[VickyXAI]

Problem

The gateway sometimes serves a different model than the one requested:

• Health reroute: a free model whose health breaker is open is rerouted before dispatch.
• Cascade fallback: a failed free call falls through the free cascade.

In both cases SmartChatResponse.Model still reported the id the router requested. Since #44 routes the free tiers to primaries whose breakers can be open, this is the common case on the free profile. Live example: requesting nvidia/nemotron-3.5-lightning was answered by nvidia/nemotron-3-super-120b.

What the gateway sends

Checked read-only in blockrun origin/main, src/app/api/v1/chat/completions/route.ts:

• Health reroute: X-Health-Reroute: true, X-Original-Model, and X-Served-Model (route.ts:3421-3424).
• Cascade or rescue fallback: X-Original-Model and X-Fallback-Model (route.ts:3441-3442, 3552, 3621, 3685, 4811).
• The response body's model is the served model in both cases (confirmed live).

Change

• SmartChatResponse.Model is now the model that answered. It is resolved in this order:
  1. the response body's model
  2. the X-Served-Model header
  3. the X-Fallback-Model header
  4. the requested id
• New field SmartChatResponse.RequestedModel (json:"requested_model") holds the router's pick. Routing.Model already held it and is unchanged.
• The change is additive: no existing field changed name, type or JSON key.
• Internals: ChatCompletion now wraps a new unexported chatCompletionHeaders, which uses the existing doRequestHeaders, so SmartChat can read the response headers. Its public behaviour is unchanged. When a response comes from the local cache, headers are nil and the body's model still applies.
• README and the CHANGELOG Unreleased entry are updated.

Tests

router_served_model_test.go uses an httptest server to cover five cases:

• no reroute
• body model differs from the request
• header only: health reroute (X-Served-Model)
• header only: cascade fallback (X-Fallback-Model)
• no body model and no headers (falls back to the requested id)

Each case also asserts RequestedModel and Routing.Model. A separate test checks the JSON keys stay additive.

Checks

• go build ./...: ok
• go vet ./...: ok
• go test ./...: ok
• BLOCKRUN_LIVE_CATALOG=1 go test -run TestRoutingTableMatchesLiveCatalog .: ok