fix(model-resolution): add free-model fallback for free-only provider setups (fixes #1883)

[mrosnerr]

Fixes #1883

Summary

Subagents resolve to paid models when only free providers are configured. This adds a free-model fallback that appends free opencode models to the fallback chain when the user only has free models available.

Paid users are unaffected — detection is based on availableModels, not connectedProviders, so Zen subscribers don't get downgraded.

Free model list is sourced from a generated JSON snapshot refreshed by the existing weekly refresh-model-capabilities workflow. Model rotation is a JSON edit, not a code change.

Changes

File	Change
free-model-fallback.ts	Free-only detection + append strategy
model-selection.ts	Wire in free-only logic before fallback chain resolution
model-selection-input.ts	Extract existing helpers (pure refactor)
free-opencode-models.generated.json	Generated snapshot from models.dev
script/build-free-models.ts	Standalone build script for the snapshot
script/free-model-extraction.ts	Extraction logic (testable, separate from runner)
refresh-model-capabilities.yml	Also runs build:free-models on weekly cron
*test.ts (×3)	Unit, integration, and extraction tests

Testing

• bun run build:free-models — generates snapshot, verified output matches live models.dev/api.json
• bun run typecheck — clean
• bun run build — clean
• bun run test:model-capabilities — 58 pass (includes extraction edge cases + snapshot guardrails)
• All 41 model-selection tests pass, 0 regressions

Context

Builds on #3529 (closed by @MoerAI, who created the initial module structure).

[cubic-dev-ai]

2 issues found across 11 files

Confidence score: 3/5

• Free-model detection in script/free-model-extraction.ts only checks cost.input, which can misclassify models with billed output or other costs as free and lead to incorrect listings
• Workflow change in .github/workflows/refresh-model-capabilities.yml adds Opencode snapshot generation without the required cloning/reading step, which may break the intended automation flow
• Given the two medium-severity issues, there is some risk of functional inaccuracies or workflow failures, so the merge is not risk-free
• Pay close attention to script/free-model-extraction.ts - incomplete cost checks, and .github/workflows/refresh-model-capabilities.yml - missing Opencode source read step.

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="script/free-model-extraction.ts">

<violation number="1" location="script/free-model-extraction.ts:18">
P2: Free-model detection is incomplete because it only checks `cost.input` and can include models with non-zero output or other billed costs.</violation>
</file>

<file name=".github/workflows/refresh-model-capabilities.yml">

<violation number="1" location=".github/workflows/refresh-model-capabilities.yml:32">
P2: Custom agent: **Opencode Compatibility**

Opencode snapshot generation is added without cloning/reading anomalyco/opencode as required by the rule.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

0 issues found across 2 files (changes from recent commits).

_{Requires human review: Auto-approval blocked by 1 unresolved issue from previous reviews.}

[code-yeongyu]

[sisyphus-bot]

PR sweep first-pass triage on dev.

• Author: mrosnerr
• Title: fix(model-resolution): add free-model fallback for free-only provider setups (fixes #1883)
• Closing issues: Bug: Should use only free models when no providers configured #1883
• Review decision: none yet
• Mergeable state: CONFLICTING (rebase needed)
• CI status: green / no failing checks

Needs rebase + review. Please rebase onto current dev first; then a review can land cleanly.

Assigning code-yeongyu so the maintainer can prioritize a focused review of this PR. If the linked issue above has been triaged, the verdict there is the authoritative direction for this change.

[code-yeongyu]

[sisyphus-bot] Hi mrosnerr. 🙏 Thanks for the free-model fallback work for #1883.

Coming back to this from the 5/16 triage queue. Issue #1883 was closed on 5/13 with this PR (#3821) linked as the auto-closer reference, but the PR itself hasn't landed yet, so the underlying behavior is still on the prior path. The PR also currently reports CONFLICTING against current dev (11 files in src/ and src/cli/ have all moved since 5/06).

If you can spare the time, the cleanest next step is a rebase onto current dev (git fetch upstream && git rebase upstream/dev), resolving any conflicts in the model-resolution + provider-detection files. Once it's clean I'll run a focused review against the 463-line diff against the latest provider-availability shape; some of the related files (detect-current-config.ts, provider-availability.ts) were touched by other in-flight PRs this week so the rebase will need to dovetail with those.

If you'd rather close this and re-open a smaller, more focused PR layered on top of the current free-provider detection code, that's also fine. Either way, thanks for caring enough to fix the silent paid-model fallthrough; it's a real footgun for users who deliberately configured only free providers.

[mrosnerr]

@code-yeongyu rebased 👍