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ADR-PROTO-001: Defer Kafka to architecture diagram only

Status: Accepted Source: prd-v2.1.md §C.8

Context

PRD v2 §B.4 specifies Kafka as event transport. For the 1-day prototype, building Kafka costs hours that should go to Databricks integration, while delivering zero demonstrable value in a 90-second demo (sub-second transport is invisible on screen).

Decision

Do not build Kafka in the prototype. Show it in the architecture diagram with a "Phase 2 — production transport" annotation. The defense in Q&A is: "the prototype proves the more uncertain piece (data binding); Kafka is straightforward production wiring."

Consequences

  • Hours saved go to Databricks integration where they produce visible demo value.
  • Narrative continuity preserved between v1.x and full v2 sprint.
  • Risk: a sponsor asks "why isn't Kafka working?" — answered by docs/whats-mocked-in-prototype.md and prd-v2.1.md §B.4.
  • This ADR does NOT supersede ADR-V2-001; that ADR remains the production decision.

Cross-references