Session config | Select the LLM from a model ref

[BrianGenisio]

Summary

• Move LLM selection out of .env (LLM_PROVIDER, *_MODEL) into session.config.json.
• model is a provider/model-id ref (openai/gpt-5.6-luna, google/gemini-3.6-flash, anthropic/…). The prefix picks the adapter. API keys and optional *_BASE_URL stay in .env.
• allowedModels is the picker list. Eval returns 503 if model is not on it.

Changes

The interesting bit is lib/llm/model-ref.js: one parser for routing, key lookup, and allowlist membership. Providers still strip their own prefix on the API call, so a leftover openai/ on complete() is harmless.

normalizeSessionConfig keeps a provided model even when it is not allowed, so /api/session-config mirrors the file. The reject happens at eval time (assertAllowedModel), not by silently swapping models.

If allowedModels is omitted, it defaults to the three example refs in the README. Custom models have to be added to that list first.

Test plan

• npm test
• Copy session.config.example.json to session.config.json, set model to a listed ref, fill the matching API key in .env, and run an eval
• Point model at a ref that is not in allowedModels and confirm compare returns 503
• Confirm .env no longer needs LLM_PROVIDER or *_MODEL

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• tests/session-config.test.js

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📝 Walkthrough

Walkthrough

LLM provider selection now uses provider/model-id references from session.config.json. Model references support provider aliases, validation, API-key lookup, and allowlist enforcement. Anthropic, OpenAI, and Gemini adapters receive the selected model ID directly. The server validates configuration at startup, caches providers by model, and returns HTTP 503 for configuration errors. Documentation, examples, and tests now use the model-reference configuration path.

Merge Risk: ⚪ Minimal · up to db570

LLM selection is moved to session configuration with centralized model-reference parsing and evaluation-time allowlist enforcement. No concrete current change risk remains identified.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly summarizes the main change: selecting the LLM through a model reference in session configuration.
Description check	✅ Passed	The description directly explains moving LLM selection to session.config.json, model-reference routing, allowlist validation, API-key handling, and test coverage.

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Actionable comments posted: 1

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Inline comments:
In `@lib/session-config.js`:
- Line 113: Update the allowed-model validation around parseModelRef so
configured and requested references are parsed and compared by canonical
provider and modelId, allowing equivalent google and gemini aliases while
preserving existing rejection behavior for different models. Retain raw
configured references in normalized session-config output, and add coverage for
provider aliases and differing prefix case.

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📒 Files selected for processing (16)

• .env.example
• README.md
• lib/llm/anthropic.js
• lib/llm/gemini.js
• lib/llm/model-ref.js
• lib/llm/openai.js
• lib/llm/provider.js
• lib/session-config.js
• server.js
• session.config.example.json
• tests/llm-gemini.test.js
• tests/llm-model-ref.test.js
• tests/llm-openai.test.js
• tests/llm-provider.test.js
• tests/server.test.js
• tests/session-config.test.js

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