fix(interpreter): preserve stdout from if/elif condition commands

execute_if only used condition_result.exit_code, discarding stdout/stderr.
Patterns like `if echo "hello"; then ...` or `if ! cmd | jq; then ...` lost
the condition's output. Now condition output is prepended to the branch result.

Author: chaliy

crates/bashkit/src/interpreter/mod.rs

@@ -1432,29 +1432,52 @@ impl Interpreter {
 
     /// Execute an if statement
     async fn execute_if(&mut self, if_cmd: &IfCommand) -> Result<ExecResult> {
+        // Accumulate stdout/stderr from all condition evaluations
+        let mut cond_stdout = String::new();
+        let mut cond_stderr = String::new();
+
         // Execute condition (no errexit checking - conditions are expected to fail)
         let condition_result = self.execute_condition_sequence(&if_cmd.condition).await?;
+        cond_stdout.push_str(&condition_result.stdout);
+        cond_stderr.push_str(&condition_result.stderr);
 
         if condition_result.exit_code == 0 {
             // Condition succeeded, execute then branch
-            return self.execute_command_sequence(&if_cmd.then_branch).await;
+            let mut result = self.execute_command_sequence(&if_cmd.then_branch).await?;
+            result.stdout = cond_stdout + &result.stdout;
+            result.stderr = cond_stderr + &result.stderr;
+            return Ok(result);
         }
 
         // Check elif branches
         for (elif_condition, elif_body) in &if_cmd.elif_branches {
             let elif_result = self.execute_condition_sequence(elif_condition).await?;
+            cond_stdout.push_str(&elif_result.stdout);
+            cond_stderr.push_str(&elif_result.stderr);
+
             if elif_result.exit_code == 0 {
-                return self.execute_command_sequence(elif_body).await;
+                let mut result = self.execute_command_sequence(elif_body).await?;
+                result.stdout = cond_stdout + &result.stdout;
+                result.stderr = cond_stderr + &result.stderr;
+                return Ok(result);
             }
         }
 
         // Execute else branch if present
         if let Some(else_branch) = &if_cmd.else_branch {
-            return self.execute_command_sequence(else_branch).await;
+            let mut result = self.execute_command_sequence(else_branch).await?;
+            result.stdout = cond_stdout + &result.stdout;
+            result.stderr = cond_stderr + &result.stderr;
+            return Ok(result);
         }
 
-        // No branch executed, return success
-        Ok(ExecResult::ok(String::new()))
+        // No branch executed, return condition output with success exit code
+        Ok(ExecResult {
+            stdout: cond_stdout,
+            stderr: cond_stderr,
+            exit_code: 0,
+            ..Default::default()
+        })
     }
 
     /// Execute a for loop

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

@@ -239,3 +239,27 @@ echo SHOULD_NOT_REACH
 ### expect
 in_func
 ### end
+
+### if_condition_stdout
+# stdout from if condition is preserved
+if echo "from_condition"; then echo "from_body"; fi
+### expect
+from_condition
+from_body
+### end
+
+### if_negated_condition_stdout
+# stdout from negated if condition
+if ! echo "negated"; then echo "no"; else echo "yes"; fi
+### expect
+negated
+yes
+### end
+
+### if_condition_pipeline_stdout
+# stdout from pipeline in if condition
+if echo "hello" | cat; then echo "ok"; fi
+### expect
+hello
+ok
+### end