Pi context-window usage stays stale during multi-tool turns

[ymichael]

Summary

During a Pi run with multiple assistant/tool subturns, bb does not refresh the context-window meter until the entire agent run finishes. The meter should update after each Pi turn_end, when the assistant response and its tool results have entered the context used by the next request.

Versions and environment

• bb 0.39.0 (packaged app), also confirmed in source at 05cc16d140e40c2e901de1046b07738fff89eb9f
• macOS 26.5.1 (25F80)
• Pi provider using bundled @earendil-works/pi-coding-agent 0.84.0
• Worktree environment; browser connected remotely through bb Connect

Steps to reproduce

1. Start a Pi thread.

2. Send a prompt that requires more than one model/tool cycle, for example: Read package.json, run git status, then summarize what you found.

3. While Pi performs the tool calls and subsequent assistant responses, watch the context-window meter.

4. After the run finishes, inspect the thread's persisted event ordering:

   sqlite3 ~/.bb/bb.db "SELECT sequence, type, item_kind, json_extract(data, '$.contextWindowUsage.usedTokens') FROM events WHERE thread_id = '<thread-id>' ORDER BY sequence;"

Expected vs actual

Actual, trimmed from thr_25drjv95tn:

23|item/started|fileChange|
24|item/started|commandExecution|
25|item/completed|fileChange|
26|item/completed|commandExecution|
27|item/started|fileChange|
28|item/completed|fileChange|
29|item/started|commandExecution|
30|item/commandExecution/outputDelta||
31|item/completed|commandExecution|
32|item/started|agentMessage|
40|item/completed|agentMessage|
41|thread/tokenUsage/updated||
42|turn/completed||
43|thread/contextWindowUsage/updated||5084

The context-window update arrives only after turn/completed, so the meter remains stale throughout the tool loop. Expected: one thread/contextWindowUsage/updated snapshot after every Pi SDK turn_end, including intermediate assistant responses followed by tool results.

Evidence

• Base commit: 05cc16d140e40c2e901de1046b07738fff89eb9f
• createOnPiEvent reports context only for agent_end and compaction_end.
• Persisted context snapshots on thr_25drjv95tn show that Pi's values do move across completed runs: 4909, 5084, 5202, 5329, 5467. The broken part is the reporting cadence within a multi-tool run, not getContextUsage() itself.
• Investigation thread: Investigate pi context window reporting

What you ruled out

• Not a duplicate of Show Context Window Usage for ACP clients #1111: context-window display exists; this bug is that Pi refreshes it only at full agent completion.
• Not solely compact-number rounding: no context-window event is emitted during intermediate Pi subturns at all.
• The SDK context value is not permanently stuck; persisted snapshots increase across completed runs.

Suggested priority and effort (optional)

Medium — affects Pi users during every multi-tool run; no data loss, but the live context indicator is misleading. Effort is low.

Checks

• I reproduced this on the latest release or on main, or I say above that I could not.
• I searched open and closed issues for the same problem.
• If an agent wrote this, the body ends with > AGENT GENERATED: by <model> and links the thread or report.

AGENT GENERATED: by GPT-5