Session idles silently when a turn ends with stop and no model output #50250

Description

A provider can end a stream early with a clean stop finish and 0 output tokens — no error, no text, no tool calls. opencode treats this as a normal end-of-turn: the prompt loop exits, the session idles, and the TUI shows nothing. From the user's perspective the session just stops mid-task, and nothing in the logs or transcript distinguishes the truncated turn from a deliberate completion.

We hit this with a self-hosted glm-5.3-fp4 endpoint. Two turns in one session (a coding turn and a reviewer subagent turn) ended with reason: "stop", output: 0, and reasoning cut mid-sentence at the same content position ~3s into each step. Step-finish parts from the session DB:

{"reason":"stop","type":"step-finish","tokens":{"total":126576,"input":559,"output":0,"reasoning":706,...}}
{"reason":"stop","type":"step-finish","tokens":{"total":126126,"input":123006,"output":0,"reasoning":1841,...}}

No errors, aborts, or retries in the server log — the provider returned a clean stop both times. Sending a fresh user message recovers, which points to a deterministic premature stop rather than a transient network failure.

There is currently no signal at all when this happens. A log warning and/or a UI indicator when a turn ends with stop, no error, and no visible output would make these turns diagnosable.

Plugins

None

OpenCode version

1.18.31

Steps to reproduce

Not reliably reproducible on demand — it depends on the provider emitting a premature clean stop. The signature in the session DB is an assistant message with finish: "stop", no error, no text or tool parts, and step-finish tokens with output: 0 (in our case with nonzero reasoning).

Operating System

macOS