Qualify cross-process provider credential ownership

[piclaw-bot]

Cross-process credential ownership qualification

Refs #1458 and #1442; both stay open.

• Exercise public exact-0.99.1 ModelRuntime consumers in independent disposable children sharing only the explicit Piclaw FileCredentialStore path.
• Verify one refresh supplies concurrent auth, logout commits after held refresh, and a rejected refresh releases the lock before a contender rotates.
• Require storage-entry barriers, lock-release rejection fence, exact final credential IDs, synthetic auth outcomes and unrelated-provider preservation.
• Add an opt-in owned-SIGKILL pre-write holder case: unchanged auth bytes/leftover lock, real35s stale window, fresh successor recovery. No clock or lock-option changes.

The public app-store subclass observes entry/rejection only; it delegates to the real store and never patches SDK internals. IPC carries events/commands only. No provider network, inference, live credentials, deployment or restart.

This proves serialization/pre-write holder recovery, not crash-safe file writes. Current in-place writeFileSync overwrite can corrupt under mid-write loss; that durability boundary, legacy backups, complete CLI/device/Delegate/live acceptance remain open.

Validation

Opt-in full fixture: 4 pass / 35 assertions plus child assertions. Post-merge fast+lifecycle: 9 pass / 42 assertions, one documented slow opt-in skip. Strict fixtures, five types and scoped lint pass. Review corrected barriers, rejection fence, final cardinality and termination signal; rereview green. Canonical gate: 5,954 passed, eight skipped, zero failed; 25 feature and nine web checks passed. Seven existing skips plus the documented slow opt-in crash case (separately passed). Pack hygiene: 24,741 files; final five types/diff passed at baseline 7ed2e7187, unchanged compose baseline. Initial static guard caught an empty cleanup catch; corrected error propagation/finally cleanup passed guard and full gate with no relaxed limits. Environment snapshot change is docs-only opt-in reference, no production readers.