FN-8093: rescue dist-barrel coverage

Restore the isolated built-core barrel regression guard to the default CLI test lane.

- Hoist recompilation and PostgreSQL fixture setup outside timed test bodies.
- Inject the fixture store into the dynamic extension and retain text-budget assertions.
- Skip cleanly per test when a transitive dist artifact is unavailable.
- Remove the matching CLI quarantine exclusion and ledger entry.

Files changed:
 .../src/__tests__/extension-dist-barrel.test.ts    | 234 +++++++++++----------
 packages/cli/vitest.config.ts                      |   8 +-
 scripts/lib/test-quarantine.json                   |   5 -
 3 files changed, 121 insertions(+), 126 deletions(-)

Fusion-Task-Id: FN-8093

Fusion-Task-Lineage: 352b3675-0579-43bc-acd9-6a11919ed646

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

scripts/lib/test-quarantine.json

@@ -1,11 +1,6 @@
 {
   "$comment": "Flaky-test quarantine ledger (deletion ratchet — see AGENTS.md 'Flaky tests: quarantine on sight' and docs/testing.md 'Quarantine ledger and the deletion ratchet'). A test observed failing without a corresponding real bug is quarantined ON SIGHT: add an entry here AND a matching one-line `exclude` entry in that package's vitest config, in the same commit. Every entry needs a non-empty `reason` (link the failing run) and a `quarantinedAt` date — the entry expires 14 days later, at which point the test file is DELETED unless someone rescues it with evidence it catches real regressions plus a root-cause fix (never appeasement). There is deliberately no loader module and no automation around this file: it is a dated record, the vitest config is the enforcement.",
   "entries": [
-    {
-      "file": "packages/cli/src/__tests__/extension-dist-barrel.test.ts",
-      "reason": "FN-7530 RESCUE-by-split of the prior extension.test.ts entry: the dist-barrel fn_task_list test timed out at 5000ms in the full-suite shard 4/4 (run https://github.com/Runfusion/Fusion/actions/runs/28697507894) while passing locally in ~1.2s and in 3 of the 4 surrounding CI runs. Root-cause invariant: the test does in-test module recompilation (vi.resetModules + vi.importActual of the full @fusion/core dist barrel + a fresh dynamic import of extension.js) inside the default 5s test timeout; that work is CPU-bound and degrades non-linearly under 4-shard CI contention (same loaded-lane signature as FN-6483/FN-6705/FN-6795/FN-6839). Widening the timeout is forbidden by the flaky-test rule and removing the recompilation removes the test's only point, so the file is quarantined pending a split into smaller compilation units.",
-      "quarantinedAt": "2026-07-04"
-    },
     {
       "file": "packages/engine/src/__tests__/backlog-pressure-reporter.test.ts",
       "reason": "VAL-REMOVAL-005 PG migration: fails due to SQLite removal or sync API incompatibility in backend mode. Failing run: https://github.com/Runfusion/Fusion/actions/runs/29344576232. Mirrored in packages/engine/vitest.config.ts.",