fix(flare-proxy): substitute route.upstream_model into the outgoing request

[getappz]

Summary

Fixes agentflare item #211.

crates/flare-proxy/src/providers.rs defines ModelRoute.upstream_model (e.g. openrouter/auto, meta/llama-3.1-405b-instruct) but forward.rs::proxy_request never read it. shape_xlat::messages_to_chat copies the incoming Anthropic model string as-is into the translated OpenAI-shaped request, so upstream providers received the raw Anthropic model id (e.g. claude-sonnet-4-5-20250601) verbatim and rejected it.

Fix: after translation, override openai_req["model"] with route.upstream_model.

Verification (live, manual — no mock-server test harness exists yet for forward.rs's HTTP layer, a pre-existing gap)

• Before fix: POST /proxy/v1/messages with model: claude-sonnet-4-5-20250601 (routes to OpenRouter) → OpenRouter rejected with "claude-sonnet-4-5-20250601 is not a valid model ID".
• After fix: same request → correct provider-native model (openrouter/auto, resolved by OpenRouter to openai/gpt-5.6-sol) is called, valid Anthropic-shaped SSE stream returned.
• cargo test -p flare-proxy: 16/16 pass (pre-existing unit tests for shape_xlat/heuristic/think; none previously covered forward.rs's request-building path, which is why this shipped unnoticed).

Follow-up (not fixed here, filed separately)

providers.rs's NVIDIA NIM default_free() config hardcodes meta/llama-3.1-405b-instruct, which no longer exists in NVIDIA's current model catalog (confirmed via live /v1/models call — only meta/llama-3.1-70b-instruct/8b/meta/llama-3.3-70b-instruct exist now). Separate stale-config issue.

Summary by CodeRabbit

• Bug Fixes
  • Provider-routed requests now use the configured upstream model, improving compatibility with upstream APIs.
  • Prevents requests from being rejected or ignored when the incoming model name isn’t recognized.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 80e14d6c-33e7-40dc-b71a-e3e07db39495

📥 Commits

Reviewing files that changed from the base of the PR and between d9cdcdd and c5cba64.

📒 Files selected for processing (1)

• crates/flare-proxy/src/forward.rs

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📝 Walkthrough

Walkthrough

The proxy forwarding path now overwrites the translated request’s model with the provider route’s configured upstream model before forwarding.

Changes

Provider model forwarding

Layer / File(s)	Summary
Override translated model crates/flare-proxy/src/forward.rs	Makes the translated request mutable and replaces its model field with route.upstream_model, with an inline comment documenting the translation behavior.

Estimated code review effort: 2 (Simple) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: using route.upstream_model in outgoing proxy requests.
Description check	✅ Passed	It covers the summary, verification, and follow-up notes, with only the template’s exact Test plan and Notes for reviewers sections omitted.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/flare-proxy-upstream-model-211

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