feat: add OpenRouter adapter

[ChiragAgg5k]

Summary

• Adds OpenRouter adapter extending OpenAI with support for OpenRouter's API endpoint, custom headers (HTTP-Referer, X-Title), and provider-prefixed model ID normalization
• Introduces OpenRouter\Models class with named constants for major providers (OpenAI, Anthropic, Google, Meta, DeepSeek, Mistral, xAI) and the full 346-model catalog
• Adds scripts/sync-openrouter-models.php to regenerate model constants from the live OpenRouter API
• Refactors OpenAI adapter to extract createClient() and normalizeModelForCompatibilityChecks() for clean subclassing

Test plan

• Verify OpenRouter adapter constructs with default model and endpoint
• Verify arbitrary provider-prefixed model IDs (e.g. meta-llama/llama-3.3-70b-instruct) are accepted
• Run ConversationOpenRouterTest with LLM_KEY_OPENROUTER set to confirm live API connectivity
• Run php scripts/sync-openrouter-models.php to verify model sync generates valid PHP
• Confirm existing OpenAI adapter tests still pass after the refactor

[greptile-apps]

Greptile Summary

This PR adds an OpenRouter adapter that extends the OpenAI adapter, routing requests through OpenRouter's unified API endpoint. The core adapter logic is clean and well-structured: createClient() is overridden to inject the optional HTTP-Referer and X-Title attribution headers, and normalizeModelForCompatibilityChecks() correctly strips provider prefixes (e.g. openai/gpt-4o → gpt-4o) so that OpenAI-specific token-limit and temperature constraints are applied only when routing to compatible OpenAI models.\n\nKey additions:\n- OpenRouter adapter with clean subclassing of the refactored OpenAI base\n- OpenRouter\\Models class with 115 named constants for curated providers and a full 346-entry MODELS catalog\n- scripts/sync-openrouter-models.php to regenerate Models.php from the live OpenRouter API\n- Integration test, env/compose wiring, and README documentation\n\nThe main concerns are all in the sync script: the DEFAULT_MODEL constant reference is hardcoded with no validation guard (could silently produce broken PHP on a future sync run), toConstantName() has a double-prefix latent bug, and generated string literals are not single-quote-escaped.

Confidence Score: 4/5

Safe to merge; the current generated Models.php is correct and the adapter logic is sound — the main fix needed is a validation guard in the sync script.

The adapter and test code are well-implemented with no runtime issues in the current state. The one targeted fix is adding a guard in sync-openrouter-models.php so future runs cannot silently produce a Models.php with an unresolvable constant reference.

scripts/sync-openrouter-models.php — hardcoded DEFAULT_MODEL reference and toConstantName double-prefix bug.

Important Files Changed

Filename	Overview
src/Agents/Adapters/OpenRouter.php	New adapter extending OpenAI; cleanly overrides createClient() to inject HTTP-Referer/X-Title headers and normalizeModelForCompatibilityChecks() to strip provider prefixes before OpenAI-specific token/temperature constraint checks.
src/Agents/Adapters/OpenAI.php	Refactored to extract createClient() and normalizeModelForCompatibilityChecks() as protected overridable methods; no behavioral changes to the existing OpenAI adapter.
scripts/sync-openrouter-models.php	New code-generation script; has a hardcoded DEFAULT_MODEL reference with no validation guard, a double-prefix bug in toConstantName(), and no single-quote escaping for generated string literals.
src/Agents/Adapters/OpenRouter/Models.php	Generated model catalog with 115 named constants and a 346-entry MODELS array; currently correct and MODEL_OPENAI_GPT_4O is present as required by DEFAULT_MODEL.
tests/Agents/Conversation/ConversationOpenRouterTest.php	Simple integration test extending ConversationBase; correctly reads LLM_KEY_OPENROUTER from env and constructs the adapter with a named model constant.
.env.example	Adds LLM_KEY_OPENROUTER placeholder and fixes missing newline at end of file.
docker-compose.yml	Passes LLM_KEY_OPENROUTER env var into the test container, consistent with other adapter keys.
README.md	Adds OpenRouter usage section with code example and feature notes; straightforward documentation update.

_{Reviews (1): Last reviewed commit: "feat: add OpenRouter adapter" | Re-trigger Greptile}