diff --git a/crates/forge_infra/src/executor.rs b/crates/forge_infra/src/executor.rs
index af8718738d..a613f66285 100644
--- a/crates/forge_infra/src/executor.rs
+++ b/crates/forge_infra/src/executor.rs
@@ -11,6 +11,10 @@ use tokio::sync::Mutex;
 
 use crate::console::StdConsoleWriter;
 
+/// Environment variables that let supported shells select startup files before
+/// executing the requested command.
+const SHELL_STARTUP_ENV_VARS: [&str; 3] = ["BASH_ENV", "ENV", "ZDOTDIR"];
+
 /// Service for executing shell commands
 #[derive(Clone, Debug)]
 pub struct ForgeCommandExecutorService {
@@ -87,6 +91,12 @@ impl ForgeCommandExecutorService {
             }
         }
 
+        // Project `.env` files are loaded into Forge's process environment.
+        // Do not let them configure shell startup behavior for subprocesses.
+        for env_var in SHELL_STARTUP_ENV_VARS {
+            command.env_remove(env_var);
+        }
+
         command
     }
 
@@ -273,6 +283,7 @@ impl CommandInfra for ForgeCommandExecutorService {
 mod tests {
 
     use pretty_assertions::assert_eq;
+    use serial_test::serial;
 
     use super::*;
 
@@ -293,6 +304,32 @@ mod tests {
         Arc::new(StdConsoleWriter::default())
     }
 
+    #[cfg(unix)]
+    struct EnvVarGuard {
+        key: &'static str,
+        previous: Option<std::ffi::OsString>,
+    }
+
+    #[cfg(unix)]
+    impl EnvVarGuard {
+        fn set(key: &'static str, value: &Path) -> Self {
+            let previous = std::env::var_os(key);
+            unsafe { std::env::set_var(key, value) };
+            Self { key, previous }
+        }
+    }
+
+    #[cfg(unix)]
+    impl Drop for EnvVarGuard {
+        fn drop(&mut self) {
+            if let Some(previous) = &self.previous {
+                unsafe { std::env::set_var(self.key, previous) };
+            } else {
+                unsafe { std::env::remove_var(self.key) };
+            }
+        }
+    }
+
     #[tokio::test]
     async fn test_command_executor() {
         let fixture = ForgeCommandExecutorService::new(test_env(), test_printer());
@@ -319,6 +356,64 @@ mod tests {
         assert_eq!(actual.stderr, expected.stderr);
         assert_eq!(actual.success(), expected.success());
     }
+
+    #[cfg(unix)]
+    #[tokio::test]
+    #[serial]
+    async fn test_command_executor_does_not_source_bash_env() {
+        let fixture_dir = tempfile::tempdir().unwrap();
+        let marker = fixture_dir.path().join("marker.txt");
+        let startup = fixture_dir.path().join("startup.sh");
+        std::fs::write(&startup, "touch marker.txt\n").unwrap();
+        let _guard = EnvVarGuard::set("BASH_ENV", &startup);
+        let fixture = ForgeCommandExecutorService::new(test_env(), test_printer());
+
+        let actual = fixture
+            .execute_command(
+                "echo ok".to_string(),
+                fixture_dir.path().to_path_buf(),
+                true,
+                None,
+            )
+            .await
+            .unwrap();
+        assert!(actual.success());
+        assert!(
+            !marker.exists(),
+            "BASH_ENV startup script ran before the requested command"
+        );
+    }
+
+    #[test]
+    fn test_prepare_command_removes_shell_startup_environment() {
+        let fixture = ForgeCommandExecutorService::new(test_env(), test_printer());
+
+        let command = fixture.prepare_command("echo ok", Path::new("."), None);
+        let mut actual = command
+            .as_std()
+            .get_envs()
+            .filter(|(key, _)| {
+                SHELL_STARTUP_ENV_VARS
+                    .iter()
+                    .any(|candidate| *key == std::ffi::OsStr::new(candidate))
+            })
+            .map(|(key, value)| {
+                (
+                    key.to_string_lossy().into_owned(),
+                    value.map(|value| value.to_string_lossy().into_owned()),
+                )
+            })
+            .collect::<Vec<_>>();
+        actual.sort();
+        let expected = vec![
+            ("BASH_ENV".to_string(), None),
+            ("ENV".to_string(), None),
+            ("ZDOTDIR".to_string(), None),
+        ];
+
+        assert_eq!(actual, expected);
+    }
+
     #[tokio::test]
     async fn test_command_executor_with_env_vars_success() {
         // Set up test environment variables