fix(provider): respect configured small_model and add opencode handling to smallOptions

[lexlian]

Issue for this PR

Closes#31042

Type of change

• Bug fix

What does this PR do?

Two bugs cause the symptoms in #31042:

Bug 1 — silent fallback in getSmallModel. When small_model is configured but the model isn't in the provider catalog, the function returns undefined and the title agent silently uses the main model. The fallback behavior is correct (per the documented design and the changelog: "Invalid small_model config no longer poisons fallback paths"), but the user has no way to know their config was ignored. The fix adds a WARN log inside the catchTag handler so users see why.

Bug 2 — smallOptions missing opencode handling. When the title agent calls the LLM with small: true for an opencode provider model, smallOptions returned {} because it only handled openai, openrouter/llmgateway, and venice. The opencode API call was missing the include and reasoningSummary options that options() already sets for opencode, so the request would fail/behave unexpectedly, and the LLM runtime would retry — that's the ~90s delay users reported. The fix adds the same opencode options to smallOptions, scoped to the small-model call path.

Related: #8609 (misleading docs), #14807 (silent failure), #30662 (smallOptions missing opencode).

How did you verify your code works?

cd packages/opencode
bun typecheck # passes
bun test ./test/provider/provider.test.ts # 88/88 pass
bun test ./test/provider/transform.test.ts # 250/250 pass (was 248, +2 new for opencode)
bun test ./test/session/prompt.test.ts -t "loop calls LLM" # passes

To verify the warning manually: set small_model: "opencode/some-invalid-model" in your config, start a session, and you should see a WARN line configured small_model not found, falling back to main model in the logs.

Screenshots / recordings

N/A — no UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[beenotung]

This PR will also fix issue #30662 (Auto session title generation fails for opencode provider models). The root cause is the same - smallOptions() missing opencode provider handling.

[Jackdrakes]

Hi maintainers! Could someone please review and approve the workflow for this PR? It's been waiting for about three weeks now, and we're looking forward to having this feature available. Thanks for your time and all your work on the project!

[github-actions]

Automated PR Cleanup

Thank you for contributing to opencode.

Due to the high volume of PRs from users and AI agents, we periodically close older PRs using automated criteria so maintainers can focus review time on the most active and community-supported contributions.

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[beenotung]

Requesting this PR be reopened. It was auto-closed by the cleanup bot (created >1 month ago, <2 positive reactions), but it fixes a real, still-active bug — it should not have been swept up.

The bug is still present in the latest release (v1.18.19): auto session title generation silently fails for opencode (Zen) provider models, because smallOptions() in src/provider/transform.ts still has no opencode branch (it only handles openai, openrouter/llmgateway, and venice). Issue #30662 is open and multiple users are affected.

This PR is the proper fix: it adds the missing opencode handling to smallOptions() (the same promptCacheKey/include/reasoningSummary that options() already sets), plus a useful warning when a configured small_model isn't found. Author verified: bun typecheck passes, provider tests 88/88, transform tests 250/250 (+2 new for opencode).

A config workaround exists ("small_model": "<working-model>"), but it shouldn't be required — users on the opencode provider hit silent title failure by default. Could a maintainer review and reopen this so it can be merged?