compaction: automatic compaction can fail with provider invalid_prompt

Summary

Automatic compaction can fail because OpenAI rejects the generated compaction prompt as potentially violating usage policy. The raw provider error interrupts session draining instead of recovering gracefully.

Environment

• opencode version: 0.0.0-beta-19296
• OS: Windows 10.0.26200.9168
• Terminal: TERM=xterm-256color; terminal program unavailable
• Shell: C:\WINDOWS\system32\cmd.exe
• Install/channel: beta, reported as up to date
• Active plugins: none found in global or project configuration

Reproduction

1. Continue a sufficiently long session until automatic compaction runs.
2. Allow OpenCode to compact the existing conversation automatically.
3. Observe the session fail with a raw invalid_prompt provider error.

Reproduction is intermittent: one automatic compaction failed, while a later automatic compaction in the same session completed.

Expected Behavior

Automatic compaction should complete, retry safely, or surface a recoverable compaction-specific error without failing the session drain.

Actual Behavior

The automatic compaction record was marked failed with error type provider.invalid-request, and the server logged:

Failed to drain Session

The user-facing error was:

invalid_prompt: Invalid prompt: your prompt was flagged as potentially violating our usage policy. Please try again with a different prompt: https://platform.openai.com/docs/guides/reasoning#advice-on-prompting

Additional Context

• The failure occurred during automatic compaction.
• The failed record contained no summary or model metadata.
• A later automatic compaction completed with OpenAI gpt-5.6-sol.
• No prompt or conversation content is included here for privacy.