Bind communication wakes to concrete inbox rows

Replace the worker's generic `"Continue."` default with a dispatch-time
`initialUserTurn` that is resolved per trigger. Message and peer-request
wakes now enumerate the actual unread messages (id, sender, channel,
subject, reply-to) so the agent's first user turn carries the entities
it is expected to act on, instead of idling into a status summary.

Drop the system-prompt `heartbeatFallbackSection`: its "respond with a
brief status summary" line fought the wake-reason block above it and
was the main reason communication wakes degraded into self-narration.
The wake-reason section plus the bound initial user turn now cover
every case that section was carrying.

src/main/prompt-builder/index.ts

@@ -69,10 +69,14 @@ export function buildTaskPrompt(ctx: PromptContext): string {
 
   parts.push(`\n${m.timeAwarenessSection}`);
 
+  // Taskless runs used to emit a "respond with a brief status summary"
+  // nudge here. That text fought the wake-reason block above and caused
+  // communication wakes to degrade into self-narration. The wake-reason
+  // section already tells the agent what to do; the initial user turn
+  // (assembled at dispatch) supplies the concrete action cue — no fallback
+  // text is needed for the system prompt anymore.
   if (ctx.task) {
     parts.push(m.immediateTaskSection(ctx.task.title, ctx.task.description, ctx.task.priority));
-  } else {
-    parts.push(m.heartbeatFallbackSection);
   }
 
   return parts.join("");