Description

Bug: Session auto-naming silently fails when small_model is invalid

Summary

When small_model is configured to an invalid model ID (example: openai/gpt-nano), session auto-title generation fails, but the failure is silent in normal UX. The session keeps the default title (New session - ...) and only an unhandled rejection is logged.

Environment

• Source analysis branch/commit: dev @ 8f2d8dd47a45a4b3972ac8badc09cc280f84b838

Why this happens (source-level)

1. ensureTitle() is invoked without await and without a top-level .catch(...):
   • packages/opencode/src/session/prompt.ts:329
2. ensureTitle() resolves model with Provider.getSmallModel(...) first:
   • packages/opencode/src/session/prompt.ts:1923
3. If cfg.small_model is set, getSmallModel() does strict lookup and returns getModel(...) directly:
   • packages/opencode/src/provider/provider.ts:1215
4. Invalid small_model throws ProviderModelNotFoundError, which bubbles to unhandled rejection path:
   • packages/opencode/src/index.ts:36

Suggested fix (error handling + resilience)

1) Prevent silent failure at call site

Wrap title task invocation in a safe fire-and-forget pattern:

void ensureTitle({...}).catch((err) => {
  log.error("failed to generate session title", { error: err })
  // optionally emit a non-blocking session warning event
})

2) Harden getSmallModel() against invalid small_model

If cfg.small_model is invalid:

• log a warning with configured value,
• fall back to provider heuristics (haiku/flash/gpt-5-nano) or current conversation model,
• avoid throwing in non-critical title-generation path.

3) Optional startup/config validation

Validate small_model exists at startup or config load and surface a clear warning immediately.

User workaround

Use a valid small_model ID. For example:

{
  "small_model": "openai/gpt-5-nano"
}

After switching to a valid ID, auto-naming works again.

Related issues

• OpenCode Desktop Session Name is no longer written with AI at times
• Show error message when session auto-naming fails due to disabled small model

Plugins

No response

OpenCode version

1.2.10

Steps to reproduce

Reproduction

1. Set an invalid small model in config:

{
  "$schema": "https://opencode.ai/config.json",
  "small_model": "openai/gpt-nano"
}

2. Start OpenCode and create a new session.
3. Send the first user message.
4. Wait for auto-title generation.

Expected behavior

• Either:
  • Session title is auto-generated successfully, or
  • User receives a visible warning/error that title generation failed.
• The failure should not be silent.

Actual behavior

• Session title remains default (New session - ...).
• No clear user-facing error for title generation failure.
• Log shows only unhandled rejection:

ERROR ... service=default e=ProviderModelNotFoundError rejection

Screenshot and/or share link

No response

Operating System

macOS 26.3

Terminal

Ghostty