[BUG] Tool name is required for Gemini requests

[gbudge]

Problem (one or two sentences)

HTTP 400 "Tool name is required for Gemini requests" when using copilot - gemini-3-pro model.

Context (who is affected and when)

Happens when using Roo Code in Orchestrator mode, creating as new application with test cases.

Reproduction steps

High Level Flow

[MacOS Sonoma 14.8.2] --> [Microsoft Remote - SSH Extension] --> [Linux Mint 21.3 Virginia]

Sequence of Events

1. Connect to remote server via VS Code, open empty directory.

2. Prompt the model in Orchestrator mode, to create a VS Code Extension (LSP).

3. The model appears to work fine. It was creating the files, asking questions, etc.

4. The model then starts to exhibit the error message.

   

   Details:
   

5. Allowed it to retry a few times, without any improvement.

6. Changed to copilot - gemini-2.5-pro and copilot - gemini-3-flash without any improvement.

7. Changed to copilot - claude-haiku-4.5 and it was successfully able to continue.

8. The model summarised what it had built.

9. Roo Code believes all tasks are now complete.

10. Restarted VS Code, resumed the Roo Code session.

11. Changed to copilot - gemini-3-pro and prompted the model to review it completed everything.

12. The same error message started appearing again.

13. Changed to copilot - gpt-5-codex and it was successfully able to continue the review.

MacOS Info

Version: 1.107.1 (Universal)
Commit: 994fd12f8d3a5aa16f17d42c041e5809167e845a
Date: 2025-12-17T14:15:14.850Z
Electron: 39.2.3
ElectronBuildId: 12895514
Chromium: 142.0.7444.175
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin x64 23.6.0

(base) user@MacBook:~/build$ code --list-extensions --show-versions
github.copilot@1.388.0
github.copilot-chat@0.35.2
ms-vscode-remote.remote-ssh@0.122.0
ms-vscode-remote.remote-ssh-edit@0.87.0
ms-vscode.remote-explorer@0.5.0
upstash.context7-mcp@1.0.1
(base) user@MacBook:~/build$

Linux Mint Info

(base) user@server:~ % cat /etc/linuxmint/info
RELEASE=21.3
CODENAME=virginia
EDITION="Cinnamon"
DESCRIPTION="Linux Mint 21.3 Virginia"
DESKTOP=Gnome
TOOLKIT=GTK
NEW_FEATURES_URL=https://www.linuxmint.com/rel_virginia_whatsnew.php
RELEASE_NOTES_URL=https://www.linuxmint.com/rel_virginia.php
USER_GUIDE_URL=https://www.linuxmint.com/documentation.php
GRUB_TITLE=Linux Mint 21.3 Cinnamon
(base) user@server:~ %  uname -a
Linux server 5.15.0-164-generic #174-Ubuntu SMP Fri Nov 14 20:25:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
(base) user@server:~ % code --list-extensions --show-versions
bierner.markdown-mermaid@1.29.0
docker.docker@0.18.0
github.copilot@1.388.0
github.copilot-chat@0.35.2
moozzyk.arduino@0.0.4
ms-azuretools.vscode-containers@2.3.0
ms-azuretools.vscode-docker@2.0.0
ms-python.debugpy@2025.18.0
ms-python.pylint@2025.2.0
ms-python.python@2025.20.1
ms-python.vscode-pylance@2025.10.4
ms-python.vscode-python-envs@1.14.0
ms-vscode-remote.remote-containers@0.434.0
ms-vscode.cmake-tools@1.21.36
ms-vscode.cpptools@1.29.3
ms-vscode.cpptools-extension-pack@1.3.1
ms-vscode.cpptools-themes@2.0.0
twxs.cmake@0.0.17
(base) user@server:~ % 

Expected result

Roo Code can use the Gemini 3 Pro, Gemini 3 Flash and Gemini 2.5 Pro models, etc.

Actual result

Request Failed: 400 {"error":{"message":"Tool name is required for Gemini requests","code":"invalid_tool_call_format"}}

Variations tried (optional)

Tried the following models that also failed:

• ❌ copilot - gemini-3-pro
• ❌ copilot - gemini-3-flash
• ❌ copilot - gemini-2.5-pro

Tried the following models that did not have the issue:

• ✅ copilot - claude-haiku-4.5
• ✅ copilot - gpt-5-codex

App Version

v3.36.16

API Provider (optional)

VS Code Language Model API

Model Used (optional)

gemini-3-pro

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

### Basic error info


Date/time: 2025-12-23T03:27:29.951Z
Extension version: 3.36.16
Provider: vscode-lm
Model: copilot/gemini-3-pro

Request Failed: 400 {"error":{"message":"Tool name is required for Gemini requests","code":"invalid_tool_call_format"}}

[roomote]

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

Root Cause Analysis

The error "Tool name is required for Gemini requests" occurs because:

1. Gemini models require the tool name to be included in tool result messages (see gemini-format.ts lines 87-97)
2. When using the VS Code Language Model API with Copilot + Gemini models, we create LanguageModelToolResultPart objects that only contain callId and content - no tool name
3. The VS Code LanguageModelToolResultPart class doesn't officially support a toolName property in its constructor
4. The Copilot extension should internally map callId back to tool name from the conversation history, but it appears this isn't working correctly for Gemini models

Proposed Solution

Since we can add arbitrary properties to JavaScript objects, I propose modifying convertToVsCodeLmMessages() in src/api/transform/vscode-lm-format.ts to:

1. Build a toolIdToName map by scanning through the messages array for tool_use blocks in assistant messages
2. Add a toolName property to each LanguageModelToolResultPart when creating tool results

Code Changes

In src/api/transform/vscode-lm-format.ts:

export function convertToVsCodeLmMessages(
    anthropicMessages: Anthropic.Messages.MessageParam[],
): vscode.LanguageModelChatMessage[] {
    const vsCodeLmMessages: vscode.LanguageModelChatMessage[] = []
    
    // Build a map of tool_use_id -> tool_name from assistant messages
    const toolIdToName = new Map<string, string>()
    for (const msg of anthropicMessages) {
        if (msg.role === 'assistant' && Array.isArray(msg.content)) {
            for (const block of msg.content) {
                if (block.type === 'tool_use') {
                    toolIdToName.set(block.id, block.name)
                }
            }
        }
    }
    
    // ... existing conversion logic ...
    
    // When creating LanguageModelToolResultPart, add toolName property:
    const resultPart = new vscode.LanguageModelToolResultPart(
        toolMessage.tool_use_id, 
        toolContentParts
    )
    // Add toolName for providers that need it (like Gemini via Copilot)
    const toolName = toolIdToName.get(toolMessage.tool_use_id)
    if (toolName) {
        (resultPart as any).toolName = toolName
    }
    return resultPart

Testing

I'll add tests to verify:

1. The toolIdToName map is correctly built from the conversation history
2. The toolName property is correctly added to LanguageModelToolResultPart objects
3. Tool results without matching tool_use blocks are handled gracefully

Alternative/Backup Plan

If adding the toolName property doesn't get picked up by the Copilot extension (since it's not part of the official API), this may need to be reported as a bug to the VS Code/Copilot team. In that case, I can help document the issue and create a minimal reproduction case.

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

[hannesrudolph]

I was unable to repro this with vscode lm api on my end. Can you please provide the full contents of the conversation?

[gbudge]

I'll have to remove some sensitive things from it then will provide.

FWIW, when I start a new session in Roo Code and copy/paste the same code review prompt, using the copilot - gemini-3-pro model, it works, so there must be something happening along the way in the original prompt.