diff --git a/hooks/session-start-profiler-binary-resolution.test.ts b/hooks/session-start-profiler-binary-resolution.test.ts
new file mode 100644
index 0000000..09c50a4
--- /dev/null
+++ b/hooks/session-start-profiler-binary-resolution.test.ts
@@ -0,0 +1,66 @@
+import { describe, expect, test } from "bun:test";
+import {
+  binaryNeedsShell,
+  getBinaryPathCandidates,
+} from "./src/session-start-profiler.mts";
+
+// npm lays down three entries per global binary in %APPDATA%\npm:
+// `vercel` (POSIX sh shim), `vercel.CMD` and `vercel.ps1`. Only the .CMD is
+// usable from Node, so candidate ordering decides whether the CLI is found.
+const NPM_STYLE_PATHEXT = ".COM;.EXE;.BAT;.CMD;.VBS;.JS;.PS1".split(";");
+
+describe("getBinaryPathCandidates", () => {
+  test("returns the bare name on non-Windows platforms", () => {
+    expect(getBinaryPathCandidates("vercel", "linux")).toEqual(["vercel"]);
+    expect(getBinaryPathCandidates("vercel", "darwin")).toEqual(["vercel"]);
+  });
+
+  test("prefers a spawnable extension over npm's extensionless POSIX shim", () => {
+    const candidates = getBinaryPathCandidates("vercel", "win32", NPM_STYLE_PATHEXT);
+
+    expect(candidates.indexOf("vercel.CMD")).toBeLessThan(candidates.indexOf("vercel"));
+    expect(candidates[candidates.length - 1]).toBe("vercel");
+  });
+
+  test("never ranks a non-spawnable PATHEXT entry above a real executable", () => {
+    const candidates = getBinaryPathCandidates("vercel", "win32", NPM_STYLE_PATHEXT);
+
+    for (const spawnable of ["vercel.COM", "vercel.EXE", "vercel.BAT", "vercel.CMD"]) {
+      for (const rejected of ["vercel.VBS", "vercel.JS", "vercel.PS1"]) {
+        expect(candidates.indexOf(spawnable)).toBeLessThan(candidates.indexOf(rejected));
+      }
+    }
+  });
+
+  test("keeps every PATHEXT entry as a candidate", () => {
+    const candidates = getBinaryPathCandidates("vercel", "win32", NPM_STYLE_PATHEXT);
+
+    expect(candidates.length).toBe(NPM_STYLE_PATHEXT.length + 1);
+    for (const extension of NPM_STYLE_PATHEXT) {
+      expect(candidates).toContain(`vercel${extension}`);
+    }
+  });
+
+  test("does not append extensions to an already-qualified name", () => {
+    expect(getBinaryPathCandidates("vercel.cmd", "win32", NPM_STYLE_PATHEXT)).toEqual([
+      "vercel.cmd",
+    ]);
+  });
+});
+
+describe("binaryNeedsShell", () => {
+  test("requires a shell for Windows batch wrappers", () => {
+    // Node rejects these with EINVAL when spawned directly (CVE-2024-27980 fix).
+    expect(binaryNeedsShell("C:\\npm\\vercel.CMD", "win32")).toBe(true);
+    expect(binaryNeedsShell("C:\\npm\\vercel.bat", "win32")).toBe(true);
+  });
+
+  test("spawns real executables directly", () => {
+    expect(binaryNeedsShell("C:\\tools\\vercel.exe", "win32")).toBe(false);
+  });
+
+  test("never asks for a shell off Windows", () => {
+    expect(binaryNeedsShell("/usr/local/bin/vercel", "linux")).toBe(false);
+    expect(binaryNeedsShell("/usr/local/bin/weird.cmd", "darwin")).toBe(false);
+  });
+});
diff --git a/hooks/session-start-profiler.mjs b/hooks/session-start-profiler.mjs
index 8eac1c7..04c1a49 100644
--- a/hooks/session-start-profiler.mjs
+++ b/hooks/session-start-profiler.mjs
@@ -565,14 +565,38 @@ var SPAWN_STDIO = "ignore pipe ignore".split(" ");
 var EXEC_SYNC_TIMEOUT_MS = 3e3;
 var NUMERIC_VERSION_RE = /\d+(?:\.\d+)*/;
 var WINDOWS_EXECUTABLE_EXTENSIONS = (process.env.PATHEXT || ".EXE;.CMD;.BAT;.COM").split(";").filter(Boolean);
-function getBinaryPathCandidates(binaryName) {
-  if (process.platform !== "win32") {
+var WINDOWS_SPAWNABLE_EXTENSIONS = ".EXE;.COM;.CMD;.BAT".split(";");
+var WINDOWS_SHELL_SCRIPT_RE = /\.(?:cmd|bat)$/i;
+function getBinaryPathCandidates(binaryName, platform = process.platform, pathExtensions = WINDOWS_EXECUTABLE_EXTENSIONS) {
+  if (platform !== "win32") {
     return [binaryName];
   }
   const hasExecutableExtension = /\.[^./\\]+$/.test(binaryName);
-  const suffixes = hasExecutableExtension ? [""] : ["", ...WINDOWS_EXECUTABLE_EXTENSIONS];
+  if (hasExecutableExtension) {
+    return [binaryName];
+  }
+  const isSpawnable = (extension) => WINDOWS_SPAWNABLE_EXTENSIONS.includes(extension.toUpperCase());
+  const suffixes = [
+    ...pathExtensions.filter(isSpawnable),
+    ...pathExtensions.filter((extension) => !isSpawnable(extension)),
+    ""
+  ];
   return suffixes.map((suffix) => `${binaryName}${suffix}`);
 }
+function binaryNeedsShell(binaryPath, platform = process.platform) {
+  return platform === "win32" && WINDOWS_SHELL_SCRIPT_RE.test(binaryPath);
+}
+function runBinarySync(binaryPath, args) {
+  const needsShell = binaryNeedsShell(binaryPath);
+  const command = needsShell ? `"${binaryPath}"` : binaryPath;
+  return execFileSync(command, args, {
+    timeout: EXEC_SYNC_TIMEOUT_MS,
+    encoding: "utf-8",
+    stdio: SPAWN_STDIO,
+    shell: needsShell,
+    windowsHide: true
+  }).trim();
+}
 function resolveBinaryFromPath(binaryName) {
   try {
     const pathEntries = (process.env.PATH || "").split(delimiter).filter(Boolean);
@@ -629,11 +653,7 @@ function checkVercelCli() {
   }
   let currentVersion;
   try {
-    const raw = execFileSync(vercelBinary, VERCEL_VERSION_ARGS, {
-      timeout: EXEC_SYNC_TIMEOUT_MS,
-      encoding: "utf-8",
-      stdio: SPAWN_STDIO
-    }).trim();
+    const raw = runBinarySync(vercelBinary, VERCEL_VERSION_ARGS);
     const lines = raw.split("\n").map((l) => l.trim()).filter(Boolean);
     currentVersion = lines[lines.length - 1];
   } catch (error) {
@@ -641,7 +661,7 @@ function checkVercelCli() {
       command: vercelBinary,
       args: VERCEL_VERSION_ARGS.join(" ")
     });
-    return { installed: false, needsUpdate: false };
+    return { installed: true, needsUpdate: false };
   }
   const npmBinary = resolveBinaryFromPath("npm");
   if (!npmBinary) {
@@ -649,12 +669,7 @@ function checkVercelCli() {
   }
   let latestVersion;
   try {
-    const raw = execFileSync(npmBinary, NPM_VIEW_ARGS, {
-      timeout: EXEC_SYNC_TIMEOUT_MS,
-      encoding: "utf-8",
-      stdio: SPAWN_STDIO
-    }).trim();
-    latestVersion = raw;
+    latestVersion = runBinarySync(npmBinary, NPM_VIEW_ARGS);
   } catch (error) {
     logCaughtError(log, "session-start-profiler:npm-latest-version-check-failed", error, {
       command: npmBinary,
@@ -888,12 +903,14 @@ if (isSessionStartProfilerEntrypoint) {
   main();
 }
 export {
+  binaryNeedsShell,
   buildSessionStartProfilerEnvVars,
   buildSessionStartProfilerUserMessages,
   checkGreenfield,
   detectAgentHarness,
   detectSessionStartPlatform,
   formatSessionStartProfilerCursorOutput,
+  getBinaryPathCandidates,
   logBrokenSkillFrontmatterSummary,
   normalizeDetectedAgentHarness,
   normalizeSessionStartSessionId,
diff --git a/hooks/src/session-start-profiler.mts b/hooks/src/session-start-profiler.mts
index ba6b892..f36f7c0 100644
--- a/hooks/src/session-start-profiler.mts
+++ b/hooks/src/session-start-profiler.mts
@@ -339,16 +339,64 @@ const WINDOWS_EXECUTABLE_EXTENSIONS = (process.env.PATHEXT || ".EXE;.CMD;.BAT;.C
   .split(";")
   .filter(Boolean);
 
-function getBinaryPathCandidates(binaryName: string): string[] {
-  if (process.platform !== "win32") {
+// Extensions Node can hand to CreateProcess — directly, or through the shell for
+// .cmd/.bat. Other PATHEXT entries (.PS1, .PY, .JS, ...) resolve to files
+// spawnSync rejects with EFTYPE, so they must never outrank a real executable.
+const WINDOWS_SPAWNABLE_EXTENSIONS: string[] = ".EXE;.COM;.CMD;.BAT".split(";");
+const WINDOWS_SHELL_SCRIPT_RE = /\.(?:cmd|bat)$/i;
+
+export function getBinaryPathCandidates(
+  binaryName: string,
+  platform: string = process.platform,
+  pathExtensions: string[] = WINDOWS_EXECUTABLE_EXTENSIONS,
+): string[] {
+  if (platform !== "win32") {
     return [binaryName];
   }
 
   const hasExecutableExtension = /\.[^./\\]+$/.test(binaryName);
-  const suffixes = hasExecutableExtension ? [""] : ["", ...WINDOWS_EXECUTABLE_EXTENSIONS];
+  if (hasExecutableExtension) {
+    return [binaryName];
+  }
+
+  const isSpawnable = (extension: string): boolean =>
+    WINDOWS_SPAWNABLE_EXTENSIONS.includes(extension.toUpperCase());
+  // The bare name goes last. On Windows an extensionless entry sitting next to a
+  // .cmd is npm's POSIX shim — an sh script spawnSync fails on with ENOENT.
+  const suffixes = [
+    ...pathExtensions.filter(isSpawnable),
+    ...pathExtensions.filter((extension: string) => !isSpawnable(extension)),
+    "",
+  ];
   return suffixes.map((suffix: string) => `${binaryName}${suffix}`);
 }
 
+/**
+ * Windows batch wrappers cannot be spawned directly: since the fix for
+ * CVE-2024-27980, Node rejects .cmd/.bat without `shell: true` (EINVAL).
+ */
+export function binaryNeedsShell(
+  binaryPath: string,
+  platform: string = process.platform,
+): boolean {
+  return platform === "win32" && WINDOWS_SHELL_SCRIPT_RE.test(binaryPath);
+}
+
+/** Run a resolved binary and return its trimmed stdout. */
+function runBinarySync(binaryPath: string, args: string[]): string {
+  const needsShell = binaryNeedsShell(binaryPath);
+  // Under `shell: true` the command is re-parsed by cmd.exe, which would
+  // otherwise split an unquoted path on its spaces.
+  const command = needsShell ? `"${binaryPath}"` : binaryPath;
+  return execFileSync(command, args, {
+    timeout: EXEC_SYNC_TIMEOUT_MS,
+    encoding: "utf-8",
+    stdio: SPAWN_STDIO,
+    shell: needsShell,
+    windowsHide: true,
+  }).trim();
+}
+
 function resolveBinaryFromPath(binaryName: string): string | null {
   try {
     const pathEntries = (process.env.PATH || "").split(delimiter).filter(Boolean);
@@ -422,11 +470,7 @@ function checkVercelCli(): VercelCliStatus {
   // 1. Check if vercel is installed
   let currentVersion: string | undefined;
   try {
-    const raw: string = execFileSync(vercelBinary, VERCEL_VERSION_ARGS, {
-      timeout: EXEC_SYNC_TIMEOUT_MS,
-      encoding: "utf-8",
-      stdio: SPAWN_STDIO,
-    }).trim();
+    const raw: string = runBinarySync(vercelBinary, VERCEL_VERSION_ARGS);
     // Output may include extra lines; version is typically last non-empty line
     const lines: string[] = raw.split("\n").map((l: string) => l.trim()).filter(Boolean);
     currentVersion = lines[lines.length - 1];
@@ -435,7 +479,9 @@ function checkVercelCli(): VercelCliStatus {
       command: vercelBinary,
       args: VERCEL_VERSION_ARGS.join(" "),
     });
-    return { installed: false, needsUpdate: false };
+    // The binary is on PATH — only the version probe failed. Reporting "not
+    // installed" here would tell the user to install a CLI they already have.
+    return { installed: true, needsUpdate: false };
   }
 
   const npmBinary = resolveBinaryFromPath("npm");
@@ -446,12 +492,7 @@ function checkVercelCli(): VercelCliStatus {
   // 2. Fetch latest version from npm registry
   let latestVersion: string | undefined;
   try {
-    const raw: string = execFileSync(npmBinary, NPM_VIEW_ARGS, {
-      timeout: EXEC_SYNC_TIMEOUT_MS,
-      encoding: "utf-8",
-      stdio: SPAWN_STDIO,
-    }).trim();
-    latestVersion = raw;
+    latestVersion = runBinarySync(npmBinary, NPM_VIEW_ARGS);
   } catch (error) {
     logCaughtError(log, "session-start-profiler:npm-latest-version-check-failed", error, {
       command: npmBinary,