fix(#1995): widen worktree branch regex to accept agent-<id> namespace (#2548)

* test(#1995): regression test for agent-<id> branch namespace

Add failing-first tests proving that normalizeCleanupManifestEntry and
planWorktreeRecordAgent reject Claude Code's current agent-<id> isolation
branches (only worktree-agent-<id> is accepted). Boundary tests cover both
namespaces plus rejection cases.

* fix(#1995): widen worktree branch regex to accept agent-<id> namespace

Claude Code's isolation="worktree" branch naming changed from
worktree-agent-<id> to agent-<id>. Widen the regex in all 7 locations
from ^worktree-agent-[A-Za-z0-9._/-]+$ to ^(worktree-)?agent-[A-Za-z0-9._/-]+$
so both namespaces are accepted. Introduce a shared WORKTREE_AGENT_BRANCH_RE
constant in src/worktree-safety.cts to prevent future drift.

Closes #1995

* fix(#1995): update workflow guards, test assertions, and baselines

Widen the branch-check regex in execute-phase.md and execute-plan.md.
Update all test assertions that checked for ^worktree-agent- to expect
the widened ^(worktree-)?agent- pattern. Regenerate golden-install-parity
fixtures, agent-size-baseline, and workflow-size-baseline.

Closes #1995

* fix(#1995): update extractCwdGuardBash sanity check for widened regex

The e2e test's sanity check verified the extracted bash block contained
'worktree-agent-'. After widening to '(worktree-)?agent-', update the
check to match the new pattern.

* fix(#1995): widen missed workflow-guard branch check + changeset + lint fixes

- hooks/gsd-workflow-guard.js: widen startsWith('worktree-agent-') to
  /^(worktree-)?agent-/ regex — same defect class, was missed in prior commit
- tests/worktree.test.cjs: fix indentation regression from prior edit
- Add .changeset/1995-worktree-agent-branch-namespace.md (pr:0 placeholder)

Found by orthogonal code review (Step 4).

* fix(#1995): regenerate golden + size baselines for workflow-guard change

* docs(#1995): backfill changeset PR number (2548)

hooks/gsd-workflow-guard.js

@@ -143,11 +143,11 @@ process.stdin.on('end', () => {
       const command = data.tool_input?.command || '';
       for (const gitCwd of forceGitAddCwds(command, cwd)) {
         const branch = currentBranch(gitCwd);
-        if (branch.startsWith('worktree-agent-')) {
+        if (/^(worktree-)?agent-/.test(branch)) {
           const output = {
             decision: 'block',
             code: 'WORKTREE_AGENT_FORCE_ADD_FORBIDDEN',
-            reason: 'worktree-agent branches must not run git add -f or git add --force. Respect the SDK skipped_gitignored/skipped_commit_docs_false contract and leave gitignored files untracked.',
+            reason: 'agent/worktree-agent branches must not run git add -f or git add --force. Respect the SDK skipped_gitignored/skipped_commit_docs_false contract and leave gitignored files untracked.',
           };
           process.stdout.write(JSON.stringify(output));
           // Kimi CLI's exit-2 protocol feeds stderr back to the model (#2304)

hooks/gsd-worktree-path-guard.js

@@ -118,13 +118,14 @@ process.stdin.on('end', () => {
     }
 
     // #1342: Only enforce inside a GSD-managed isolated executor worktree. Those
-    // are always on a `worktree-agent-*` branch (the positive allow-list enforced
-    // by worktree-branch-check.md, #2924). A manually-created linked worktree (plain
-    // non-GSD work, e.g. Claude Code plan-mode) is on the user's own branch, so the
-    // guard must be a no-op there. Detached HEAD / error → not GSD-managed → no-op.
+    // are always on an `agent-*` or legacy `worktree-agent-*` branch (the positive
+    // allow-list enforced by worktree-branch-check.md, #2924, #1995). A manually-
+    // created linked worktree (plain non-GSD work, e.g. Claude Code plan-mode) is
+    // on the user's own branch, so the guard must be a no-op there. Detached HEAD
+    // / error → not GSD-managed → no-op.
     const branchResult = git(['symbolic-ref', '--short', 'HEAD'], cwd);
     const branch = branchResult.status === 0 && branchResult.stdout ? branchResult.stdout.trim() : '';
-    if (!/^worktree-agent-[A-Za-z0-9._/-]+$/.test(branch)) {
+    if (!/^(worktree-)?agent-[A-Za-z0-9._/-]+$/.test(branch)) {
       process.exit(0); // not a GSD-managed executor worktree — no-op
     }