Bug Report

Description

When using Effect.log() with Logger.pretty in Cloudflare Workers, the first argument is consistently missing from the log output. Single-argument log calls produce no output at all.

Environment

• Effect Version: 3.17.7
• Runtime: Cloudflare Workers (Wrangler 3.114.13)
• Logger: Logger.pretty

Expected Behavior

All arguments passed to Effect.log() should be logged:

Effect.log("First", "second", "third") // Should show: "First second third"
Effect.log("Single test") // Should show: "Single test"

Actual Behavior

First argument is missing, single arguments disappear:

Effect.log("First", "second", "third") // Shows: "second third"
Effect.log("Single test") // Shows: (nothing)

Reproduction

Repository: https://github.com/schickling-repros/2025-08-effect-pretty-logger-cloudflare

Steps:

1. Clone the reproduction repo
2. Run pnpm install && pnpm dev
3. Execute curl http://localhost:8787
4. Observe missing first arguments in console

Comparison with Default Logger

The default logger works correctly and shows all arguments as separate message= fields:

timestamp=2025-08-18T13:43:37.844Z level=INFO fiber=#0 message="First argument" message="second argument" message="third argument"

Impact

• Silent data loss in logging output
• Debugging difficulties as primary context is often the first argument
• Single-argument logs completely disappear

Code Sample

import { Effect, Logger } from "effect"

const program = Effect.gen(function* () {
  yield* Effect.log("Context:", "important", "data") // Only shows "important data"
  yield* Effect.log("Debug info") // Shows nothing
})

await Effect.runPromise(
  program.pipe(Effect.provide(Logger.pretty))
)

This appears to be specific to the Cloudflare Workers environment, as the bug doesn't occur with the default structured logger.