fix: skip tool_use blocks with stopReason error in transcript repair

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: unexpected tool_use_id found in tool_result blocks

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

This ensures sessions remain usable after tool execution errors or
interruptions, without requiring manual JSONL editing.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/agents/session-transcript-repair.ts

@@ -116,6 +116,16 @@ export function repairToolUseResultPairing(messages: AgentMessage[]): ToolUseRep
     }
 
     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);
     if (toolCalls.length === 0) {
       out.push(msg);