links: bind a [[link]] to a note, not to a string

A wiki-link was stored only as normalized TEXT, so a note's NAME was the edge.
Renaming it broke every inbound link — and the fix that shipped for that
(task 1848, option b) was `_rename_inbound_links`: rewrite the `[[Old Name]]`
text inside the body of every note that linked to the renamed one.

That works while an explicit title exists to hold still. It stops being
defensible the moment a note's name is just its first body line, which is where
M13 is going: fixing a typo in your opening sentence would silently edit other
notes' words, with nothing to opt out to. So this lands first, before the title
comes out, and that window never ships.

`note_links` gains `target_id`, bound when the link is written. `target_norm`
stays and is what an UNRESOLVED link carries — linking to a note that doesn't
exist yet is a supported way to create one, so a link has to be able to name a
target that isn't there. Resolution reads the id, falling back to the name only
where nothing was bound, which is what lets a forward link connect the moment
its target appears. `_claim_unresolved_links` then binds it, so the fallback is
a transitional state rather than a permanent one.

`_rename_inbound_links` and `rewrite_link_title` are gone. What replaced them
touches link rows only: a note's text is never modified by something happening
to a different note.

The client can no longer resolve links for itself, and that is the point. It
used to look `[[text]]` up in a client-side name index, which only held together
BECAUSE renaming rewrote the text everywhere. Now the written text can name
something the target is no longer called, and only the server holds the binding
— so each note serializes its resolved links (`norm`, `id`, and the target's
name as it stands NOW). A renamed note reads correctly everywhere it is linked
from, without a single body having been edited. Unresolved links are simply
absent and fall through to the create-on-click affordance that already existed;
so does the offline desktop store, which derives links at query time and has no
binding to send.

The name-fallback join is owner-scoped everywhere it appears. Bound ids were
resolved owner-scoped when written, but matching on display_title alone would
have let two users who each have a note called "Groceries" see the other's id
and name through an unresolved link (rule 47).

The new behaviour is all SQL and this suite runs without a database, so the
dead helpers' tests are removed rather than replaced. This repo has no
integration lane to hold that ground — noted, not papered over.

src/thoughtsync/notes/__init__.py

@@ -19,7 +19,7 @@ import zipfile
 from datetime import datetime, timedelta, timezone
 
 from quart import Response, g, jsonify, request, send_file
-from sqlalchemy import case, func, literal_column, select
+from sqlalchemy import and_, case, func, literal_column, or_, select
 
 from ..acl import visible_to_user
 from ..auth import login_required
@@ -67,11 +67,10 @@ from .import_export import (
 )
 from .links import (
     _reconcile_tags,
-    _rename_inbound_links,
+    _claim_unresolved_links,
     _rewrite_links,
     parse_link_titles,
     parse_tags,
-    rewrite_link_title,
 )
 from .recurrence import REMINDER_RECURRENCES, next_occurrence, normalize_recurrence
 from .serialize import _items_for_notes, _labels_for_notes, _serialize_note, _serialize_notes
@@ -83,12 +82,11 @@ __all__ = [
     "parse_list_items",
     "parse_tags",
     "parse_link_titles",
-    "rewrite_link_title",
     "normalize_color",
     "normalize_recurrence",
     "next_occurrence",
     "_reconcile_tags",
-    "_rename_inbound_links",
+    "_claim_unresolved_links",
     "_rewrite_links",
     "_serialize_notes",
     "_escape_like",
@@ -435,15 +433,20 @@ async def note_backlinks(note_id: str):
         )
         if note is None:
             return not_found()
-        if not note.display_title:
-            return jsonify({"backlinks": []})
-        norm = note.display_title.strip().lower()
+        # Bound links (target_id) OR unbound ones still naming this note. The second
+        # half is what catches a link written before this note existed and not yet
+        # claimed; without it a forward link would go quiet until its source is next
+        # saved.
+        norm = (note.display_title or "").strip().lower()
+        matches = NoteLink.target_id == nid
+        if norm:
+            matches = or_(matches, and_(NoteLink.target_id.is_(None), NoteLink.target_norm == norm))
         sources = (
             await db.scalars(
                 select(Note)
                 .join(NoteLink, NoteLink.source_id == Note.id)
                 .where(
-                    NoteLink.target_norm == norm,
+                    matches,
                     Note.owner_id == g.user_id,
                     Note.deleted_at.is_(None),
                     Note.id != nid,
@@ -524,6 +527,9 @@ async def create_note():
             db.add(NoteItem(note_id=note.id, text=text, position=pos))
         await _rewrite_links(db, note)
         await _reconcile_tags(db, note)
+        # A new note may be exactly what earlier `[[links]]` were pointing at — the
+        # create-by-linking flow writes the link first and the note second.
+        await _claim_unresolved_links(db, note)
         await db.commit()
         await db.refresh(note)
         return jsonify(await _serialize_note(db, note)), 201
@@ -587,12 +593,12 @@ async def update_note(note_id: str):
         if "body" in data:
             await _rewrite_links(db, note)
             await _reconcile_tags(db, note)
-        # The display NAME changing — via an explicit title OR the first body line —
-        # repoints inbound [[Old Name]] references so backlinks survive (skip pure
-        # case/whitespace changes, which still resolve).
+        # A rename no longer touches anything else's TEXT. Inbound links already hold
+        # this note's id, so they follow it automatically; all that is left is to
+        # adopt any still-unresolved link that was waiting for this name.
         new_display = note.display_title
-        if old_display and new_display and old_display.strip().lower() != new_display.strip().lower():
-            await _rename_inbound_links(db, note, old_display, new_display)
+        if old_display != new_display:
+            await _claim_unresolved_links(db, note)
         # Version history: snapshot the PRE-edit title+body whenever either changed.
         if note.title != old_title or note.body != old_body:
             db.add(NoteRevision(note_id=note.id, title=old_title, body=old_body))
@@ -653,8 +659,8 @@ async def restore_revision(note_id: str, rev_id: str):
         await _rewrite_links(db, note)
         await _reconcile_tags(db, note)
         new_display = note.display_title
-        if old_display and new_display and old_display.strip().lower() != new_display.strip().lower():
-            await _rename_inbound_links(db, note, old_display, new_display)
+        if old_display != new_display:
+            await _claim_unresolved_links(db, note)
         await db.commit()
         await db.refresh(note)
         return jsonify(await _serialize_note(db, note))