## Summary
- Non-Anthropic providers (OpenAI, Google, Ollama, etc.) error with "The
model does not support assistant message prefill" when the unclosed
`dyad-write` continuation retry triggers
- The continuation logic was using an assistant message as the last
message (prefill pattern), which only Anthropic supports
- Replaced with a user message that includes the partial response and
asks the model to continue where it left off

## Test plan
- Use a non-Anthropic provider (e.g. OpenAI, Gemini) in build mode
- Trigger a response that produces an unclosed `<dyad-write>` tag (e.g.
a large file write that gets cut off)
- Verify the continuation retry no longer errors and the model completes
the response

🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>