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_notes.py

@@ -5,6 +5,14 @@ import pytest
 from thoughtsync.app import create_app
 from thoughtsync.common import coerce_bool, parse_dt
 from thoughtsync.models.note import NOTE_COLORS, Note
+from thoughtsync.notes.checklist import (
+    append_item,
+    parse_items,
+    remove_item,
+    set_item_checked,
+    set_item_text,
+    strip_marker,
+)
 from thoughtsync.unfurl_queue import detect_urls
 from thoughtsync.notes import (
     _attachment_ext,
@@ -42,7 +50,7 @@ def test_all_note_routes_registered(app):
             "reorder_notes", "create_note",
             "get_note", "update_note", "list_revisions", "restore_revision",
             "set_note_labels", "add_item", "update_item", "delete_item",
-            "reorder_items", "upload_attachment", "get_attachment",
+            "upload_attachment", "get_attachment",
             "delete_attachment", "unfurl_link", "delete_preview", "trash_note",
             "restore_note", "delete_note",
         )
@@ -406,3 +414,120 @@ def test_detect_urls_ignores_non_http():
     assert detect_urls("ftp://example.com and mailto:a@b.c and bare example.com") == []
     assert detect_urls(None) == []
     assert detect_urls("") == []
+
+
+# --- checklist items: the body IS the checklist (M304) -----------------------
+#
+# The same table of cases as core/src/local/derive.rs. Deliberately duplicated
+# rather than shared: the point of three implementations is that each is checked
+# against the same grammar, and a test that only ran once would not catch the two
+# drifting apart.
+
+
+def test_parse_items_reads_a_list_out_of_prose():
+    body = "shopping\n\n- [ ] milk\n- [x] eggs"
+    assert [(i.text, i.checked) for i in parse_items(body)] == [("milk", False), ("eggs", True)]
+
+
+def test_parse_items_between_paragraphs():
+    # The case a side table could not express, which is the whole reason for M304.
+    assert [i.text for i in parse_items("before\n- [ ] middle\nafter")] == ["middle"]
+
+
+@pytest.mark.parametrize(
+    "body",
+    [
+        "-[ ] no space after the dash",
+        "- [] empty brackets",
+        "- [ ]no space after the brackets",
+        "- [y] not a mark",
+        "a [ ] mid sentence",
+        "[ ] no bullet at all",
+    ],
+)
+def test_parse_items_rejects_near_misses(body):
+    assert parse_items(body) == []
+
+
+def test_parse_items_accepts_star_bullets_and_indentation():
+    # `*` because markdown.ts already takes it for a plain bullet.
+    body = "* [ ] star\n    - [x] indented"
+    assert [(i.text, i.checked) for i in parse_items(body)] == [("star", False), ("indented", True)]
+
+
+def test_an_empty_item_is_still_an_item():
+    # What pressing Enter on a list leaves behind.
+    assert [i.text for i in parse_items("- [ ]")] == [""]
+    assert [i.text for i in parse_items("- [ ] ")] == [""]
+
+
+def test_uppercase_x_parses_and_normalises_on_rewrite():
+    assert parse_items("- [X] done")[0].checked
+    assert set_item_checked("- [X] done", 0, True) == "- [x] done"
+
+
+def test_rewriters_preserve_indent_bullet_and_neighbours():
+    assert set_item_checked("  * [ ] milk", 0, True) == "  * [x] milk"
+    assert set_item_text("- [x] old", 0, "new") == "- [x] new"
+    assert remove_item("keep\n- [ ] drop\n- [ ] stay", 0) == "keep\n- [ ] stay"
+    # Addressed by ITEM, not by line.
+    assert set_item_checked("note\n- [ ] a\nprose\n- [ ] b", 1, True) == "note\n- [ ] a\nprose\n- [x] b"
+
+
+def test_a_stale_index_does_nothing():
+    # The index comes from a client that may be a moment behind. A late request
+    # should be inert, not a 500.
+    body = "- [ ] only"
+    assert set_item_checked(body, 7, True) == body
+    assert remove_item(body, 7) == body
+    assert set_item_text(body, 7, "x") == body
+
+
+def test_a_plain_body_is_returned_unchanged():
+    body = "just prose\nwith two lines"
+    assert set_item_checked(body, 0, True) == body
+    assert remove_item(body, 0) == body
+
+
+def test_append_item_spacing():
+    # Prose, blank line, list — the layout _note_markdown has always exported, and
+    # what the migration folds existing rows into.
+    assert append_item("a note", "milk") == "a note\n\n- [ ] milk"
+    # Nothing between consecutive items.
+    assert append_item("a note\n\n- [ ] milk", "eggs") == "a note\n\n- [ ] milk\n- [ ] eggs"
+    # A list-only note starts at the first line.
+    assert append_item("", "milk") == "- [ ] milk"
+    assert append_item("\n\n", "milk") == "- [ ] milk"
+    # Carries state, which is what the migrations need of it.
+    assert append_item("", "done", True) == "- [x] done"
+
+
+def test_strip_marker_and_display_title():
+    assert strip_marker("- [x] milk") == "milk"
+    assert strip_marker("just prose") == "just prose"
+    # A list-only note is named by its first item, without the marker.
+    assert derive_display_title("- [ ] milk\n- [ ] eggs") == "milk"
+    # An EMPTY item does not name the note "" — a half-typed list still has a name.
+    assert derive_display_title("- [ ]\n- [ ] eggs") == "eggs"
+
+
+def test_the_migration_folds_exactly_like_the_app():
+    """0027 inlines its own copy of append_item, deliberately — a migration has to keep
+    producing what it produced the day it ran, so it must not follow the app if the
+    app's spacing ever changes. This is what keeps the copy honest until then."""
+    import importlib.util
+    from pathlib import Path
+
+    path = Path(__file__).resolve().parents[1] / "alembic" / "versions" / "0027_checklist_items_into_body.py"
+    spec = importlib.util.spec_from_file_location("_m0027", path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+
+    for body, text, checked in [
+        ("a note", "milk", False),
+        ("a note\n\n- [ ] milk", "eggs", True),
+        ("", "milk", False),
+        ("\n\n", "milk", False),
+        ("prose\n", "  padded  ", True),
+    ]:
+        assert module._append_item(body, text, checked) == append_item(body, text, checked)