server: the body is the checklist here too, and note_items is dropped

M304 steps 3 and the server half of 4. The client half landed in 668f7fa; these
belong in one deploy, and the protocol floor below is what enforces that.

notes/checklist.py is the Python half of a grammar that now exists three times —
here, core/src/local/derive.rs, and (next) frontend/src/notes/markdown.ts. That
triplication is the deliberate cost: the alternative is a round trip to the server
before a phone can draw a checkbox. Each copy names the other two, and each is
tested against the same table of cases, including the near-misses that must stay
prose: `-[ ] x`, `- []`, `- [ ]x`, a `[ ]` mid-sentence.

Routes: add/update/delete items stop touching rows and rewrite note.body, all
through one _rewrite_body that runs the same sequence the PATCH route runs for a
body change — because it IS a body change. Revisions, #tag reconciliation, the
name, and link unfurls therefore happen in one place rather than three routes each
remembering to.

The reorder route is gone (rule 22). Reordering a checklist is moving a line, and
no client ever called it — the only reference in the tree was a test asserting the
route existed.

The API still returns `items`, DERIVED from the body on the way out. That is not a
second source of truth and it cannot disagree with the body it came from; it keeps
the web client working across the rest of this milestone and saves any consumer
that only wants to draw checkboxes from carrying a parser.

Export drops its separate items block, in both formats. The body already ends with
those exact lines, so writing them again would double every checklist in an export
and then double it again on re-import. Import still ACCEPTS items, because a Keep
takeout has a list and not a blob; it folds them in before the Note is built, so
display_title and _reconcile_tags both see the finished text.

Protocol 3 on both sides now. A v2 client is refused rather than half-served —
which matters more than I first said: _apply_note_items returned early on an absent
`items` key, so an un-bumped v3 client against a v2 server would not have LOST the
rows, it would have kept them and then had the migration fold them a second time.
Duplicated lists rather than missing ones. The floor prevents both.

Migration 0027 folds every existing row into its note's body and drops the table.
It inlines its own copy of the fold on purpose — a migration has to keep producing
what it produced the day it ran — and a test pins that copy against the app's until
they are allowed to diverge. updated_at is deliberately untouched: a client holding
an unpushed edit keeps the newer timestamp, so last-write-wins keeps its work
instead of the migration silently winning.

The downgrade is honest rather than faithful. It recreates an empty note_items and
leaves the bodies alone, because once items are lines nothing distinguishes one this
migration wrote from one somebody typed, and a downgrade that guessed would eat
hand-written lists. Recreating the table is still necessary: 0015's downgrade drops
a trigger ON note_items, and IF EXISTS covers the trigger, not the table.

tests/test_integration.py

@@ -26,21 +26,20 @@ from thoughtsync import ratelimit
 from thoughtsync.app import create_app
 from thoughtsync.db import dispose_engine, session_scope
 from thoughtsync.models.note import Note
-from thoughtsync.models.note_item import NoteItem
 from thoughtsync.models.user import User
 from thoughtsync.settings import get_setting, live, refresh_live, reset_live, set_settings
+from thoughtsync.notes.checklist import parse_items, set_item_checked
 from thoughtsync.notes.helpers import derive_display_title
 from thoughtsync.models.note_link_preview import NoteLinkPreview
 from thoughtsync.models.note_revision import NoteRevision
 from thoughtsync.revisions import REVISION_WINDOW_MINUTES, should_snapshot
-from thoughtsync.sync import _apply_note_items
 from thoughtsync.unfurl_queue import _unfurl_new_urls, detect_urls
 
 pytestmark = pytest.mark.integration
 
 # Every table the tests touch, child-first so FKs never block the truncate.
 # RESTART IDENTITY + CASCADE keeps this honest if a table gains children later.
-_TABLES = "notes, note_items, note_revisions, note_labels, note_link_previews, labels, users"
+_TABLES = "notes, note_revisions, note_labels, note_link_previews, labels, users"
 
 
 @pytest_asyncio.fixture
@@ -160,65 +159,55 @@ async def test_the_search_vector_was_rebuilt_over_the_name(db, owner):
     assert body_only == 1
 
 
-async def test_a_note_keeps_both_its_body_and_its_items(db, owner):
-    """The shape M13 step 2 made normal: a note HAS a checklist, it isn't one."""
-    note = Note(owner_id=owner.id, body="weekend shop", display_title="weekend shop")
-    db.add(note)
-    await db.flush()
-    db.add_all(
-        [
-            NoteItem(note_id=note.id, text="milk", position=0),
-            NoteItem(note_id=note.id, text="eggs", position=1),
-        ]
-    )
-    await db.commit()
+async def test_a_note_keeps_its_prose_on_both_sides_of_its_list(db, owner):
+    """The shape M304 made expressible at all.
 
-    items = (
-        await db.scalars(select(NoteItem).where(NoteItem.note_id == note.id).order_by(NoteItem.position))
-    ).all()
-    assert [i.text for i in items] == ["milk", "eggs"]
-    assert (await db.scalar(select(Note.body).where(Note.id == note.id))) == "weekend shop"
-
-
-async def test_sync_no_longer_deletes_items_from_a_note_with_a_body(db, owner):
-    """The data-loss path step 2 removed, pinned against a real database.
-
-    `_apply_note_items` used to delete every item when the note wasn't `kind = "list"`.
-    Nothing can produce that state any more, but this is the regression that would
-    have silently eaten a checklist, and it deserves a test that would catch its
-    return.
+    The old model could not hold this: a row had a position in a table and none in the
+    text, so a checklist could only ever render AFTER the body. Prose, list, prose is
+    the case that proves the storage changed, not just the styling.
     """
-    note = Note(owner_id=owner.id, body="packing", display_title="packing")
+    body = "weekend shop\n\n- [ ] milk\n- [x] eggs\n\nback before six"
+    note = Note(owner_id=owner.id, body=body, display_title=derive_display_title(body))
     db.add(note)
-    await db.flush()
-    db.add(NoteItem(note_id=note.id, text="socks", position=0))
     await db.commit()
 
-    # A change that says nothing about items must LEAVE them alone — absent means
-    # "not telling us", not "empty".
-    await _apply_note_items(db, note, {"body": "packing"})
-    await db.commit()
-    assert (await db.scalar(select(NoteItem.text).where(NoteItem.note_id == note.id))) == "socks"
-
-    # An explicit list replaces them.
-    await _apply_note_items(db, note, {"items": [{"text": "charger", "checked": True}]})
-    await db.commit()
-    rows = (await db.scalars(select(NoteItem).where(NoteItem.note_id == note.id))).all()
-    assert [(r.text, r.checked) for r in rows] == [("charger", True)]
+    stored = await db.scalar(select(Note.body).where(Note.id == note.id))
+    assert [(i.text, i.checked) for i in parse_items(stored)] == [("milk", False), ("eggs", True)]
+    assert stored.splitlines()[0] == "weekend shop"
+    assert stored.splitlines()[-1] == "back before six"
 
 
-async def test_a_note_with_only_items_still_has_a_name(db, owner):
-    """The hole that made removing the title unsafe until step 2 closed it."""
-    note = Note(owner_id=owner.id, body="", display_title="")
+async def test_ticking_an_item_is_a_body_edit(db, owner):
+    """What replaced `_apply_note_items`: there is no separate thing left to apply.
+
+    The regression that function guarded against — a sync silently eating a checklist
+    off a note that also had a body — cannot recur, because there is nothing to delete.
+    A pushed body either has the lines or it does not.
+    """
+    body = "packing\n\n- [ ] socks"
+    note = Note(owner_id=owner.id, body=body, display_title="packing")
     db.add(note)
-    await db.flush()
-    db.add(NoteItem(note_id=note.id, text="milk", position=0))
     await db.commit()
 
-    first = await db.scalar(
-        select(NoteItem.text).where(NoteItem.note_id == note.id).order_by(NoteItem.position).limit(1)
-    )
-    note.display_title = derive_display_title(note.body, first)
+    note.body = set_item_checked(note.body, 0, True)
+    await db.commit()
+
+    stored = await db.scalar(select(Note.body).where(Note.id == note.id))
+    assert stored == "packing\n\n- [x] socks"
+    assert parse_items(stored)[0].checked
+    # The prose is untouched — a tick rewrites one line, not the note.
+    assert stored.splitlines()[0] == "packing"
+
+
+async def test_a_note_with_only_a_list_still_has_a_name(db, owner):
+    """The hole that made removing the title unsafe, still closed — by a different
+    mechanism. There is no item table to fall back to any more; the name comes from
+    the first line with its marker stripped, because calling the note "- [ ] milk"
+    would show someone the storage instead of the note.
+    """
+    body = "- [ ] milk\n- [ ] eggs"
+    note = Note(owner_id=owner.id, body=body, display_title=derive_display_title(body))
+    db.add(note)
     await db.commit()
 
     assert (await db.scalar(select(Note.display_title).where(Note.id == note.id))) == "milk"