Expose materialization source metadata

[marcus-pousette]

Summary

• add optional source metadata to each materialization change
• expose the causative operation as source.operation.id.{replica,counter} plus source.operation.lamport
• preserve source through core coalescing and the SQLite/wa-sqlite and Postgres adapters
• extend conformance coverage so local materialization events expose the operation that caused the visible change

Before:

{
  headSeq: 42,
  changes: [
    {
      kind: 'payload',
      node: '...',
      payload: new Uint8Array([...]),
    },
  ],
}

After:

{
  headSeq: 42,
  changes: [
    {
      kind: 'payload',
      node: '...',
      payload: new Uint8Array([...]),
      source: {
        operation: {
          id: {
            replica: new Uint8Array([...]),
            counter: 7,
          },
          lamport: 123,
        },
      },
    },
  ],
}

Notes

• source.operation.id.replica is a low-level CRDT replica id, not auth/user identity
• source.signer.publicKey is reserved in the TypeScript shape for a later auth-aware follow-up
• source is optional because conservative catch-up can derive visible changes from rebuilt state instead of one exact operation
• this gives apps enough metadata to maintain local projections such as lastUpdated or updatedBy without putting that bookkeeping into payload bytes