Fix unsafe test fixtures and the Bun version pin (#26051)

* Keep test interruption signals within owned processes

* Pin Bun and add optional unit runner shutdown diagnostics

* Unblock CI lint without changing session host runtime

* Avoid duplicating runtime import-check dependency bundles

* Leave unit runner diagnostics disabled by default

* test: keep runner incident follow-up focused on durable guards

* test: apply transcript replacements as authoritative snapshots

.github/workflows/pr.yml

@@ -201,7 +201,7 @@ jobs:
         if: needs.code_paths.outputs.static_analysis == 'true'
         uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
         with:
-          bun-version-file: config/bun-version
+          bun-version-file: config/.bun-version
 
       # Keep each check in its own log while sharing this runner.
       - name: Lint

.github/workflows/unit-tests.yml

@@ -50,7 +50,7 @@ jobs:
 
       - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
         with:
-          bun-version-file: config/bun-version
+          bun-version-file: config/.bun-version
 
       - uses: actions/download-artifact@v8
         continue-on-error: true