Support Vertex AI publisher URLs for Gemini

[hijos]

Summary

• add Gemini upstream URL handling for Vertex AI / Agent Platform publisher endpoints
• support both bare https://aiplatform.googleapis.com/ and https://aiplatform.googleapis.com/v1/publishers/google upstream bases
• reuse the same URL construction for Gemini key validation
• add unit tests for developer API, Vertex publisher paths, model redirect, and validation

Tests

• npm run build
• go test ./...

Summary by CodeRabbit

• Refactor
  • Improved Gemini upstream request URL handling, including correct Vertex AI Publisher-style path rewriting and consistent forwarding of query parameters during proxying.
• Bug Fixes
  • Fixed API key validation and model-path redirection to use the correct Vertex AI Publisher .../models/<model>:generateContent endpoint and preserve the request body.
• Tests
  • Added unit tests covering upstream URL construction, request mutation behavior, and API key validation across multiple configuration scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: cb09b003-d39f-4893-be8b-1ea0df5cb514

📥 Commits

Reviewing files that changed from the base of the PR and between 24d9aea and fdd2919.

📒 Files selected for processing (2)

• internal/channel/gemini_channel.go
• internal/channel/gemini_channel_test.go

🚧 Files skipped from review as they are similar to previous changes (2)

• internal/channel/gemini_channel_test.go
• internal/channel/gemini_channel.go

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Walkthrough

GeminiChannel gains a BuildUpstreamURL method that trims the /proxy/{groupName} prefix from incoming paths, detects Vertex AI publisher-style base URLs, and conditionally rewrites Gemini-native model paths. ValidateKey is updated to delegate URL construction to BuildUpstreamURL and apply API keys via ModifyRequest. A set of internal path/URL helpers and a new test file covering all URL-rewriting scenarios are added.

Changes

Gemini upstream URL construction and ValidateKey refactor

Layer / File(s)	Summary
BuildUpstreamURL, path helpers, and ValidateKey updates internal/channel/gemini_channel.go	Adds BuildUpstreamURL that resolves the upstream base, trims the proxy prefix, and rewrites paths for Vertex publisher base URLs. Introduces internal helpers (trimProxyPrefix, isVertexPublisherBase, rewriteGeminiNativePath, path-join/normalization). Updates ValidateKey to call BuildUpstreamURL and apply the API key via ModifyRequest.
Unit tests for BuildUpstreamURL, ApplyModelRedirect, and ValidateKey internal/channel/gemini_channel_test.go	New test file with four BuildUpstreamURL cases (developer API preservation, Vertex publisher base conversion, bare aiplatform root conversion, no-duplication), one ApplyModelRedirect path-rewrite case, and one ValidateKey case using an httptest server to assert endpoint path and key query parameter. Includes newTestGeminiChannel and mustParseURL helpers.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐇 Hop hop, the proxy prefix falls away,
Vertex paths rewritten, hip hooray!
BuildUpstreamURL leads the way,
No duplicate publishers shall stay.
The tests all pass — what a fine day! 🌿

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The pull request description is largely incomplete. It lacks the required sections from the template: no linked issue number, no checkbox selection for change type, and no completion of the self-checklist items.	Complete the description template by: (1) adding the related issue number after 'Closes #', (2) selecting the appropriate change type checkbox, (3) checking the testing and documentation checklist items with explanations.
Docstring Coverage	⚠️ Warning	Docstring coverage is 5.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: adding support for Vertex AI publisher URLs for Gemini, which is the core objective of the pull request.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@internal/channel/gemini_channel.go`:
- Around line 49-52: The else branch at line 52 unconditionally prepends
base.Path to requestPath using joinURLPath, causing path duplication when
non-Vertex upstreams are configured with a path component. Before calling
joinURLPath for the non-Vertex case, add a guard check to verify that the
requestPath does not already contain the base.Path value, similar to how the
Vertex branch mitigates this. This ensures that paths like /v1beta are not
duplicated in the final URL when a base upstream path is already present in the
request.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ad050093-0bdc-429a-aab2-aa25488ff266

📥 Commits

Reviewing files that changed from the base of the PR and between 5579930 and 24d9aea.

📒 Files selected for processing (2)

• internal/channel/gemini_channel.go
• internal/channel/gemini_channel_test.go