Compaction fails with 400 Bad Request when using GitHub Copilot Enterprise

[unimun]

Description

Problem

Compaction (conversation summarization) fails with 400 Bad Request when using GitHub Copilot Enterprise provider with Claude models.

Root Cause

GitHub Copilot API's /chat/completions endpoint rejects messages with role: "tool" during summarization requests.

API Validation

Test Case	Request Contains	Response	Status
Test 1	Simple user message only	Success (200)	✅ PASS
Test 2	Assistant message with tool_calls	Success (200)	✅ PASS
Test 3	Tool result message (role: "tool")	Bad Request (400)	❌ FAIL
Test 4	Both tool_calls + tool result	Bad Request (400)	❌ FAIL

Solution

Provider-specific filtering in packages/opencode/src/session/compaction.ts:

• Check model.providerID for "copilot"
• Only sanitize tool messages for GitHub Copilot
• Other providers pass messages unchanged

Verification

• Compaction works for GitHub Copilot
• Regular chat with tools still works
• API behavior validated with curl tests
• Build passes

Plugins

No response

OpenCode version

dev build

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

No response

Terminal

No response

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• GitHub Copilot GPT-5 throwing "invalid_request_body" on requests after compaction #10650: GitHub Copilot GPT-5 throwing invalid_request_body on requests after compaction - Similar provider/compaction issue with GitHub Copilot
• Anthropic models fail with 404 on GitHub Enterprise (GHE.com) #11105: Anthropic models fail with 404 on GitHub Enterprise (GHE.com) - Related to GitHub Enterprise Copilot endpoint issues
• fix: Perplexity Sonar models return 400 error with consecutive user messages #9416: Perplexity Sonar models return 400 error with consecutive user messages - Similar 400 error with provider-specific message handling

Feel free to ignore if none of these address your specific case.

[unimun]

Root Cause (Confirmed)

The issue is not about tool messages being rejected by GitHub Copilot Enterprise API itself. The actual problem is:

Empty tools: {} parameter + message history with tool calls = 400 Bad Request

Why This Happens

During compaction:

1. Tools are intentionally removed to prevent execution during compaction
2. This leaves tools: {} (empty object)
3. GitHub Copilot Enterprise validates: "If message history contains tool calls, tools parameter must not be empty"
4. Validation fails → 400 Bad Request

[amarjandu]

I don't mean to thread-hijack (and can start a new issue if needed I just searched for the error response), but these 400 errors occur for me outside of compaction. I notice that this frequently happens to me w/ models that are provided through github.

After this the session is effectively dead, I have to start a new session :(