fix: guard writeIntegrationBranch against workflow-template branches

writeIntegrationBranch already rejects slice branches (SLICE_BRANCH_RE) and
quick-task branches (QUICK_BRANCH_RE), but has no guard for the 8 workflow-
template branches (gsd/hotfix/*, gsd/bugfix/*, gsd/spike/*, etc.). When a
user runs `/gsd start hotfix` during an active milestone, the ephemeral
hotfix branch gets recorded as the integration target and the milestone
later merges to the wrong branch.

Add WORKFLOW_BRANCH_RE (/^gsd\/(?!M\d)[\w-]+\//) that matches all
gsd/<templateId>/<slug> branches while excluding milestone slice branches
(gsd/M001/S01). The negative lookahead ensures milestone branches starting
with 'M' followed by a digit are not affected.

Same root cause as gsd/quick/* (#1293, PR #1342).

Closes #2498

src/resources/extensions/gsd/git-service.ts

@@ -246,6 +246,15 @@ export function readIntegrationBranch(basePath: string, milestoneId: string): st
 /** Regex matching GSD quick-task branches: gsd/quick/<num>-<slug> */
 export const QUICK_BRANCH_RE = /^gsd\/quick\//;
 
+/**
+ * Matches all GSD workflow-template branches: gsd/<templateId>/<slug>.
+ *
+ * Template IDs are lowercase alphanumeric with hyphens (e.g. hotfix, bugfix,
+ * small-feature, dep-upgrade). The negative lookahead excludes milestone
+ * branches (gsd/M001/... or gsd/M001-abc123/...) which use SLICE_BRANCH_RE.
+ */
+export const WORKFLOW_BRANCH_RE = /^gsd\/(?!M\d)[\w-]+\//;
+
 export function writeIntegrationBranch(
   basePath: string,
   milestoneId: string,
@@ -257,6 +266,10 @@ export function writeIntegrationBranch(
   // to their origin branch on completion. Recording one as the integration
   // target causes milestone merges to land on the wrong branch (#1293).
   if (QUICK_BRANCH_RE.test(branch)) return;
+  // Don't record workflow-template branches (hotfix, bugfix, spike, etc.) —
+  // same root cause as quick-task branches (#2498). All templates create
+  // gsd/<templateId>/<slug> branches that are ephemeral.
+  if (WORKFLOW_BRANCH_RE.test(branch)) return;
   // Validate
   if (!VALID_BRANCH_NAME.test(branch)) return;
   // Skip if already recorded with the same branch (idempotent across restarts).

src/resources/extensions/gsd/tests/git-service.test.ts

@@ -868,6 +868,55 @@ describe('git-service', async () => {
     rmSync(repo, { recursive: true, force: true });
   });
 
+  // ─── writeIntegrationBranch: rejects workflow-template branches (#2498) ─
+
+  test('Integration branch: rejects workflow-template branches', () => {
+    const repo = initBranchTestRepo();
+
+    // All 8 registered workflow templates should be rejected
+    writeIntegrationBranch(repo, "M001", "gsd/hotfix/fix-login");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "hotfix branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/bugfix/null-pointer");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "bugfix branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/small-feature/add-button");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "small-feature branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/refactor/rename-module");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "refactor branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/spike/evaluate-lib");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "spike branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/security-audit/owasp-scan");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "security-audit branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/dep-upgrade/bump-react");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "dep-upgrade branch is not recorded");
+
+    writeIntegrationBranch(repo, "M001", "gsd/full-project/new-app");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), null, "full-project branch is not recorded");
+
+    rmSync(repo, { recursive: true, force: true });
+  });
+
+  // ─── writeIntegrationBranch: still records legitimate branches ────────
+
+  test('Integration branch: records non-ephemeral gsd branches', () => {
+    const repo = initBranchTestRepo();
+
+    // A normal feature branch should still be recorded
+    writeIntegrationBranch(repo, "M001", "feature/new-thing");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M001"), "feature/new-thing", "normal branches are recorded");
+
+    // The main branch should be recorded
+    writeIntegrationBranch(repo, "M002", "main");
+    assert.deepStrictEqual(readIntegrationBranch(repo, "M002"), "main", "main branch is recorded");
+
+    rmSync(repo, { recursive: true, force: true });
+  });
+
   // ─── writeIntegrationBranch: rejects invalid branch names ─────────────
 
   test('Integration branch: rejects invalid names', () => {