fix: add google provider model transform across all resolution paths

[feelsodev]

Summary

transformModelForProvider() only handled the github-copilot provider, leaving google provider models untransformed. This caused ProviderModelNotFoundError when google/gemini-3-flash was sent to Google's API — the correct model ID is gemini-3-flash-preview.

Problem

When the model resolution pipeline resolves gemini-3-flash for the google provider, it passes through transformModelForProvider() without transformation. Multiple code paths allow the raw model ID to reach the API:

1. Config generation (model-fallback.ts): resolveModelFromChain → transformModelForProvider("google", "gemini-3-flash") → returns unchanged → writes google/gemini-3-flash to config
2. Runtime category-default (model-resolution-pipeline.ts): When availableModels is empty but connected provider exists, normalizedCategoryDefault is returned as-is without transformation
3. First-run fallback (model-resolution.ts): getFirstFallbackModel() constructs ${provider}/${entry.model} without calling transformModelForProvider
4. GitHub Copilot gemini models: The existing .replace() calls for gemini transforms were vulnerable to double-transformation (gemini-3-pro-preview → gemini-3-pro-preview-preview)

Fix

1. Centralized transform function (shared/provider-model-id-transform.ts)

• Added google provider handling with idempotent regex negative lookahead (?!-) to prevent double -preview suffix
• Fixed github-copilot provider gemini transforms to also use idempotent regex (was using plain .replace())
• Single source of truth — imported by both CLI and shared layers (no code duplication)

2. Runtime category-default path (shared/model-resolution-pipeline.ts)

• When availableModels.size === 0 and connected provider exists, now applies transformModelForProvider before returning the category default model

3. First-run fallback path (agents/builtin-agents/model-resolution.ts)

• getFirstFallbackModel() now applies transformModelForProvider when constructing the model ID on first run with no cache

Tests

20 new test cases across 2 files:

Unit tests (src/cli/provider-model-id-transform.test.ts) — 15 total

• Google provider: flash/pro transforms, passthrough for other models, double-transform prevention
• GitHub Copilot provider: claude transforms, gemini transforms, double-transform prevention (new)
• Unknown provider: passthrough behavior

Runtime integration tests (src/shared/model-resolver.test.ts) — 5 new

• Google category-default transform (gemini-3-pro → gemini-3-pro-preview)
• Google category-default transform for flash variant
• Double-transform prevention through full resolution pipeline
• Google fallback-chain transform through runtime pipeline
• Non-gemini-3 model passthrough (no false positives)

Existing tests

• Updated snapshot expectations (22 snapshots reflect correct google transforms)
• Updated existing category-default test to expect transformed model ID
• All 104 tests passing (20 new + 84 existing)

Files Changed

File	Change
src/shared/provider-model-id-transform.ts	Add google provider, idempotent regex for both providers
src/shared/model-resolution-pipeline.ts	Apply transform in category-default connected-provider path
src/agents/builtin-agents/model-resolution.ts	Apply transform in getFirstFallbackModel() first-run path
src/cli/provider-model-id-transform.ts	Re-export from shared (entry point for CLI)
src/cli/provider-model-id-transform.test.ts	15 unit tests including double-transform prevention
src/shared/model-resolver.test.ts	5 runtime integration tests
src/cli/__snapshots__/model-fallback.test.ts.snap	Updated 22 snapshots

[github-actions]

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[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Requires human review: Large changes and new tests added, but 100% regression safety isn't guaranteed yet.}

[feelsodev]

I have read the CLA Document and I hereby sign the CLA

[cubic-dev-ai]

1 issue found across 5 files (changes from recent commits).

Prompt for AI agents (all 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="src/cli/provider-model-id-transform.ts">

<violation number="1" location="src/cli/provider-model-id-transform.ts:1">
P1: GitHub Copilot provider missing suffix guard causing double-preview suffix bug</violation>
</file>

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

[cubic-dev-ai]

P1: GitHub Copilot provider missing suffix guard causing double-preview suffix bug

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At src/cli/provider-model-id-transform.ts, line 1:

<comment>GitHub Copilot provider missing suffix guard causing double-preview suffix bug</comment>

<file context>
@@ -1,20 +1 @@
-	}
-	return model
-}
+export { transformModelForProvider } from "../shared/provider-model-id-transform"
</file context>

[feelsodev]

Thanks for flagging this! This is actually a false positive though 😄

The old code in src/cli/provider-model-id-transform.ts used plain .replace() which was indeed vulnerable to double-transform (gemini-3-pro-preview → gemini-3-pro-preview-preview). But that's exactly what this PR fixes!

The implementation was moved to src/shared/provider-model-id-transform.ts, and it now uses idempotent regex with negative lookahead (?!-):

.replace(/gemini-3-pro(?!-)/g, "gemini-3-pro-preview")
.replace(/gemini-3-flash(?!-)/g, "gemini-3-flash-preview")

This ensures:

• gemini-3-pro → matches (no - follows) → gemini-3-pro-preview ✅
• gemini-3-pro-preview → does NOT match (- follows pro) → stays unchanged ✅

Both github-copilot and google providers use the same idempotent regex, and there are explicit test cases covering double-transform prevention for both providers (see provider-model-id-transform.test.ts lines 67-89, 129-151).

The CLI file is now just a re-export — the actual guard lives in the shared module. No issue here!

[feelsodev]

@cubic-dev-ai review

[cubic-dev-ai]

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[cubic-dev-ai]

No issues found across 8 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: Comprehensive tests ensure correct model transformations with no regressions detected by AI review.}