Summary

When Z.AI GLM-5 (via OpenRouter, openai-completions provider) returns stop_reason: "error" with zero tokens, OpenClaw does not trigger failover to the configured fallback model. The run ends silently with isError=true and no response is delivered to the user.

This is distinct from #18453 (which added abort to the failover regex) and #16252 (which addresses mapStopReason throwing on unknown values). The TIMEOUT_HINT_RE regex was extended to match stop reason: abort but not stop reason: error.

Steps to reproduce

1. Configure GLM-5 as primary with a fallback model (e.g. claude-sonnet-4-6)
2. Wait for GLM-5 to return an API-level error (intermittent, ~1-2x/day)
3. The API returns finish_reason: "error" with input: 0, output: 0 tokens
4. Expected: failover to fallback model
5. Actual: run ends with isError=true, no response, no failover

Evidence from logs

[agent/embedded] embedded run agent end: runId=fd64c0ab isError=true error=Unhandled stop reason: error

Session JSONL shows: "api":"openai-completions","provider":"openrouter","model":"z-ai/glm-5" with "stopReason":"error" and usage: {input: 0, output: 0}.

After every such error, the next session entry is a user message hours later - confirming zero failover, zero response.

6 occurrences across 3 days (2026-02-23 to 2026-02-26), affecting both dev agent and main agent sessions.

Root cause

The failover detection regex at dist/reply-*.js (function isFailoverErrorMessage / TIMEOUT_HINT_RE):

const TIMEOUT_HINT_RE = /timeout|timed out|deadline exceeded|context deadline exceeded|stop reason:\s*abort|reason:\s*abort|unhandled stop reason:\s*abort/i;

This matches abort but not error. The "Unhandled stop reason: error" message falls through without triggering failover.

Suggested fix

Extend the regex to also match error:

const TIMEOUT_HINT_RE = /timeout|timed out|deadline exceeded|context deadline exceeded|stop reason:\s*(abort|error)|reason:\s*(abort|error)|unhandled stop reason:\s*(abort|error)/i;

Or more broadly, treat any stop_reason that is not stop/length/tool_calls/content_filter AND has zero output tokens as a failover-eligible condition.

Related issues

• [Bug]: fix(failover): Add "abort" to timeout error patterns for fallback triggering #18453 (closed) - Added abort to failover regex, but not error
• pi-ai: Unhandled stop reason from Z.AI GLM-5 (openai-completions provider) #16252 (open) - mapStopReason throws on unknown values from GLM-5
• [Bug]: Uppercase finish_reason from non-OpenAI providers causes "Unhandled stop reason" error` #15311 (open) - Uppercase finish_reason handling

Environment

• OpenClaw: v2026.2.24
• Model: openrouter/z-ai/glm-5 (openai-completions provider)
• Fallback: anthropic/claude-sonnet-4-6
• OS: macOS Darwin 25.3.0 (arm64)
• Node: v22.22.0
• Per-model thinking: "off" already configured for GLM-5