unsubscribe(callback) on a shared live query removes all subscribers and tears down the query

[viswa-abe]

Passing a specific callback to unsubscribe() on a live query removes every subscriber, not just that callback, and destroys the query's backing state. With two callbacks subscribed to one live.query, calling unsubscribe(cbA) and then committing a mutation delivers nothing to cbB; a second mutation delivers nothing either, so the query is fully torn down rather than left running for the remaining subscriber.

Environment:

• @electric-sql/pglite 0.5.4 (latest on npm), also present on current main
• Node v22.23.1, Linux

Reproduction:

npm i @electric-sql/pglite@0.5.4
node repro.mjs

repro.mjs

import { PGlite } from '@electric-sql/pglite'
import { live } from '@electric-sql/pglite/live'

const db = await PGlite.create({ extensions: { live } })
await db.exec(`CREATE TABLE t (id int primary key, v text);`)

let aCalls = 0, bCalls = 0
const cbA = () => { aCalls++ }
const cbB = () => { bCalls++ }

const sub = await db.live.query('SELECT * FROM t ORDER BY id', [], cbA)
sub.subscribe(cbB)
await new Promise((r) => setTimeout(r, 100))

// remove only cbA; cbB is still a subscriber
await sub.unsubscribe(cbA)
const bBefore = bCalls

await db.exec(`INSERT INTO t VALUES (1, 'a');`)
await new Promise((r) => setTimeout(r, 100))
console.log(`cbB fired ${bCalls - bBefore} time(s) after the INSERT; expected 1`)

await db.close()

Observed output:

cbB fired 0 time(s) after the INSERT; expected 1

Expected: cbB should keep receiving updates. The live-query docs describe multiple consumers sharing one live query, and the API exposes unsubscribe(callback) specifically to remove one callback while leaving the others subscribed. https://pglite.dev/docs/live-queries

This appears to come from the selective-unsubscribe filter in packages/pglite/src/live/index.ts (lines 243, 506, 666), which reads callbacks = callbacks.filter((callback) => callback !== callback). The arrow's parameter shadows the outer callback, so the predicate is always false, the filtered array is empty, and the length === 0 branch then drops the view and deallocates the query's state. Binding the predicate to the outer callback ((cb) => cb !== callback) would remove only the named one.