fix(model-fetch): probe /models on versioned /vN base URLs

The model-list probe assumed any base URL not ending in /v1 needs /v1/models appended. For providers whose base URL already ends in a version segment like /v4 (Zhipu/Z.AI GLM Coding Plan at .../api/coding/paas/v4), this produced .../v4/v1/models which 404s, so the "Fetch models" button always failed.

Detect a trailing /v{N} version segment and probe {base}/models first, keeping /v1/models as a fallback candidate for non-/v1 versions. Fixes Codex/OpenCode/OpenClaw/Hermes GLM presets and any other vN-style endpoint, with no behavior change for /v1 or non-versioned URLs.

src-tauri/src/services/model_fetch.rs

@@ -121,9 +121,10 @@ pub async fn fetch_models(
 ///
 /// 候选顺序：
 /// 1. `models_url_override` 非空 → 只返回它
-/// 2. baseURL 直接拼 `/v1/models`（若已有 `/v1` 结尾则拼 `/models`）
-/// 3. 若 baseURL 命中 [`KNOWN_COMPAT_SUFFIXES`]，剥离后缀再拼 `/v1/models`
-/// 4. 同上，但拼 `/models`（部分站点如 DeepSeek 官方只暴露 `/models`）
+/// 2. baseURL 拼 `/v1/models`；若已以版本段 `/v{N}` 结尾（`/v1`、智谱
+///    `/api/coding/paas/v4` 等），版本号已在路径里，改拼 `/models`
+/// 3. 版本段非 `/v1`（如 `/v4`）时再追加 `/v1/models` 作为兜底次候选
+/// 4. 若 baseURL 命中 [`KNOWN_COMPAT_SUFFIXES`]，剥离后缀再拼 `/v1/models`、`/models`
 ///
 /// 结果已去重且保持首次出现顺序。
 pub fn build_models_url_candidates(
@@ -160,12 +161,18 @@ pub fn build_models_url_candidates(
         return Ok(candidates);
     }
 
-    let primary = if trimmed.ends_with("/v1") {
-        format!("{trimmed}/models")
+    // baseURL 已以版本段 /v{N} 结尾时（如 `/v1`、智谱 `/api/coding/paas/v4`），
+    // OpenAI 惯例的模型端点是 `{base}/models`，不能再补 `/v1`
+    // （否则 .../coding/paas/v4/v1/models → 404）。
+    if ends_with_version_segment(trimmed) {
+        candidates.push(format!("{trimmed}/models"));
+        // 版本段非 /v1 时，保留旧的 /v1/models 作为兜底次候选（正确路径已在前）。
+        if !trimmed.ends_with("/v1") {
+            candidates.push(format!("{trimmed}/v1/models"));
+        }
     } else {
-        format!("{trimmed}/v1/models")
-    };
-    candidates.push(primary);
+        candidates.push(format!("{trimmed}/v1/models"));
+    }
 
     if let Some(stripped) = strip_compat_suffix(trimmed) {
         let root = stripped.trim_end_matches('/');
@@ -210,6 +217,15 @@ fn strip_compat_suffix(base_url: &str) -> Option<&str> {
     None
 }
 
+/// 判断 baseURL 是否以 OpenAI 风格的版本段 `/v{N}` 结尾（`N` 为一个或多个数字），
+/// 例如 `/v1`、`.../paas/v4`。这类 URL 版本号已在路径中，模型端点应为
+/// `{base}/models`，不能再补 `/v1`（智谱 Coding Plan 即 `.../coding/paas/v4`）。
+fn ends_with_version_segment(url: &str) -> bool {
+    let last = url.rsplit('/').next().unwrap_or("");
+    last.strip_prefix('v')
+        .is_some_and(|digits| !digits.is_empty() && digits.bytes().all(|b| b.is_ascii_digit()))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -232,6 +248,48 @@ mod tests {
         assert_eq!(c, vec!["https://api.example.com/v1/models"]);
     }
 
+    #[test]
+    fn test_candidates_zhipu_coding_paas_v4() {
+        // 智谱 Coding Plan 端点以 /v4 版本段结尾：模型端点是 {base}/models，
+        // 正确路径必须排在 .../v4/v1/models（404）之前。
+        let c =
+            build_models_url_candidates("https://open.bigmodel.cn/api/coding/paas/v4", false, None)
+                .unwrap();
+        assert_eq!(
+            c,
+            vec![
+                "https://open.bigmodel.cn/api/coding/paas/v4/models",
+                "https://open.bigmodel.cn/api/coding/paas/v4/v1/models",
+            ]
+        );
+    }
+
+    #[test]
+    fn test_candidates_zai_coding_paas_v4() {
+        let c = build_models_url_candidates("https://api.z.ai/api/coding/paas/v4", false, None)
+            .unwrap();
+        assert_eq!(
+            c,
+            vec![
+                "https://api.z.ai/api/coding/paas/v4/models",
+                "https://api.z.ai/api/coding/paas/v4/v1/models",
+            ]
+        );
+    }
+
+    #[test]
+    fn test_ends_with_version_segment() {
+        assert!(ends_with_version_segment("https://x.com/v1"));
+        assert!(ends_with_version_segment(
+            "https://open.bigmodel.cn/api/coding/paas/v4"
+        ));
+        assert!(ends_with_version_segment("https://x.com/v10"));
+        assert!(!ends_with_version_segment("https://x.com/api"));
+        assert!(!ends_with_version_segment("https://x.com/vX"));
+        assert!(!ends_with_version_segment("https://x.com/models"));
+        assert!(!ends_with_version_segment("https://api.siliconflow.cn"));
+    }
+
     #[test]
     fn test_candidates_full_url() {
         let c = build_models_url_candidates(