User Story

As the Hybrid Search experiment team, we need to adopt a Search API that supports both lexical and semantic retrieval in a single contract, so that the Android app can reliably run Hybrid Search experiments and compare retrieval approaches.

Description

Adopt (or extend) a Search API that supports lexical search, and semantic retrieval via embeddings, suitable for use in the Android Hybrid Search MVP.

This task establishes the server-side contract required to power all Hybrid Search experiment variants, including:

• Lexical-first layouts
• Semantic-first layouts

This task is a blocking dependency for Hybrid Search downstream UX experimentation.

Requirements

API Availability & Contract

• A Search API endpoint is available to Android that supports:
  • Lexical retrieval
  • Semantic retrieval via embeddings
• API response includes, at minimum:
  • Result type (lexical or semantic)
  • Article title
  • Section identifier (when applicable) that supports highlighting text
  • Excerpt/snippet text (for semantic results)
  • Provenance metadata sufficient for UI labeling
• API supports limiting result counts independently for:
  • Lexical results (e.g., top N)
  • Semantic results (e.g., top N excerpts)

Routing & Fallback Behavior

• API supports or clearly defines:
  • Failure and timeout behavior for semantic retrieval
• In the event semantic retrieval fails or times out:
  • Lexical results are still returned
  • No API error blocks search execution

Performance & Reliability

• Median response latency for hybrid requests is documented

Experiment Support

• API responses include metadata allowing:
  • Experiment variant attribution
  • Retrieval-path logging (including query)
• API can be safely gated behind feature flags or experiment cohorts

Design: TBA
Copy and Translation: TBA