fix: robust worktree repo-path derivation and branch typing (review)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_sessions.py

@@ -1433,3 +1433,38 @@ async def test_worktree_state_for_worktree_session_returns_state(
 
     assert state is fake_worktree.state_result
     assert fake_worktree.state_calls == [(Path("/tmp/myproj"), WT_PATH, "feature-x")]
+
+
+@pytest.mark.asyncio
+async def test_repo_path_fallback_slash_branch_when_project_gone(
+    factory, db, tmux, harnesses, fake_worktree
+):
+    """When the project row is gone, the repo is derived from the worktree
+    layout even for slash-containing branch names (feature/foo).
+
+    create_worktree builds the path as <repo>/.worktrees/<branch>, so for a
+    branch like 'feature/foo' the path is <repo>/.worktrees/feature/foo. The
+    fallback must strip '.worktrees/feature/foo' and recover <repo>, not the
+    wrong parent.parent result (<repo>/.worktrees).
+    """
+    from hqt.db.models import Session
+
+    repo = Path("/tmp/myproj")
+    branch = "feature/foo"
+    # Mirror how worktree.create_worktree builds the path.
+    wt_path = repo / ".worktrees" / branch
+    sess = _seed_worktree_session(db, branch=branch, path=str(wt_path))
+    sess_id = sess.id
+
+    # Delete the project row so the fallback derivation is exercised.
+    db.query(Project).delete()
+    db.commit()
+    db.expire_all()
+    # Session row outlives the project (no FK cascade in this seed).
+    assert db.get(Session, sess_id) is not None
+
+    service = SessionService(factory=factory, tmux=tmux, harnesses=harnesses)
+    await service.worktree_state_for(sess_id)
+
+    # The fallback must recover the real repo, not <repo>/.worktrees.
+    assert fake_worktree.state_calls == [(repo, wt_path, branch)]