementation unchanged.
• Sync and async reapers avoid unused alias regexes for terminal names; quarantine decoding, filters, native effects and accounting unchanged.
• Strict fixture still creates ALL50,001 real aged entries and protects evidence/young/unrelated/hardlink/symlink entries under the original20s deadline. Timestamp effects stay real; use synchronous timestamp syscall after each batched Bun.write to remove separate threadpool dispatch. No test assertions, cardinality or deadline changes.

Actual red/green evidence

Current-base unchanged fullunion failed20,041.38ms then20,124.53ms; both1211pass30existing-skips1fail, packagecheckNOTRUN. Retained both failures, no blind subsequent replay. One focused baseline passed near deadline; instrumentation then failed21,088.25ms and measured setup3816ms/effect17258ms. Root cause of timing variation not proven. Instrumentation fully removed.
Genuine source-bound native build on67c0c8de772fae4b47b4b8402687fb7e679e6d41 exits0;115explicit exports/10constenums; version0.18.7. Descriptor generated by build, NEVER manually stamped. AddonSHA256ed6fa1b9e21d44e395c3e6ee5c4c233f8f95f7cb5f265e8a92b23a26062cea8a; sourceSHA2567307e6644582648c8ea41ec634d30fc6a8fab9b60ae1ada001d5cde214b663fe; crateTree9a5bfa9ef444051b63c70cd502fb721ee0b78938. Rebased exact head has same native source/crate tree and authenticated generated descriptor.

Fresh exact current-owner composed qualification

Clean strict-native independent QA native-parent-open-first-currentbb00:1248pass32EXISTINGplatform skips0fail7987assertions1280tests34files505.56s; complete coding-agent package/vendor/Biome/types check0; diff0; clean exactHEAD beforeafter. Includes all installed consumer/owner cases, actual new initial-task owner regression, both previously missed lifecycle files, unchanged full strict fixture, current Codex stream/provider tests and native symlink/parent/file guards.
New real POSIX immediate/intermediate parent-symlink and missing/non-directory cases refuse without deleting retained/foreign payload. Native guardunion125pass17existing-skips0fail724assertions142tests3files; focused unchanged strictfixture1pass11assertions17.84s. Native and coding-agent package checks0, Rustaggregate0; existing warnings retained. Full cumulative workspace gates are separately recorded when executed, not inferred from these tests.

Budget and boundaries

Formatted production own AND actualdev60: Rust25+25=50, TS4+4=8, genuine descriptor1+1=2. Sevenfiles; tests/changelogs excluded. No native ABI/public schema/worker changes. Darwin evidence is not all-platform execution, filesystem-global writer linearizability or FD revocation. Caller-owned MCP and task admission authority unchanged. Committed-generation admission remains separate pending implementation qualification. No final goal/cohort/critic completion claim. Leader does not merge; fresh code CI, exact posted write-access approval and external installation remain distinct.

[probepark]

Code review (CI still running on 059c5ac; approval decision follows once CI finishes).

Review (head 059c5ac, gajae-reviewer on behalf of probepark)

CI: all planned checks green except Virtual integration validation (pending). check:@gajae-code/natives, check:@gajae-code/coding-agent, rust-check/rust-test, native-build and test:packages/natives/test/path-identity-posix.test.ts / session-directory.test.ts passed at this head.
Scope: +106 / -31, 7 files: crates/pi-natives (path_identity.rs), packages/coding-agent (managed-session-storage.ts, session-directory test, changelog fragment), packages/natives (diagnostic-artifact.json descriptor, posix test, changelog fragment).
Conventions: changelog fragments present for both packages; no hand-edited generated files (models.json/schemas/docs-index untouched); no labels.

Notable:

• crates/pi-natives/src/path_identity.rs:5485-5509: I checked the error-code mapping against the removed pre-fstatat path. Symlink ancestor: Linux openat(O_NOFOLLOW|O_DIRECTORY) gives ELOOP, and security_code maps that to reparse_point (L2738). Darwin gives ENOTDIR, the new fstatat probe sees S_IFLNK and returns reparse_point. Missing ancestor: ENOENT maps to not_found, as before. Regular file: ENOTDIR, the probe sees no symlink, so it returns not_directory, as before. errno is captured before the probe and before close. parent_fd is closed exactly once on both the failure and success branches. The probe never retries the open and never continues the walk. The four new posix tests (immediate/intermediate symlink, missing/regular) pin these codes.
• packages/coding-agent/src/session/internal/managed-session-storage.ts:954-955,1034-1035: the !terminalRemnant && short-circuit does not change behaviour. Both candidate flags are read only in the terminalRemnant ? undefined : … alias branch and in the continue guard, and that guard is already satisfied by terminalRemnant.
• session-directory.test.ts:3558: syncFs.utimesSync inside the async batch blocks the loop per entry. That is acceptable for a fixture, and the assertions, cardinality and deadline are unchanged.

Blocking: none.

Checked clean: native ancestor walk fd ownership and error codes; reaper candidate classification in both the sync and async twins; test coverage of the new native branches. Not checked: Darwin execution locally. The reviewer pod has no macOS; CI darwin-arm64 tab-worker smoke passed.

[snowykr]

Fresh full cumulative qualification completed on EXACT059c5ac412a4bc4d462d8d058c381f102262ce80/baseinstalledbb00: bun run check exit0, check:ts864.97s; current TypeScript/Rust/schema/API/workspace/source-doc gates. IndependentQA exactHEAD clean before/after, diffcheck0, existingwarnings retained (not suppressed). Genuine source-bound optimized0.18.7addon ed6/source7307/crate9a5 remains unchanged; descriptor generated by actualbuild, noQAstamp. Fresh strict-native34-file composed union1248pass32EXISTINGplatform skips0fail7987assertions1280tests505.56s/package0 includes installed6349 owner and initial-task refusal plus unchanged50001/20sreaper. This repairs repeated realdeadlinefailures; failurehistory preserved, no scope/cardinality/deadline waiver. SourceownANDactualdevproduction60. Localgates≠currentcodeCI≠exactpostedwrite-accessapproval≠externalinstallation; leaderdoesnotmerge. Committedtaskadmission remains separate uncommitted implementation/qualification work, nofinalcohortclosure.

[probepark]

Review (head 059c5ac, gajae-reviewer on behalf of probepark)

CI finished; no blocking findings. Code review: #6353 (review)

CI: green. All 35 checks at this head passed or were skipped, including Virtual integration validation, check:@gajae-code/natives, check:@gajae-code/coding-agent, rust-check/rust-test and darwin-arm64 tab-worker smoke (run https://github.com/Yeachan-Heo/gajae-code/actions/runs/37269984906). The approve gate returned ALLOW: 0 pending, 0 failed, and the plan covered check:@gajae-code/natives and check:@gajae-code/coding-agent.
Scope: +106 / -31, 7 files: crates/pi-natives, packages/coding-agent, packages/natives.
Conventions: changelog fragments present; no generated files; no labels.
Blocking: none.

Body verdict line count=0; not updated. Suggested verdict line: gajae.pr-review-verdict.v1 merge-approved sha256:96d8eae054fb697c0b1047ca06da7df821f05a043fa1f82d0f33d6c51c60fcbc reviewer:human reviewer-id:probepark evidence:ci-green;approve-gate-allow;native-fd-close-once-checked;error-code-mapping-checked

Verdict: gajae.pr-review-verdict.v1 merge-approved sha256:96d8eae054fb697c0b1047ca06da7df821f05a043fa1f82d0f33d6c51c60fcbc reviewer:human reviewer-id:probepark evidence:ci-green;approve-gate-allow;native-fd-close-once-checked;error-code-mapping-checked