fix(agents): a claude leftover behind a link still selects claude for its residual (Issue #31, review)

has_artifacts counted only the paths a purge may remove. When all that was
left lay behind a linked dir, `purge claude <uuid>` (or auto) found no
adapter and exited 5 with an empty residual, hiding the path the purge
had refused to follow. has_artifacts now counts every candidate; _inside
still decides what is removed, so the CLI exits 0, removes nothing and
lists the linked path as residual.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_issue31_purge_residual.py

@@ -355,6 +355,26 @@ def test_claude_purge_never_follows_a_linked_dir_below_a_root(home, tmp_path, co
          str(cfg / "projects" / key / conv), str(cfg / "file-history" / conv)])
 
 
+def test_purge_cli_reports_a_linked_orphan_it_will_not_remove(home, tmp_path, conv):
+    """A candidate behind a link is all that is left: the CLI still picks
+    claude, so its residual names it, and removes nothing."""
+    ws = tmp_path / "ws"
+    ws.mkdir()
+    keep = tmp_path / "outside" / conv / "keep.txt"
+    keep.parent.mkdir(parents=True)
+    keep.write_text("keep")
+    troot = tmp_path / "ctmp" / f"claude-{UID}"
+    troot.mkdir(parents=True)
+    (troot / "linked-workspace").symlink_to(tmp_path / "outside")
+
+    res = _agents_cli(["purge", "claude", conv, str(ws)], ws)
+
+    assert res.returncode == 0, res.stdout + res.stderr
+    assert json.loads(res.stdout) == {"agent": "claude", "purged": [],
+                                      "residual": [str(troot / "linked-workspace" / conv)], "in_use": False}
+    assert keep.exists()
+
+
 def test_claude_purge_removes_only_the_link_at_the_leaf(home, tmp_path, conv):
     ws = tmp_path / "ws"
     ws.mkdir()