fix: sum tool usage from dual sources instead of taking max

[nightq]

Summary

The Insights tool was undercounting tool usage when tool_name and tool_calls sources coexisted across different sessions.

Root Cause

_get_tool_usage() in agent/insights.py used max() to merge the two tool-count sources, assuming they were duplicate views of the same calls. However, across mixed session sources (gateway / CLI / ACP), one session may record via tool_name while another records only via tool_calls, making them disjoint. When the same tool appeared once in each source, the count was max(1, 1) = 1 instead of the correct 2.

Fix

Changed the merge logic from max() to sum (+), since tool_name (from tool execution results) and tool_calls (from assistant-side call records) can capture disjoint sets of calls across different session sources.

Test Plan

• Generate insights with mixed gateway + CLI sessions
• Verify tool counts reflect total invocations across all sources
• Single-source sessions (tool_name only or tool_calls only) unchanged

Closes #9814

[teknium1]

Thanks for identifying the real mixed-session undercount: current main still applies a global per-tool max() in agent/insights.py:281.

Problems

• The proposed addition at agent/insights.py:280 double-counts normal completed calls. agent/tool_executor.py:938 appends a tool-result message, and run_agent.py:1882-1895 persists both assistant tool_calls and tool-result tool_name. The existing fixture records both representations and expects two terminal calls at tests/agent/test_insights.py:348-350; this change would report four.
• No regression test accompanies the behavior change. The linked related PR #9896 uses (session_id, tool_name) aggregation before the per-source max, which preserves paired calls while adding disjoint sessions.

Suggested changes

• Merge per (session_id, tool_name), then total by tool name.
• Add paired-source and disjoint-session regression cases in tests/agent/test_insights.py.

Automated hermes-sweeper review.

[teknium1]

This sums globally aggregated counters, so it doubles ordinary completed calls that have both assistant tool_calls and a tool-result tool_name row. Merge by (session_id, tool_name) first, then aggregate by tool name.

[teknium1]

Salvaged onto current main as #109132 with your commit authorship preserved where the diff still applied (the file moved/was restructured since April, so some of it is a hand-port with credit in the commit message). Once #109132 merges this PR will be closed with a link to the landed SHA. Thanks for the fix.

[teknium1]

Landed via #109132 (merge b5b697e) with your commit cherry-picked so authorship is preserved — thank you @nightq. Closing this PR as superseded by the merged salvage; the fix is on main now.