fix(ci): cancel a destroyed merge group's queued Check run

.github/actionlint.yaml

@@ -0,0 +1,5 @@
+paths:
+  .github/workflows/check.yml:
+    ignore:
+      # Delivered to Actions but missing from its event docs: https://github.com/rhysd/actionlint/issues/726
+      - 'invalid activity type "destroyed" for "merge_group" Webhook event'

.github/workflows/check.yml

@@ -14,11 +14,16 @@ on:
     # would post a passing context over a failed one; on main PRs that is free.
     types: [opened, synchronize, reopened, edited, closed]
   merge_group:
-    types: [checks_requested]
+    # `destroyed` only cancels the dead group's in-flight run, like `closed`.
+    # GitHub keeps that run queued when the group is rebuilt behind a departed
+    # entry, where it holds the queue runner ahead of the live groups until they
+    # time out. Actions delivers this type although its docs omit it.
+    types: [checks_requested, destroyed]
 
 # Cancel in-flight runs when a new commit lands on the same PR, or when the PR
 # is merged/closed (the close event shares this group and supersedes the build).
-# Each merge group has its own queue ref, separate from the PR ref.
+# Each merge group has its own queue ref, shared by its `destroyed` event and
+# separate from the PR ref.
 concurrency:
   group: check-${{ github.ref }}
   cancel-in-progress: true
@@ -27,9 +32,9 @@ jobs:
   # One checkout, dev shell, cache restore, and dispatcher for lints and tests.
   check:
     name: Check
-    # A close/merge run exists only to cancel the superseded in-flight build via
-    # the concurrency group above.
-    if: github.event.action != 'closed' && (github.event_name != 'pull_request' || github.base_ref == 'release')
+    # A close/merge or destroyed-group run exists only to cancel the superseded
+    # in-flight build via the concurrency group above.
+    if: github.event.action != 'closed' && github.event.action != 'destroyed' && (github.event_name != 'pull_request' || github.base_ref == 'release')
     # Leave the variable unset until the local runner is online and verified.
     runs-on: ${{ github.event_name == 'merge_group' && vars.MOQ_QUEUE_RUNNER || 'ubuntu-24.04-arm' }}
     # `main` and its merge queue write the Rust cache; see .github/actions/rust-cache.

sh/gh/queue.test.ts

@@ -29,8 +29,14 @@ for (const job of [check.jobs.check]) {
 	assert.equal(condition(job.if, "pull_request", "release"), true);
 	assert.equal(condition(job.if, "pull_request", "release", true, "edited"), true);
 	assert.equal(condition(job.if, "pull_request", "release", true, "closed"), false);
-	assert.equal(condition(job.if, "merge_group", ""), true);
+	assert.equal(condition(job.if, "merge_group", "", true, "checks_requested"), true);
+	// A destroyed group's run only cancels its stale build through the shared queue ref.
+	assert.equal(condition(job.if, "merge_group", "", true, "destroyed"), false);
 }
+assert.deepEqual(check.on.merge_group.types, ["checks_requested", "destroyed"]);
+// biome-ignore lint/suspicious/noTemplateCurlyInString: GitHub expression is literal YAML.
+assert.equal(check.concurrency.group, "check-${{ github.ref }}");
+assert.equal(check.concurrency["cancel-in-progress"], true);
 
 // Every other workflow stays out of main PRs and main's merge groups: optional
 // checks run nightly on main and on release PRs, retargeted ones included.

sh/gh/setup.test.ts

@@ -55,7 +55,7 @@ for (const name of ["check"]) {
 }
 
 test("scope queries support both merge groups and release PRs without path filters", () => {
-	expect(workflow.on.merge_group).toEqual({ types: ["checks_requested"] });
+	expect(workflow.on.merge_group).toEqual({ types: ["checks_requested", "destroyed"] });
 	expect(workflow.on.pull_request).toBeDefined();
 	expect(workflow.on.pull_request).not.toHaveProperty("paths");
 	expect(workflow.on.pull_request).not.toHaveProperty("branches");
@@ -67,7 +67,7 @@ test("main PRs skip Check while the queue and release PRs run it", () => {
 	expect(workflow.on.pull_request).toEqual({ types: ["opened", "synchronize", "reopened", "edited", "closed"] });
 	for (const name of ["check"]) {
 		expect(workflow.jobs[name].if).toBe(
-			"github.event.action != 'closed' && (github.event_name != 'pull_request' || github.base_ref == 'release')",
+			"github.event.action != 'closed' && github.event.action != 'destroyed' && (github.event_name != 'pull_request' || github.base_ref == 'release')",
 		);
 	}
 });