fix(#1967): build hooks/dist once upfront in run-tests to close scoped-CI empty-dir race (#1968)

* fix(#1967): build hooks/dist once upfront in run-tests to close scoped-CI empty-dir race

hooks/dist/ is gitignored and not built by prepare (build:lib only), so the
scoped CI lane starts with it absent. The first install test's before() hook
triggers build-hooks.js, which creates DIST_DIR empty then fills it file-by-
file; a concurrently-spawned install.js reader can observe the empty window and
fail with 'Failed to install hooks: directory is empty' (intermittently failing
e.g. bug-3683-workflow-colon-namespace-leak on scoped legs).

Add ensureBuiltHooks() to scripts/run-tests.cjs — the same upfront chokepoint as
ensureBuiltArtifacts — to build hooks/dist once, single-process, before any
concurrent test spawns install.js. Completeness is checked against
build-hooks.js HOOKS_TO_COPY (absent/empty/partial/zero-byte -> rebuild; complete
-> no-op). Folds regression coverage into bug-969-test-infra-flake-hardening
(Part C), proven fail-first (ensureBuiltHooks undefined on next).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#1967): set changeset pr to 1968

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.changeset/hooks-dist-scoped-ci-race.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 1968
+---
+Build the gitignored `hooks/dist/` artifact once upfront in `scripts/run-tests.cjs` (the same chokepoint as `ensureBuiltArtifacts`), before any concurrent install test spawns `install.js`. Closes the scoped-CI first-build empty-dir race that intermittently failed install tests with `Failed to install hooks: directory is empty` (e.g. `bug-3683-workflow-colon-namespace-leak`). (#1967)