diff --git a/src/jobs/spawn.rs b/src/jobs/spawn.rs
index 88340f6..7d36aa4 100644
--- a/src/jobs/spawn.rs
+++ b/src/jobs/spawn.rs
@@ -19,7 +19,8 @@ pub struct SpawnDetachedOpts<'a> {
 
 /// Spawn a detached background job that survives crabcode exit.
 ///
-/// Unix: `/bin/sh -c command` in its own process group, stdout/stderr → output.log,
+/// Unix: `/bin/sh -c command` in its own session/process group (no controlling
+/// terminal), stdin → /dev/null, stdout/stderr → output.log.
 /// A detached waiter reaps the child (lazy status updates via prune).
 /// Windows: best-effort CREATE_NEW_PROCESS_GROUP + log redirect.
 pub async fn spawn_detached(opts: SpawnDetachedOpts<'_>) -> Result<JobMeta> {
@@ -76,18 +77,7 @@ fn spawn_detached_into(
     cmd.stderr(Stdio::from(log_err));
 
     #[cfg(unix)]
-    {
-        use std::os::unix::process::CommandExt;
-        unsafe {
-            cmd.pre_exec(|| {
-                // Put child in its own process group (equivalent to setpgid(0,0)).
-                if libc::setpgid(0, 0) != 0 {
-                    return Err(std::io::Error::last_os_error());
-                }
-                Ok(())
-            });
-        }
-    }
+    crate::utils::process::detach_from_terminal(&mut cmd);
 
     #[cfg(windows)]
     {
diff --git a/src/tools/bash.rs b/src/tools/bash.rs
index 6b447fd..7c7b90c 100644
--- a/src/tools/bash.rs
+++ b/src/tools/bash.rs
@@ -112,9 +112,7 @@ impl BashTool {
         cmd.kill_on_drop(true);
 
         #[cfg(unix)]
-        {
-            cmd.process_group(0);
-        }
+        crate::utils::process::detach_from_terminal(cmd.as_std_mut());
 
         let mut child = cmd
             .spawn()
diff --git a/src/utils/mod.rs b/src/utils/mod.rs
index e54cce0..c222734 100644
--- a/src/utils/mod.rs
+++ b/src/utils/mod.rs
@@ -5,6 +5,8 @@ pub mod frecency;
 pub mod git;
 pub mod ignore;
 pub mod image_attachment;
+#[cfg(unix)]
+pub mod process;
 pub mod sanitize;
 pub mod storage;
 pub mod time;
diff --git a/src/utils/process.rs b/src/utils/process.rs
new file mode 100644
index 0000000..a719282
--- /dev/null
+++ b/src/utils/process.rs
@@ -0,0 +1,142 @@
+use std::os::unix::process::CommandExt;
+use std::process::Command;
+
+/// Isolate a non-interactive child from the TUI's controlling terminal.
+///
+/// Redirecting stdio and setting a process group are not enough: descendants
+/// can still open `/dev/tty` and change its modes or foreground process group.
+/// `setsid` removes that access and also creates a PID-led process group, so
+/// existing group-based cancellation continues to work. Callers must redirect
+/// stdio separately and must not also set `process_group(0)` (which makes
+/// `setsid` fail because the child is already a process group leader).
+pub fn detach_from_terminal(command: &mut Command) {
+    // SAFETY: only the async-signal-safe setsid syscall and errno retrieval run
+    // in the child after fork; the closure does not allocate or acquire locks.
+    unsafe {
+        command.pre_exec(|| {
+            if libc::setsid() == -1 {
+                return Err(std::io::Error::last_os_error());
+            }
+            Ok(())
+        });
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::jobs::{spawn, test_env::TempState};
+    use crate::tools::{bash::BashTool, ToolContext, ToolHandler};
+    use portable_pty::{native_pty_system, CommandBuilder, PtySize};
+    use std::path::Path;
+    use std::time::{Duration, Instant};
+    use tokio_util::sync::CancellationToken;
+
+    const PROBE_ENV: &str = "CRABCODE_TEST_JOB_TTY_PROBE";
+    const PROBE_TEST: &str = "utils::process::tests::non_interactive_job_pty_probe";
+    const PROBE_COMMAND: &str = "if (exec 3<>/dev/tty) 2>/dev/null; then printf 'tty-attached'; else printf 'tty-detached'; fi";
+
+    #[test]
+    fn non_interactive_jobs_cannot_access_controlling_terminal() {
+        // Running under a PTY is essential: ordinary CI stdin often has no
+        // controlling terminal, which would hide inherited-session bugs.
+        let pair = native_pty_system().openpty(PtySize::default()).unwrap();
+        let temp = tempfile::tempdir().unwrap();
+        let log = temp.path().join("probe.log");
+        let mut command = CommandBuilder::new("sh");
+        command.args([
+            "-c",
+            "exec \"$CRABCODE_TEST_BINARY\" --exact \"$CRABCODE_TEST_NAME\" --nocapture --test-threads=1 >\"$CRABCODE_TEST_LOG\" 2>&1",
+        ]);
+        command.env("CRABCODE_TEST_BINARY", std::env::current_exe().unwrap());
+        command.env("CRABCODE_TEST_NAME", PROBE_TEST);
+        command.env("CRABCODE_TEST_LOG", &log);
+        command.env(PROBE_ENV, "1");
+        let mut child = pair.slave.spawn_command(command).unwrap();
+        drop(pair.slave);
+
+        let deadline = Instant::now() + Duration::from_secs(10);
+        let status = loop {
+            if let Some(status) = child.try_wait().unwrap() {
+                break status;
+            }
+            if Instant::now() >= deadline {
+                if let Some(pid) = child.process_id() {
+                    unsafe { libc::killpg(pid as i32, libc::SIGKILL) };
+                }
+                let _ = child.kill();
+                let _ = child.wait();
+                panic!("PTY probe hung or was suspended by terminal job control");
+            }
+            std::thread::sleep(Duration::from_millis(20));
+        };
+
+        let output = std::fs::read_to_string(log).unwrap();
+        assert!(status.success(), "PTY probe failed: {output}");
+        assert!(output.contains("job-tty-isolation-ok"), "{output}");
+    }
+
+    #[tokio::test]
+    async fn non_interactive_job_pty_probe() {
+        if std::env::var_os(PROBE_ENV).is_none() {
+            return;
+        }
+        let tty = std::fs::File::open("/dev/tty").expect("probe must have a controlling terminal");
+        use std::os::fd::AsRawFd;
+        let foreground_group = unsafe { libc::tcgetpgrp(tty.as_raw_fd()) };
+        assert_eq!(foreground_group, unsafe { libc::getpgrp() });
+
+        let ctx =
+            ToolContext::from_cancel_token("session", "message", "Build", CancellationToken::new());
+        let result = BashTool::new()
+            .execute(serde_json::json!({"command": PROBE_COMMAND}), &ctx)
+            .await
+            .unwrap();
+        assert_eq!(
+            result.output, "tty-detached",
+            "foreground job inherited tty"
+        );
+
+        let _state = TempState::new();
+        let meta = spawn::spawn_detached_blocking(spawn::SpawnDetachedOpts {
+            command: PROBE_COMMAND,
+            name: "tty-isolation-test",
+            workdir: Path::new("."),
+            session_id: None,
+        })
+        .unwrap();
+        let (output, _, exited) = spawn::wait_for_log_growth(&meta.id, 0, 2000).await.unwrap();
+        assert_eq!(output, "tty-detached", "background job inherited tty");
+        // Wait for the reaper before restarting so the old incarnation cannot
+        // write output into the new incarnation's log.
+        if !exited {
+            for _ in 0..100 {
+                if !crate::jobs::ledger::is_pid_alive(meta.pid) {
+                    break;
+                }
+                tokio::time::sleep(Duration::from_millis(10)).await;
+            }
+        }
+        spawn::restart_job(&meta.id).unwrap();
+        let deadline = Instant::now() + Duration::from_secs(2);
+        loop {
+            let (output, _, _) = spawn::read_log_from(&meta.id, 0).unwrap();
+            assert!(
+                !output.contains("tty-attached"),
+                "restarted job inherited tty"
+            );
+            if output.matches("tty-detached").count() == 2 {
+                break;
+            }
+            assert!(
+                Instant::now() < deadline,
+                "restarted job did not produce output"
+            );
+            tokio::time::sleep(Duration::from_millis(10)).await;
+        }
+        assert_eq!(
+            unsafe { libc::tcgetpgrp(tty.as_raw_fd()) },
+            foreground_group
+        );
+        println!("job-tty-isolation-ok");
+    }
+}