test: verify issues #275, #279, #282 are not reproducible (#306)

## Summary
- Add regression tests confirming 3 reported issues work correctly
- #275: `\(` in single-quoted strings preserved as literal
- #279: Reserved words like `done` work as case patterns  
- #282: `find -type f` enumerates VFS files correctly

## Test plan
- [x] All 4 tests pass locally
- [ ] CI green

Closes #275 #279 #282

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: chaliy

crates/bashkit/tests/issue_275_279_282_test.rs

@@ -0,0 +1,90 @@
+//! Regression tests verifying issues #275, #279, #282 are not reproducible.
+//!
+//! These issues were reported but code review and testing confirm
+//! they work correctly in the current implementation.
+
+use bashkit::Bash;
+
+async fn run(script: &str) -> String {
+    let mut bash = Bash::builder().build();
+    let result = bash.exec(script).await.expect("exec failed");
+    result.stdout
+}
+
+/// Issue #275: Parser corrupts \( in single-quoted strings
+/// Single-quoted strings should be completely literal.
+#[tokio::test]
+async fn test_issue_275_backslash_paren_in_single_quotes() {
+    // \( inside single quotes should be passed literally to sed
+    let output = run(r#"echo "test pattern here" | sed 's/\(pattern\)/[\1]/'"#).await;
+    assert!(
+        output.contains("[pattern]"),
+        "Expected '[pattern]' in output, got: {}",
+        output
+    );
+}
+
+/// Issue #279: "done" as case pattern should work
+#[tokio::test]
+async fn test_issue_279_done_as_case_pattern() {
+    let output = run(r#"
+status="done"
+case "$status" in
+  done) echo "matched" ;;
+  *) echo "nope" ;;
+esac
+"#)
+    .await;
+    assert_eq!(output.trim(), "matched");
+}
+
+/// Issue #279: Other reserved words as case patterns
+#[tokio::test]
+async fn test_issue_279_reserved_words_as_case_patterns() {
+    let output = run(r#"
+word="in"
+case "$word" in
+  in) echo "matched_in" ;;
+  do) echo "matched_do" ;;
+  *) echo "nope" ;;
+esac
+"#)
+    .await;
+    assert_eq!(output.trim(), "matched_in");
+}
+
+/// Issue #282: find -type f should enumerate VFS files
+#[tokio::test]
+async fn test_issue_282_find_type_f_vfs() {
+    let mut bash = Bash::builder()
+        .mount_text("/data/file1.txt", "hello")
+        .mount_text("/data/file2.txt", "world")
+        .mount_text("/data/subdir/file3.txt", "nested")
+        .build();
+    let result = bash
+        .exec("find /data -type f | sort")
+        .await
+        .expect("exec failed");
+    let lines: Vec<&str> = result.stdout.trim().lines().collect();
+    assert!(
+        lines.len() >= 3,
+        "Expected at least 3 files, got {}: {:?}",
+        lines.len(),
+        lines
+    );
+    assert!(
+        result.stdout.contains("file1.txt"),
+        "Missing file1.txt in: {}",
+        result.stdout
+    );
+    assert!(
+        result.stdout.contains("file2.txt"),
+        "Missing file2.txt in: {}",
+        result.stdout
+    );
+    assert!(
+        result.stdout.contains("file3.txt"),
+        "Missing file3.txt in: {}",
+        result.stdout
+    );
+}