Keep groups, comments and silent music in view for the agent (#429)

A live test of the music areas built a pattern, a song and a
composition that stayed silent: no instrument at first, and later
notes outside the C4 to B4 range of a new Notes node. The agent got
no hint of either. The same test showed that new nodes left groups
behind, that a comment could end up under other nodes, and that an
end node like Output stayed left of the devices put in front of it.

- get_asset lists under silent what of a pattern, song or
  composition is not heard. That is a missing instrument, an
  instrument that sounds no note, or notes outside what its Notes
  nodes take in, in a song after the transpose.
- soundingNotes moves from the pattern tab to
  src/core/instrument/compile.ts. The tab and the agent use the
  same rule.
- When new nodes go between two that have no room, everything from
  the fed node on moves right together. This holds for Arrange with
  a selection too, so no link runs backwards.
- A new node linked to a node in a group joins that group, and the
  group grows in the same undo step. A group that would take in a
  foreign node stays as it is.
- Arrange takes groups and comments along: a group whose nodes all
  moved the same keeps its size, otherwise it is fitted anew. The
  rules live in the new src/editor/graph/annotationFollow.ts.
- add_comment and fit_group put a comment below its nodes when a
  node or a group title is in the way above. lint_graph counts
  covered comments as coveredNotes.
- add_notes, get_asset, lint_graph and the relay instructions name
  the default range and how to mend a covered comment.

Tests:
- graph-follow (new, 12), agent-edit, agent-music (11) and the
  other agent, graph, pattern and relay tests green
- 10 deliberate breakages, each one red in its own test
- e2e 71: 25/25
- Gate: CHECK EXIT 0, 324 files, 5002 tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/agent/tools.json

@@ -44,7 +44,7 @@
   {
     "name": "get_asset",
     "title": "Read an asset",
-    "description": "One asset as stored: its property values, the rows of its properties (key, kind, default), the objects of a scene or container with their names and positions (the content of a placed container too, marked fromContainer), what the rows of an animation may aim at (targets), the cells of a small tilemap, the pixels of small pixel art as rows of palette indices (colors as \"#rrggbb\"), the notes of a pattern with their names and how many ticks it is long, the rows a clip of a sound or video has (clipProperties), how many seconds a loaded sound lasts. A graph is only counted here; read it with get_graph.",
+    "description": "One asset as stored: its property values, the rows of its properties (key, kind, default), the objects of a scene or container with their names and positions (the content of a placed container too, marked fromContainer), what the rows of an animation may aim at (targets), the cells of a small tilemap, the pixels of small pixel art as rows of palette indices (colors as \"#rrggbb\"), the notes of a pattern with their names and how many ticks it is long, the rows a clip of a sound or video has (clipProperties), how many seconds a loaded sound lasts, and under silent what of a pattern, song or composition is not heard: all of it without an instrument, or the notes its instrument does not sound. A graph is only counted here; read it with get_graph.",
     "inputSchema": {
       "type": "object",
       "properties": { "asset": { "type": "string", "description": "Id of the asset." } },
@@ -68,7 +68,7 @@
   {
     "name": "lint_graph",
     "title": "Check how a graph reads",
-    "description": "Counts what makes a graph hard to read, as the user sees it: nodes on top of each other (overlaps), links that cross (crossings), links running over a node that is not theirs (throughNodes), links running right to left (backwards), and the longest links, with a few ids of each. Aim for 0 overlaps, 0 throughNodes and 0 backwards, and for no more crossings than the links need: two links leaving one node far apart, like exec and dt, cross what comes in between them. To mend: the command arrange_graph, or a second Get or Owner node next to a far-off user instead of one long link.",
+    "description": "Counts what makes a graph hard to read, as the user sees it: nodes on top of each other (overlaps), links that cross (crossings), links running over a node that is not theirs (throughNodes), links running right to left (backwards), comments a node lies on (coveredNotes), and the longest links, with a few ids of each. Aim for 0 overlaps, 0 throughNodes, 0 backwards and 0 coveredNotes, and for no more crossings than the links need: two links leaving one node far apart, like exec and dt, cross what comes in between them. To mend: the command arrange_graph, or a second Get or Owner node next to a far-off user instead of one long link; a covered comment goes back by its nodes with fit_group.",
     "inputSchema": {
       "type": "object",
       "properties": { "asset": { "type": "string", "description": "Id of the asset holding the graph." } },