fix(manifest): lexical pre-check for record_existing + add error-case tests

Address Copilot review (2026-05-11, review id 4266902103):

1. `record_existing` was calling `(self.project_root / rel).is_symlink()`
   BEFORE validating containment. For absolute paths or paths containing
   `..`, this performed a filesystem stat outside the project root before
   `_validate_rel_path()` raised. Add a cheap lexical pre-check that
   delegates to `_validate_rel_path()` for the canonical error messages,
   so the symlink stat only ever runs on paths that are already lexically
   inside the project root.

2. Add focused unit tests in `tests/integrations/test_manifest.py` for
   the symlink and non-regular-file error paths, including:
     - symlink target rejection
     - dangling symlink rejection (caught by the symlink guard before
       the is_file check)
     - directory path rejection (is_file == False)
     - missing-path rejection (is_file == False)
     - absolute-path lexical pre-check
   The Copilot reviewer noted these guards had no focused coverage in
   `test_manifest.py`, only via the `test_integration_claude.py`
   regression test.

3. The third Copilot finding (repeated `dict(self._files)` copies via
   `manifest.files` in the skip branches) is already resolved on this
   branch by using `prior_hashes` — the function-scope snapshot taken at
   the top of `install_shared_infra` — for the membership check, instead
   of `manifest.files`.

AI disclosure: drafted with assistance from Claude (Opus 4.7).

src/specify_cli/integrations/manifest.py

@@ -157,6 +157,15 @@ class IntegrationManifest:
                 treat the entry as permanently broken.
         """
         rel = Path(rel_path)
+        # Cheap lexical pre-check first so absolute / parent-traversal paths
+        # don't trigger a filesystem stat outside the project root before
+        # ``_validate_rel_path`` raises. ``_validate_rel_path`` produces the
+        # canonical error messages used elsewhere.
+        if rel.is_absolute() or ".." in rel.parts:
+            _validate_rel_path(rel, self.project_root)
+            # Defensive: _validate_rel_path always raises on these inputs,
+            # but make the contract explicit if it is ever loosened.
+            raise ValueError(f"Manifest path escapes project root: {rel}")
         # Check ``is_symlink()`` on the un-resolved path because
         # ``_validate_rel_path`` resolves the path (which would follow
         # the symlink and silently record the target instead).

tests/integrations/test_manifest.py

@@ -34,6 +34,57 @@ class TestManifestRecordFile:
         assert m.files["existing.txt"] == _sha256(f)
 
 
+class TestManifestRecordExistingErrors:
+    """Error-case coverage for ``record_existing`` symlink + non-file guards.
+
+    Added in #2483 — Copilot review flagged these as un-tested regressions
+    after the ``is_symlink``/``is_file`` guards were introduced.
+    """
+
+    def test_rejects_symlink_target(self, tmp_path):
+        target = tmp_path / "target.txt"
+        target.write_text("target content", encoding="utf-8")
+        link = tmp_path / "link.txt"
+        link.symlink_to(target)
+        m = IntegrationManifest("test", tmp_path)
+        with pytest.raises(ValueError, match="symlinked"):
+            m.record_existing("link.txt")
+
+    def test_rejects_dangling_symlink(self, tmp_path):
+        # A symlink pointing nowhere should still be rejected before the
+        # ``is_file()`` check (which would itself be False on a dangler).
+        link = tmp_path / "dangler.txt"
+        link.symlink_to(tmp_path / "no-such-target.txt")
+        m = IntegrationManifest("test", tmp_path)
+        with pytest.raises(ValueError, match="symlinked"):
+            m.record_existing("dangler.txt")
+
+    def test_rejects_directory_path(self, tmp_path):
+        (tmp_path / "a_dir").mkdir()
+        m = IntegrationManifest("test", tmp_path)
+        with pytest.raises(ValueError, match="not a regular file"):
+            m.record_existing("a_dir")
+
+    def test_rejects_missing_path(self, tmp_path):
+        # ``is_file()`` is False for non-existent paths too; the same error
+        # surface keeps callers from having to distinguish "missing" from
+        # "wrong kind" — both mean "cannot hash this".
+        m = IntegrationManifest("test", tmp_path)
+        with pytest.raises(ValueError, match="not a regular file"):
+            m.record_existing("never-existed.txt")
+
+    def test_lexical_prevalidation_for_absolute_path(self, tmp_path):
+        # ``record_existing`` must reject absolute paths via the lexical
+        # pre-check, NOT via the filesystem-touching ``is_symlink()`` call.
+        # Verified by passing an absolute path that points to a directory
+        # outside the project root — the canonical "Absolute paths" error
+        # must surface before any stat on the absolute path.
+        m = IntegrationManifest("test", tmp_path)
+        abs_path = "C:\\tmp\\escape.txt" if sys.platform == "win32" else "/tmp/escape.txt"
+        with pytest.raises(ValueError, match="Absolute paths"):
+            m.record_existing(abs_path)
+
+
 class TestManifestPathTraversal:
     def test_record_file_rejects_parent_traversal(self, tmp_path):
         m = IntegrationManifest("test", tmp_path)