CI: paths-ignore keeps docs/start/README.md in the portability run (read by first-call tests)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.github/workflows/cultmesh-portability.yml

@@ -1,13 +1,14 @@
 name: CultMesh portability and performance
 
 # The forge runs one job at a time and this workflow holds the slot 14 to 30 minutes, so it runs once per change:
-# on the pull request (never again on the push that merges it), skipped for documentation-only changes, and on a
+# on the pull request (never again on the push that merges it; a break that merges from a stale base waits for the
+# schedule), skipped for design-note-only changes, and on a
 # daily schedule so main is still exercised when nobody opens a pull request.
 on:
   pull_request:
     paths-ignore:
-      - "**/*.md"
-      - "docs/**"
+      # Not `**/*.md` or `docs/**`: docs/start/README.md is read by the first-call tests of every runtime.
+      - "docs/*.md"
       - "research/**"
       - ".voidbot/**"
   schedule: