fix(worktrees): a session spelled through the case's symlink blocks removal

The removal guard and the per-worktree session count compared each
session's workingDir lexically against the worktree paths git lists,
which are real paths. POST /api/sessions stores workingDir as it was
spelled, so a session started in a worktree of a linked case whose
folder is a symlink (a repository on another disk, macOS /tmp, a
symlinked cases folder), named through that link, counted for no
worktree, and DELETE /api/cases/:name/worktrees/:worktree removed the
folder under the running agent (reproduced: 200 instead of 409).

Each session folder under the case path is now respelled onto the
repository's real top level before the comparison (respellUnder, pure
and lexical, so no filesystem call per session).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/git-worktrees.test.ts

@@ -21,6 +21,7 @@ import {
   removeCaseWorktree,
   resolveCaseRepository,
   resolveManagedWorktree,
+  respellUnder,
   unquoteGitPath,
   worktreeBaseError,
   worktreeBranchError,
@@ -103,6 +104,15 @@ describe('paths', () => {
     expect(isPathWithin('/r/.claude/worktrees/a/src', '/r/.claude/worktrees/a')).toBe(true);
     expect(isPathWithin('/r/.claude/worktrees/ab', '/r/.claude/worktrees/a')).toBe(false);
   });
+  it('respellUnder moves a path named through the case link onto the real repository root', () => {
+    expect(respellUnder('/link/.claude/worktrees/a', '/link', '/real')).toBe('/real/.claude/worktrees/a');
+    expect(respellUnder('/link/.claude/worktrees/a/src/', '/link', '/real')).toBe('/real/.claude/worktrees/a/src');
+    expect(respellUnder('/link', '/link', '/real')).toBe('/real');
+    // Not under the alias (a segment match, never a string prefix), or no alias at all: unchanged.
+    expect(respellUnder('/linked/x', '/link', '/real')).toBe('/linked/x');
+    expect(respellUnder('/real/.claude/worktrees/a', '/link', '/real')).toBe('/real/.claude/worktrees/a');
+    expect(respellUnder('/real/x', '/real', '/real')).toBe('/real/x');
+  });
 });
 
 describe('parseWorktreeList', () => {