diff --git a/app/src/adapters/gitea/client/transport.ts b/app/src/adapters/gitea/client/transport.ts
index 2319c19..eec6fc1 100644
--- a/app/src/adapters/gitea/client/transport.ts
+++ b/app/src/adapters/gitea/client/transport.ts
@@ -95,7 +95,10 @@ export class GiteaTransport {
                     attempt === attempts - 1 ||
                     (!retryable && lastError instanceof GiteaHttpError)
                 ) {
-                    throw lastError;
+                    if (lastError instanceof GiteaHttpError) throw lastError;
+                    throw new Error(`${method} ${this.apiBase}${path} failed`, {
+                        cause: lastError,
+                    });
                 }
             }
             await abortableDelay(1_000 * 2 ** attempt, this.signal);
diff --git a/app/src/core/contracts.ts b/app/src/core/contracts.ts
index 49d7033..4bc0672 100644
--- a/app/src/core/contracts.ts
+++ b/app/src/core/contracts.ts
@@ -123,7 +123,13 @@ export function statusMarker(issue: number, mode: Mode): Marker {
 }
 
 export function formatError(error: unknown): string {
-    if (error instanceof Error) return error.message;
+    if (error instanceof Error) {
+        if (error.cause === undefined) return error.message;
+        const cause = formatError(error.cause);
+        return cause && cause !== error.message
+            ? `${error.message}: ${cause}`
+            : error.message;
+    }
     return String(error);
 }
 
diff --git a/app/src/tests/core/webhook.test.ts b/app/src/tests/core/webhook.test.ts
index ec86e3d..686d627 100644
--- a/app/src/tests/core/webhook.test.ts
+++ b/app/src/tests/core/webhook.test.ts
@@ -6,13 +6,25 @@ import {
     findAcceptedPlan,
 } from "../../adapters/gitea/issues.js";
 import type { GiteaComment, GiteaIssue } from "../../adapters/gitea/types.js";
-import { marker, sha256 } from "../../core/contracts.js";
+import { formatError, marker, sha256 } from "../../core/contracts.js";
 import {
     parseAgentCommand,
     parseCommentPayload,
     verifyGiteaSignature,
 } from "../../core/webhook.js";
 
+test("formats nested transport error causes", () => {
+    const error = new Error("GET https://git.example/api/v1/user failed", {
+        cause: new TypeError("fetch failed", {
+            cause: new Error("getaddrinfo ENOTFOUND git.example"),
+        }),
+    });
+    assert.equal(
+        formatError(error),
+        "GET https://git.example/api/v1/user failed: fetch failed: getaddrinfo ENOTFOUND git.example",
+    );
+});
+
 test("verifies the raw Gitea HMAC signature", () => {
     const body = Buffer.from('{"action":"created"}');
     const signature = createHmac("sha256", "secret").update(body).digest("hex");