diff --git a/src/application/binary/BinarySession.ts b/src/application/binary/BinarySession.ts
index f1a096196d..0ef2236f4d 100644
--- a/src/application/binary/BinarySession.ts
+++ b/src/application/binary/BinarySession.ts
@@ -224,7 +224,10 @@ export class BinarySession
     options: Pick<ExecutionOptions, "signal"> = {},
   ): Promise<Result<ResolvedAppBundleResourceRoot, AnalysisError>> {
     return this.#serialize(async (admittedThrough) => {
-      const refused = this.#targetAcquisitionRefused("open_bundle_resources");
+      const refused = this.#targetAcquisitionRefused(
+        "open_bundle_resources",
+        options.signal,
+      );
       if (refused !== undefined) return refused;
       await this.#drainCalls(admittedThrough);
       if (isAborted(options.signal))
@@ -530,7 +533,10 @@ export class BinarySession
       const attempt = async (): Promise<
         Result<BinaryTarget, AnalysisError>
       > => {
-        const refused = this.#targetAcquisitionRefused("open_binary");
+        const refused = this.#targetAcquisitionRefused(
+          "open_binary",
+          options.signal,
+        );
         if (refused !== undefined) return refused;
         const admitted = await this.#withLoadedSnapshot(options);
         if (!admitted.ok) return admitted;
@@ -790,6 +796,12 @@ export class BinarySession
       failure: AnalysisError | undefined,
     ) => Promise<Result<null, AnalysisError>>,
   ): Promise<Result<Result<Value, AnalysisError>, AnalysisError>> {
+    if (this.#shutdownStarted)
+      return Promise.resolve(
+        err(
+          new AnalysisCancelledError(operationName, { cause: signal?.reason }),
+        ),
+      );
     return this.#serialize(async (admittedThrough) => {
       if (this.#activeBundleResources !== undefined)
         return err(
@@ -921,9 +933,12 @@ export class BinarySession
 
   #targetAcquisitionRefused(
     operation: "open_binary" | "open_bundle_resources",
+    signal?: AbortSignal,
   ): Result<never, AnalysisCancelledError> | undefined {
     if (!this.#shutdownStarted) return undefined;
-    return err(new AnalysisCancelledError(operation));
+    return err(
+      new AnalysisCancelledError(operation, { cause: signal?.reason }),
+    );
   }
 
   /** Release the engine and replay state while retaining investigation history. */
@@ -1004,7 +1019,11 @@ export class BinarySession
   ): Promise<Result<ResetInvestigationReceipt, AnalysisError>> {
     if (this.#shutdownStarted)
       return Promise.resolve(
-        err(new AnalysisCancelledError("reset_investigation")),
+        err(
+          new AnalysisCancelledError("reset_investigation", {
+            cause: options.signal?.reason,
+          }),
+        ),
       );
     return this.#serialize(async (admittedThrough) => {
       await this.#drainCalls(admittedThrough);
@@ -1410,6 +1429,12 @@ export class BinarySession
     options?: ExecutionOptions,
     recoveryParameters?: Readonly<Record<string, JsonValue>>,
   ): Promise<Result<AnalysisExecution, AnalysisError>> {
+    if (this.#shutdownStarted)
+      return Promise.resolve(
+        err(
+          new AnalysisCancelledError(name, { cause: options?.signal?.reason }),
+        ),
+      );
     const generation = this.#transitionGeneration;
     const call = this.#execute(
       name,
@@ -1430,6 +1455,7 @@ export class BinarySession
   ): Promise<Result<AnalysisExecution, AnalysisError> | undefined> {
     const active = this.#active;
     if (
+      this.#shutdownStarted ||
       this.#transitionPending > 0 ||
       active === undefined ||
       active.client.executeIfReady === undefined
@@ -1461,7 +1487,11 @@ export class BinarySession
     operation: (analysis: AnalysisOperationPort) => Promise<Value>,
   ): Promise<Result<Value, AnalysisError>> {
     if (this.#shutdownStarted)
-      return Promise.resolve(err(new AnalysisCancelledError(operationName)));
+      return Promise.resolve(
+        err(
+          new AnalysisCancelledError(operationName, { cause: signal?.reason }),
+        ),
+      );
     const generation = this.#transitionGeneration;
     const transition = this.#transition;
     const call = (async (): Promise<Result<Value, AnalysisError>> => {
diff --git a/src/application/binary/BinarySessionInvestigation.test.ts b/src/application/binary/BinarySessionInvestigation.test.ts
index 81039e084c..7c81592fe8 100644
--- a/src/application/binary/BinarySessionInvestigation.test.ts
+++ b/src/application/binary/BinarySessionInvestigation.test.ts
@@ -570,3 +570,119 @@ it("retains exact cancellation reason and a complete checkpoint during final cle
     await session.dispose();
   }
 });
+
+it.each(
+  (
+    [
+      "execute",
+      "direct observation",
+      "external mutation",
+      "composed analysis",
+      "reset",
+      "open binary",
+      "open resources",
+    ] as const
+  ).flatMap((entrypoint) =>
+    [false, true].map((aborted) => ({ entrypoint, aborted })),
+  ),
+)(
+  "seals new $entrypoint admission at shutdown with caller aborted=$aborted",
+  async ({ entrypoint, aborted }) => {
+    const [target] = await createBinarySessionTargets();
+    const calls: string[] = [];
+    const session = createTestBinarySession(createCacheProvider(calls));
+    const entered = createDeferred<void>();
+    const release = createDeferred<void>();
+    const parameters = { address: "0x1000", document: "fixture" };
+    const mutation = vi.fn(async () => ok(null));
+    let earlier: Promise<unknown> | undefined;
+    try {
+      const opened = await session.open(target);
+      if (!opened.ok) throw opened.error;
+      earlier = session.withAdmittedAnalysis(
+        "earlier",
+        undefined,
+        async (analysis) => {
+          entered.resolve();
+          await release.promise;
+          return analysis.execute("address_name", parameters);
+        },
+      );
+      await awaitAcknowledgement(
+        entered.promise,
+        earlier,
+        "earlier analysis admission",
+      );
+      const controller = new AbortController();
+      const reason = { caller: "opaque shutdown cancellation", entrypoint };
+      if (aborted) controller.abort(reason);
+      session.beginShutdown();
+      const options = { signal: controller.signal };
+      const late = {
+        execute: () => session.execute("address_name", parameters, options),
+        "direct observation": () =>
+          session.executeForDirectObservation(
+            "address_name",
+            parameters,
+            parameters,
+            options,
+          ),
+        "external mutation": () =>
+          session.withAdmittedExternalMutation(
+            undefined,
+            controller.signal,
+            mutation,
+            (_value, error) => error,
+          ),
+        "composed analysis": () =>
+          session.withAdmittedAnalysis("late", controller.signal, mutation),
+        reset: () => session.resetInvestigation(options),
+        "open binary": () => session.open(target, options),
+        "open resources": () => session.openBundleResources(target, options),
+      }[entrypoint]();
+      release.resolve();
+      const result = await late;
+      if (result.ok) throw new Error("Expected shutdown admission refusal");
+      expect(result.error._tag).toBe("AnalysisCancelledError");
+      expect(result.error.cause).toBe(aborted ? reason : undefined);
+      expect(mutation).not.toHaveBeenCalled();
+      expect(await earlier).toMatchObject({ ok: true, value: { ok: true } });
+      expect(calls.filter((name) => name === "address_name")).toHaveLength(1);
+    } finally {
+      release.resolve();
+      await earlier;
+      await session.dispose();
+    }
+  },
+);
+
+it("stops prompt completion dispatch as soon as shutdown seals admission", async () => {
+  const [target] = await createBinarySessionTargets();
+  const calls: string[] = [];
+  const base = createCacheProvider(calls);
+  const session = createTestBinarySession({
+    ...base,
+    createClient: (...arguments_) => {
+      const client = base.createClient(...arguments_);
+      return { ...client, executeIfReady: client.execute.bind(client) };
+    },
+  });
+  try {
+    const opened = await session.open(target);
+    if (!opened.ok) throw opened.error;
+    // Instantiate the real composite's child before exercising its ready path.
+    const initial = await session.execute("address_name", {});
+    if (!initial.ok) throw initial.error;
+    expect(
+      await session.executeIfProviderReady("address_name", {}),
+    ).toMatchObject({ ok: true });
+    const before = calls.length;
+    session.beginShutdown();
+    expect(
+      await session.executeIfProviderReady("address_name", {}),
+    ).toBeUndefined();
+    expect(calls).toHaveLength(before);
+  } finally {
+    await session.dispose();
+  }
+});