Agent loop runs 500+ steps with zero user input — no guard against runaway auto-continue

Environment

• opencode TUI, Linux, custom OpenAI-compatible provider (@ai-sdk/openai-compatible → koa-proxy → z.ai GLM-5.2).
• Session storage: ~/.local/share/opencode/opencode.db (SQLite).

What happens

The agent loop auto-continues indefinitely after the model produces its final text response. Two sessions on 2026-09-14:

Log signature: message=loop session.id=… step=N incrementing every ~5 s with no interleaved user activity. All messages share one parentID (the last real user message). The model's outputs in the runaway tail are minimal closings ("(fin)", "🤘", "·") — i.e. the model DID produce text-only terminal responses, but the loop kept stepping instead of ending the turn.

A contributing trigger observed with reasoning models: GLM-5.2 sometimes returns reasoning_content with empty content; opencode logs a placeholder _(reasoning-only response — model emitted no final text)_ and re-prompts. But the runaway also occurs after normal text responses, so the missing piece is a loop guard, not just empty-output handling.

Expected

After an assistant turn with no tool calls and no user input, the loop should end. At minimum: a guard that halts after N consecutive steps without human input or tool activity, surfacing "possible runaway loop — press Enter to continue".

Why doom_loop doesn't catch it

doom_loop permission triggers only on the same tool call repeating 3× with identical input. Text-only runaway has no tool calls at all — no knob covers it.

Repro

1. Use a reasoning-capable model via OpenAI-compatible provider that occasionally returns empty content.
2. Let a task complete; observe step=N climbing in the logs with no input.
3. Loop sustains itself for hours until manually interrupted (Esc).

Workaround

Esc / close session. A pending question tool call also parks the loop (it blocks awaiting real input).