fix(interpreter): truncate exit codes to 8-bit range

crates/bashkit/src/builtins/flow.rs

@@ -43,6 +43,7 @@ impl Builtin for False {
 }
 
 /// The exit builtin - exit the shell with a status code.
+/// Bash truncates exit codes to 8-bit unsigned range (0-255) via `& 0xFF`.
 pub struct Exit;
 
 #[async_trait]
@@ -52,7 +53,8 @@ impl Builtin for Exit {
             .args
             .first()
             .and_then(|s| s.parse::<i32>().ok())
-            .unwrap_or(0);
+            .unwrap_or(0)
+            & 0xFF;
 
         // For now, we just return the exit code
         // In a full implementation, this would terminate the shell
@@ -92,7 +94,8 @@ impl Builtin for Continue {
     }
 }
 
-/// The return builtin - return from a function
+/// The return builtin - return from a function.
+/// Bash truncates return codes to 8-bit unsigned range (0-255) via `& 0xFF`.
 pub struct Return;
 
 #[async_trait]
@@ -102,7 +105,8 @@ impl Builtin for Return {
             .args
             .first()
             .and_then(|s| s.parse::<i32>().ok())
-            .unwrap_or(0);
+            .unwrap_or(0)
+            & 0xFF;
 
         Ok(ExecResult::with_control_flow(ControlFlow::Return(
             exit_code,

crates/bashkit/src/interpreter/mod.rs

@@ -2894,10 +2894,19 @@ impl Interpreter {
             });
         }
 
-        // If name is empty, this is an assignment-only command - keep permanently.
-        // Preserve last_exit_code from any command substitution in the value
-        // (bash behavior: `x=$(false)` sets $? to 1).
+        // If name is empty after expansion, behavior depends on context:
+        // - Quoted empty string ('', "", "$empty") -> "command not found" (exit 127)
+        // - Unquoted expansion that vanished ($empty, $(true)) -> no-op, preserve $?
+        // - Assignment-only (VAR=val) -> no-op, preserve $?
         if name.is_empty() {
+            if command.name.quoted && command.assignments.is_empty() {
+                // Bash: '' as a command is "command not found"
+                self.last_exit_code = 127;
+                return Ok(ExecResult::err(
+                    "bash: : command not found\n".to_string(),
+                    127,
+                ));
+            }
             return Ok(ExecResult {
                 stdout: String::new(),
                 stderr: String::new(),

crates/bashkit/tests/spec_cases/bash/exit-status.test.sh

@@ -12,7 +12,6 @@ status=255
 
 ### exit_truncation_256
 # exit 256 truncates to 0
-### skip: TODO exit status not truncated to 8-bit range
 bash -c 'exit 256'
 echo status=$?
 ### expect
@@ -21,7 +20,6 @@ status=0
 
 ### exit_truncation_257
 # exit 257 truncates to 1
-### skip: TODO exit status not truncated to 8-bit range
 bash -c 'exit 257'
 echo status=$?
 ### expect
@@ -30,7 +28,6 @@ status=1
 
 ### exit_negative_minus1
 # exit -1 wraps to 255
-### skip: TODO negative exit codes not wrapped to unsigned 8-bit
 bash -c 'exit -1' 2>/dev/null
 echo status=$?
 ### expect
@@ -39,7 +36,6 @@ status=255
 
 ### exit_negative_minus2
 # exit -2 wraps to 254
-### skip: TODO negative exit codes not wrapped to unsigned 8-bit
 bash -c 'exit -2' 2>/dev/null
 echo status=$?
 ### expect
@@ -56,7 +52,6 @@ status=255
 
 ### return_truncation_256
 # return 256 truncates to 0
-### skip: TODO return status not truncated to 8-bit range
 f() { return 256; }; f
 echo status=$?
 ### expect
@@ -65,7 +60,6 @@ status=0
 
 ### return_truncation_257
 # return 257 truncates to 1
-### skip: TODO return status not truncated to 8-bit range
 f() { return 257; }; f
 echo status=$?
 ### expect
@@ -74,7 +68,6 @@ status=1
 
 ### return_negative_minus1
 # return -1 wraps to 255
-### skip: TODO negative return codes not wrapped to unsigned 8-bit
 f() { return -1; }; f 2>/dev/null
 echo status=$?
 ### expect
@@ -83,7 +76,6 @@ status=255
 
 ### return_negative_minus2
 # return -2 wraps to 254
-### skip: TODO negative return codes not wrapped to unsigned 8-bit
 f() { return -2; }; f 2>/dev/null
 echo status=$?
 ### expect
@@ -92,7 +84,6 @@ status=254
 
 ### if_empty_command
 # If empty command string - '' as command should fail
-### skip: TODO empty string as command not treated as failed command
 if ''; then echo TRUE; else echo FALSE; fi
 ### exit_code: 0
 ### expect