[BUG] Tool calling broken on 3.37.1 for VS Code API and Opus 4.5.

[azaricstefan]

Problem (one or two sentences)

Tool calling broken on 3.37.1 for VS Code API and Opus 4.5.

Context (who is affected and when)

Date/time: 2025-12-24T00:16:32.635Z
Extension version: 3.37.1
Provider: vscode-lm
Model: copilot/claude-opus-4.5

Request Failed: 400 {"error":{"message":"messages.0.content.0: unexpected tool_use_id found in tool_result blocks: toolu_vrtx_017zoz78rZkfhPsVf1SJkx1k. Each tool_result block must have a corresponding tool_use block in the previous message.","code":"invalid_request_body"}}

Reproduction steps

After couple of responses it will fail to call tools.

Expected result

Tools use work

Actual result

Tools use fail

Variations tried (optional)

No response

App Version

3.37.1

API Provider (optional)

VS Code Language Model API

Model Used (optional)

Claude Opus 4.5

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

[roomote]

I've analyzed this issue and here's my proposed implementation plan:

Root Cause Analysis

The error "unexpected tool_use_id found in tool_result blocks" occurs because of a mismatch between:

1. Validation timing: validateAndFixToolResultIds() validates tool_result IDs against the full apiConversationHistory (line 877 in Task.ts)
2. API request timing: The messages sent to the API use getEffectiveApiHistory() which filters out condensed messages (line 3830 in Task.ts)

When conversation history is condensed, the summary message includes preserved tool_use blocks to maintain proper pairing with tool_result blocks in kept messages. However, if the validation happens against the full history (which includes the original tool_use blocks that are now tagged with condenseParent), but the API receives the effective history (where those original messages are filtered out), the tool_result blocks may reference tool_use IDs that exist in the full history but not in the effective history sent to the API.

Proposed Solution

Add a validation step in attemptApiRequest() that validates tool_result IDs against the effective history (after filtering) rather than relying solely on the validation at message insertion time. This ensures the messages actually sent to the API have properly paired tool_use/tool_result blocks.

Implementation Details

1. Modify src/core/task/Task.ts in the attemptApiRequest() method (around line 3830-3833):

   • After calling getEffectiveApiHistory() and before building cleanConversationHistory
   • Add a validation pass that ensures all tool_result blocks in the effective history have corresponding tool_use blocks in the immediately preceding assistant message
   • If mismatches are found, either fix them or add placeholder tool_use blocks to the summary message

2. Alternative approach (simpler): Modify getEffectiveApiHistory() or getKeepMessagesWithToolBlocks() in src/core/condense/index.ts to ensure that when filtering messages, any tool_result blocks in kept messages have their corresponding tool_use blocks preserved in the summary message.

Recommended Approach

I recommend Option 2 as it addresses the root cause at the source (during condensing) rather than adding a band-aid fix at API request time. The getKeepMessagesWithToolBlocks() function already attempts to preserve tool_use blocks, but there may be edge cases where:

• Multiple condensing operations occur
• The tool_use blocks are in messages that get filtered by getEffectiveApiHistory() but weren't properly included in the summary

The fix would ensure that getEffectiveApiHistory() validates tool_use/tool_result pairing after filtering and includes any missing tool_use blocks from the summary message.

Testing Plan

1. Add unit tests for the edge case where condensed history has tool_result blocks without corresponding tool_use blocks
2. Test with VS Code LM API provider using Claude Opus 4.5 to verify the fix
3. Ensure existing tests for validateToolResultIds and condense functionality continue to pass

Please mention @roomote in a comment saying that you approve this plan, and I'll proceed with the implementation.

[hannesrudolph]

Can't repro. Are you able to share the larger error that contains your api history please?

[jiangbing321]

I have the same error .

[hannesrudolph]

I have the same error .

Can't repro. Are you able to share the larger error that contains your api history please? https://docs.roocode.com/reporting-errors

[azaricstefan]

I just sent email with detailed error information.