small_model is silently ignored once its model is marked deprecated in the catalog #51159

Description

If the model set as small_model is later marked deprecated in the catalog, OpenCode drops it from the provider and Provider.getSmallModel turns the lookup error into undefined without logging anything. The title agent then quietly falls back to the session's main model.

The config never changes, so from the user's side this is a silent behavior change on the day the catalog updates. For me it was deepseek/deepseek-v4-flash, marked deprecated in anomalyco/models.dev#7727. The DeepSeek API still accepts that alias (it is served by V4.1 Flash), so the configured model itself kept working; only OpenCode stopped using it. From then on every session title ran on my main model, Claude Opus 5.5 through a subscription proxy, instead of DeepSeek. That spent subscription quota and triggered a title/first-turn race in the proxy (rynfar/meridian#1024), which took a while to trace back to this one config line.

The same id used as the main model fails loudly, with a useful hint (from the log):

ProviderModelNotFoundError: Model not found: deepseek/deepseek-v4-flash. Did you mean: deepseek-flash, deepseek-v4-pro?

As small_model it produces nothing, not even with --log-level DEBUG.

Relevant code on dev (0f54984):

• deprecated models are deleted from the provider: provider.ts#L1694
• getSmallModel catches ProviderModelNotFoundError and returns undefined: provider.ts#L1942-L1946
• the title agent then uses the session model: prompt.ts#L218-L221

I understand the fallback itself is intentional, so I'm not asking to remove it, only to make it visible: a WARN in that catchTag, ideally reusing the "Did you mean" suggestions that getModel already computes. #31092 proposed the warning part for #31042, but both were closed automatically by the cleanup bots before anyone reviewed them.

Plugins

[email protected], context-mode (loaded globally; the repro below does not go through them)

OpenCode version

1.18.32

Steps to reproduce

1. In an empty project, add .opencode/opencode.json with DeepSeek credentials configured (opencode models deepseek no longer lists this id):

   { "small_model": "deepseek/deepseek-v4-flash" }

2. Run opencode run --print-logs -m deepseek/deepseek-v4-pro "Reply with exactly: MODEL_OK".
3. The title request streams with the main model, and no log line mentions small_model:

   level=INFO message=stream providerID=deepseek modelID=deepseek-v4-pro small=true agent=title mode=primary
   level=INFO message=stream providerID=deepseek modelID=deepseek-v4-pro small=false agent=build mode=primary
   

Operating System

Windows 11 Pro (10.0.26200)

Terminal

WezTerm with Git Bash (not terminal-specific)