[Router][Bugfix]: parseBestMatch select best match from all KNN candidates

[drivebyer]

parseBestMatch relies on Go map iteration order to pick the "best" KNN result, but Go maps have randomized iteration order. When Search.TopK > 1, this returns a random candidate instead of the closest match, causing false cache misses, non-deterministic behavior, and inaccurate similarity metrics.

Purpose

• What does this PR change?
• Why is this change needed?
• Which module(s) does this affect? Router

Test Plan

• What commands, checks, or manual steps should reviewers use?
• Why is this validation sufficient for the affected module(s)?

Test Result

• What were the actual results?
• Any follow-up risks, gaps, or blockers?

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Semantic Router PR Checklist

• PR title uses module-aligned prefixes such as [Router], [CLI], [Dashboard], [Operator], [Fleet-Sim], [Bindings], [Training], [E2E], [Docs], or [CI/Build]
• If the PR spans multiple modules, the title includes all relevant prefixes
• Commits in this PR are signed off with git commit -s
• The Purpose, Test Plan, and Test Result sections reflect the actual scope, commands, and blockers for this change

See CONTRIBUTING.md for the full contributor workflow and commit guidance.

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[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 src/semantic-router

Owners: @rootfs, @Xunzhuo, @szedan-rh, @yehuditkerido, @abdallahsamabd, @asaadbalum, @liavweiss, @noalimoy
Files changed:

• src/semantic-router/pkg/cache/valkey_cache_helpers.go
• src/semantic-router/pkg/cache/valkey_cache_helpers_test.go

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🎉 Thanks for your contributions!

This comment was automatically generated based on the OWNER files in the repository.

[github-actions]

✅ Supply Chain Security Report — All Clear

Scanner	Status	Findings
AST Codebase Scan (Py, Go, JS/TS, Rust)	✅	27 finding(s) — MEDIUM: 21 · LOW: 6
AST PR Diff Scan	✅	No issues detected
Regex Fallback Scan	✅	No issues detected

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Scanned at 2026-04-10T13:03:00.477Z · View full workflow logs