ci: pin browser jobs to supported Ubuntu 24.04 for release validation

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     timeout-minutes: 45
     strategy:
       matrix:
@@ -96,7 +96,7 @@ jobs:
   # deploy-cache-state CDN purge below. Real build/lint failures still gate the
   # deploy via the build job.
   visual-regression:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     timeout-minutes: 30
     strategy:
       matrix:
@@ -401,7 +401,7 @@ jobs:
         run: npm run test:dm:unit
 
   e2e-tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     timeout-minutes: 35
     strategy:
       fail-fast: false
@@ -489,7 +489,7 @@ jobs:
         run: npm run test:dm:integration
 
   e2e-headless:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     timeout-minutes: 45
     strategy:
       matrix:

docs/testing/release-ci-runner-2026-10-29.md

@@ -0,0 +1,7 @@
+# Release CI runner compatibility correction
+
+Candidate a2dbaccc CI run 40896227464 failed all browser-installing jobs before tests: Playwright reports `does not support chromium on ubuntu26.04-x64`. The lint suite, app build, archive and DM checks passed separately. This is not a browser assertion result or a resolution of the earlier Firefox failures.
+
+Pin only build, visual-regression, e2e-tests and e2e-headless runner definitions to ubuntu-24.04, which is explicitly supported by the installed Playwright registry and native dependencies. Matrix coverage, assertions, retries, timeouts, steps and deploy gating are unchanged. The broader duplicate-build/browser-job simplification remains deferred for timing-based evaluation.
+
+Validation: exact four-line runner-only workflow delta verified; normal landing gate and hosted corrected-candidate CI results are recorded separately in the release evidence directory. Never treat unsupported-runner failure as a passing test suite.