fix(core): repair dangling tool_use on every request, not just load

A turn aborted mid-flight (cancel, connection drop, dev-server
ECONNREFUSED) can leave an assistant tool_use block with no matching
tool_result in the live transcript. repairToolUseResultPairs already
fixes this, but only ran in OpenSession (load time), so an in-process
abort left the transcript broken until restart. The next request was
then rejected by Anthropic/OpenAI with 'tool_use ids were found without
tool_result blocks'.

Run the same repair on the outbound messages in oneTurn. It is pure and
a no-op on valid transcripts, so there is no hot-path cost beyond a
single linear scan and no behavior change for healthy sessions.

commit: b25b860b0988dad734f065f9ab1d337ccec357b4
author: patriceckhart · 4mo ago · 2026-06-09 10:56 UTC
parent: f7bf4a9
signature: unsigned

1 file · +11 -3

M packages/core/agent.go +11 -3


@@ -502,9 +502,17 @@ func (a *Agent) dropLastAssistantMessage() {
502	502		// and the assembled assistant message (already appended to the transcript).
503	503		func (a *Agent) oneTurn(ctx context.Context, sink func(AgentEvent)) (provider.StopReason, provider.Message, error) {
504	504		req := provider.Request{
505		-	Model: a.Model,
506		-	System: a.System,
507		-	Messages: a.Messages(),
	505	+	Model: a.Model,
	506	+	System: a.System,
	507	+	// Repair any dangling tool_use blocks before sending. A turn
	508	+	// aborted mid-flight (cancel, connection drop, ECONNREFUSED to a
	509	+	// dev server, etc.) can leave an assistant tool_use with no
	510	+	// matching tool_result in the live transcript. The load-time
	511	+	// repair in OpenSession only runs on restart, so without this the
	512	+	// next in-process request is rejected by providers like Anthropic
	513	+	// with "tool_use ids were found without tool_result blocks". The
	514	+	// repair is pure and a no-op on already-valid transcripts.
	515	+	Messages: repairToolUseResultPairs(a.Messages()),
508	516		Tools: a.Tools.Specs(),
509	517		Reasoning: a.Reasoning,
510	518		}

 // and the assembled assistant message (already appended to the transcript).
 func (a *Agent) oneTurn(ctx context.Context, sink func(AgentEvent)) (provider.StopReason, provider.Message, error) {
 	req := provider.Request{
-		Model:     a.Model,
+		Model:  a.Model,
-		System:    a.System,
+		System: a.System,
-		Messages:  a.Messages(),
+		// Repair any dangling tool_use blocks before sending. A turn
+		// aborted mid-flight (cancel, connection drop, ECONNREFUSED to a
+		// dev server, etc.) can leave an assistant tool_use with no
+		// matching tool_result in the live transcript. The load-time
+		// repair in OpenSession only runs on restart, so without this the
+		// next in-process request is rejected by providers like Anthropic
+		// with "tool_use ids were found without tool_result blocks". The
+		// repair is pure and a no-op on already-valid transcripts.
+		Messages:  repairToolUseResultPairs(a.Messages()),
 		Tools:     a.Tools.Specs(),
 		Reasoning: a.Reasoning,
 	}