fix: support lazy apply for non-Sonnet models like qwen3-coder-plus

[ajayjha1]

Title: fix: support lazy apply for non-Sonnet models like qwen3-coder-plus

lazyApplyPromptForModel returned undefined for any model not containing 'sonnet', causing streamLazyApply to throw 'Lazy apply not supported' whenever edit_existing_file fell back to the LLM-based apply path. Use the general-purpose prompt as the default for all models.

Description

edit_existing_file fails silently for non-Sonnet models (e.g. qwen3-coder-plus, gpt-4o, deepseek-coder, etc.) when the model generates lazy edits with // ... existing code ... placeholders. The deterministic apply path skips those (since onlyFullFileRewrite: true), so it falls through to streamLazyApply — which threw an error because lazyApplyPromptForModel only returned a prompt for models containing "sonnet" in their name.

The claudeSonnetLazyApplyPrompt is a general-purpose lazy-apply prompt (the name is just historical). This PR removes the model-name guard and makes it the default for all models, eliminating the error and making edit_existing_file work across providers.

Fixes the issue reported with qwen3-coder-plus via DashScope where users had to add rules to force the agent away from edit_existing_file.

Checklist

• I've read the contributing guide (https://github.com/continuedev/continue/blob/main/CONTRIBUTING.md)
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

N/A — the fix is in the apply pipeline; visible effect is that edit_existing_file no longer fails with a silent error for non-Sonnet models.

Tests

Existing tests in core/edit/lazy/streamLazyApply.test.ts continue to pass. No new tests added — the previous code path that threw was unreachable by any test since all mock LLMs used a "sonnet" model name.

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Summary by cubic

Enable lazy apply for all models by defaulting to the general-purpose prompt. Prevents silent failures in edit_existing_file for non-Sonnet models like qwen3-coder-plus, gpt-4o, and deepseek-coder.

• Bug Fixes
  • lazyApplyPromptForModel always returns the general-purpose claudeSonnetLazyApplyPrompt; removed the model-name check.
  • Removed the "Lazy apply not supported" error path in streamLazyApply, allowing LLM-based apply across providers.

^{Written for commit 46f0922. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}