fix(projection): a re-keyed record is new, not a renamed file

The ad-hoc requalification changed 30 identifiers while deliberately keeping
the filenames, per canon. The matcher's path fallback therefore matched every
old row to its new record and updated it in place — so the files said
CUST-WP-ADHOC-2026-08-25 while the hub still said adhoc-2026-08-25, with the
row's UUID still encoding the old identifier. Exactly the file/hub identity
divergence ADR-007 exists to prevent.

Path matching cannot distinguish a re-key from a rename when the path does not
change. Identity can: a derived row is UUIDv5 over the record id, so a changed
id is a different record — the old row retires and the new one is created.
Rows predating derived identity carry v4 UUIDs, where the identifier is a label
rather than the identity; those keep path matching, so rename detection still
works where it is the right answer.

The unmatched old row keeps its own slug as key, so it lands in `stale` and
becomes a retirement candidate rather than disappearing from the outcome.

720 pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 2583210@bnt-lap001
Assistant-Session: f2bff2d5-e9b2-4338-92ca-10282a927006

tests/test_forge_projection.py

@@ -684,3 +684,44 @@ class TestForgeCredential:
         monkeypatch.setattr(fp.subprocess, "run", fake_run)
         assert fp._run_git("status") == "ok"
         assert "GIT_CONFIG_COUNT" not in seen["env"]
+
+
+class TestRekeyIsNotRename:
+    """A changed identifier is a new record, not a moved file.
+
+    The ad-hoc requalification (CUST-WP-0066) keeps the filename by design, so
+    for those records a re-key never changes the path. Matching on path there
+    cannot distinguish the two cases, and choosing rename updates a row whose
+    UUID still encodes the old identifier — leaving the file and the hub
+    disagreeing about what the record is called.
+    """
+
+    class _Row:
+        def __init__(self, id, slug, path):
+            self.id = id
+            self.slug = slug
+            self.backing_relative_path = path
+            self.projection_retired_at = None
+            self.status = "finished"
+
+    def test_a_derived_row_is_not_matched_by_path(self):
+        """uuid5 means identity is a function of the identifier."""
+        import uuid as _u
+        old = self._Row(
+            _u.UUID(fp.derived_record_uuid("ADHOC-2026-08-25")),
+            "adhoc-2026-08-25",
+            "workplans/ADHOC-2026-08-25.md",
+        )
+        assert fp._identity_is_derived(old)
+
+    def test_a_legacy_row_keeps_path_matching(self):
+        """v4 rows predate derived identity; there the identifier is a label."""
+        import uuid as _u
+        legacy = self._Row(_u.uuid4(), "repo-wp-0001", "workplans/REPO-WP-0001.md")
+        assert not fp._identity_is_derived(legacy)
+
+    def test_the_two_uuids_actually_differ(self):
+        """Guards the premise: if they were equal the distinction is moot."""
+        assert fp.derived_record_uuid("ADHOC-2026-08-25") != fp.derived_record_uuid(
+            "CUST-WP-ADHOC-2026-08-25"
+        )