fix: #24090 preserve assistant tool_calls in openai-compatible replay

[supernovae]

Issue for this PR

Closes #24090

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This fixes missing assistant tool_calls during OpenAI-compatible history replay.

I added a focused repair in MessageV2.toModelMessagesEffect so when replay contains tool result messages, the nearest preceding assistant message is guaranteed to include matching tool-call entries (rehydrated from recorded session tool parts, including original tool name/input).

I also added a send-time guard in session/llm middleware for OpenAI-compatible models. If tool-call parts are dropped during prompt conversion, the guard restores them from the original model-message source before provider serialization, keeping tool_calls and tool_call_id paired.

Regression coverage was added in:

• packages/opencode/test/session/message-v2.test.ts
• packages/opencode/test/session/llm.test.ts

How did you verify your code works?

• Ran bun --config=./bunfig.test.toml test test/session/llm.test.ts locally (from packages/opencode) and all tests passed, including the new replay pairing case.
• Attempted bun --config=./bunfig.test.toml test test/session/message-v2.test.ts; this currently fails before test execution due a pre-existing initialization error in src/session/session.ts (ReferenceError: Cannot access 'Assistant' before initialization), not from this diff.

Screenshots / recordings

N/A (non-UI change)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[supernovae]

#24090

[github-actions]

Hey! Your PR title fixes: (24090) preserve assistant tool_calls in openai-compatible replay doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍