fix(agents): fix reasoning model routing for gpt-5.4 and gpt-5.5

[vladyslav-yurchenko1]

Summary

Adds gpt-5.5 model support with correct routing to OpenAI Responses API and consolidates Responses API model detection into a single source of truth.

Changes

• Added gpt-5.5 and gpt-5.5-2026-04-24 static entries with use_responses_api: true in opencode-model-configs.ts
• Moved RESPONSES_API_MODEL_PATTERNS and isResponsesApiModel() from opencode-dynamic-models.ts to opencode-model-configs.ts (single source of truth)
• Fixed getModelConfig() fallback to apply isResponsesApiModel() so unknown future models are auto-routed correctly
• Removed duplicate pattern array from opencode-dynamic-models.ts

Impact

Before: gpt-5.5 was routed to /v1/chat/completions — no reasoning output, tool calls crashed with reasoning_effort not supported error.
After: gpt-5.5 routes to /v1/responses — reasoning blocks visible in CLI, tool calls work correctly.

Checklist

• Self-reviewed
• Manual testing performed
• Documentation updated (if needed)
• No breaking changes (or clearly documented)

[mykolanehrych]

context.url is assigned directly from req.url — the /v1 prefix is ​​never stripped, so the second condition (=== '/responses') is dead code. The first condition (includes) is a substring match and would
incorrectly treat /v1/responses/stream as a Responses API request. Fix: context.url === '/v1/responses'

[mykolanehrych]

'gpt-5.4': { cost: { input: 1.75, output: 14, cache_read: 0.175 }, ... }
'gpt-5.4-2026-03-05': { cost: { input: 1.75, output: 14, cache_read: 0.175 }, ... }

These four config blocks are nearly identical only id, name, and displayName differ. If pricing changes, it needs to be updated in multiple places and it's easy to miss one. maybe worth extracting shared fields into a base object?

[mykolanehrych]

Approved