Make bars navigable and editable with _meta export

Navigation:
- SubObjects: bar → voice (with chevron when offsets exist) → offsets
- PaneCP shortView handles voice and offset types

FO pane:
- Bar: editable beats_per_minute, stress_pattern (serialized as
  groups string), upper/lower stress bounds and tempo shape via
  ShapeEditor; sets bar.isDirty on change
- Voice: read-only name, articles, motifs, offset count
- Offset: read-only tick, stem notes and clusters as label strings
  (note re-serialization deferred)

Export:
- exporter.patchScore() now accepts optional bars[] parameter
- Splits rawScoreText by \n---\n; instruments patched in header,
  dirty bar _meta blocks regenerated, voice note lines kept verbatim
- ast-parser buildBar() adds isDirty:false
- PaneCP passes scoreModel.bars to patchScore

static/exporter.js

@@ -134,11 +134,11 @@ export function exportInstrument(instr) {
 }
 
 // ── Score patch ────────────────────────────────────────────────────────────
-// Replace dirty instrument blocks in rawScoreText with RFC-serialized output.
-// Non-dirty instruments are left verbatim.
+// Replace dirty instrument blocks and dirty bar _meta blocks.
+// Voice note content in bar documents is left verbatim.
 
-export function patchScore(rawScoreText, instruments) {
-    const lines = rawScoreText.split('\n');
+function patchInstrumentHeader(text, instruments) {
+    const lines = text.split('\n');
     const result = [];
     const instrMap = {};
     for (const instr of instruments) {
@@ -149,7 +149,6 @@ export function patchScore(rawScoreText, instruments) {
     let i = 0;
     while (i < lines.length) {
         const line = lines[i];
-        // RFC §4.4: "instrument NAME:" — strip optional quotes around name
         const m = line.match(/^instrument\s+(.+?)\s*:/);
         if (m) {
             const rawName = m[1].replace(/^'|'$/g, '');
@@ -171,3 +170,62 @@ export function patchScore(rawScoreText, instruments) {
 
     return result.join('\n');
 }
+
+function patchBarMeta(doc, bar) {
+    const props = [];
+    if (bar.stressor?.groups?.length)
+        props.push(`  stress_pattern: ${bar.stressor.groups.map(g => g.join(',')).join(';')}`);
+    if (bar.tempoLevels != null)
+        props.push(`  beats_per_minute: ${bar.tempoLevels}`);
+    const ub = serializeShape(bar.upperStressBound);
+    if (ub) props.push(`  upper_stress_bound: ${ub}`);
+    const lb = serializeShape(bar.lowerStressBound);
+    if (lb) props.push(`  lower_stress_bound: ${lb}`);
+    if (bar.tempoShape) { const ts = serializeShape(bar.tempoShape); if (ts) props.push(`  tempo_shape: "${ts}"`); }
+
+    const lines = doc.split('\n');
+    const out = [];
+    let i = 0;
+    let replaced = false;
+
+    while (i < lines.length) {
+        if (lines[i] === '_meta:') {
+            replaced = true;
+            i++;
+            while (i < lines.length && lines[i].startsWith('  ')) i++;
+            if (props.length) { out.push('_meta:'); out.push(...props); }
+        } else {
+            out.push(lines[i]);
+            i++;
+        }
+    }
+
+    if (!replaced && props.length) {
+        const idIdx = out.findIndex(l => /^_id:/.test(l));
+        if (idIdx !== -1) out.splice(idIdx + 1, 0, '_meta:', ...props);
+    }
+
+    return out.join('\n');
+}
+
+export function patchScore(rawScoreText, instruments, bars = []) {
+    const SEP = '\n---\n';
+    const [header, ...barDocs] = rawScoreText.split(SEP);
+
+    const patchedHeader = patchInstrumentHeader(header, instruments);
+
+    if (!barDocs.length) return patchedHeader;
+
+    const barMap = {};
+    for (const bar of bars) barMap[bar.id] = bar;
+
+    const patchedBarDocs = barDocs.map(doc => {
+        const m = doc.match(/^_id:\s*(\S+)/m);
+        if (!m) return doc;
+        const bar = barMap[m[1]];
+        if (!bar?.isDirty) return doc;
+        return patchBarMeta(doc, bar);
+    });
+
+    return [patchedHeader, ...patchedBarDocs].join(SEP);
+}