Summary

Fixes #1826

When an assistant message has stopReason: "error", the tool_use blocks within it are incomplete/terminated and were never actually executed. The transcript repair mechanism was incorrectly creating synthetic tool_results for these errored tool calls, causing all subsequent API requests to fail with:

invalid_request_error: messages.X.content.Y: unexpected tool_use_id found in tool_result blocks: toolu_XXX. 
Each tool_result block must have a corresponding tool_use block in the previous message.

This breaks the session permanently until the synthetic tool_result is manually removed from the JSONL file.

Changes

• Check stopReason before extracting tool calls in repairToolUseResultPairing()
• Skip tool call extraction when stopReason is "error"
• Prevents synthetic tool_results for incomplete/terminated tool calls

Root Cause

The issue occurred in src/agents/session-transcript-repair.ts at line 119:

Before:

const assistant = msg as Extract<AgentMessage, { role: "assistant" }>;
const toolCalls = extractToolCallsFromAssistant(assistant);  // ❌ Extracts from errored messages too

After:

const assistant = msg as Extract<AgentMessage, { role: "assistant" }>;

// Skip tool call extraction if the assistant turn errored/terminated.
// When stopReason is "error", the tool_use blocks are incomplete and were never executed,
// so we should not create synthetic tool_results for them.
const stopReason = (assistant as { stopReason?: unknown }).stopReason;
if (stopReason === "error") {
  out.push(msg);
  continue;
}

const toolCalls = extractToolCallsFromAssistant(assistant);

Impact

Before this fix:

• Tool execution error/interruption → session permanently broken
• Requires manual JSONL editing to recover
• Confusing error messages for users

After this fix:

• Tool execution error/interruption → session remains usable
• No manual intervention needed
• Clean recovery from errors

Testing Status

⚠️ Lightly tested

• ✅ TypeScript compiles without errors
• ✅ Linter passes (oxlint)
• ⚠️ No specific test for errored tool_use scenario (would need integration test with actual API error)
• ⚠️ Needs real-world validation

Files Changed

• src/agents/session-transcript-repair.ts - Added stopReason check (10 lines added)

AI-Assisted Development

🤖 This PR was created with assistance from Claude Sonnet 4.5

• Analyzed issue Synthetic tool_result for terminated tool_use causes all subsequent requests to fail #1826 and traced root cause through codebase
• Designed minimal fix following existing code patterns
• Generated fix implementation and PR
• Testing level: lightly tested (compiles + lints, needs integration testing)

Checklist

• Code follows existing patterns
• Linter passes
• TypeScript compiles without errors
• Integration tested (needs validation with actual error scenarios)
• Marked as AI-assisted
• References issue Synthetic tool_result for terminated tool_use causes all subsequent requests to fail #1826

Generated with Claude Code