feat(fuzz): add csv_fuzz target (#1149)

## Summary
- Add fuzz target for the custom CSV parser in `builtins/csv.rs`
- Tests `headers`, `count`, `select`, and custom delimiter (`-d`)
operations
- Exercises mismatched quotes, embedded newlines, and empty fields

Closes #1100

## Test plan
- [x] `cargo check` in fuzz crate passes
- [x] `cargo fmt --check` clean
- [x] `cargo clippy` clean

Author: chaliy

crates/bashkit/fuzz/Cargo.toml

@@ -115,3 +115,10 @@ path = "fuzz_targets/grep_fuzz.rs"
 test = false
 doc = false
 bench = false
+
+[[bin]]
+name = "csv_fuzz"
+path = "fuzz_targets/csv_fuzz.rs"
+test = false
+doc = false
+bench = false

crates/bashkit/fuzz/fuzz_targets/csv_fuzz.rs

@@ -0,0 +1,74 @@
+//! Fuzz target for the csv builtin
+//!
+//! Tests the custom CSV parser to find:
+//! - Panics on mismatched quotes or malformed fields
+//! - Edge cases with embedded newlines, empty fields, various delimiters
+//! - Memory exhaustion from pathological input
+//! - Incorrect parsing of escaped quotes
+//!
+//! Run with: cargo +nightly fuzz run csv_fuzz -- -max_total_time=300
+
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    // Only process valid UTF-8
+    if let Ok(input) = std::str::from_utf8(data) {
+        // Limit input size to prevent OOM
+        if input.len() > 1024 {
+            return;
+        }
+
+        // Skip empty input
+        if input.trim().is_empty() {
+            return;
+        }
+
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+
+        rt.block_on(async {
+            let mut bash = bashkit::Bash::builder()
+                .limits(
+                    bashkit::ExecutionLimits::new()
+                        .max_commands(50)
+                        .max_subst_depth(3)
+                        .max_stdout_bytes(4096)
+                        .max_stderr_bytes(4096)
+                        .timeout(std::time::Duration::from_millis(200)),
+                )
+                .build();
+
+            // Test 1: parse CSV and list headers
+            let script = format!(
+                "echo '{}' | csv headers 2>/dev/null; true",
+                input.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script).await;
+
+            // Test 2: parse CSV and count rows
+            let script2 = format!(
+                "echo '{}' | csv count 2>/dev/null; true",
+                input.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script2).await;
+
+            // Test 3: parse CSV and select first column
+            let script3 = format!(
+                "echo '{}' | csv select 1 2>/dev/null; true",
+                input.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script3).await;
+
+            // Test 4: parse CSV with custom delimiter
+            let script4 = format!(
+                "echo '{}' | csv -d '\\t' headers 2>/dev/null; true",
+                input.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script4).await;
+        });
+    }
+});