bifrost: a base url with a path is the complete api root

Appending /v1 by testing only the last path segment doubled Google's
/v1beta/openai into /v1beta/openai/v1, where a POST hangs with zero
bytes and GET /models still answers 200. Only a bare authority now
gets the default; /v1, /v4 and /zen/go/v1 roots pass through.

src/bridge/bifrost.rs

@@ -528,15 +528,15 @@ enum ErrorClass {
     Permanent,
 }
 
-/// True if the URL's final path segment is a version tag like `v1`, `v4`.
+/// True if the base URL carries a path past the authority. Such a base is the
-/// Used to avoid appending `/v1` to an already-versioned base URL.
+/// complete API root; only a bare host gets the OpenAI default `/v1`.
-fn last_segment_is_version(url: &str) -> bool {
+///
-    match url.rsplit('/').next() {
+/// Measured 2026-08-18: testing only the last segment for `v<digits>` appended
-        Some(seg) if seg.len() >= 2 => {
+/// `/v1` to Google's `/v1beta/openai`, and a POST to the doubled path hangs
-            seg.starts_with('v') && seg[1..].chars().all(|c| c.is_ascii_digit())
+/// (40s, zero bytes) while `GET /models` returns 200 on both — so the mangled
-        }
+/// base looks healthy on a listing.
-        _ => false,
+fn has_own_path(url: &str) -> bool {
-    }
+    reqwest::Url::parse(url).is_ok_and(|u| u.path() != "/")
 }
 
 impl BifrostClient {
@@ -548,10 +548,7 @@ impl BifrostClient {
         timeout_secs: u64,
     ) -> Result<Self> {
         let base = base_url.trim_end_matches('/').to_string();
-        // Only append "/v1" when the base URL has no version path segment.
+        let base_url = if has_own_path(&base) {
-        // A URL already ending in "/v<digits>" (Bifrost's "/v1", z.ai's
-        // "/api/coding/paas/v4") is left untouched.
-        let base_url = if last_segment_is_version(&base) {
             base
         } else {
             format!("{}/v1", base)
@@ -922,6 +919,59 @@ mod tests {
         assert_eq!(reset_hint(None), "");
     }
 
+    /// Google's OpenAI-compatible root nests its version: `/v1beta/openai`.
+    /// Appending `/v1` there produced a path that hangs on POST.
+    #[test]
+    fn google_nested_version_path_is_not_doubled() {
+        let client = BifrostClient::new(
+            "https://generativelanguage.googleapis.com/v1beta/openai",
+            "",
+            "",
+            "gemini-3.6-flash",
+            300,
+        )
+        .unwrap();
+        assert_eq!(
+            client.base_url,
+            "https://generativelanguage.googleapis.com/v1beta/openai"
+        );
+    }
+
+    /// Every `[providers.*]` base URL on disk 2026-08-18 and the API root the
+    /// client must end up posting to.
+    #[test]
+    fn base_url_completion_across_configured_providers() {
+        let cases = [
+            // Paths of their own — taken as complete, nested version or not.
+            (
+                "https://generativelanguage.googleapis.com/v1beta/openai",
+                "https://generativelanguage.googleapis.com/v1beta/openai",
+            ),
+            (
+                "https://generativelanguage.googleapis.com/v1beta/openai/",
+                "https://generativelanguage.googleapis.com/v1beta/openai",
+            ),
+            (
+                "https://api.z.ai/api/coding/paas/v4",
+                "https://api.z.ai/api/coding/paas/v4",
+            ),
+            (
+                "https://token-plan-sgp.xiaomimimo.com/v1",
+                "https://token-plan-sgp.xiaomimimo.com/v1",
+            ),
+            ("https://opencode.ai/zen/go/v1", "https://opencode.ai/zen/go/v1"),
+            // Bare hosts — get the OpenAI default.
+            ("https://api.deepseek.com", "https://api.deepseek.com/v1"),
+            ("https://api.deepseek.com/", "https://api.deepseek.com/v1"),
+            ("http://10.10.20.120:3360", "http://10.10.20.120:3360/v1"),
+            ("http://10.10.20.19:8080", "http://10.10.20.19:8080/v1"),
+        ];
+        for (base, want) in cases {
+            let client = BifrostClient::new(base, "", "", "m", 30).unwrap();
+            assert_eq!(client.base_url, want, "base {base}");
+        }
+    }
+
     #[test]
     fn test_client_creation() {
         let client = BifrostClient::new(