fix(server): make paseo worktree archive idempotent after partial teardown

If a first archive attempt removed git's admin dir but failed to clean the
working tree (e.g. due to file churn during setup), retrying the archive
failed the ownership gate with "Worktree is not a Paseo-owned worktree"
because isPaseoOwnedWorktreeCwd required the worktree to still appear in
git worktree list.

- isPaseoOwnedWorktreeCwd now decides ownership by path shape
  ($PASEO_HOME/worktrees/<hash>/<slug>[/...]) and treats git as
  best-effort for resolving repoRoot.
- deletePaseoWorktree tolerates a missing admin dir: it skips teardown
  when the tree is absent, swallows a failing git worktree remove so
  the rmSync fallback always runs, and follows up with git worktree
  prune to clear stale admin refs.
- Relabel the post-creation setup failure log as
  "Background worktree setup failed" since the worktree itself already
  exists at that point.

packages/server/src/utils/worktree.test.ts

@@ -789,6 +789,96 @@ describe("paseo worktree manager", () => {
     expect(existsSync(created.worktreePath)).toBe(true);
     expect(existsSync(join(repoDir, "teardown-start.log"))).toBe(true);
   });
+
+  it("treats a worktree as paseo-owned even when its .git admin is missing", async () => {
+    const created = await createWorktree({
+      branchName: "orphan-admin-branch",
+      cwd: repoDir,
+      baseBranch: "main",
+      worktreeSlug: "orphan-admin",
+      paseoHome,
+    });
+
+    // Simulate a previous archive attempt that removed git's admin dir but left
+    // the working tree on disk (e.g. because file churn prevented full cleanup).
+    rmSync(join(repoDir, ".git", "worktrees", "orphan-admin"), {
+      recursive: true,
+      force: true,
+    });
+    expect(existsSync(created.worktreePath)).toBe(true);
+
+    const ownership = await isPaseoOwnedWorktreeCwd(created.worktreePath, { paseoHome });
+    expect(ownership.allowed).toBe(true);
+  });
+
+  it("rejects paths that are not under the paseo worktrees root", async () => {
+    const outsidePath = join(tempDir, "outside-paseo-home");
+    mkdirSync(outsidePath, { recursive: true });
+
+    const ownership = await isPaseoOwnedWorktreeCwd(outsidePath, { paseoHome });
+
+    expect(ownership.allowed).toBe(false);
+  });
+
+  it("rejects the worktrees root itself and the per-repo hash dir", async () => {
+    const projectHash = await deriveWorktreeProjectHash(repoDir);
+    const worktreesRoot = join(paseoHome, "worktrees");
+    const projectHashDir = join(worktreesRoot, projectHash);
+    mkdirSync(projectHashDir, { recursive: true });
+
+    await expect(isPaseoOwnedWorktreeCwd(worktreesRoot, { paseoHome })).resolves.toMatchObject({
+      allowed: false,
+    });
+    await expect(isPaseoOwnedWorktreeCwd(projectHashDir, { paseoHome })).resolves.toMatchObject({
+      allowed: false,
+    });
+  });
+
+  it("deletes a worktree whose .git admin dir has already been removed", async () => {
+    const created = await createWorktree({
+      branchName: "orphan-delete-branch",
+      cwd: repoDir,
+      baseBranch: "main",
+      worktreeSlug: "orphan-delete",
+      paseoHome,
+    });
+
+    rmSync(join(repoDir, ".git", "worktrees", "orphan-delete"), {
+      recursive: true,
+      force: true,
+    });
+    expect(existsSync(created.worktreePath)).toBe(true);
+
+    await deletePaseoWorktree({
+      cwd: repoDir,
+      worktreePath: created.worktreePath,
+      paseoHome,
+    });
+
+    expect(existsSync(created.worktreePath)).toBe(false);
+  });
+
+  it("is idempotent: deleting an already-absent worktree succeeds", async () => {
+    const created = await createWorktree({
+      branchName: "idempotent-delete-branch",
+      cwd: repoDir,
+      baseBranch: "main",
+      worktreeSlug: "idempotent-delete",
+      paseoHome,
+    });
+
+    await deletePaseoWorktree({
+      cwd: repoDir,
+      worktreePath: created.worktreePath,
+      paseoHome,
+    });
+    expect(existsSync(created.worktreePath)).toBe(false);
+
+    // Second call — nothing left on disk and no admin entry — must not throw.
+    await expect(
+      deletePaseoWorktree({ cwd: repoDir, worktreePath: created.worktreePath, paseoHome }),
+    ).resolves.toBeUndefined();
+  });
 });
 
 describe("slugify", () => {