fix(copilot): route responses-only models (grok-4.x, gpt-5.x) to /responses API

[MaxMoldmann]

Problem

Models like grok-4.5, grok-4.6, grok-4.7, gpt-5.3-codex, gpt-5.5, and other newer Copilot models fail with HTTP 400 unsupported_api_for_model when selected in jcode. The root cause is that Copilot only exposes these models via the OpenAI Responses API (/responses endpoint), not /chat/completions.

From the /models catalog for these models:

{ "supported_endpoints": ["/responses"] }

Fix

Read supported_endpoints from the /models catalog at startup. For any model that lists /responses but not /chat/completions, route requests to /responses instead.

Changed Files

• crates/jcode-base/src/auth/copilot.rs - Add supported_endpoints: Vec<String> to CopilotModelInfo; add needs_responses_api() method.
• crates/jcode-provider-copilot-runtime/src/lib.rs - Add responses_model_ids set populated from /models on startup. In stream_request, branch on model_needs_responses_api(): convert messages to Responses API input items and POST to /responses. Add process_responses_sse_stream to parse SSE events.
• crates/jcode-provider-copilot-runtime/Cargo.toml - Add jcode-provider-openai dependency.
• crates/jcode-tui/src/tui/app/commands.rs - Add unsupported_api_for_model to is_fatal_model_endpoint_error.

Tests

34/34 copilot-runtime unit tests pass. 7 new needs_responses_api auth tests, 3 new routing tests added.

Live integration test against api.githubcopilot.com:

Check	Result
/models lists grok-4.5/4.6/4.7 as responses-only	✓ 13 responses-only models confirmed
/chat/completions for gpt-5.3-codex	✓ HTTP 400 unsupported_api_for_model (root cause)
/responses streaming for gpt-5.3-codex	✓ HTTP 200, text delta received
/responses streaming for grok-4.5	✓ HTTP 200
/responses streaming for grok-4.6	✓ HTTP 200
/responses streaming for grok-4.7	✓ HTTP 200

Affected Models

gpt-5.3-codex, gpt-5.4-mini, gpt-5.5, gpt-5.6-luna, gpt-5.6-sol, gpt-5.6-terra, gpt-6-astra, gpt-6-luna, gpt-6-sol, grok-4.5, grok-4.6, grok-4.7, mai-code-1.1-flash

Linked Issues

Closes 1jehuang#1128