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/pattern/PatternEditor.ts

@@ -1,10 +1,5 @@
 import { SetAssetPropertyCommand } from '../../core/commands/assetCommands';
-import {
-  instrumentBuildFor,
-  instrumentSourcesOf,
-  namedNotes,
-  playedNotes,
-} from '../../core/instrument/compile';
+import { instrumentSourcesOf, namedNotes, soundingNotes } from '../../core/instrument/compile';
 import { ghostNotes, placeOf } from '../../core/music/ghosts';
 import {
   GRID_OPTIONS,
@@ -263,11 +258,8 @@ export class PatternEditor extends AssetTabEditor<PatternAsset, PianoRoll> {
       ? findAssetOf(this.state.project, patternInstrument(asset.props), 'instrument')
       : undefined;
     if (instrument) {
-      const sources = instrumentSourcesOf(this.state.project);
-      const sounding = [...playedNotes(instrument.graph)].filter(
-        (note) => instrumentBuildFor(instrument, note, sources).layers.length > 0,
-      );
-      this.canvas.setInstrument(new Set(sounding), namedNotes(instrument.graph));
+      const sounding = soundingNotes(instrument, instrumentSourcesOf(this.state.project));
+      this.canvas.setInstrument(sounding, namedNotes(instrument.graph));
     } else this.canvas.setInstrument(new Set(), new Map());
     this.syncGhosts(asset);
     this.bakeButton.sync();