🤖 feat: add AI app attribution headers

[ThomasK33]

Adds default app attribution headers (HTTP-Referer, X-Title) to all AI SDK provider requests, enabling OpenRouter (and compatible gateways) to attribute mux usage.

• Implemented buildAppAttributionHeaders (case-insensitive merge, never overwrites user-provided values)
• Applied during model creation so all streamText() calls inherit it
• Added unit tests

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📋 Implementation Plan

🤖 Plan: Add app attribution headers to AI SDK streaming (OpenRouter leaderboard)

Goal

Ensure mux’s streamText() calls include app attribution so OpenRouter (and any other compatible gateway) can attribute traffic to mux (e.g., for leaderboards).

For OpenRouter specifically, this means sending these request headers:

• HTTP-Referer: a stable URL for the app (recommended by OpenRouter)
• X-Title: a human-readable app name

Recommended approach (A): Inject attribution headers for all providers in AIService.createModel() (default-on)

Net new product LoC: ~30–55

Why this approach

• Covers every provider (OpenRouter + others) without needing to touch streamText() call sites.
• Future-proof: any future non-streaming usage will automatically carry the same attribution.
• Allows user overrides via providers.jsonc headers (we never overwrite existing HTTP-Referer / X-Title, case-insensitive).

Implementation steps

1. Add centralized constants for mux attribution values

   • Add src/constants/appAttribution.ts exporting:
     • MUX_APP_ATTRIBUTION_TITLE = "mux"
     • MUX_APP_ATTRIBUTION_URL = "https://mux.coder.com"

2. Add a small, tested header-merge helper (defensive + case-insensitive)

   • In src/node/services/aiService.ts, export:
     • buildAppAttributionHeaders(existing?: Record<string, string>): Record<string, string>
   • Behavior:
     • Preserve all unrelated headers.
     • Add missing headers using canonical casing (HTTP-Referer, X-Title).
     • Never overwrite existing values (match keys case-insensitively).

3. Wire into model creation once

   • In AIService.createModel() (after baseUrl → baseURL normalization), apply:
     • providerConfig.headers = buildAppAttributionHeaders(providerConfig.headers)
   • This automatically affects OpenRouter and every other provider branch because they all pass headers through to the provider factory.

4. Unit tests

   • Extend src/node/services/aiService.test.ts with describe("buildAppAttributionHeaders", ...).
   • Test cases:
     • adds both headers when no headers exist
     • adds only the missing header when one is present
     • does not overwrite existing values (including different casing like http-referer, X-TITLE)
     • preserves unrelated headers

Validation

• make typecheck
• bun test src/node/services/aiService.test.ts
• Manual: run a request through any provider (especially OpenRouter) and confirm the headers appear upstream.

Rollout / compatibility notes

• This should be a non-breaking behavioral addition.
• We must ensure we never overwrite user-provided HTTP-Referer / X-Title (case-insensitive check).

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Generated with mux • Model: "unknown" • Thinking: "unknown"

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[ThomasK33]

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