fix(interpreter): set BASH_SOURCE[0] when running bash /path/script.sh

Closes #942

Author: chaliy

crates/bashkit/src/interpreter/mod.rs

@@ -2680,8 +2680,20 @@ impl Interpreter {
         self.insert_variable_checked("OPTIND".to_string(), "1".to_string());
         self.variables.remove("_OPTCHAR_IDX");
 
+        // Set BASH_SOURCE for script file execution
+        if let Some(ref file) = script_file {
+            self.bash_source_stack.push(file.clone());
+            self.update_bash_source();
+        }
+
         let result = self.execute(&script).await;
 
+        // Restore BASH_SOURCE
+        if script_file.is_some() {
+            self.bash_source_stack.pop();
+            self.update_bash_source();
+        }
+
         // Restore state
         if let Some(val) = saved_optind {
             self.insert_variable_checked("OPTIND".to_string(), val);

crates/bashkit/tests/spec_cases/bash/bash-source-var.test.sh

@@ -0,0 +1,15 @@
+### bash_source_in_executed_script
+# BASH_SOURCE[0] should equal script path when run via bash
+echo 'echo "${BASH_SOURCE[0]}"' > /tmp/bsrc_test.sh
+bash /tmp/bsrc_test.sh
+### expect
+/tmp/bsrc_test.sh
+### end
+
+### bash_source_dirname_pattern
+# Common pattern: find script's own directory
+echo 'echo "$(dirname "${BASH_SOURCE[0]}")"' > /tmp/bsrc_dir.sh
+bash /tmp/bsrc_dir.sh
+### expect
+/tmp
+### end