epic(meta): testing and reliability remediation

[LMLiam]

Outcome

Bounded tests protect snapshot, timing, coverage, parser, compile-time, diagnostic, and concurrency contracts under #403.

Implementation order

Run these delivery issues in this order. #467 and #505 consume #55. #414 consumes #399 and #446.

1. refactor(test): decouple matcher tests from incidental messages #331 — decouple matcher tests from incidental messages
2. test(snapshot): harden storage and cross-platform behaviour #381 — harden snapshot storage and cross-platform behaviour
3. test(core): align and enforce the Ticker timing contract #382 — align and enforce the Ticker timing contract
4. test(dsl): maintain compile-pass and compile-fail API fixtures #467 — maintain compile-pass and compile-fail API fixtures
5. test(dsl): add bounded property and differential conformance tests #416 — add bounded property and differential conformance tests
6. test(concurrency): stress high-risk state-machine contracts #417 — stress high-risk state-machine contracts
7. feat(diagnostics): stabilise selected validation diagnostics #505 — stabilise selected validation diagnostics
8. test(coverage): make module and patch coverage visible and ratcheted #414 — make module and patch coverage visible and ratcheted

#381 blocks only the snapshot-name slice of #416. #382 blocks only the timed-boss-bar slice of #417. Keep #416 at 250 cases, 50-element generated values, five seconds per property, and 1,000 shrink attempts unless measured evidence supports a reviewed change. Keep #417 on finite two-worker schedules with explicit per-schedule and test time limits.

Completion

Close this epic when every retained native child is complete or explicitly not planned. Optional mutation testing in #462 is outside this epic.