fix(interpreter): exit builtin terminates execution in compound commands (#904)

## Summary

- The `exit` builtin returned a plain exit code without `ControlFlow`
signaling, so commands after `exit` in if/while/for/case blocks kept
running
- Added `ControlFlow::Exit(i32)` variant and wired it through the
interpreter: propagates past function boundaries, consumed at subshell
and command substitution boundaries (matching bash semantics)

## Test plan

- [x] 7 new spec tests: exit in if, while, for, case, function, subshell
isolation
- [x] `cargo test --all-features` passes
- [x] `cargo clippy` and `cargo fmt` clean
- [ ] CI green

Author: chaliy

crates/bashkit/src/builtins/flow.rs

@@ -56,9 +56,11 @@ impl Builtin for Exit {
             .unwrap_or(0)
             & 0xFF;
 
-        // For now, we just return the exit code
-        // In a full implementation, this would terminate the shell
-        Ok(ExecResult::err(String::new(), exit_code))
+        Ok(ExecResult {
+            exit_code,
+            control_flow: ControlFlow::Exit(exit_code),
+            ..Default::default()
+        })
     }
 }
 

crates/bashkit/src/interpreter/mod.rs

@@ -1408,6 +1408,16 @@ impl Interpreter {
                 self.last_exit_code = saved_exit;
                 self.aliases = saved_aliases;
                 self.coproc_buffers = saved_coproc;
+
+                // Consume Exit control flow at subshell boundary — exit only
+                // terminates the subshell, not the parent shell.
+                if let Ok(ref mut res) = result
+                    && let ControlFlow::Exit(code) = res.control_flow
+                {
+                    res.exit_code = code;
+                    res.control_flow = ControlFlow::None;
+                }
+
                 result
             }
             CompoundCommand::BraceGroup(commands) => self.execute_command_sequence(commands).await,
@@ -1680,6 +1690,15 @@ impl Interpreter {
                         ..Default::default()
                     });
                 }
+                ControlFlow::Exit(code) => {
+                    return Ok(ExecResult {
+                        stdout,
+                        stderr,
+                        exit_code: code,
+                        control_flow: ControlFlow::Exit(code),
+                        ..Default::default()
+                    });
+                }
                 ControlFlow::None => {}
             }
         }
@@ -5880,6 +5899,9 @@ impl Interpreter {
                         let cmd_result = self.execute_command(cmd).await?;
                         stdout.push_str(&cmd_result.stdout);
                         self.last_exit_code = cmd_result.exit_code;
+                        if matches!(cmd_result.control_flow, ControlFlow::Exit(_)) {
+                            break;
+                        }
                     }
                     // Fire EXIT trap set inside the command substitution
                     if let Some(trap_cmd) = self.traps.get("EXIT").cloned()

crates/bashkit/src/interpreter/state.rs

@@ -11,6 +11,8 @@ pub enum ControlFlow {
     Continue(u32),
     /// Return from a function (with exit code)
     Return(i32),
+    /// Exit the shell (with exit code)
+    Exit(i32),
 }
 
 /// Structured side-effect channel for builtins that need to communicate
@@ -174,6 +176,7 @@ impl LoopAccumulator {
             ControlFlow::Return(code) => {
                 LoopAction::Exit(self.build_exit(ControlFlow::Return(code)))
             }
+            ControlFlow::Exit(code) => LoopAction::Exit(self.build_exit(ControlFlow::Exit(code))),
             ControlFlow::None => LoopAction::None,
         }
     }
@@ -193,7 +196,7 @@ impl LoopAccumulator {
     /// Build an exit result, draining accumulated stdout/stderr.
     fn build_exit(&mut self, control_flow: ControlFlow) -> ExecResult {
         let exit_code = match control_flow {
-            ControlFlow::Return(code) => code,
+            ControlFlow::Return(code) | ControlFlow::Exit(code) => code,
             _ => self.exit_code,
         };
         ExecResult {

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

@@ -168,3 +168,74 @@ false || false; echo $?
 1
 0
 ### end
+
+### exit_in_if_block
+# exit inside if block terminates script
+if true; then echo before; exit 0; fi
+echo SHOULD_NOT_REACH
+### expect
+before
+### end
+
+### exit_in_if_block_with_code
+# exit with non-zero code inside if block
+if true; then exit 42; fi
+echo SHOULD_NOT_REACH
+### exit_code: 42
+### expect
+### end
+
+### exit_in_while_loop
+# exit inside while loop terminates script
+i=0
+while true; do
+  echo "iter $i"
+  if [ "$i" -eq 1 ]; then exit 0; fi
+  i=$((i + 1))
+done
+echo SHOULD_NOT_REACH
+### expect
+iter 0
+iter 1
+### end
+
+### exit_in_for_loop
+# exit inside for loop terminates script
+for x in a b c; do
+  echo "$x"
+  if [ "$x" = "b" ]; then exit 5; fi
+done
+echo SHOULD_NOT_REACH
+### exit_code: 5
+### expect
+a
+b
+### end
+
+### exit_in_case_block
+# exit inside case block terminates script
+case "yes" in
+  yes) echo matched; exit 0 ;;
+esac
+echo SHOULD_NOT_REACH
+### expect
+matched
+### end
+
+### exit_in_subshell_does_not_propagate
+# exit inside subshell only terminates the subshell
+(exit 7)
+echo "after subshell: $?"
+### expect
+after subshell: 7
+### end
+
+### exit_in_function
+# exit inside function terminates the whole script
+f() { echo in_func; exit 3; }
+f
+echo SHOULD_NOT_REACH
+### exit_code: 3
+### expect
+in_func
+### end

supply-chain/config.toml

@@ -663,7 +663,7 @@ version = "0.1.34"
 criteria = "safe-to-deploy"
 
 [[exemptions.js-sys]]
-version = "0.3.92"
+version = "0.3.93"
 criteria = "safe-to-deploy"
 
 [[exemptions.leb128fmt]]
@@ -1467,23 +1467,23 @@ version = "0.4.0+wasi-0.3.0-rc-2026-01-06"
 criteria = "safe-to-run"
 
 [[exemptions.wasm-bindgen]]
-version = "0.2.115"
+version = "0.2.116"
 criteria = "safe-to-deploy"
 
 [[exemptions.wasm-bindgen-futures]]
-version = "0.4.65"
+version = "0.4.66"
 criteria = "safe-to-deploy"
 
 [[exemptions.wasm-bindgen-macro]]
-version = "0.2.115"
+version = "0.2.116"
 criteria = "safe-to-deploy"
 
 [[exemptions.wasm-bindgen-macro-support]]
-version = "0.2.115"
+version = "0.2.116"
 criteria = "safe-to-deploy"
 
 [[exemptions.wasm-bindgen-shared]]
-version = "0.2.115"
+version = "0.2.116"
 criteria = "safe-to-deploy"
 
 [[exemptions.wasm-encoder]]
@@ -1503,7 +1503,7 @@ version = "0.244.0"
 criteria = "safe-to-deploy"
 
 [[exemptions.web-sys]]
-version = "0.3.92"
+version = "0.3.93"
 criteria = "safe-to-deploy"
 
 [[exemptions.web-time]]