Channel.decodeText corrupts UTF-8 across chunk boundaries

[skoshx]

What version of Effect is running?

effect@4.0.0-beta.66

What steps can reproduce the bug?

Single file, single dependency. Crafts one JSONL line where an em-dash (e2 80 94) straddles byte 65535/65536 — the default
fs.stream chunk boundary — then runs it through Ndjson.decodeSchema.

// repro.mjs
import { Effect, FileSystem, Schema, Stream } from "effect"
import * as Ndjson from "effect/unstable/encoding/Ndjson"
import * as NodeServices from "@effect/platform-node/NodeServices"
import { writeFileSync } from "node:fs"

const filler = "x".repeat(65526)
const line = JSON.stringify({ msg: `${filler}—end` }) + "\n"
writeFileSync("/tmp/repro.jsonl", line, "utf8")

const Row = Schema.Struct({ msg: Schema.String })

const program = Effect.gen(function* () {
  const fs = yield* FileSystem.FileSystem
  const rows = yield* fs.stream("/tmp/repro.jsonl").pipe(
    Stream.pipeThroughChannel(
      Ndjson.decodeSchema(Row)({ ignoreEmptyLines: true }),
    ),
    Stream.runCollect,
  )
  const tail = rows[0].msg.slice(-10)
  console.log("tail (chars):", JSON.stringify(tail))
  console.log("tail (bytes):", Buffer.from(tail, "utf8").toString("hex"))
  console.log("contains em-dash:", tail.includes("\u2014"))
})

await Effect.runPromise(program.pipe(Effect.provide(NodeServices.layer)))

{
  "type": "module",
  "dependencies": {
    "@effect/platform-node": "4.0.0-beta.66",
    "effect": "4.0.0-beta.66"
  }
}

pnpm i && node repro.mjs

Expected

tail (chars): "xxxxx—end"
tail (bytes): 7878787878e28094656e64
contains em-dash: true

Actual

tail (chars): "xxxxx��end"
tail (bytes): 7878787878efbfbdefbfbd656e64
contains em-dash: false

What is the expected behavior?

Expected

tail (chars): "xxxxx—end"
tail (bytes): 7878787878e28094656e64
contains em-dash: true

What do you see instead?

Actual

tail (chars): "xxxxx��end"
tail (bytes): 7878787878efbfbdefbfbd656e64
contains em-dash: false

Additional information

a similar bug was fixed in the Stream module, but looks like Channel.decodeText was missed