fix(setup): use monotonic time for lock deadlines

[627150795]

Problem

After #863 replaced per-process start-time queries with heartbeat leases, setup-config lock acquisition still used wall-clock time for its elapsed patience and hard deadlines. A system clock adjustment can shorten or extend a wait on an untrusted lock.

Value

Elapsed lock-wait budgets now use a monotonic clock, while stale-lock checks continue to compare filesystem timestamps with wall-clock time. Uncertain lock ownership still fails closed without changing the configuration.

Approach

• Use performance.now() for the patience deadline, hard deadline, and recheck timer.
• Keep wall-clock comparisons for lock-file modification times.
• Add a regression that simulates normal, forward, and backward wall-clock movement while asserting the same five-second patience deadline and preserving the uncertain lock and config.
• Narrow this PR to the deadline behavior that remains after fix(setup): use a heartbeat lease for the config lock #863; it no longer changes process-start queries.

Validation

Base: 708a44b52cb260cb6c35c25c4f5bd63ebfec369c
Final HEAD: 598f429ae266f666a959e54150042ca6f335624a

• node --test --experimental-strip-types tests/extensions/shared/setup-config.test.ts — 47 passed, 0 failed.
• bun run check — passed.
• bun run test — 2,473 passed, 14 skipped, 35 failed. Thirty-four failures were Windows EPERM while creating symlink fixtures; one dependent transcript-search assertion also failed after its symlink fixture could not be created.
• git diff --check origin/main...HEAD — passed.
• GitHub Actions run 39017765773 — 17/17 jobs succeeded; the PR reports 18/18 checks successful on this final HEAD.

Impact

No persisted config or lock-file schema changes. Only elapsed wait timing changes; filesystem timestamp checks retain wall-clock semantics. No config mutation occurs while lock ownership is uncertain.

[tt-a1i]

Reviewed exact head 415f35bfe3653913f133194f48cc211f79e16438 against f98d6a4737461ba8d8ee100f113b5a7c3a0001a0. Independent design and correctness passes found no blocking findings. Focused setup-config tests (36/36), bun run check, and the full macOS Node 26 suite passed; current-head CI is green. The successful-current-process identity cache preserves unknown-owner fail-closed behavior, and the wait deadline uses monotonic time. Scope remains Issue #829 item 3; no broader closure or Windows manual-smoke claim.