ci: run the Rust gates on stacked PRs, not only PRs targeting main

.github/workflows/crap.yml

@@ -12,9 +12,10 @@ name: "CRAP"
 # branch-protection settings. To soften it back to report-only, drop the
 # "Enforce CRAP threshold" step — the sticky comment keeps working either way.
 on:
+  # No branch filter: a stacked PR (a feature branch as base) must run this
+  # gate too. With `branches: [main]` here, retargeting a PR onto its
+  # parent branch silently switched every Rust gate off; see go.yml.
   pull_request:
-    branches:
-      - main
     paths:
       - "packages/**"
       - "Cargo.toml"

.github/workflows/miri.yml

@@ -15,9 +15,10 @@ name: "Miri"
 # and `protected` is where the only unsafe lives. Expand the matrix if other
 # crates grow pure-Rust `unsafe`.
 on:
+  # No branch filter: a stacked PR (a feature branch as base) must run this
+  # gate too. With `branches: [main]` here, retargeting a PR onto its
+  # parent branch silently switched every Rust gate off; see go.yml.
   pull_request:
-    branches:
-      - main
     paths:
       - "packages/protected/**"
       - ".github/workflows/miri.yml"

.github/workflows/mutants.yml

@@ -17,9 +17,10 @@ name: "Mutants"
 # step; the sticky comment keeps working either way. To block merges, mark this
 # check ("🧬 Mutants gate") as required in the repo's branch-protection settings.
 on:
+  # No branch filter: a stacked PR (a feature branch as base) must run this
+  # gate too. With `branches: [main]` here, retargeting a PR onto its
+  # parent branch silently switched every Rust gate off; see go.yml.
   pull_request:
-    branches:
-      - main
     paths:
       - "packages/**"
       - "Cargo.toml"

.github/workflows/test.yml

@@ -3,9 +3,10 @@ on:
   push:
     branches:
       - main
+  # No branch filter: a stacked PR (a feature branch as base) must run this
+  # gate too. With `branches: [main]` here, retargeting a PR onto its
+  # parent branch silently switched every Rust gate off; see go.yml.
   pull_request:
-    branches:
-      - main
   workflow_dispatch:
 
 defaults: