Zen: x-preview-f-free fails 100% of attempts from one project directory while sibling directories pass simultaneously

Description

Since ~2026-08-25 01:05 UTC, every request to x-preview-f-free (zen/v1) launched from one specific project directory fails within ~4-8 s with:
503 {"error":{"type":"server_error","message":"Error from provider (Console): Upstream request failed: Endpoint is unavailable."}}
while other directories on the same machine/key/binary pass intermittently during the same minutes.

One day of data, same key/machine/binary, variant max:

A brand-new session in Z failed on its first try while X passed repeatedly at overlapping timestamps. Sessions in Z on another zen model streamed immediately; switching back resumed instant failures. Z worked normally on this model ~10 h before onset - no local files changed in between.

Suspect something assembled from Z's project context (system prompt / project instructions) trips the Ox Alpha upstream deterministically, stacked on top of the intermittent flakiness tracked in #44300. Fresh-session control rules out sticky-hash luck.

Plugins

slim-tools.ts, caveman, ponytail.mjs (global)

OpenCode version

1.18.21

Steps to reproduce

Not reproducible on demand outside the affected directory - observational over 481 requests:

1. During the degraded window, send single-turn messages from new sessions in different local directories on x-preview-f-free.
2. Affected directory fails every attempt; others fail intermittently only.
3. Switching the affected directory's sessions to another zen model streams immediately; switching back re-fails instantly.

Operating System

Windows 11 x64

Terminal

Windows Terminal