diff --git a/src/hopper/HopperCleanup.test.ts b/src/hopper/HopperCleanup.test.ts
new file mode 100644
index 000000000..9d2a7c633
--- /dev/null
+++ b/src/hopper/HopperCleanup.test.ts
@@ -0,0 +1,121 @@
+import { EventEmitter } from "node:events";
+import { Socket } from "node:net";
+
+import pino from "pino";
+import { describe, expect, it } from "vitest";
+
+import { ok } from "../domain/result.js";
+import type { BridgeLaunch } from "./BridgeLauncher.js";
+import { cleanupHopperSession } from "./HopperCleanup.js";
+
+const loggerHarness = () => {
+  const logs: unknown[] = [];
+  return {
+    logs,
+    logger: pino(
+      { level: "warn" },
+      {
+        write: (line) => logs.push(JSON.parse(line)),
+      },
+    ),
+  };
+};
+
+const processCleanupLaunch = (): BridgeLaunch => ({
+  process: Object.assign(new EventEmitter(), {
+    stdout: null,
+    stderr: null,
+    exitCode: null,
+    signalCode: null,
+    kill: () => true,
+  }),
+  ownsProcessLifetime: true,
+  shutdownMode: "process-cleanup",
+  cleanup: () =>
+    Promise.resolve({
+      cleaned: false as const,
+      reason: "fixture cleanup unavailable",
+    }),
+});
+
+const failure = (message: string) =>
+  Object.assign(new TypeError(message), { code: "ECONNRESET" });
+
+describe("Hopper shutdown rejection diagnostics", () => {
+  it("retains the primary shutdown operation and rejection cause", async () => {
+    const { logger, logs } = loggerHarness();
+    const result = await cleanupHopperSession({
+      socket: new Socket(),
+      launch: undefined,
+      processSupervisor: undefined,
+      runtimeRoot: undefined,
+      activeRequest: null,
+      retainDocument: false,
+      progress: undefined,
+      logger,
+      onDiagnostic: undefined,
+      request: () => Promise.reject(failure("fixture primary rejection")),
+      releaseTransport: () => undefined,
+    });
+
+    expect(result).toMatchObject({
+      ok: false,
+      error: { cleanupResources: ["hopper-document"] },
+    });
+    expect(logs).toContainEqual(
+      expect.objectContaining({
+        msg: "Hopper document shutdown was not confirmed",
+        status: "failed",
+        errorTag: "HopperProcessError",
+        operation: "shutdown_document",
+        failure_cause: {
+          name: "TypeError",
+          message: "fixture primary rejection",
+          code: "ECONNRESET",
+        },
+      }),
+    );
+  });
+
+  it("retains the fallback shutdown operation and rejection cause", async () => {
+    const { logger, logs } = loggerHarness();
+    const methods: string[] = [];
+    const result = await cleanupHopperSession({
+      socket: new Socket(),
+      launch: processCleanupLaunch(),
+      processSupervisor: undefined,
+      runtimeRoot: undefined,
+      activeRequest: null,
+      retainDocument: false,
+      progress: undefined,
+      logger,
+      onDiagnostic: undefined,
+      request: (method) => {
+        methods.push(method);
+        return method === "shutdown"
+          ? Promise.resolve(ok({ shutdown: true, cleanup_required: true }))
+          : Promise.reject(failure("fixture fallback rejection"));
+      },
+      releaseTransport: () => undefined,
+    });
+
+    expect(methods).toEqual(["shutdown", "shutdown_document"]);
+    expect(result).toMatchObject({
+      ok: false,
+      error: { cleanupResources: ["hopper-document"] },
+    });
+    expect(logs).toContainEqual(
+      expect.objectContaining({
+        msg: "Hopper document shutdown fallback was not confirmed",
+        status: "failed",
+        errorTag: "HopperProcessError",
+        operation: "shutdown_document",
+        failure_cause: {
+          name: "TypeError",
+          message: "fixture fallback rejection",
+          code: "ECONNRESET",
+        },
+      }),
+    );
+  });
+});
diff --git a/src/hopper/HopperCleanup.ts b/src/hopper/HopperCleanup.ts
index e73e80079..3d31884d8 100644
--- a/src/hopper/HopperCleanup.ts
+++ b/src/hopper/HopperCleanup.ts
@@ -98,13 +98,13 @@ const requestShutdown = async (
       );
     return;
   }
+  const method =
+    input.retainDocument || input.launch?.shutdownMode === "process-cleanup"
+      ? "shutdown"
+      : "shutdown_document";
   const shutdown = await input
-    .request(
-      input.retainDocument || input.launch?.shutdownMode === "process-cleanup"
-        ? "shutdown"
-        : "shutdown_document",
-    )
-    .catch(() => err(new HopperProcessError(null)));
+    .request(method)
+    .catch((cause: unknown) => err(shutdownRequestFailure(method, cause)));
   if (
     shutdown.ok &&
     isHopperCleanupRequired(shutdown.value) &&
@@ -127,7 +127,10 @@ const requestShutdown = async (
     (!state.shutdownConfirmed && state.cleanupResult === undefined)
   )
     input.logger.warn(
-      { status: shutdown.ok ? "invalid-acknowledgement" : "failed" },
+      {
+        status: shutdown.ok ? "invalid-acknowledgement" : "failed",
+        ...(shutdown.ok ? {} : shutdownFailureDetails(shutdown.error)),
+      },
       "Hopper document shutdown was not confirmed",
     );
 };
@@ -137,17 +140,68 @@ const fallbackDocumentShutdown = async (
 ): Promise<boolean> => {
   const fallback = await input
     .request("shutdown_document")
-    .catch(() => err(new HopperProcessError(null)));
+    .catch((cause: unknown) =>
+      err(shutdownRequestFailure("shutdown_document", cause)),
+    );
   const confirmed =
     fallback.ok && isHopperShutdownAcknowledgement(fallback.value);
   if (!confirmed)
     input.logger.warn(
-      { status: fallback.ok ? "invalid-acknowledgement" : "failed" },
+      {
+        status: fallback.ok ? "invalid-acknowledgement" : "failed",
+        ...(fallback.ok ? {} : shutdownFailureDetails(fallback.error)),
+      },
       "Hopper document shutdown fallback was not confirmed",
     );
   return confirmed;
 };
 
+const shutdownRequestFailure = (
+  operation: "shutdown" | "shutdown_document",
+  cause: unknown,
+): HopperProcessError => {
+  const failure = new HopperProcessError(null, undefined, operation);
+  failure.cause = cause;
+  return failure;
+};
+
+const shutdownFailureDetails = (
+  error: HopperError,
+): Record<string, JsonValue> => ({
+  errorTag: error._tag,
+  ...(error instanceof HopperProcessError && error.operation !== undefined
+    ? { operation: error.operation }
+    : {}),
+  ...(error instanceof HopperProcessError && error.requestId !== undefined
+    ? { requestId: error.requestId }
+    : {}),
+  ...(error.cause === undefined
+    ? {}
+    : { failure_cause: describeFailureCause(error.cause) }),
+});
+
+const describeFailureCause = (cause: unknown): JsonValue => {
+  if (cause instanceof Error) {
+    const code = "code" in cause ? cause.code : undefined;
+    return {
+      name: cause.name,
+      message: cause.message,
+      ...(typeof code === "string" ||
+      (typeof code === "number" && Number.isFinite(code))
+        ? { code }
+        : {}),
+    };
+  }
+  if (typeof cause === "string") return { type: "string", message: cause };
+  if (
+    cause === null ||
+    typeof cause === "boolean" ||
+    (typeof cause === "number" && Number.isFinite(cause))
+  )
+    return { type: cause === null ? "null" : typeof cause, value: cause };
+  return { type: typeof cause };
+};
+
 const stopProcess = async (
   input: HopperCleanupInput,
   state: CleanupState,