fix: vertex count tokens unsupported fields

[TejasGhatte]

Summary

The Vertex countTokens endpoint rejects several fields that are valid in generateContent requests, causing 400 errors. Previously, the field-stripping logic incorrectly removed generationConfig and systemInstruction, which the countTokens endpoint actually supports and uses to produce accurate token counts. This PR fixes the set of fields being stripped and consolidates the logic into a dedicated helper.

Changes

• Introduced stripVertexCountTokensUnsupportedFields to replace the inline ad-hoc field deletions in CountTokens. The new helper drops only the fields the countTokens endpoint actually rejects: toolConfig, safetySettings, cachedContent, serviceTier, and labels.
• Removed the incorrect stripping of generationConfig and systemInstruction, both of which are valid and meaningful to the countTokens endpoint.
• Added unit tests covering: fields that should be preserved, fields that should be dropped, and a nil/empty body edge case.

Type of change

• Bug fix
• Feature
• Refactor
• Documentation
• Chore/CI

Affected areas

• Core (Go)
• Transports (HTTP)
• Providers/Integrations
• Plugins
• UI (React)
• Docs

How to test

go test ./core/providers/vertex/...

Verify that TestStripVertexCountTokensUnsupportedFields passes, confirming that systemInstruction, tools, and generationConfig survive stripping while toolConfig, safetySettings, cachedContent, serviceTier, and labels are removed.

Screenshots/Recordings

N/A

Breaking changes

• Yes
• No

Related issues

Security considerations

No security implications. This change only affects which JSON fields are forwarded to the Vertex countTokens endpoint.

Checklist

• I read docs/contributing/README.md and followed the guidelines
• I added/updated tests where appropriate
• I updated documentation where needed
• I verified builds succeed (Go and UI)
• I verified the CI pipeline passes locally if applicable

[coderabbitai]

📝 Walkthrough

Walkthrough

Vertex CountTokens request sanitization now uses a centralized helper that removes unsupported generateContent fields. A new test covers passthrough, field removal, and empty input behavior.

Changes

Vertex CountTokens sanitization

Layer / File(s)	Summary
Centralize CountTokens field stripping core/providers/vertex/vertex.go	A helper removes fields rejected by Vertex countTokens, and CountTokens uses it instead of inline deletions.
Test sanitization behavior core/providers/vertex/payload_ordering_test.go	Tests verify supported-field passthrough, unsupported-field removal, and empty or nil input handling.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: akshaydeo, pratham-mishra04

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR fixes Vertex countTokens stripping, but linked issue #123 requires Files API support, so the main requirement is unmet.	Implement the Files API support requested in #123 or relink the PR to the correct issue.
Out of Scope Changes check	⚠️ Warning	All code changes are unrelated to Files API support and therefore fall outside the linked issue's requested scope.	Remove or retarget this change set so it addresses the Files API support requested by #123.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title is concise and accurately summarizes the main change to Vertex countTokens field stripping.
Description check	✅ Passed	The description follows the template well, covering summary, changes, type, affected areas, testing, breaking changes, security, and checklist.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 07-28-fix_vertex_count_tokens_unsupported_fields

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[TejasGhatte]

• chore: harness tests count tokens #5648
• fix: image search for genai search tool #5647
• fix: count tokens request building #5620
• fix: vertex count tokens unsupported fields #5619 👈 (View in Graphite)
• dev

This stack of pull requests is managed by Graphite. Learn more about stacking.

[akshaydeo]

Merge activity

• Jul 29, 11:07 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jul 29, 11:07 AM UTC: @akshaydeo merged this pull request with Graphite.