[boluxx123]

Problem

backend/prisma/schema.prisma declares model IndexerDeadLetterEvent twice (lines 71 and 164), so every Prisma command fails before anything else runs:

Error: Prisma schema validation - (get-dmmf wasm)
Error code: P1012
error: The model "IndexerDeadLetterEvent" cannot be defined because a model with that name already exists.
  -->  prisma/schema.prisma:164

This breaks prisma migrate/generate, the backend build and the Ephemeral full-stack preview job.

It is a botched merge: two branches added a dead-letter feature and both copies survived. The definitions are incompatible — one uses ledger / transactionHash / rawPayload, the other eventType / txHash / ledgerSequence / cursor / payload. The second is the one the code and ADR 0003 use (indexerService.quarantineEvent, the admin dead-letter API and its tests).

Fix — resolve on the ADR-aligned shape

• drop the first, unreferenced IndexerDeadLetterEvent block from schema.prisma;
• drop the superseded migration 20260830000000_add_indexer_dead_letter_event (its CREATE TABLE matches that first shape; the newer 20260926000000_... migration already creates the final table);
• remove the worker's dead deadLetterEvent() method — the only remaining consumer of the first shape. It has not been called since the merge: the poll loop quarantines via quarantineEvent(event, err) (shape B). Its deadLetterMaxRetries field, DEAD_LETTER_MAX_RETRIES_DEFAULT constant and INDEXER_DEAD_LETTER_MAX_RETRIES read go with it, since the live path never consulted the cap.

No behaviour change — the executed quarantine path is untouched.

Verification (local)

npx prisma validate --schema backend/prisma/schema.prisma
  # before: P1012 "a model with that name already exists"
  # after:  "The schema at schema.prisma is valid"

TypeScript parses cleanly after the removal.

Note: backend/docs/SSE_ARCHITECTURE.md still documents INDEXER_DEAD_LETTER_MAX_RETRIES; that env var is not read by the live quarantine path. Left as a follow-up in case the retry cap should be reinstated.