diff --git a/CLAUDE.md b/CLAUDE.md
index 9bf54dc..521c80e 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -11,7 +11,7 @@ Transcript-based shell integration test runner. Bun + TypeScript.
 ## Architecture
 
 - `src/parse.ts` — parses `.shout` files into `ShoutFile` (list of `Command`)
-- `src/run.ts` — executes commands via `Bun.spawn(["/bin/sh"])`, captures output with sentinels
+- `src/run.ts` — executes commands via `Bun.spawn(["setsid", "/bin/sh"])`, captures output with sentinels
 - `src/match.ts` — wildcard-aware output matching and diff generation
 - `src/format.ts` — evaluates pass/fail, formats failures and summary
 - `src/update.ts` — rewrites `.shout` files with actual output (`--update` mode)
diff --git a/src/run.test.ts b/src/run.test.ts
index 37d0227..e2ab64f 100644
--- a/src/run.test.ts
+++ b/src/run.test.ts
@@ -26,11 +26,10 @@ const defaultOpts = {
 async function isProcessRunning(pid: number): Promise<boolean> {
   try {
     const stat = await readFile(`/proc/${pid}/stat`, "utf-8")
-    // State is the 3rd field: R=running, S=sleeping, Z=zombie, etc.
-    const state = stat.split(" ")[2]
+    // Find state after the comm field (which is wrapped in parens and may contain spaces)
+    const state = stat.charAt(stat.lastIndexOf(")") + 2)
     return state !== "Z" && state !== "X"
   } catch {
-    // /proc entry doesn't exist — process is fully gone
     return false
   }
 }
@@ -39,44 +38,45 @@ describe("runFile", () => {
   test("basic command", async () => {
     const file = makeFile([{ command: "echo hello" }])
     const result = await runFile(file, defaultOpts)
-    expect(result.results[0]?.actual).toEqual(["hello"])
-    expect(result.results[0]?.exitCode).toBe(0)
-    await cleanupTmpDir(result.tmpDir)
+    try {
+      expect(result.results[0]?.actual).toEqual(["hello"])
+      expect(result.results[0]?.exitCode).toBe(0)
+    } finally {
+      await cleanupTmpDir(result.tmpDir)
+    }
   })
 
   test("cleans up backgrounded processes after exit", async () => {
     const file = makeFile([
       { command: "sleep 300 >/dev/null 2>&1 & echo $!" },
     ])
-
     const result = await runFile(file, defaultOpts)
-    const pid = parseInt(result.results[0]?.actual[0] ?? "", 10)
-    expect(pid).toBeGreaterThan(0)
-
-    // Give the SIGTERM a moment to be delivered
-    await new Promise(r => setTimeout(r, 100))
-
-    expect(await isProcessRunning(pid)).toBe(false)
-    await cleanupTmpDir(result.tmpDir)
+    try {
+      const pid = parseInt(result.results[0]?.actual[0] ?? "", 10)
+      expect(pid).toBeGreaterThan(0)
+      await new Promise(r => setTimeout(r, 100))
+      expect(await isProcessRunning(pid)).toBe(false)
+    } finally {
+      await cleanupTmpDir(result.tmpDir)
+    }
   })
 
   test("cleans up multiple backgrounded processes", async () => {
     const file = makeFile([
       { command: "sleep 300 >/dev/null 2>&1 & P1=$!; sleep 300 >/dev/null 2>&1 & P2=$!; echo $P1 $P2" },
     ])
-
     const result = await runFile(file, defaultOpts)
-    const pids = (result.results[0]?.actual[0] ?? "").split(" ").map(Number)
-    expect(pids).toHaveLength(2)
-    expect(pids[0]).toBeGreaterThan(0)
-    expect(pids[1]).toBeGreaterThan(0)
-
-    await new Promise(r => setTimeout(r, 100))
-
-    for (const pid of pids) {
-      expect(await isProcessRunning(pid)).toBe(false)
+    try {
+      const pids = (result.results[0]?.actual[0] ?? "").split(" ").map(Number)
+      expect(pids).toHaveLength(2)
+      expect(pids[0]).toBeGreaterThan(0)
+      expect(pids[1]).toBeGreaterThan(0)
+      await new Promise(r => setTimeout(r, 100))
+      for (const pid of pids) {
+        expect(await isProcessRunning(pid)).toBe(false)
+      }
+    } finally {
+      await cleanupTmpDir(result.tmpDir)
     }
-
-    await cleanupTmpDir(result.tmpDir)
   })
 })
diff --git a/src/run.ts b/src/run.ts
index e5754ac..c8c9bb2 100644
--- a/src/run.ts
+++ b/src/run.ts
@@ -175,14 +175,8 @@ export async function runFile(
       error: err instanceof Error ? err.message : String(err),
     }
   } finally {
-    // Kill the shell's process group to clean up backgrounded children
     if (proc.pid) {
-      try {
-        process.kill(-proc.pid, "SIGTERM")
-      } catch {}
-      setTimeout(() => {
-        try { process.kill(-proc.pid, "SIGKILL") } catch {}
-      }, 500)
+      try { process.kill(-proc.pid, "SIGKILL") } catch {}
     }
   }
 }
@@ -194,8 +188,9 @@ async function readWithTimeout(
   const reader = stream.getReader()
   const chunks: Uint8Array[] = []
 
+  let timerId: ReturnType<typeof setTimeout>
   const timeout = new Promise<never>((_, reject) =>
-    setTimeout(() => reject(new Error("Timeout reading output")), timeoutMs),
+    timerId = setTimeout(() => reject(new Error("Timeout reading output")), timeoutMs),
   )
 
   try {
@@ -205,6 +200,7 @@ async function readWithTimeout(
       if (value) chunks.push(value)
     }
   } finally {
+    clearTimeout(timerId!)
     reader.releaseLock()
   }