Allow open_workspace to reopen persisted managed worktrees by path

[Ahmed-Hindy]

Problem

A managed worktree created through open_workspace is persisted with mode: "worktree", managed: true, its worktree root, and an allowed source repository. If the client later loses that workspace ID, reopening the existing worktree by path through open_workspace fails with Path is outside allowed roots whenever the configured worktree root is intentionally outside allowedRoots.

The persisted workspace can still be restored internally by ID, because restore validation separately verifies that its source root is allowed and its worktree root is inside the configured managed-worktree root. There is currently no path-based way to recover that registered workspace.

Reproduction

1. Configure a source repository under allowedRoots and use a separate worktreeRoot outside it.
2. Open the source in worktree mode and note the returned managed-worktree path.
3. Start a new client session without the returned workspace ID.
4. Call open_workspace with the existing managed-worktree path in checkout mode.

Actual

The call is rejected as outside allowedRoots.

Expected

An exact path match to a persisted managed worktree should restore the original workspace session, including its original workspace ID, without adding the whole worktree parent to allowedRoots.

Security constraints

The recovery must remain limited to a persisted session that is both mode: "worktree" and managed: true. Normal restored-worktree validation must still require an allowed source root and containment within the configured worktree root. Arbitrary unregistered paths under the managed-worktree parent must remain denied.

Acceptance criteria

• Reopening a persisted managed worktree by its exact path restores the recorded session.
• Home-directory path expansion is supported by the existing path resolver.
• A regular external checkout and an unregistered sibling worktree remain denied.
• The behavior is covered by a regression test using a managed-worktree root outside allowedRoots.