fix: use 'exec' in binstub

src/index.ts

@@ -525,7 +525,7 @@ fi
 `
   } else {
     sh += `\
-${shProg} ${args} ${shTarget} ${progArgs}"$@"
+exec ${shProg} ${args} ${shTarget} ${progArgs}"$@"
 exit $?
 `
   }

test/e2e.test.js

@@ -1,4 +1,4 @@
-import { spawnSync } from 'node:child_process'
+import { spawn, spawnSync } from 'node:child_process'
 import fs from 'node:fs'
 import path from 'node:path'
 import { describe, test, snapshot } from 'node:test'
@@ -11,6 +11,7 @@ import tempy from 'tempy'
 import { cmdShim } from '../index.js'
 
 const describeOnWindows = process.platform === 'win32' ? describe : describe.skip
+const describeOnPosix = process.platform === 'win32' ? describe.skip : describe
 
 describeOnWindows('create a command shim for a .exe file', () => {
   test('shim files', async (t) => {
@@ -57,3 +58,34 @@ describeOnWindows('sh shim wrapping a .cmd target invoked from Git Bash', () =>
     )
   })
 })
+
+describeOnPosix('sh shim binstub uses exec', () => {
+  // Regression for the binstub bug: without `exec`, the shell process
+  // wraps the wrapped binary, so signals sent to the shim do not reach
+  // the wrapped process and the binary's PID differs from the shim's
+  // spawn PID. With `exec`, the shell process is replaced in place and
+  // the wrapped binary inherits the shim's PID.
+  test('wrapped binary inherits the shim\'s PID (proves exec replaced the shell)', async () => {
+    const tempDir = tempy.directory()
+    // process.execPath is a no-shebang native binary, so cmdShim hits the
+    // non-shLongProg branch of generateShShim — the one that needs `exec`.
+    const shim = path.join(tempDir, 'shim')
+    await cmdShim(process.execPath, shim)
+
+    const proc = spawn('/bin/sh', [shim, '-p', 'process.pid'], {
+      stdio: ['ignore', 'pipe', 'pipe'],
+    })
+    const shimPid = proc.pid
+    let stdout = ''
+    proc.stdout.on('data', (chunk) => { stdout += chunk })
+    const exitCode = await new Promise((resolve) => proc.on('exit', resolve))
+
+    assert.equal(exitCode, 0, `shim exited ${exitCode}; stdout=${stdout}`)
+    const reportedPid = Number(stdout.trim())
+    assert.equal(
+      reportedPid,
+      shimPid,
+      `expected child to inherit shim PID via exec — got reported=${reportedPid}, shim=${shimPid}`
+    )
+  })
+})

test/e2e.test.js.snapshot

@@ -11,7 +11,7 @@ case \`uname\` in
     ;;
 esac
 
-"$basedir/foo"   "$@"
+exec "$basedir/foo"   "$@"
 exit $?
 
 `;

test/test.js.snapshot

@@ -77,7 +77,7 @@ case \`uname\` in
     ;;
 esac
 
-"/.pnpm/nodejs/16.0.0/node"  "$basedir/src.env" "$@"
+exec "/.pnpm/nodejs/16.0.0/node"  "$basedir/src.env" "$@"
 exit $?
 
 `;
@@ -818,7 +818,7 @@ case \`uname\` in
     ;;
 esac
 
-"$basedir/src.exe"   "$@"
+exec "$basedir/src.exe"   "$@"
 exit $?
 
 `;
@@ -857,7 +857,7 @@ case \`uname\` in
     ;;
 esac
 
-"$basedir/src.exe"   "$@"
+exec "$basedir/src.exe"   "$@"
 exit $?
 
 `;