diff --git a/src/process/OwnedDebuggerSessionRegistry.ts b/src/process/OwnedDebuggerSessionRegistry.ts
index 98e770a2e9..60e8aee102 100644
--- a/src/process/OwnedDebuggerSessionRegistry.ts
+++ b/src/process/OwnedDebuggerSessionRegistry.ts
@@ -139,6 +139,8 @@ export class OwnedDebuggerSessionRegistry<
       controller.abort(callerSignal?.reason);
     };
     callerSignal?.addEventListener("abort", relayAbort, { once: true });
+    // An abort dispatched while the listener was being added never reaches it.
+    if (callerSignal?.aborted) relayAbort();
     const started = Promise.resolve()
       .then(() => run(controller.signal))
       .finally(() => {
diff --git a/tests/boundary/providers/RizinDebugSessionCoverage.part1.test.ts b/tests/boundary/providers/RizinDebugSessionCoverage.part1.test.ts
index 1027f20ffa..26cd7d41f3 100644
--- a/tests/boundary/providers/RizinDebugSessionCoverage.part1.test.ts
+++ b/tests/boundary/providers/RizinDebugSessionCoverage.part1.test.ts
@@ -10,9 +10,9 @@ import type { SpawnedOwnedProviderProcess } from "../../../src/process/ProviderP
 import {
   createRizinCoverageHarness,
   createInjectedProcess,
-  abortOnCheck,
   incompleteStop,
 } from "./RizinDebugSessionCoverage.fixtures.js";
+import { OwnerCancellation } from "../../../src/domain/analysisErrorCore.js";
 
 const {
   cleanup,
@@ -135,34 +135,10 @@ it.skipIf(process.platform === "win32")(
 );
 
 it.skipIf(process.platform === "win32")(
-  "does not spawn Rizin when cancellation arrives during TTY validation",
-  async () => {
-    let spawned = false;
-    const manager = createManager(
-      { REA_RIZIN_COMMAND: "injected-rizin" },
-      {
-        spawnProcess: async () => {
-          spawned = true;
-          throw new Error("must not spawn after cancellation");
-        },
-      },
-    );
-    const result = await manager.start(
-      {
-        path: "/tmp/cancel-before-spawn",
-        inferior_tty: await rizinTestInferiorTty(),
-      },
-      abortOnCheck(2),
-    );
-    expect(result.ok).toBe(false);
-    expect(spawned).toBe(false);
-  },
-);
-
-it.skipIf(process.platform === "win32")(
-  "closeAll drains concurrent startups and blocks later admission",
+  "closeAll aborts concurrent startups as owner-closed, waits for them, and blocks later admission",
   async () => {
     let spawnCount = 0;
+    let stopCount = 0;
     let resolveSpawnCalls!: () => void;
     const bothSpawnsCalled = new Promise<void>((resolve) => {
       resolveSpawnCalls = resolve;
@@ -181,7 +157,10 @@ it.skipIf(process.platform === "win32")(
           await spawnGate;
           return injected.spawnProcess(options);
         },
-        stopProcess: async () => ({ status: "stopped" }),
+        stopProcess: async () => {
+          stopCount += 1;
+          return { status: "stopped" };
+        },
       },
     );
     const tty = await rizinTestInferiorTty();
@@ -195,14 +174,21 @@ it.skipIf(process.platform === "win32")(
       closeAllResolved = true;
     });
     await Promise.resolve();
+    // The injected spawns ignore the abort, so closeAll waits for them.
     expect(closeAllResolved).toBe(false);
     releaseSpawns();
     const started = await Promise.all(starts);
-    expect(started.every((result) => result.ok)).toBe(true);
+    for (const result of started)
+      expect(result).toMatchObject({
+        ok: false,
+        error: {
+          _tag: "AnalysisCancelledError",
+          cause: OwnerCancellation.ownerClosed,
+        },
+      });
     await closing;
-    expect(
-      manager.status(started[0]!.ok ? started[0]!.value.session_id : "missing"),
-    ).toBeUndefined();
+    // Each process spawned before the abort was observed is stopped.
+    expect(stopCount).toBe(2);
     expect(
       (await manager.start({ path: "/tmp/after-close-all", inferior_tty: tty }))
         .ok,
diff --git a/tests/boundary/providers/RizinTtyCleanup.test.ts b/tests/boundary/providers/RizinTtyCleanup.test.ts
index 04abee7475..bd59fff2fc 100644
--- a/tests/boundary/providers/RizinTtyCleanup.test.ts
+++ b/tests/boundary/providers/RizinTtyCleanup.test.ts
@@ -81,6 +81,48 @@ it.skipIf(process.platform === "win32")(
   },
 );
 
+it.skipIf(process.platform === "win32")(
+  "does not spawn Rizin when cancellation arrives during TTY validation",
+  async () => {
+    const actual =
+      await vi.importActual<typeof import("node:fs/promises")>(
+        "node:fs/promises",
+      );
+    vi.mocked(isatty).mockReturnValue(true);
+    const controller = new AbortController();
+    const reason = { cancelled: "during TTY validation" };
+    vi.mocked(open).mockImplementation(async (...args) => {
+      const handle = await actual.open(...args);
+      controller.abort(reason);
+      return handle;
+    });
+    onTestFinished(() => {
+      vi.restoreAllMocks();
+    });
+    let spawned = false;
+    const manager = new RizinDebugSessionManager(
+      {},
+      {
+        platform: "linux",
+        spawnProcess: () => {
+          spawned = true;
+          throw new Error("must not spawn after cancellation");
+        },
+      },
+    );
+    const result = await manager.start(
+      { path: "/fixture", inferior_tty: "/dev/null" },
+      controller.signal,
+    );
+    expect(result).toMatchObject({
+      ok: false,
+      error: { _tag: "AnalysisCancelledError", cause: reason },
+    });
+    expect(spawned).toBe(false);
+    await manager.closeAll();
+  },
+);
+
 it.skipIf(process.platform === "win32")(
   "preserves cancellation during final TTY close with failed cleanup",
   async () => {