fix: use OAuth access_token for Claude Code backend authentication

The get_anthropic_api_key_for_claudecode function now checks for OAuth
access tokens in addition to API keys. It also falls back to reading
from ai_providers.json if OpenCode auth.json doesn't have credentials.

This fixes the bug where Claude Code missions failed with "Invalid API
key" even when Anthropic OAuth was properly configured in the dashboard.

src/api/ai_providers.rs

@@ -137,14 +137,18 @@ pub fn routes() -> Router<Arc<super::routes::AppState>> {
 // Public API for Backend Access
 // ─────────────────────────────────────────────────────────────────────────────
 
-/// Get the Anthropic API key for the Claude Code backend.
+/// Get the Anthropic API key or OAuth access token for the Claude Code backend.
 ///
 /// This checks if the Anthropic provider has "claudecode" in its use_for_backends
-/// configuration and returns the API key if available.
+/// configuration and returns the API key or OAuth access token if available.
+///
+/// Credential sources checked (in order):
+/// 1. OpenCode auth.json (API key or OAuth)
+/// 2. Open Agent ai_providers.json (API key or OAuth)
 ///
 /// Returns None if:
 /// - Anthropic provider is not configured for claudecode
-/// - No API key is set (OAuth-only auth)
+/// - No credentials are available (neither API key nor OAuth)
 /// - Any error occurs reading the config
 pub fn get_anthropic_api_key_for_claudecode(working_dir: &Path) -> Option<String> {
     // Read the OpenCode config to check use_for_backends
@@ -163,11 +167,21 @@ pub fn get_anthropic_api_key_for_claudecode(working_dir: &Path) -> Option<String
         return None;
     }
 
-    // Get the API key from auth.json
+    // Try to get credentials from OpenCode auth.json first
+    if let Some(key) = get_anthropic_key_from_opencode_auth() {
+        return Some(key);
+    }
+
+    // Fall back to ai_providers.json
+    get_anthropic_key_from_ai_providers(working_dir)
+}
+
+/// Get Anthropic API key or OAuth access token from OpenCode auth.json.
+fn get_anthropic_key_from_opencode_auth() -> Option<String> {
     let auth = read_opencode_auth().ok()?;
     let anthropic_auth = auth.get("anthropic")?;
 
-    // Check for API key (not OAuth)
+    // Check for API key first
     let auth_type = anthropic_auth.get("type").and_then(|v| v.as_str());
     match auth_type {
         Some("api_key") | Some("api") => {
@@ -177,16 +191,64 @@ pub fn get_anthropic_api_key_for_claudecode(working_dir: &Path) -> Option<String
                 .and_then(|v| v.as_str())
                 .map(|s| s.to_string())
         }
-        _ => {
-            // Also check without type field
+        Some("oauth") => {
+            // Return OAuth access token - Claude CLI can use this
             anthropic_auth
-                .get("key")
+                .get("access")
+                .and_then(|v| v.as_str())
+                .map(|s| s.to_string())
+        }
+        _ => {
+            // Check without type field - try key first, then OAuth access token
+            if let Some(key) = anthropic_auth.get("key").and_then(|v| v.as_str()) {
+                return Some(key.to_string());
+            }
+            // Fall back to OAuth access token
+            anthropic_auth
+                .get("access")
                 .and_then(|v| v.as_str())
                 .map(|s| s.to_string())
         }
     }
 }
 
+/// Get Anthropic API key or OAuth access token from Open Agent's ai_providers.json.
+fn get_anthropic_key_from_ai_providers(working_dir: &Path) -> Option<String> {
+    let ai_providers_path = working_dir.join(".openagent/ai_providers.json");
+    if !ai_providers_path.exists() {
+        return None;
+    }
+
+    let contents = std::fs::read_to_string(&ai_providers_path).ok()?;
+    let providers: Vec<serde_json::Value> = serde_json::from_str(&contents).ok()?;
+
+    // Find Anthropic provider
+    for provider in providers {
+        let provider_type = provider.get("provider_type").and_then(|v| v.as_str());
+        if provider_type != Some("anthropic") {
+            continue;
+        }
+
+        // Check for API key first
+        if let Some(api_key) = provider.get("api_key").and_then(|v| v.as_str()) {
+            if !api_key.is_empty() {
+                return Some(api_key.to_string());
+            }
+        }
+
+        // Check for OAuth access token
+        if let Some(oauth) = provider.get("oauth") {
+            if let Some(access_token) = oauth.get("access_token").and_then(|v| v.as_str()) {
+                if !access_token.is_empty() {
+                    return Some(access_token.to_string());
+                }
+            }
+        }
+    }
+
+    None
+}
+
 /// Check if the Anthropic provider is configured for the Claude Code backend.
 pub fn is_anthropic_configured_for_claudecode(working_dir: &Path) -> bool {
     let config_path = get_opencode_config_path(working_dir);