feat(provider): enhance Claude provider configuration to support environment variable fallback

src/model/app_config.rs

@@ -143,15 +143,19 @@ struct ClaudeSettings {
     env: Option<ClaudeEnv>,
 }
 
-/// Read `~/.claude/settings.json` and return a `ProviderConfig` if the file
-/// contains `ANTHROPIC_BASE_URL` and `ANTHROPIC_API_KEY` in its `env` block.
+/// Return a `ProviderConfig` for the Claude provider, checking both
+/// `~/.claude/settings.json` and the process environment.
+///
+/// Flow: try the file (`env.ANTHROPIC_BASE_URL` + `env.ANTHROPIC_API_KEY`)
+/// first → fall back to the `ANTHROPIC_BASE_URL` / `ANTHROPIC_API_KEY` env
+/// vars → if neither source has both values, return `None`.
+///
+/// Why: Claude Code may inject credentials via env vars (OAuth session) rather
+/// than through its settings file, so reading only the file misses them.
 fn detect_claude_settings_provider() -> Option<ProviderConfig> {
-    let path = dirs::home_dir()?.join(".claude").join("settings.json");
-    let content = std::fs::read_to_string(&path).ok()?;
-    let settings: ClaudeSettings = serde_json::from_str(&content).ok()?;
-    let env = settings.env?;
-    let base_url = env.anthropic_base_url?;
-    let _ = env.anthropic_api_key?; // presence check — stored as env var, not in config.
+    // Prefer the file, then fall back to env vars.
+    let (base_url, _key) = claude_credentials_from_file()
+        .or_else(claude_credentials_from_env)?;
     Some(ProviderConfig {
         api_base: base_url,
         api_key_env: Some("ANTHROPIC_API_KEY".to_string()),
@@ -159,3 +163,22 @@ fn detect_claude_settings_provider() -> Option<ProviderConfig> {
         default_api_key: None,
     })
 }
+
+/// Try to read Claude credentials from `~/.claude/settings.json`'s `env` block.
+fn claude_credentials_from_file() -> Option<(String, String)> {
+    let path = dirs::home_dir()?.join(".claude").join("settings.json");
+    let content = std::fs::read_to_string(&path).ok()?;
+    let settings: ClaudeSettings = serde_json::from_str(&content).ok()?;
+    let env = settings.env?;
+    let base_url = env.anthropic_base_url?;
+    let key = env.anthropic_api_key?;
+    Some((base_url, key))
+}
+
+/// Try to read Claude credentials from `ANTHROPIC_BASE_URL` /
+/// `ANTHROPIC_API_KEY` environment variables.
+fn claude_credentials_from_env() -> Option<(String, String)> {
+    let base_url = std::env::var("ANTHROPIC_BASE_URL").ok()?;
+    let key = std::env::var("ANTHROPIC_API_KEY").ok()?;
+    Some((base_url, key))
+}