fix(runner): acp_get_session_status returns empty messages for all sessions

[quay-devel]

Summary

acp_get_session_status always returns recentMessages: [] and totalMessages: 0 for every session, despite the tool description promising "the most recent text messages from the conversation."

Root Cause

The message extraction code in backend_tools.py:404-414 expects a text field on TEXT_MESSAGE_CONTENT events, but AG-UI uses streaming deltas where:

• The actual text field is delta (not text)
• The role is on the TEXT_MESSAGE_START event (not on content events)

# Broken (line 408):
if event_type == "TEXT_MESSAGE_CONTENT" and event.get("text"):
#                                              ^^^^^ always None — field is "delta"

Additionally, completed/stopped sessions don't have streaming delta events at all — they use MESSAGES_SNAPSHOT events containing the full conversation array, which the code never checks.

Actual AG-UI Event Structure

// Active sessions use streaming deltas:
{"type": "TEXT_MESSAGE_START", "role": "assistant", "messageId": "msg-1"}
{"type": "TEXT_MESSAGE_CONTENT", "delta": "Hello, ", "messageId": "msg-1"}
{"type": "TEXT_MESSAGE_CONTENT", "delta": "world!", "messageId": "msg-1"}
{"type": "TEXT_MESSAGE_END", "messageId": "msg-1"}

// Completed sessions use snapshots:
{"type": "MESSAGES_SNAPSHOT", "messages": [{"role": "user", "content": "..."}, ...]}

Verification

Confirmed from a live session (2026-04-30):

• Export endpoint returns 3,796 AG-UI events for an active session with 77 TEXT_MESSAGE_CONTENT events — all have delta, none have text
• Stopped sessions have 0 TEXT_MESSAGE_CONTENT events but MESSAGES_SNAPSHOT events contain the full conversation (135 messages in one test case)
• After applying the fix, active sessions correctly yield reassembled messages from streaming deltas, and stopped sessions correctly yield messages from the last snapshot

Impact

• acp_get_session_status messages are completely broken for all sessions (active and completed)
• Blocks cross-session introspection use cases (retrospectives, monitoring, debugging)
• The max_messages parameter has never worked since launch

Affected File

components/runners/ambient-runner/ambient_runner/bridges/claude/backend_tools.py — lines 404-414