fix: ChatGPT OAuth gpt-5.5 tool support

[WqyJh]

Issue for this PR

Closes #275

Type of change

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

What does this PR do?

Fixes ChatGPT Plus/Pro OAuth handling for openai/gpt-5.5.

The OAuth loader was mutating the OpenAI provider model list with an allowlist that stopped at gpt-5.4, so gpt-5.5 was removed before users could select it. This moves subscription model filtering into the provider model hook, keeps API-key auth untouched, exposes gpt-5.5 for OAuth accounts, and applies subscription-backed cost/limit metadata there.

For request compatibility, this also avoids sending textVerbosity for gpt-5.5, includes encrypted reasoning content for GPT-5 reasoning requests, and flattens nested discriminated-union tool schemas for gpt-5.5 tool parameters.

How did you verify your code works?

• git diff --check
• npx --yes prettier@3.6.2 --check packages/opencode/src/plugin/codex.ts packages/opencode/src/provider/transform.ts packages/opencode/test/plugin/codex.test.ts packages/opencode/test/provider/transform.test.ts

I added focused regression tests for OAuth model exposure, gpt-5.5 request options, and nested tool schema flattening. In this fresh local clone, running Bun tests was blocked before assertions because dependencies were not installed, and bun install / bun install --frozen-lockfile --ignore-scripts stayed at Resolving dependencies. Running the tests from a directory without the package bunfig reached source loading but failed on missing effect.

Screenshots / recordings

Not applicable; this is not a UI change.

Checklist

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

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Mirrored from XiaomiMiMo/MiMo-Code#501 — original author @LiWithDream.