fix: cap oversized ACP event content instead of failing the send#437
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fix: cap oversized ACP event content instead of failing the send#437AlexanderZ-Band wants to merge 1 commit into
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…-1014] The Agent Events API rejects content over 16384 chars with a 422, which the ACP/GitHub Copilot backend hit when mirroring large tool_call/tool_result payloads (e.g. get_file_contents on a big file). AgentTools.send_event now truncates oversized content at the shared chokepoint, keeping both the head and tail of the string so the tail (often the informative part of a raw error dump) isn't silently dropped. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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This was referenced Jul 14, 2026
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Summary
POST /agent/chats/{id}/events) hard-capscontentat 16384 chars and rejects anything larger with a 422 — the ACP/GitHub Copilot backend hit this when mirroring largetool_call/tool_resultpayloads (e.g. a GitHub MCPget_file_contentscall on a big file), causing the send to fail outright instead of degrading gracefully.contentstring is a fan-out amplification vector. Per the platform source (thenvoi-platform/lib/thenvoi_com_web/controllers/api/v1/agent/events_controller.ex:34-39): "The caps are generous ceilings (no legitimate event hits them), purely to stop pathological payloads from being broadcast." The Copilot CLI's large tool_result is exactly the legitimate-but-oversized case that guardrail didn't anticipate.AgentTools.send_event(src/band/runtime/tools.py) — the single chokepoint every adapter funnels through — now truncates oversized content to the cap (keeping the head, dropping the tail with a"... [truncated]"marker) before sending, rather than throwing.send_eventcalls share this one path.Linear: INT-1014
Test plan
uv run pytest tests/runtime/test_tools.py -k SendEvent -v --no-cov— new truncation tests pass (pass-through under the cap, oversized content truncated with marker)uv run pytest tests/ --ignore=tests/integration/ --ignore=tests/e2e/ -q --no-cov— full suite (3800 passed, 75 skipped)uv run ruff check ./uv run ruff format --check .uv run pyrefly check🤖 Generated with Claude Code