Free tier: agent=compaction and agent=title fail with "free tier can only be used from within OpenCode"; agent=build works #49592

Description

On the Zen free tier (provider "opencode", model opencode/big-pickle), normal dialog requests (agent=build) work consistently, but background requests fail within ~1 second with:

Error from provider (Console): OpenCode's free tier can only be used from within OpenCode

Reproduced in DEBUG logs, same client/process, seconds apart from successful build requests:

• agent=title (session title generation) — fails on every new session
• agent=compaction (auto-compaction when context is nearly full) — fails

Impact: auto-compaction never succeeds, so long sessions eventually hit the context limit and stop working. This breaks long multi-session work.

Plugins

./error-logger.js (local, only writes logs; does not touch requests/headers).

OpenCode version

1.18.31 (official release) — OpenCode Desktop and npm CLI; reproduces on both.

Steps to reproduce

1. Use the Zen free tier: provider "opencode", model opencode/big-pickle (default config, no header/baseURL overrides).
2. Start a new session → title generation (agent=title) fails within ~1s.
3. Grow a session until auto-compaction triggers → agent=compaction fails with the same error.
4. Run a normal message (agent=build) to the same provider/model → succeeds.

Screenshot and/or share link

No response

Operating System

Windows 10

Terminal

OpenCode Desktop (UI); Windows Terminal / PowerShell 7 for CLI tests