Greptile Summary

This PR adds /compact and /compress as interactive TUI commands that trigger SDK session compaction on the selected agent instead of forwarding the text as a normal chat message, and records a system feedback message in the live view on completion.

• AgentCoordinator.compact_agent_session() is added to force the SDK compaction pipeline for a named agent, guarded by the existing _lock and gated on is_openai_responses_compaction_aware_session.
• send_user_message_to_agent intercepts the two slash commands and dispatches compact_agent_session via run_coroutine_threadsafe, with a done callback that writes a success/failure notice back to the live view.
• A new test file verifies both command aliases trigger compaction without forwarding a chat message to the agent.

Confidence Score: 3/5

The core compaction logic is sound, but the done-callback path writes to TuiLiveView from the event loop thread without any synchronization, which is a new concurrency pattern not present in the existing send flow.

The new _record_compaction_result callback calls live_view.record_system_message() from the event loop thread while the TUI input thread can concurrently call live_view.record_user_message() for any subsequent user input while compaction is in flight. TuiLiveView has no locks, so _next_event_id and self.events can be written by two threads simultaneously. Every prior done callback in the codebase (_log_delivery_failure) only logged — none mutated shared UI state — making this the first cross-thread live view write introduced by this PR.

strix/interface/tui/messages.py — the _record_compaction_result done callback and its thread interaction with TuiLiveView; strix/core/agents.py — the missing explicit None-session guard in compact_agent_session.

Important Files Changed

Fix the following 3 code review issues. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 3
strix/interface/tui/messages.py:64-79
**Cross-thread mutation of `TuiLiveView` via done callback**

`_record_compaction_result` calls `live_view.record_system_message()` from the event loop thread (done callbacks on `concurrent.futures.Future` run on the thread that set the result, which is the event loop thread for `run_coroutine_threadsafe`). Meanwhile, callers on the TUI input thread can invoke `live_view.record_user_message()` for a subsequent message while compaction is in flight. Both paths write to `TuiLiveView.events` and increment `_next_event_id`, neither of which is protected by a lock. If a second user message arrives before the compaction coroutine finishes, these two writes race, potentially producing duplicate event IDs or a corrupted event list.

### Issue 2 of 3
strix/core/agents.py:158-181
**Misleading log when session is not yet attached**

When `compact_agent_session` is called before `attach_runtime` has set a session, `session` is `None`. The code passes `None` straight to `is_openai_responses_compaction_aware_session`, which will return `False`, causing the log to read "SDK session does not support compaction" — even though the actual problem is that no session is attached at all. The existing `send()` method handles this with an explicit `None` guard and a distinct, accurate message. Without the same guard here, a developer debugging a "compaction not working" report will look at the wrong place.

### Issue 3 of 3
strix/interface/tui/messages.py:71-79
**Exception and "not supported" both surface as "unavailable"**

When `compact_agent_session` raises (e.g., a transient network failure during `run_compaction`), `future.result()` re-raises inside `_record_compaction_result`, `compacted` is set to `False`, and the UI shows `"Context compaction is unavailable for this agent."` — the same message used when the SDK session structurally lacks compaction support. A transient error would mislead the user into thinking compaction is a permanent capability gap rather than something that might succeed on retry.

_{Reviews (1): Last reviewed commit: "feat(tui): add manual compact command" | Re-trigger Greptile}

Addressed the Greptile review feedback in d1ca17d.

Summary:

• Routed compact feedback through the UI thread to avoid cross-thread TuiLiveView mutation.
• Added an explicit no-session guard before compaction support checks.
• Split compaction results into success, unavailable, and failed so transient failures do not show as unsupported.

Verified with:

• uv run pytest tests/test_manual_compact.py tests/test_execution.py -q -> 9 passed
• ruff check/format on touched files -> passed
• uv run mypy strix/core strix/interface/tui/messages.py -> passed

Resolved the three outdated Greptile threads after this fix.