fix: resolve undefined prisma.eventOutbox in outbox relayer

[taiwo722-blip]

Overview

This PR fixes a runtime fragility where prisma.eventOutbox resolved to undefined in certain execution paths of the outbox relayer, causing Cannot read properties of undefined (reading 'create') errors during governance test runs. The root cause was inconsistent Prisma client initialization/import paths across the backend modules, which allowed the relayer to reference an uninitialized or differently-instantiated client under load. This change consolidates client initialization and ensures eventOutbox.ts always resolves the shared, initialized Prisma client.

Related Issue

Changes

🔧 Prisma Client Initialization

• [MODIFY] backend/src/prisma.ts

  • Ensures the Prisma client is instantiated once and exported as a stable singleton, so all consumers (including the outbox relayer) resolve the same initialized instance.

• [MODIFY] backend/src/prismaClient.ts

  • Aligns the client accessor with the singleton in prisma.ts, removing the divergent initialization path that could yield an undefined eventOutbox delegate.

• [MODIFY] backend/src/database.ts

  • Routes database access through the shared client so no module constructs or imports a separate/uninitialized Prisma instance.

📤 Outbox Relayer

• [MODIFY] backend/src/eventOutbox.ts
  • References the shared, initialized Prisma client instead of a path that could resolve eventOutbox to undefined, so prisma.eventOutbox.create is always defined when writing events.

Verification Results

npm test -- eventOutbox.test.ts
✅ eventOutbox.test.ts passes

The governance test path that previously logged "Failed to write event to outbox" with Cannot read properties of undefined (reading 'create') now resolves prisma.eventOutbox.create correctly, since all modules share the same initialized client.

Acceptance Criteria	Status
prisma.eventOutbox.create is defined in all runtime paths	✅ Shared initialized client used across prisma.ts, prismaClient.ts, database.ts, and eventOutbox.ts
Outbox relayer no longer throws Cannot read properties of undefined (reading 'create')	✅ Relayer references the consolidated client
eventOutbox.test.ts continues to pass	✅ Existing test suite passes
Prisma client initialization is consistent under load	✅ Single singleton client, no divergent import paths

Closes #1370

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