v2: API key export endpoint (POST, rate-limited)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/handlers/api_keys.rs

@@ -169,6 +169,34 @@ pub async fn test_key(
     }
 }
 
+/// `POST /api/v1/user/api-keys/export`
+///
+/// Returns decrypted API keys for settings export backup.
+/// Rate-limited to 3 calls per minute. Uses POST to require CSRF token.
+pub async fn export_keys(
+    auth_user: AuthUser,
+    State(state): State<AppState>,
+) -> Result<impl IntoResponse, AppError> {
+    if !state.auth_rate_limiter.check(&format!("key-export:{}", auth_user.id)) {
+        return Err(AppError::RateLimited("Too many export requests".into()));
+    }
+
+    let stored_keys = db::api_keys::list_for_user(&state.pool, auth_user.id).await?;
+    let master_key = encryption::MasterKey::from_hex(&state.config.master_encryption_key)?;
+
+    let mut exported = Vec::new();
+    for key in &stored_keys {
+        let decrypted = encryption::decrypt(&master_key, &key.encrypted_key, &key.nonce)?;
+        exported.push(serde_json::json!({
+            "provider_name": key.provider_name,
+            "api_key": decrypted,
+        }));
+    }
+
+    tracing::info!(user_id = %auth_user.id, key_count = exported.len(), "API keys exported");
+    Ok(Json(exported))
+}
+
 /// Get a default model identifier for a provider from the admin config.
 ///
 /// Looks up the admin provider configuration for the given provider name

backend/src/router.rs

@@ -49,6 +49,7 @@ pub fn build_router(state: AppState, config: &AppConfig) -> Router {
         .route("/user/api-keys", post(handlers::api_keys::create))
         .route("/user/api-keys/{provider}", delete(handlers::api_keys::delete))
         .route("/user/api-keys/{provider}/test", post(handlers::api_keys::test_key))
+        .route("/user/api-keys/export", post(handlers::api_keys::export_keys))
         // Generation routes (authenticated) — registered before /syntheses/{id}
         // to avoid ambiguity with path parameter matching
         .route("/syntheses/generate", post(handlers::generation::trigger_generate))