Summary

Adds focused regression coverage for residual high-risk seams on main that are still untested and not claimed by open coverage PRs #298–#305 (main tip still at fa5c0f68). Also refreshes canary mobile lockfile + research-readiness desktop bridge stabilizers, and unflakes a calendar-aged composer draft prune assertion.

Risky behavior now covered

• Tool mutation-gate wrapping — createRunTurn wraps tool execute with assertCanMutate before the underlying tool runs; rejection blocks side effects.
• Codex interruptTurn compatibility — prefers turn/cancel, falls back to turn/interrupt when cancel is missing, and rethrows the original cancel error when both fail.
• Managed Codex install concurrency — concurrent installs for the same version coalesce onto one asset download; a failed in-flight install is cleared so a later retry can succeed.
• Task artifact baseline race — task/artifact/read recovers when concurrent baseline creation races, and rethrows when concurrent detail remains empty.
• Task artifact restore guards — refuse restore with no current version; pass the latest version SHA as expectedSha256.

Test files added/updated

• test/agent.mutation-gate.test.ts (new)
• test/providers/codex-app-server-client.interrupt.test.ts (new)
• test/providers/codex-app-server-resolver.concurrency.test.ts (new)
• test/jsonrpc.task-artifacts-route.test.ts
• apps/desktop/test/research-readiness.test.tsx (CI stabilizer)
• apps/mobile/bun.lock (canary lockfile)
• apps/desktop/test/composer-draft-thread-switch.test.ts (calendar-age flake fix)

Why these tests materially reduce regression risk

These paths sit on cancellation, install, mutation-permission, and artifact integrity boundaries. Silent breakage would leave turns uncancellable across Codex versions, duplicate managed installs under cold-start concurrency, allow cancelled/locked turns to mutate via tools, or overwrite/restore artifacts without SHA safety.

Deliberately avoided duplicating open #298–#305 seams (integrity mid-verify, send-queue, deferred sync timeout, MCP OAuth/retry, preflight Codex gates, etc.).

Validation

• Targeted suites green
• Touched files Biome-clean
• bun run lint / bun run typecheck / bun run docs:check clean
• Full bun run test: all 675 files passed (Bun 1.4.0-canary)