Bug: Session corrupted when tool execution is aborted - missing tool_result causes API rejection #8312

Summary

When a tool execution is aborted (e.g., user cancels during tool run), the session becomes permanently corrupted. Subsequent messages fail with Anthropic API error: tool_use ids were found without tool_result blocks.

Environment

• OS: Linux
• Provider: Anthropic (Claude)

Steps to Reproduce

1. Start a conversation that triggers tool calls
2. Abort/cancel during tool execution (e.g., press Ctrl+C or cancel button)
3. Try to continue the conversation in the same session
4. API returns error: messages.N: tool_use ids were found without tool_result blocks immediately after: toolu_XXXXX

Root Cause Analysis

When a tool is aborted, the tool call part is saved with status: "error" and error: "Tool execution aborted":

{
  "type": "tool",
  "callID": "toolu_019ArjTH5XqPy66uTLZ8KHpM",
  "tool": "edit",
  "state": {
    "status": "error",
    "input": {},
    "error": "Tool execution aborted",
    "time": { "start": 1768350546106, "end": 1768350546106 }
  }
}

However, no corresponding tool_result message is created. When the conversation is reconstructed for the next API call, it sends the tool_use block but not a matching tool_result, violating Anthropic's API contract.

Current Behavior in agent.go

In streamAndHandleEvents() (line 350-420), tool results are properly generated for:

• ✅ Context cancellation (ctx.Done()) - lines 353-364
• ✅ Permission denied - lines 396-410

But not for:

• ❌ Tool execution errors/aborts that occur through other paths

Suggested Fix

In internal/llm/agent/agent.go, ensure ALL tool calls get a tool_result, even on error:

// After tool.Run() fails with any error (not just permission denied)
if toolErr != nil {
    toolResults[i] = message.ToolResult{
        ToolCallID: toolCall.ID,
        Content:    fmt.Sprintf("Tool execution failed: %v", toolErr),
        IsError:    true,
    }
    // Don't break - continue to generate results for remaining tools
}

Or in convertMessages() in anthropic.go, filter out incomplete tool calls when reconstructing messages.

Impact

• Session becomes unusable after any tool abort
• User must start a new session, losing conversation context
• Particularly problematic for long sessions with valuable context

Workaround

Start a new session. The corrupted session cannot be recovered without manually editing the stored message files.

I'd like to work on this fix if that's okay. Happy to submit a PR.