diff --git a/src/application/binary/BinarySession.ts b/src/application/binary/BinarySession.ts
index 7053d3efce..91bc936e31 100644
--- a/src/application/binary/BinarySession.ts
+++ b/src/application/binary/BinarySession.ts
@@ -10,7 +10,11 @@ import {
   AnalysisCapabilityUnavailableError,
   AnalysisOutputError,
 } from "../../domain/analysisErrorCore.js";
-import { AnalysisError } from "../../domain/analysisErrorBase.js";
+import {
+  AnalysisError,
+  primaryAnalysisError,
+} from "../../domain/analysisErrorBase.js";
+import { projectAnalysisError } from "../../domain/analysisErrorProjection.js";
 import { err, ok, type Result } from "../../domain/result.js";
 import type { JsonValue } from "../../domain/jsonValue.js";
 import { createAnalysisExecutionEvidence } from "../../domain/analysisObservation.js";
@@ -1031,9 +1035,15 @@ export class BinarySession
     primary: AnalysisError,
   ): Promise<AnalysisError> {
     const restored = await this.#restore(previous);
-    return restored.ok
-      ? primary
-      : sessionCleanupFailure(primary, restored.error, "open_binary");
+    if (restored.ok) return primary;
+    primary.retainSecondaryFailure(restored.error, {
+      restoration_error: projectAnalysisError(
+        primaryAnalysisError(restored.error),
+      ),
+    });
+    return restored.error.cleanupIncomplete
+      ? sessionCleanupFailure(primary, restored.error, "open_binary")
+      : primary;
   }
 
   /** Describe the active binary session. */
@@ -1460,7 +1470,7 @@ export class BinarySession
     }
     const closed = await this.#retireClient(run);
     return closed.ok
-      ? ok(null)
+      ? err(started.error)
       : err(sessionCleanupFailure(started.error, closed.error, "open_binary"));
   }
 
diff --git a/src/application/binary/BinarySessionRestoration.test.ts b/src/application/binary/BinarySessionRestoration.test.ts
new file mode 100644
index 0000000000..6720d03d99
--- /dev/null
+++ b/src/application/binary/BinarySessionRestoration.test.ts
@@ -0,0 +1,139 @@
+import { expect, it } from "vitest";
+import {
+  AnalysisCancelledError,
+  AnalysisOutputError,
+} from "../../domain/analysisErrorCore.js";
+import { projectAnalysisError } from "../../domain/analysisErrorProjection.js";
+import { createAnalysisProfile } from "../../domain/analysisProfile.js";
+import { ProviderCleanupError } from "../../domain/providerCleanupError.js";
+import { err, ok } from "../../domain/result.js";
+import { createAnalysisExecution } from "../AnalysisProvider.js";
+import { AnalysisProviderRegistry } from "./AnalysisProviderRegistry.js";
+import { BinarySession } from "./BinarySession.js";
+import {
+  SessionProviderRouter,
+  type SessionProviderRoute,
+} from "./SessionProviderRouter.js";
+
+it.each([
+  { cancelled: false, cleanupFails: false },
+  { cancelled: true, cleanupFails: false },
+  { cancelled: false, cleanupFails: true },
+  { cancelled: true, cleanupFails: true },
+])(
+  "retains failed restoration after switch cancellation=$cancelled, cleanup failure=$cleanupFails",
+  async ({ cancelled, cleanupFails }) => {
+    const session = new BinarySession(
+      SessionProviderRouter.selectable(new AnalysisProviderRegistry([]), []),
+    );
+    const controller = new AbortController();
+    const identity = {
+      id: "restoration-test",
+      name: "Restoration test",
+      version: "1",
+    };
+    const restorationFailure = new AnalysisOutputError(
+      "health",
+      "Previous target could not restart",
+    );
+    const switchFailure = new AnalysisOutputError(
+      "health",
+      "Selected target could not start",
+    );
+    const cleanupFailure = new ProviderCleanupError(
+      identity.id,
+      ["restored-client"],
+      { reason: "close failed" },
+    );
+    let created = 0;
+    let restorationCloseCalls = 0;
+    const route: SessionProviderRoute = {
+      identity,
+      capabilities: new Map(),
+      profile: createAnalysisProfile(identity, { fixture: "original" }),
+      binding: null,
+      selection: undefined,
+      createClient: () => {
+        const restoring = created++ > 0;
+        return {
+          execute: async () =>
+            restoring
+              ? err(restorationFailure)
+              : ok(createAnalysisExecution(null, identity)),
+          close: async () => {
+            if (!restoring) {
+              if (cancelled) controller.abort("cancel switch");
+              return ok(null);
+            }
+            restorationCloseCalls += 1;
+            if (cleanupFails && restorationCloseCalls === 1)
+              return err(cleanupFailure);
+            cleanupFailure.resolveCleanup();
+            return ok(null);
+          },
+        };
+      },
+    };
+    try {
+      const target = await session.resolveTarget(process.execPath);
+      expect(target.ok).toBe(true);
+      if (!target.ok) return;
+      expect(
+        (await session.openResolvedTarget({ target: target.value, route })).ok,
+      ).toBe(true);
+      expect(session.activeTarget()).toEqual(target.value);
+      const result = await session.openResolvedTarget(
+        {
+          target: target.value,
+          route: {
+            ...route,
+            profile: createAnalysisProfile(identity, { fixture: "selected" }),
+            createClient: () => ({
+              execute: async () => err(switchFailure),
+              close: async () => ok(null),
+            }),
+          },
+        },
+        { signal: controller.signal },
+      );
+      expect(result.ok).toBe(false);
+      if (result.ok) return;
+      expect(session.activeTarget()).toBeUndefined();
+      expect(await session.status()).toMatchObject({
+        open: false,
+        cleanup_pending: cleanupFails,
+      });
+      expect(projectAnalysisError(result.error)).toMatchObject({
+        code: cleanupFails
+          ? "cleanup_incomplete"
+          : cancelled
+            ? "cancelled"
+            : "unreadable_output",
+      });
+      expect((await session.close()).ok).toBe(true);
+      expect(restorationCloseCalls).toBe(cleanupFails ? 2 : 1);
+      expect(await session.status()).toMatchObject({
+        open: false,
+        cleanup_pending: false,
+      });
+      expect(projectAnalysisError(result.error).code).toBe(
+        cancelled ? "cancelled" : "unreadable_output",
+      );
+      expect(projectAnalysisError(result.error)).toMatchObject({
+        details: {
+          diagnostics: {
+            restoration_error: projectAnalysisError(restorationFailure),
+          },
+        },
+      });
+      if (cancelled) {
+        const primary = result.error.cleanupPrimary ?? result.error;
+        expect(primary).toBeInstanceOf(AnalysisCancelledError);
+      } else {
+        expect(result.error.cleanupPrimary ?? result.error).toBe(switchFailure);
+      }
+    } finally {
+      await session.close();
+    }
+  },
+);