chore(stryker): register 3 covering unit tests missing from tap.testFiles (#13357)

* fix(test): make npm run test terminate and restore RAYCAST env-doc sync

Two independent defects, both in the test/dev entrypoint layer.

1. `npm run test` never terminated. It was a hand-maintained copy of
   `test:unit` that had drifted: it omitted `--test-force-exit` on BOTH
   node invocations and dropped the trailing `&& npm run test:unit:serial`.
   Per AGENTS.md ('Database Handles in Tests'), unreleased SQLite handles
   make Node's native runner hang indefinitely — every sibling script
   (`test:unit`, `test:unit:ci`, `test:unit:ci:shard`) already carried the
   flag; only `test` did not. Measured on m1max at 84c6ad7c2, same suite
   both arms: without the flag the runner was killed at the 420s ceiling
   (exit 137, no summary line, 23 orphaned node processes); with it the
   runner exited on its own in 419s leaving 1. `test` now delegates to
   `test:unit` so the two cannot drift again, which also makes the serial
   suite reachable from `npm run test` for the first time.

2. Removing the RAYCAST_* rows from ENVIRONMENT.md (#9) broke
   check-env-doc-sync. `parseEnvExampleVars` matches `^#?\s*(VAR)=`, so it
   counts COMMENTED-OUT vars: the four entries still sat at
   .env.example:1263-1266 and became `envMissingDoc` drift the moment their
   docs disappeared. The #9 verification only ran the fabricated-docs gate
   and missed this one. The block is dead either way — it documents
   open-sse/services/raycast.ts and scripts/raycast/usage-benchmark.mjs,
   both deleted with the GPL-derived provider in #11691, and no live code
   reads the vars — so it is removed rather than re-documented.

envMissingDoc is now []. The remaining codeMissingEnv failure
(CURSOR_AGENT_BINARY, CURSOR_MAX_FRAME_BYTES, OMNIROOT) is pre-existing
drift on the base, absent from this diff, and left alone.

* chore(stryker): register 3 covering unit tests missing from tap.testFiles

check:mutation-test-coverage --strict fails identically on pristine
release/v3.8.51 (f1e7148c1) with an empty diff — base debt blocking this PR.

- combo-identical-error-streak.test.ts -> comboPredicates.ts
- 13601-header-drop-count-surfaced.test.ts -> responseHeaders.ts
- semantic-cache-no-truncated-writes.test.ts -> semanticCache.ts

* fix(test): keep the #13187 concurrency-4 cap in test:unit

The dedupe made `test` delegate to `test:unit`, but it also silently
reverted the deliberate local concurrency cap from #13187 ("cap local
unit-test concurrency at 4 to avoid exhausting commit charge") back to 20.

Measured on m1max (16 cores), same suite and same tree, only the flag differs:
  concurrency=20 -> 356 cancelled, 356 "event loop has already resolved" bailouts
  concurrency=4  -> 0 cancelled, 0 bailouts
So 20 does not just slow the run down, it makes the runner abandon tests and
still print a summary -- a false green. Restore 4; termination is preserved via
delegation to test:unit, which already carries --test-force-exit.

* revert(test): drop redundant test-script delegation

The #13187 batch commit (178d25250) already gave `test` both `--test-force-exit` flags and the trailing `&& npm run test:unit:serial` step, so the delegation fix was redundant. It also broke tests/unit/test-serial-quarantine.test.ts, which asserts every parallel runner script ends with the serial step (base 4/4 -> head 3/4). package.json is now byte-identical to base; this PR is the stryker tap.testFiles fix only.

stryker.conf.json

@@ -138,6 +138,7 @@
       "tests/unit/chatcore-executor-proxy.test.ts",
       "tests/unit/chatcore-extracted-modules-3821.test.ts",
       "tests/unit/chatcore-header-drop-warn-dedupe-10315.test.ts",
+      "tests/unit/13601-header-drop-count-surfaced.test.ts",
       "tests/unit/chatcore-headers.test.ts",
       "tests/unit/chatcore-imports-cleanly.test.ts",
       "tests/unit/chatcore-log-truncation.test.ts",
@@ -149,6 +150,7 @@
       "tests/unit/chatcore-sanitization.test.ts",
       "tests/unit/chatcore-semantic-cache-store.test.ts",
       "tests/unit/chatcore-semantic-cache.test.ts",
+      "tests/unit/semantic-cache-no-truncated-writes.test.ts",
       "tests/unit/chatcore-strip-stale-headers.test.ts",
       "tests/unit/chatcore-telemetry-helpers.test.ts",
       "tests/unit/chatcore-translation-paths.test.ts",
@@ -205,6 +207,7 @@
       "tests/unit/combo-omnimodel-tag-stripping.test.ts",
       "tests/unit/combo-param-validation-fallback-4519.test.ts",
       "tests/unit/combo-prescreen.test.ts",
+      "tests/unit/combo-identical-error-streak.test.ts",
       "tests/unit/combo-priority-quota-exhaustion-cutoff-5923.test.ts",
       "tests/unit/combo-provider-cooldown-sibling.test.ts",
       "tests/unit/combo-provider-cooldown.test.ts",