links: rename repoints inbound backlinks (fix orphaning)

Renaming a note now rewrites [[Old Title]] references (and their note_links
rows) in every note that links to it, so backlinks survive the rename
instead of silently orphaning. Pure/case-only renames are skipped since they
still resolve. New pure helper rewrite_link_title() (DB-free unit tests) does
the token rewrite; _rename_inbound_links() applies it across owner-scoped,
non-trashed sources.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

src/thoughtsync/notes.py

@@ -153,6 +153,41 @@ async def _rewrite_links(db, note: Note) -> None:
         db.add(NoteLink(source_id=note.id, target_norm=norm))
 
 
+def rewrite_link_title(body: str | None, old_norm: str, new_title: str) -> str:
+    """Repoint every [[token]] whose normalized form == old_norm to [[new_title]]."""
+    if not body:
+        return body or ""
+
+    def _sub(match: re.Match) -> str:
+        return f"[[{new_title}]]" if match.group(1).strip().lower() == old_norm else match.group(0)
+
+    return _LINK_RE.sub(_sub, body)
+
+
+async def _rename_inbound_links(db, renamed: Note, old_title: str, new_title: str) -> None:
+    """Rewrite [[old title]] references (and their link rows) in every note that
+    links to the renamed note, so its backlinks survive the title change."""
+    old_norm = old_title.strip().lower()
+    sources = (
+        await db.scalars(
+            select(Note)
+            .join(NoteLink, NoteLink.source_id == Note.id)
+            .where(
+                NoteLink.target_norm == old_norm,
+                Note.owner_id == renamed.owner_id,
+                Note.deleted_at.is_(None),
+            )
+        )
+    ).all()
+    seen: set = set()
+    for source in sources:
+        if source.id in seen:
+            continue
+        seen.add(source.id)
+        source.body = rewrite_link_title(source.body, old_norm, new_title)
+        await _rewrite_links(db, source)
+
+
 @bp.get("")
 @login_required
 async def list_notes():
@@ -347,6 +382,7 @@ async def update_note(note_id: str):
         note = await _get_owned(db, note_id)
         if note is None:
             return jsonify({"error": "not found"}), 404
+        old_title = note.title
         if "title" in data:
             title = data["title"] if isinstance(data["title"], str) else ""
             note.title = title.strip() or None
@@ -371,6 +407,15 @@ async def update_note(note_id: str):
                     return jsonify({"error": "invalid remind_at"}), 400
         if "body" in data:
             await _rewrite_links(db, note)
+        # A rename repoints inbound [[Old Title]] references so backlinks survive
+        # (skip pure case/whitespace changes, which still resolve).
+        if (
+            "title" in data
+            and old_title
+            and note.title
+            and old_title.strip().lower() != note.title.strip().lower()
+        ):
+            await _rename_inbound_links(db, note, old_title, note.title)
         await db.commit()
         await db.refresh(note)
         return jsonify(await _serialize_note(db, note))

tests/test_notes.py

@@ -2,7 +2,7 @@ import pytest
 
 from thoughtsync.app import create_app
 from thoughtsync.models.note import NOTE_COLORS, Note
-from thoughtsync.notes import is_empty_note, normalize_color, parse_link_titles
+from thoughtsync.notes import is_empty_note, normalize_color, parse_link_titles, rewrite_link_title
 
 
 @pytest.fixture
@@ -86,6 +86,17 @@ def test_parse_link_titles_empty():
     assert parse_link_titles("no links here") == []
 
 
+def test_rewrite_link_title():
+    body = "see [[Alpha]] and [[ alpha ]] and [[Beta]]"
+    assert rewrite_link_title(body, "alpha", "Gamma") == "see [[Gamma]] and [[Gamma]] and [[Beta]]"
+
+
+def test_rewrite_link_title_noop():
+    assert rewrite_link_title("", "alpha", "Gamma") == ""
+    assert rewrite_link_title(None, "alpha", "Gamma") == ""
+    assert rewrite_link_title("no links here", "alpha", "Gamma") == "no links here"
+
+
 async def test_titles_requires_auth(app):
     client = app.test_client()
     resp = await client.get("/api/notes/titles")