## Summary
Buzz Mobile now expands decrypted ACP observer batch envelopes into
their inner telemetry frames before sending them through the existing
per-agent dedupe, ordering, cap, and channel-filter pipeline. Singleton
observer events keep their existing behavior.
Malformed batch envelopes remain visible as outer frames, matching the
desktop consumer convention, while invalid inner frames use the existing
observer decrypt error path. This restores batched agent progress, tool
activity, and incremental transcript updates that Mobile previously
ignored.
### Related issue
Related to #4917.
### Testing
Added tests:
-
[`observer_subscription_test.dart`](https://github.com/block/buzz/blob/main/mobile/test/features/channels/agent_activity/observer_subscription_test.dart)
covers valid batches, singleton behavior, malformed envelopes, and
invalid inner frames.
Full mobile analysis, formatting, file-size validation, and Flutter
tests passed. The repository pre-push gate also passed.
---------
Signed-off-by: Tom Brow <tomb@block.xyz>
Co-authored-by: Tom Brow <tomb@block.xyz>
Co-authored-by: Codex <noreply@openai.com>
