feat(indexer): support multiple contract IDs with per-contract data partitioning

[mohadon0]

Summary

Extends the indexer so one deployment can track and correctly separate data for multiple TrustLink contract instances simultaneously. Previously only a single CONTRACT_ID was supported; now CONTRACT_IDS (comma-separated) is accepted and each contract gets an independent event-processing loop with fully isolated data.

Changes

indexer/src/indexer.ts

• New resolveContractIds() reads CONTRACT_IDS (comma-separated, takes precedence) or falls back to CONTRACT_ID for backward compatibility
• startIndexer spawns a runContractIndexer loop per contract via Promise.all — each loop has its own cursor and checkpoint
• Every db.attestation and db.multisigProposal write now includes contractId
• Revocation and subscription publishes include contractId
• getLastLedger() returns the minimum across all tracked contracts

indexer/src/graphql.ts

• attestations — new optional contractId filter argument
• attestationsByIssuer — new optional contractId filter argument
• issuerStats — new optional contractId filter (returns cross-contract totals when omitted)
• proposals — new optional contractId filter
• trackedContracts — new query returning the list of contract IDs the indexer knows about
• onAttestationCreated subscription — new optional contractId filter
• onAttestationRevoked subscription — new optional contractId filter

indexer/src/schema.graphql

• Attestation and MultisigProposal types gain contractId: String!
• All query/subscription arguments updated to accept optional contractId
• trackedContracts: [String!]! query added
• AttestationRevoked event gains contractId: String!

indexer/prisma/schema.prisma

• Attestation.contractId String (required) with compound indexes
• MultisigProposal.contractId String (required)
• Checkpoint table re-keyed by contractId (was singleton id=1)

indexer/prisma/migrations/0003_multi_contract/migration.sql

• Adds contractId columns to Attestation and MultisigProposal
• Backfills existing rows from the app.legacy_contract_id Postgres setting
• Drops the singleton Checkpoint and recreates it keyed by contractId
• Adds all new composite indexes

indexer/.env.example

• Documents CONTRACT_IDS alongside the old CONTRACT_ID

Acceptance criteria

• One deployment can track two or more contract IDs simultaneously
• Each contract ID has its own checkpoint and event loop (data is correctly partitioned)
• contractId filter argument on all relevant GraphQL queries
• Backward compatible: existing single-CONTRACT_ID deployments continue working unchanged