Fix Cohere provider-prefixed model routing

[parteeksingh24]

Summary

Rewrite and route public cohere/ and deepseek/ model IDs correctly, from one shared prefix list.

• Strip cohere/ public model prefixes before forwarding to Cohere
• Detect cohere/ and deepseek/ providers by name from that same list
• Add AutoRouter regression coverage for a prefixed Cohere catalog ID
• Update the gated AI Gateway live regression to cover the prefixed ID shape
• Add a drift guard so the strip list and routing list can't diverge again

Why

When AI Gateway sends a public model ID like cohere/command-a-plus-05-2026, Cohere's compatibility API expects the native model ID:

{
  "model": "command-a-plus-05-2026"
}

AutoRouter keeps provider-prefix knowledge in one map, knownProviderPrefixes, used for two jobs:

• Stripping (stripProviderPrefix) rewrites cohere/x → x before forwarding.
• Routing (DetectProviderFromModel) maps cohere/x → provider cohere.

These previously read two separate hand-maintained lists. cohere (this PR) and deepseek (an earlier PR) were added to the strip list but never the routing switch, so a direct consumer sending cohere/... with no X-Provider header got ErrNoProvider. Through AI Gateway the gap was masked (Ion sets X-Provider and carries its own prefix fallback), so it was latent rather than a live outage.

flowchart TD
    R["model: cohere/command-a-plus-05-2026"] --> H{"X-Provider header set?"}
    H -- yes --> U["use header value"]
    H -- no --> D["DetectProviderFromModel(model)"]
    D --> M{"prefix in knownProviderPrefixes?"}
    M -- yes --> PV["provider = cohere"]
    M -- no --> NH["name heuristics, else ErrNoProvider"]
    PV --> SP["stripProviderPrefix() reads same map"]
    SP --> UP["upstream gets command-a-plus-05-2026"]

Loading

Implementation

Cohere stays in the central prefix-stripping path used by providers such as DeepSeek:

var knownProviderPrefixes = map[string]bool{
    "deepseek": true,
    "cohere":   true,
}

DetectProviderFromModel now reads that same map instead of a second hardcoded switch, so a prefix the router strips is always a prefix it can route:

// detection.go
if idx := strings.Index(model, "/"); idx >= 0 {
    if prefix := model[:idx]; knownProviderPrefixes[prefix] {
        return prefix
    }
}

A new guard asserts every stripped prefix is routable, so the two lists can't silently drift again:

func TestDetectProviderFromModel_KnownPrefixesAreDetected(t *testing.T) {
    for prefix := range knownProviderPrefixes {
        model := prefix + "/some-model"
        if got := DetectProviderFromModel(model); got != prefix {
            t.Errorf("DetectProviderFromModel(%q) = %q, want %q", model, got, prefix)
        }
    }
}

The AutoRouter regression still exercises AutoRouter.Forward and asserts the fake Cohere upstream receives the stripped model, and the gated live regression still uses the public ID shape cohere/command-a-plus-05-2026.

Verification

Prefix-routing change (this commit):

• go test . -run 'TestDetectProviderFromModel|TestDefaultProviderDetector|TestAutoRouter_Cohere|TestStripProviderPrefix' -count=1
• go build ./... and go vet ./...
• go test ./... -count=1

Carried from the strip commit (re-run after stacking before merge):

• go test -race ./... -count=1
• go test -tags integration ./... -run 'TestLiveAIGatewayRegressionModels' -count=1
• make test blocked locally at govulncheck because local Go is go1.26.2 and the stdlib vuln gate requires a newer Go patch version

Summary by CodeRabbit

• Bug Fixes

  • Provider-prefixed Cohere model names are now correctly stripped before forwarding requests to upstream services.

• Tests

  • Added regression tests to verify provider prefix stripping behavior for Cohere models.

[coderabbitai]

📝 Walkthrough

Walkthrough

Refactors provider detection to use knownProviderPrefixes as the single source of truth for explicit provider-prefix matching, adds "cohere" to that map, and verifies prefix detection and stripping through unit tests and a live regression test using the cohere/command-a-plus-05-2026 model.

Changes

Cohere Provider Prefix Stripping and Detection Unification

Layer / File(s)	Summary
Provider detection refactor to use knownProviderPrefixes detection.go, detection_test.go	DetectProviderFromModel replaces hard-coded prefix switch with knownProviderPrefixes map lookup, and tests verify correct detection for cohere/ and deepseek/ prefixes plus all registered known prefixes.
Cohere prefix registration and unit tests autorouter.go, autorouter_test.go	Adds "cohere": true to knownProviderPrefixes, introduces TestAutoRouter_CohereStripsProviderPrefixBeforeForwarding verifying upstream receives command-a-plus-05-2026, and extends TestStripProviderPrefix with a cohere test vector.
Live regression test update aigateway_regression_live_test.go	Updates cohere live test case name and model from command-r-08-2024 to cohere/command-a-plus-05-2026 to exercise end-to-end prefix stripping.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}