[AI GATEWAY] Rename openai-header-router policy to llm-header-router in multi provider routing

[Aakashwije]

Purpose

The header-based provider-selection policy added for LLM multi-provider routing in #2586 was named openai-header-router. That name is misleading: the policy is not OpenAI-specific — it selects among any configured LLM provider (Anthropic, Azure OpenAI, Mistral, Gemini, AWS Bedrock, …) based on a request header, writing the choice into metadata["selected_provider"]. The openai- prefix implies an OpenAI-only scope and confuses users wiring up non-OpenAI backends.

This PR renames the policy references to the provider-agnostic llm-header-router, as a follow-up cleanup to the multi-provider routing introduced in #2586.

Relates to #2586.

Goals

• Rename the api-platform references openai-header-router → llm-header-router so they match the renamed policy.
• Keep the change surgical and reference-only — no behavioural change.

Approach

Pure string rename across the only two files in this repo that reference the policy by name (confirmed with a full-clone grep):

File	Change
gateway/examples/openai-multi-provider-proxy.yaml	doc comment + policies[].name → llm-header-router
gateway/gateway-controller/pkg/utils/llm_transformer_multiprovider_test.go	test fixture Name → llm-header-router

No transformer/controller logic is touched. The router policy name is a free-form string in the proxy config, and LLMProviderTransformer.Transform passes user policy names through as-is (it does not validate them against a catalog), so this is a safe reference update. The actual policy rename — directory, Go package, PolicyName constant, policy-definition.yaml, and go.mod module path — lands in the wso2/gateway-controllers policy repository (companion change). Both must merge together, otherwise the example/test reference a policy name the gateway build does not yet contain.

User stories

• As an operator configuring an LLM proxy that fans out to multiple providers, the routing policy name (llm-header-router) reflects that it routes among any provider — not just OpenAI — removing confusion when setting up Anthropic / Gemini / Bedrock / Mistral / Azure OpenAI backends.

Documentation

N/A — no committed product documentation references the policy name; the multi-provider proxy example (gateway/examples/openai-multi-provider-proxy.yaml) doubles as the sample and is updated in this PR.

Automation tests

• Unit tests
  • TestLLMProviderTransformer_TransformProxy_AdditionalProviderAuthIsConditional uses the policy name in its fixture; updated to llm-header-router and passing. Sibling ...TransformerIsConditional also green.
  • No coverage delta — the change is reference-only, not new logic. gofmt clean.
• Integration tests
  • N/A — no integration/BDD test references this policy name; runtime behaviour is unchanged.

Security checks

• Followed secure coding standards (WSO2 secure engineering guidelines)? yes — reference-only rename; no logic or security surface changed.
• Ran FindSecurityBugs plugin and verified report? N/A — no Java / security-relevant code changed (Go + YAML string rename only).
• Confirmed this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes — verified; the diff is a 3-line string rename across 2 files.

Samples

gateway/examples/openai-multi-provider-proxy.yaml — the multi-provider proxy sample now attaches the router as llm-header-router. Applied via ap gateway apply -f gateway/examples/openai-multi-provider-proxy.yaml (or POST /llm-proxies on the gateway-controller) once the renamed policy is present in the gateway build.

Related PRs

• [AI Gateway] Add multi-provider routing for LLM proxies #2586 — [AI Gateway] Add multi-provider routing for LLM proxies (introduced the openai-header-router policy this renames).
• [FIX] Address further review comments on multi-provider routing #2590 — [FIX] Address further review comments on multi-provider routing (prior review-comment thread on the same branch).
• Companion policy rename in wso2/gateway-controllers (the actual llm-header-router policy source) — add link — must merge in lockstep with this PR.

Test environment

• Go 1.26.x
• macOS (darwin) / Linux
• JDK / Database / Browser: N/A (no Java, DB, or UI changes)
• Verified: go test ./pkg/utils/ -run TestLLMProviderTransformer_TransformProxy_AdditionalProvider → PASS

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