diff --git a/src/process/kill-tree.test.ts b/src/process/kill-tree.test.ts
new file mode 100644
index 0000000000..48f081f19e
--- /dev/null
+++ b/src/process/kill-tree.test.ts
@@ -0,0 +1,135 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+const { spawnMock } = vi.hoisted(() => ({
+  spawnMock: vi.fn(),
+}));
+
+vi.mock("node:child_process", () => ({
+  spawn: (...args: unknown[]) => spawnMock(...args),
+}));
+
+async function withPlatform<T>(platform: NodeJS.Platform, run: () => Promise<T> | T): Promise<T> {
+  const originalPlatform = Object.getOwnPropertyDescriptor(process, "platform");
+  Object.defineProperty(process, "platform", { value: platform, configurable: true });
+  try {
+    return await run();
+  } finally {
+    if (originalPlatform) {
+      Object.defineProperty(process, "platform", originalPlatform);
+    }
+  }
+}
+
+describe("killProcessTree", () => {
+  let killSpy: ReturnType<typeof vi.spyOn>;
+
+  beforeEach(() => {
+    spawnMock.mockReset();
+    killSpy = vi.spyOn(process, "kill");
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    killSpy.mockRestore();
+    vi.useRealTimers();
+    vi.resetModules();
+    vi.clearAllMocks();
+  });
+
+  it("on Windows skips delayed force-kill when PID is already gone", async () => {
+    killSpy.mockImplementation(((pid: number, signal?: NodeJS.Signals | number) => {
+      if (pid === 4242 && signal === 0) {
+        throw new Error("ESRCH");
+      }
+      return true;
+    }) as typeof process.kill);
+
+    await withPlatform("win32", async () => {
+      const { killProcessTree } = await import("./kill-tree.js");
+      killProcessTree(4242, { graceMs: 25 });
+
+      expect(spawnMock).toHaveBeenCalledTimes(1);
+      expect(spawnMock).toHaveBeenNthCalledWith(
+        1,
+        "taskkill",
+        ["/T", "/PID", "4242"],
+        expect.objectContaining({ detached: true, stdio: "ignore" }),
+      );
+
+      await vi.advanceTimersByTimeAsync(25);
+      expect(spawnMock).toHaveBeenCalledTimes(1);
+    });
+  });
+
+  it("on Windows force-kills after grace period only when PID still exists", async () => {
+    killSpy.mockImplementation(((pid: number, signal?: NodeJS.Signals | number) => {
+      if (pid === 5252 && signal === 0) {
+        return true;
+      }
+      return true;
+    }) as typeof process.kill);
+
+    await withPlatform("win32", async () => {
+      const { killProcessTree } = await import("./kill-tree.js");
+      killProcessTree(5252, { graceMs: 10 });
+
+      await vi.advanceTimersByTimeAsync(10);
+
+      expect(spawnMock).toHaveBeenCalledTimes(2);
+      expect(spawnMock).toHaveBeenNthCalledWith(
+        1,
+        "taskkill",
+        ["/T", "/PID", "5252"],
+        expect.objectContaining({ detached: true, stdio: "ignore" }),
+      );
+      expect(spawnMock).toHaveBeenNthCalledWith(
+        2,
+        "taskkill",
+        ["/F", "/T", "/PID", "5252"],
+        expect.objectContaining({ detached: true, stdio: "ignore" }),
+      );
+    });
+  });
+
+  it("on Unix sends SIGTERM first and skips SIGKILL when process exits", async () => {
+    killSpy.mockImplementation(((pid: number, signal?: NodeJS.Signals | number) => {
+      if (pid === -3333 && signal === 0) {
+        throw new Error("ESRCH");
+      }
+      if (pid === 3333 && signal === 0) {
+        throw new Error("ESRCH");
+      }
+      return true;
+    }) as typeof process.kill);
+
+    await withPlatform("linux", async () => {
+      const { killProcessTree } = await import("./kill-tree.js");
+      killProcessTree(3333, { graceMs: 10 });
+
+      await vi.advanceTimersByTimeAsync(10);
+
+      expect(killSpy).toHaveBeenCalledWith(-3333, "SIGTERM");
+      expect(killSpy).not.toHaveBeenCalledWith(-3333, "SIGKILL");
+      expect(killSpy).not.toHaveBeenCalledWith(3333, "SIGKILL");
+    });
+  });
+
+  it("on Unix sends SIGKILL after grace period when process is still alive", async () => {
+    killSpy.mockImplementation(((pid: number, signal?: NodeJS.Signals | number) => {
+      if (pid === -4444 && signal === 0) {
+        return true;
+      }
+      return true;
+    }) as typeof process.kill);
+
+    await withPlatform("linux", async () => {
+      const { killProcessTree } = await import("./kill-tree.js");
+      killProcessTree(4444, { graceMs: 5 });
+
+      await vi.advanceTimersByTimeAsync(5);
+
+      expect(killSpy).toHaveBeenCalledWith(-4444, "SIGTERM");
+      expect(killSpy).toHaveBeenCalledWith(-4444, "SIGKILL");
+    });
+  });
+});
diff --git a/src/process/kill-tree.ts b/src/process/kill-tree.ts
index ce12ca9c5b..e3f83f63a0 100644
--- a/src/process/kill-tree.ts
+++ b/src/process/kill-tree.ts
@@ -1,5 +1,8 @@
 import { spawn } from "node:child_process";
 
+const DEFAULT_GRACE_MS = 3000;
+const MAX_GRACE_MS = 60_000;
+
 /**
  * Best-effort process-tree termination with graceful shutdown.
  * - Windows: use taskkill /T to include descendants. Sends SIGTERM-equivalent
@@ -14,7 +17,7 @@ export function killProcessTree(pid: number, opts?: { graceMs?: number }): void
     return;
   }
 
-  const graceMs = opts?.graceMs ?? 3000;
+  const graceMs = normalizeGraceMs(opts?.graceMs);
 
   if (process.platform === "win32") {
     killProcessTreeWindows(pid, graceMs);
@@ -24,6 +27,22 @@ export function killProcessTree(pid: number, opts?: { graceMs?: number }): void
   killProcessTreeUnix(pid, graceMs);
 }
 
+function normalizeGraceMs(value?: number): number {
+  if (typeof value !== "number" || !Number.isFinite(value)) {
+    return DEFAULT_GRACE_MS;
+  }
+  return Math.max(0, Math.min(MAX_GRACE_MS, Math.floor(value)));
+}
+
+function isProcessAlive(pid: number): boolean {
+  try {
+    process.kill(pid, 0);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 function killProcessTreeUnix(pid: number, graceMs: number): void {
   // Step 1: Try graceful SIGTERM to process group
   try {
@@ -40,55 +59,46 @@ function killProcessTreeUnix(pid: number, graceMs: number): void {
 
   // Step 2: Wait grace period, then SIGKILL if still alive
   setTimeout(() => {
-    try {
-      // Check if still alive by sending signal 0
-      process.kill(-pid, 0);
-      // Still alive - hard kill
+    if (isProcessAlive(-pid)) {
       try {
         process.kill(-pid, "SIGKILL");
+        return;
       } catch {
-        try {
-          process.kill(pid, "SIGKILL");
-        } catch {
-          // Gone now
-        }
+        // Fall through to direct pid kill
       }
+    }
+    if (!isProcessAlive(pid)) {
+      return;
+    }
+    try {
+      process.kill(pid, "SIGKILL");
     } catch {
-      // Process group gone - check direct
-      try {
-        process.kill(pid, 0);
-        try {
-          process.kill(pid, "SIGKILL");
-        } catch {
-          // Gone
-        }
-      } catch {
-        // Already terminated
-      }
+      // Process exited between liveness check and kill
     }
   }, graceMs).unref(); // Don't block event loop exit
 }
 
-function killProcessTreeWindows(pid: number, graceMs: number): void {
-  // Step 1: Try graceful termination (taskkill without /F)
+function runTaskkill(args: string[]): void {
   try {
-    spawn("taskkill", ["/T", "/PID", String(pid)], {
+    spawn("taskkill", args, {
       stdio: "ignore",
       detached: true,
     });
   } catch {
-    // Ignore spawn failures
+    // Ignore taskkill spawn failures
   }
+}
 
-  // Step 2: Wait grace period, then force kill if still alive
+function killProcessTreeWindows(pid: number, graceMs: number): void {
+  // Step 1: Try graceful termination (taskkill without /F)
+  runTaskkill(["/T", "/PID", String(pid)]);
+
+  // Step 2: Wait grace period, then force kill only if pid still exists.
+  // This avoids unconditional delayed /F kills after graceful shutdown.
   setTimeout(() => {
-    try {
-      spawn("taskkill", ["/F", "/T", "/PID", String(pid)], {
-        stdio: "ignore",
-        detached: true,
-      });
-    } catch {
-      // Ignore taskkill failures
+    if (!isProcessAlive(pid)) {
+      return;
     }
+    runTaskkill(["/F", "/T", "/PID", String(pid)]);
   }, graceMs).unref(); // Don't block event loop exit
 }
diff --git a/src/process/supervisor/adapters/pty.test.ts b/src/process/supervisor/adapters/pty.test.ts
index c6753251be..4b45fd17e6 100644
--- a/src/process/supervisor/adapters/pty.test.ts
+++ b/src/process/supervisor/adapters/pty.test.ts
@@ -36,9 +36,11 @@ describe("createPtyAdapter", () => {
     spawnMock.mockReset();
     ptyKillMock.mockReset();
     killProcessTreeMock.mockReset();
+    vi.useRealTimers();
   });
 
   afterEach(() => {
+    vi.useRealTimers();
     vi.resetModules();
     vi.clearAllMocks();
   });
@@ -79,6 +81,53 @@ describe("createPtyAdapter", () => {
     expect(ptyKillMock).not.toHaveBeenCalled();
   });
 
+  it("wait does not settle immediately on SIGKILL", async () => {
+    vi.useFakeTimers();
+    spawnMock.mockReturnValue(createStubPty());
+    const { createPtyAdapter } = await import("./pty.js");
+
+    const adapter = await createPtyAdapter({
+      shell: "bash",
+      args: ["-lc", "sleep 10"],
+    });
+
+    const waitPromise = adapter.wait();
+    const settled = vi.fn();
+    void waitPromise.then(() => settled());
+
+    adapter.kill();
+
+    await Promise.resolve();
+    expect(settled).not.toHaveBeenCalled();
+
+    await vi.advanceTimersByTimeAsync(3999);
+    expect(settled).not.toHaveBeenCalled();
+
+    await vi.advanceTimersByTimeAsync(1);
+    await expect(waitPromise).resolves.toEqual({ code: null, signal: "SIGKILL" });
+  });
+
+  it("prefers real PTY exit over SIGKILL fallback settle", async () => {
+    vi.useFakeTimers();
+    const stub = createStubPty();
+    spawnMock.mockReturnValue(stub);
+    const { createPtyAdapter } = await import("./pty.js");
+
+    const adapter = await createPtyAdapter({
+      shell: "bash",
+      args: ["-lc", "sleep 10"],
+    });
+
+    const waitPromise = adapter.wait();
+    adapter.kill();
+    stub.emitExit({ exitCode: 0, signal: 9 });
+
+    await expect(waitPromise).resolves.toEqual({ code: 0, signal: 9 });
+
+    await vi.advanceTimersByTimeAsync(10_000);
+    await expect(adapter.wait()).resolves.toEqual({ code: 0, signal: 9 });
+  });
+
   it("resolves wait when exit fires before wait is called", async () => {
     const stub = createStubPty();
     spawnMock.mockReturnValue(stub);
diff --git a/src/process/supervisor/adapters/pty.ts b/src/process/supervisor/adapters/pty.ts
index 966b534243..e93c42a00b 100644
--- a/src/process/supervisor/adapters/pty.ts
+++ b/src/process/supervisor/adapters/pty.ts
@@ -1,7 +1,9 @@
-import { killProcessTree } from "../../kill-tree.js";
 import type { ManagedRunStdin } from "../types.js";
+import { killProcessTree } from "../../kill-tree.js";
 import { toStringEnv } from "./env.js";
 
+const FORCE_KILL_WAIT_FALLBACK_MS = 4000;
+
 type PtyExitEvent = { exitCode: number; signal?: number };
 type PtyDisposable = { dispose: () => void };
 type PtySpawnHandle = {
@@ -70,11 +72,21 @@ export async function createPtyAdapter(params: {
     | null = null;
   let waitPromise: Promise<{ code: number | null; signal: NodeJS.Signals | number | null }> | null =
     null;
+  let forceKillWaitFallbackTimer: NodeJS.Timeout | null = null;
+
+  const clearForceKillWaitFallback = () => {
+    if (!forceKillWaitFallbackTimer) {
+      return;
+    }
+    clearTimeout(forceKillWaitFallbackTimer);
+    forceKillWaitFallbackTimer = null;
+  };
 
   const settleWait = (value: { code: number | null; signal: NodeJS.Signals | number | null }) => {
     if (waitResult) {
       return;
     }
+    clearForceKillWaitFallback();
     waitResult = value;
     if (resolveWait) {
       const resolve = resolveWait;
@@ -83,6 +95,16 @@ export async function createPtyAdapter(params: {
     }
   };
 
+  const scheduleForceKillWaitFallback = (signal: NodeJS.Signals) => {
+    clearForceKillWaitFallback();
+    // Some PTY hosts fail to emit onExit after kill; use a delayed fallback
+    // so callers can still unblock without marking termination immediately.
+    forceKillWaitFallbackTimer = setTimeout(() => {
+      settleWait({ code: null, signal });
+    }, FORCE_KILL_WAIT_FALLBACK_MS);
+    forceKillWaitFallbackTimer.unref();
+  };
+
   exitListener =
     pty.onExit((event) => {
       const signal = event.signal && event.signal !== 0 ? event.signal : null;
@@ -151,9 +173,10 @@ export async function createPtyAdapter(params: {
     } catch {
       // ignore kill errors
     }
-    // Some PTY hosts do not emit `onExit` reliably after kill.
-    // Ensure waiters can progress on forced termination.
-    settleWait({ code: null, signal });
+
+    if (signal === "SIGKILL") {
+      scheduleForceKillWaitFallback(signal);
+    }
   };
 
   const dispose = () => {
@@ -167,6 +190,7 @@ export async function createPtyAdapter(params: {
     } catch {
       // ignore disposal errors
     }
+    clearForceKillWaitFallback();
     dataListener = null;
     exitListener = null;
     settleWait({ code: null, signal: null });