fix(integrations): guard _sha256 against unreadable managed files (#3376)

manifest.py::_sha256 does an unguarded open(). check_modified() and
uninstall() both call it on a readable-but-unopenable regular file
(e.g. permission denied) without catching OSError, so
'specify integration upgrade/uninstall/switch' surface a raw
PermissionError traceback. Guard both call sites: in check_modified()
treat an unreadable file as modified (consistent with the adjacent
symlink / non-regular-file handling); in uninstall() treat it as skipped
and preserve it (mirroring the existing path.unlink() OSError guard just
below). The force short-circuit is unchanged.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

tests/integrations/test_manifest.py

@@ -481,3 +481,40 @@ class TestRecordExistingNewGuards:
         m = IntegrationManifest("test", tmp_path)
         with pytest.raises(ValueError, match=r"canonical|'\.\.' segments"):
             m.record_existing("dir/../file.txt")
+
+
+class TestManifestUnreadableFile:
+    """A managed file that is unreadable (e.g. PermissionError) must not crash
+    check_modified()/uninstall() — the CLI handlers surfaced a raw traceback."""
+
+    def _mk(self, tmp_path):
+        m = IntegrationManifest("test", tmp_path)
+        m.record_file("sub/f.md", "content")
+        return m
+
+    def test_check_modified_treats_unreadable_as_modified(self, tmp_path, monkeypatch):
+        m = self._mk(tmp_path)
+
+        def raise_perm(_path):
+            raise PermissionError("unreadable")
+
+        monkeypatch.setattr(
+            "specify_cli.integrations.manifest._sha256", raise_perm
+        )
+        # Before the fix this raised PermissionError.
+        assert m.check_modified() == ["sub/f.md"]
+
+    def test_uninstall_preserves_unreadable_file(self, tmp_path, monkeypatch):
+        m = self._mk(tmp_path)
+
+        def raise_perm(_path):
+            raise PermissionError("unreadable")
+
+        monkeypatch.setattr(
+            "specify_cli.integrations.manifest._sha256", raise_perm
+        )
+        removed, skipped = m.uninstall(force=False)
+        # Can't verify ownership => preserve, don't crash and don't delete.
+        assert removed == []
+        assert (tmp_path / "sub" / "f.md") in skipped
+        assert (tmp_path / "sub" / "f.md").exists()