Announce a merged pull request's branch, not its pull ref, so its delivery group is found (hq issue 578)

The merge tool deletes the branch after merging; the forge then reads head.ref as refs/pull/<n>/head and only
head.label names the branch. pull.merged carried the pull ref, so the controller found no group for the merge,
cut mesh-catalog #251's walk at once and walked it before mesh-controller #271's, against the group's order.

modules/gitea/client.ts

@@ -49,6 +49,23 @@ export interface GiteaIssue {
   body?: string;
 }
 
+/**
+ * **The branch a pull request was opened from, also once it is deleted** (novox/hq issue 578). The forge says it as
+ * `head.ref` while the branch exists; once it is gone — the merge tool deletes it after the merge by default —
+ * `head.ref` reads `refs/pull/<n>/head`, and only `head.label` still names the branch. A delivery group is the pull
+ * requests sharing a head branch name (novox/hq ADR 0249), and the controller finds a merge's group, and joins the
+ * group's merges in one batch, by the head its `pull.merged` names (ADR 0276 decision 5, ADR 0306 decision 2). With
+ * the pull ref it found no group: on 2026-10-12 mesh-catalog #251's walk was cut at once and went before
+ * mesh-controller #271's, which the group's order put first.
+ */
+export function headBranchOf(head: { ref?: unknown; label?: unknown } | null | undefined): string | undefined {
+  const said = (v: unknown): string | undefined => (typeof v === "string" && v !== "" ? v : undefined);
+  const ref = said(head?.ref);
+  const label = said(head?.label);
+  if (ref === undefined || /^refs\/pull\/\d+\/head$/.test(ref)) return label ?? ref;
+  return ref;
+}
+
 /** A pull request, trimmed to the fields a reviewer or an event body needs. */
 export interface GiteaPull {
   number: number;
@@ -673,7 +690,7 @@ export class GiteaClient {
       merge_commit_sha: p.merge_commit_sha ?? undefined,
       merged_at: p.merged_at ?? undefined,
       user: p.user?.login,
-      head: p.head?.ref,
+      head: headBranchOf(p.head),
       head_sha: p.head?.sha ?? undefined,
       base: p.base?.ref,
       updated_at: p.updated_at ?? undefined,

modules/gitea/test/announcing.test.ts

@@ -93,3 +93,47 @@ test("a pull request or issue number that is not one is refused before the forge
     server.close();
   }
 });
+
+// **A merge names the branch it came from, also once that branch is deleted** (novox/hq issue 578). On 2026-10-12
+// the merge tool merged mesh-controller #271 and mesh-catalog #251, one delivery group, and deleted each branch. The
+// forge then read each pull request's head.ref as `refs/pull/<n>/head`, and `pull.merged` named that as the head: the
+// controller asked mesh-delivery for a group of that name, found none, and cut #251's walk at once, before #271's,
+// which the group's order put first.
+test("a merged pull request whose branch was deleted is announced with its branch, not its pull ref", async () => {
+  const { GiteaClient, headBranchOf } = await import("../client.ts");
+  const group = "feat/341-a-merge-check-judges-the-merge";
+  // As the forge answered for #251 after its merge.
+  const merged = {
+    number: 251, title: "A verdict goes out of date when its trunk moves", state: "closed", merged: true,
+    merged_at: "2026-10-12T16:11:29Z", merge_commit_sha: "23ea0f431faf91aa83e7b0297e0a9e442180f0c7",
+    head: { label: group, ref: "refs/pull/251/head", sha: "41b6e10077efdef694b519879fcbaeaf69d472b1" },
+    base: { label: "main", ref: "main" }, html_url: "http://fake/novox/mesh-catalog/pulls/251",
+  };
+  const server = createServer((req, res) => {
+    const url = req.url ?? "";
+    const send = (v: unknown) => res.end(JSON.stringify(v));
+    if (url.startsWith("/api/v1/repos/novox/mesh-catalog/pulls/251")) return send(merged);
+    if (url.startsWith("/api/v1/repos/novox/mesh-catalog/pulls?")) return send([merged]);
+    res.statusCode = 404;
+    res.end("{}");
+  });
+  await new Promise<void>((r) => server.listen(0, r));
+  const client = new GiteaClient(`http://127.0.0.1:${(server.address() as any).port}`, "t");
+  try {
+    // What the announcer reads each pass, and what `pull.merged` carries as its head.
+    const listed = await client.listPullRequests("novox", "mesh-catalog", { state: "closed", sort: "recentupdate", limit: "20" });
+    assert.deepEqual(listed.map((p) => p.head), [group], "the pass names the group's branch, never refs/pull/251/head");
+    assert.equal((await client.getPullRequest("novox", "mesh-catalog", 251)).head, group);
+  } finally {
+    server.close();
+  }
+  // While the branch exists the forge says it as ref, and that is what is named; a label alone is the branch too.
+  assert.equal(headBranchOf({ label: "feat/x", ref: "feat/x" }), "feat/x");
+  assert.equal(headBranchOf({ label: "feat/x" }), "feat/x");
+  assert.equal(headBranchOf({ ref: "feat/x" }), "feat/x");
+  // A branch whose own name only looks like a pull ref's start is still a branch.
+  assert.equal(headBranchOf({ label: "y", ref: "refs/pulled" }), "refs/pulled");
+  // No label to read: the pull ref is all the forge said, and it is kept rather than made up.
+  assert.equal(headBranchOf({ ref: "refs/pull/7/head" }), "refs/pull/7/head");
+  assert.equal(headBranchOf(undefined), undefined);
+});