fix(compact): address manual compaction review

packages/compact/command-compact/src/index.ts

@@ -79,9 +79,25 @@ async function executeCompact(
  * @param ctx - context carrying the command registry and the compaction seam.
  */
 export function apply(ctx: Context): void {
-  ctx.commands.register({
-    name: 'compact',
-    description: 'Compact older conversation history',
-    handler: invocation => executeCompact(ctx, invocation),
-  })
+  const active = new Set<Promise<CommandResult>>()
+  const handler = (invocation: CommandInvocation): Promise<CommandResult> => {
+    const operation = executeCompact(ctx, invocation)
+    active.add(operation)
+    const retire = (): void => { active.delete(operation) }
+    // Both branches retire without rethrowing, so the derived observer promise
+    // cannot become an unhandled mirror of an expected handler rejection.
+    void operation.then(retire, retire)
+    return operation
+  }
+
+  ctx.effect(function* () {
+    // Yield drain before registration: composite teardown is LIFO, so no new
+    // invocation can enter while already-started handler promises quiesce.
+    yield async () => { await Promise.allSettled(active) }
+    yield ctx.commands.register({
+      name: 'compact',
+      description: 'Compact older conversation history',
+      handler,
+    })
+  }, 'command-compact lifecycle')
 }