Repository navigation
Quadratic tool-call repair before message-filtered requests #7746
Description
Summary
messageFilter repairs a retained parallel tool-call group in quadratic time. Each retained tool result expands its issuing assistant message again, including every sibling result that has already been emitted.
On current main (be3a15c82f0df78e5c90b2f07f178662d9e1e97e), one assistant message with N tool calls and its N result messages causes exactly N² + 2N tool-call ID reads. The input and output each contain N + 1 messages.
Reproduction
Run from the repository root with Node 22.23.3:
node --experimental-strip-types --input-type=module <<'JS'
import { ɵrepairToolCallPairs } from './packages/core/src/core/message-filter.ts';
for (const n of [1, 2, 4, 8, 16, 64, 256, 1024]) {
let reads = 0;
const toolCalls = Array.from({ length: n }, (_, i) => ({
get id() { reads++; return `call-${i}`; },
type: 'function',
function: { name: 'lookup', arguments: '{}' },
}));
const messages = [
{ id: 'assistant', role: 'assistant', content: '', toolCalls },
...Array.from({ length: n }, (_, i) => ({
id: `result-${i}`, role: 'tool', toolCallId: `call-${i}`, content: 'done',
})),
];
const result = ɵrepairToolCallPairs(messages, messages);
console.log({ n, messages: result.length, reads });
}
JSThe getter counts work performed by the repair; it is excluded from latency measurements. With plain objects, five local runs of the same repair took 24.1–26.8 ms at 1,024 calls and 504.6–521.0 ms at 4,096 calls on Node 22.23.3. These are high-fanout stress inputs and isolated repair timings.
Mechanism and affected path
emit deduplicates output by message ID. emitWithResults scans toolCallIdsOf(message) on every invocation, including invocations for an issuer whose results have already been emitted. The retained result loop invokes it once per sibling.
ProxiedCopilotRuntimeAgent.#applyMessageFilter calls this repair before HTTP run and connect requests. All four framework providers expose messageFilter. The pairing behavior introduced in #6926 remains necessary: restoring one tool result must restore its issuer and every available sibling result.
Expected behavior
Expand each distinct issuer object once per repair, retaining output order, message-ID deduplication, open calls, orphan results, and filter-synthesized messages. Object identity matters here: a filter can return a changed assistant object with the same ID as the untrimmed issuer, and those two objects can reference different call sets.
The target is one traversal of the full input followed by one expansion of each distinct retained or restored issuer object, with the same outbound content and existing fallback behavior.
Activity
copilotkit-outpost-bot commentedon Oct 9, 2026
The report is accurate about the mechanism.
emitWithResultsis called once per retained tool result, and each call iteratestoolCallIdsOf(issuer)— which isO(N)— so a single assistant message withNparallel calls producesO(N²)work. Theemittedset prevents duplicate output, but the iteration still happens.The fix is to track which issuers have already been expanded and skip the
toolCallIdsOfscan on repeat visits. Here is a drop-in replacement for the loop inɵrepairToolCallPairs(packages/core/src/core/message-filter.ts):Code example (ts)
expandedIssuersis keyed onissuer.id(the message ID from the untrimmed thread), which is whatcallIdToIssuermaps to. A filter-synthesized assistant object with the same ID as the original would be treated as the same issuer — that matches the existingemittedset behaviour, which also keys onmessage.id. If the expected behaviour for synthesized objects with colliding IDs needs to differ, that is a separate design question for the maintainers.This keeps output order, the
emitted-set deduplication, open calls, and orphan-result pass-through unchanged. Work per repair becomesO(M + C)whereMis the number of kept messages andCis the total number of distinct call IDs across all issuers — linear in the input.Engineering will need to verify the fix and confirm whether the synthesized-object edge case warrants additional handling before merging.
🤖 Generated by CopilotKit AI Support · Documentation
Was this helpful? React with 👍 or 👎