fix(translator): harden Claude format detection for model validation (#9253)

* fix(translator): harden Claude format detection for model validation

Co-authored-by: Ervareza Naurian <rianskp644@gmail.com>
Inspired-by: https://github.com/decolua/9router/pull/2949

* chore(changelog): fragment for #9253

---------

Co-authored-by: diegosouzapw <diegosouzapw@users.noreply.github.com>
Co-authored-by: Ervareza Naurian <rianskp644@gmail.com>

changelog.d/fixes/9253-translator-format-detection-2949.md

@@ -0,0 +1 @@
+- **fix(translator):** harden Claude format detection for relative message endpoints and kebab-case version metadata. (thanks @ervareza)

open-sse/services/provider.ts

@@ -135,7 +135,17 @@ export function detectFormatFromEndpoint(body, endpointPath = "") {
 // Thin wrapper for call sites that only have the full request URL (not the bare endpoint
 // path chatCore already threads) — single source of truth stays detectFormatFromEndpoint.
 export function detectFormatFromUrl(body, requestUrl) {
-  return detectFormatFromEndpoint(body, new URL(requestUrl).pathname);
+  const rawUrl = typeof requestUrl === "string" ? requestUrl : "";
+  let pathname = rawUrl;
+  try {
+    // Supplying a base URL keeps relative client endpoints (for example,
+    // `/v1/messages`) valid while preserving pathname-only detection.
+    pathname = new URL(rawUrl || "/", "http://omniroute.local").pathname;
+  } catch {
+    // Fall back to the raw value; detectFormatFromEndpoint is intentionally
+    // safe for unknown or malformed paths.
+  }
+  return detectFormatFromEndpoint(body, pathname);
 }
 
 // Detect request format from body structure
@@ -193,7 +203,7 @@ export function detectFormat(body) {
       if (firstContent?.type === "text" && !body.model?.includes("/")) {
         // Could be Claude or OpenAI multimodal
         // Check for Claude-specific fields
-        if (body.system || body.anthropic_version) {
+        if (body.system || body.anthropic_version || body["anthropic-version"]) {
           return "claude";
         }
         // Check if image format is Claude (source.type) vs OpenAI (image_url.url)
@@ -216,7 +226,7 @@ export function detectFormat(body) {
 
     // If content is string, it's likely OpenAI (Claude also supports this)
     // Check for other Claude-specific indicators
-    if (body.system !== undefined || body.anthropic_version) {
+    if (body.system !== undefined || body.anthropic_version || body["anthropic-version"]) {
       return "claude";
     }
 

tests/unit/translator-format-detection-2949.test.ts

@@ -0,0 +1,24 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { detectFormat, detectFormatFromUrl } from "../../open-sse/services/provider.ts";
+
+test("detectFormatFromUrl accepts a relative /messages endpoint", () => {
+  assert.equal(
+    detectFormatFromUrl(
+      { messages: [{ role: "user", content: "validate this model" }] },
+      "/v1/messages"
+    ),
+    "claude"
+  );
+});
+
+test("detectFormat recognizes the kebab-case anthropic-version body field", () => {
+  assert.equal(
+    detectFormat({
+      messages: [{ role: "user", content: "validate this model" }],
+      "anthropic-version": "2023-06-01",
+    }),
+    "claude"
+  );
+});