feat: add WAL extension and logical decoding startup config

[sorenbs]

Summary

This PR adds a small, ppg-dev-focused WAL API to PGlite using built-in PostgreSQL logical decoding (pgoutput) and SQL decoding functions.

This is part of a temporary Prisma fork strategy to unblock ppg-dev while we prepare upstream PRs.

What we are building (ppg-dev scoped)

A minimal PGlite extension namespace with:

• wal.ensure({ slot, publication, tables? })
• wal.poll({ slot, publication, maxChanges?, protoVersion? }) -> WalEvent[]

And a pgoutput decoder that emits typed events:

• begin
• commit
• relation
• insert
• update
• delete

Why this approach

For ppg-dev we want the simplest reliable path:

• Use PostgreSQL standard pgoutput format.
• Use SQL logical decoding functions (pg_create_logical_replication_slot, pg_logical_slot_get_binary_changes) instead of implementing replication protocol streaming.
• Avoid idle/background polling: ppg-dev polls only immediately after writes it already observes.

Changes in this PR

1) Startup Postgres config support in PGlite

• Added postgresConfig?: Record<string, string | number | boolean> to PGliteOptions.
• Startup args now append -c key=value entries from postgresConfig.

Files:

• packages/pglite/src/interface.ts
• packages/pglite/src/pglite.ts

2) WAL extension implementation

• Added new extension module implementing:
  • ensure: validates wal_level=logical, ensures publication and logical replication slot (pgoutput plugin).
  • poll: fetches binary changes and decodes pgoutput into typed events.
• Includes pgoutput binary decoder and relation cache handling.

File:

• packages/pglite/src/wal/index.ts

3) Public exports

• Exported wal extension and WalEvent type from package index.

File:

• packages/pglite/src/index.ts

4) Test coverage

Added comprehensive coverage for:

• postgresConfig startup behavior (wal_level, replication limits)
• ensure behavior and guardrails
• insert/update/delete decoding via logical decoding SQL path
• table-scoped publication behavior
• decoder strictness/error paths and tuple mapping edge cases

File:

• packages/pglite/tests/wal.test.ts

5) Test config aliasing for local pg-protocol source resolution

File:

• packages/pglite/vitest.config.ts

Validation

• Ran full packages/pglite test suite successfully.
• WAL-specific tests pass with logical slot creation + change polling + pgoutput decoding.

ppg-dev usage pattern this enables

For each write query:

1. Execute write on PGlite.
2. Call db.wal.poll(...) immediately.
3. Broadcast/apply returned events.

No LISTEN/NOTIFY or idle polling loop is required for this scoped use case.

Temporary fork publishing strategy

This branch is intended to be published as a temporary Prisma-owned package (or npm alias target) so ppg-dev can depend on deterministic builds while upstream work proceeds.

Upstream merge plan

1. Upstream runtime fixes first in electric-sql/postgres-pglite (paired repo PR).
2. Upstream postgresConfig option and WAL extension in electric-sql/pglite with this same minimal scope.
3. Keep follow-up items separate from initial merge:
   • richer batching semantics
   • optional expanded tuple behavior based on replica identity
   • any additional filtering ergonomics
4. After upstream releases include these changes, switch ppg-dev dependency back to upstream package and drop fork override.

Cross-repo dependency

This PR depends on the wasm runtime/linking fixes in:

• prisma/postgres-pglite branch wal

(Companion PR link will be attached in comments.)

Companion PR: prisma/postgres-pglite#1