Phase 664: groupDmVoiceNoteMaxBytes helper for per-participant quota.

Export groupDmVoiceNoteMaxBytes from voice-note-wire for group DM
voice message size limits divided by participant count.

Co-authored-by: Cursor <[email protected]>

index.js

@@ -682,7 +682,8 @@ const {
   VOICE_NOTE_MAX_BYTES,
   validateVoiceNoteCreatePayload,
   normalizeWaveformPeaks,
-  buildVoiceNoteCreatePayload
+  buildVoiceNoteCreatePayload,
+  groupDmVoiceNoteMaxBytes
 } = require('./voice-note-wire')
 module.exports = {
   isBenignSwarmError,
@@ -782,5 +783,6 @@ module.exports = {
   VOICE_NOTE_MAX_BYTES,
   validateVoiceNoteCreatePayload,
   normalizeWaveformPeaks,
-  buildVoiceNoteCreatePayload
+  buildVoiceNoteCreatePayload,
+  groupDmVoiceNoteMaxBytes
 }

voice-note-wire.js

@@ -81,11 +81,23 @@ function buildVoiceNoteCreatePayload (row) {
   })
 }
 
+/**
+ * Per-participant byte cap for group DMs (P664-13).
+ * @param {number} participantCount
+ * @param {number} [globalMax]
+ */
+function groupDmVoiceNoteMaxBytes (participantCount, globalMax = VOICE_NOTE_MAX_BYTES) {
+  const n = Math.max(1, Math.floor(Number(participantCount) || 1))
+  const floor = 256 * 1024
+  return Math.max(floor, Math.floor(Number(globalMax) / n))
+}
+
 module.exports = {
   VOICE_NOTE_MIME_DEFAULT,
   VOICE_NOTE_MAX_DURATION_MS,
   VOICE_NOTE_MAX_BYTES,
   validateVoiceNoteCreatePayload,
   normalizeWaveformPeaks,
-  buildVoiceNoteCreatePayload
+  buildVoiceNoteCreatePayload,
+  groupDmVoiceNoteMaxBytes
 }