feat(fuzz): add yaml_fuzz target

crates/bashkit/fuzz/Cargo.toml

@@ -94,3 +94,10 @@ path = "fuzz_targets/sed_fuzz.rs"
 test = false
 doc = false
 bench = false
+
+[[bin]]
+name = "yaml_fuzz"
+path = "fuzz_targets/yaml_fuzz.rs"
+test = false
+doc = false
+bench = false

crates/bashkit/fuzz/fuzz_targets/yaml_fuzz.rs

@@ -0,0 +1,83 @@
+//! Fuzz target for the yaml builtin
+//!
+//! Tests the hand-written YAML parser to find:
+//! - Panics on malformed YAML documents
+//! - Stack overflow from deeply nested structures
+//! - Edge cases with anchors, special characters, multiline strings
+//! - Memory exhaustion from pathological input
+//!
+//! Run with: cargo +nightly fuzz run yaml_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;
+        }
+
+        // Split input into YAML content and query path
+        let (yaml_doc, query) = match input.find('\n') {
+            Some(pos) => (&input[..pos], &input[pos + 1..]),
+            None => (input, "." as &str),
+        };
+
+        // Skip empty documents
+        if yaml_doc.trim().is_empty() {
+            return;
+        }
+
+        // Reject deeply nested structures
+        let depth = yaml_doc
+            .bytes()
+            .filter(|&b| b == b'{' || b == b'[')
+            .count();
+        if depth > 20 {
+            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 YAML and query with get
+            let script = format!(
+                "echo '{}' | yaml get '{}' 2>/dev/null; true",
+                yaml_doc.replace('\'', "'\\''"),
+                query.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script).await;
+
+            // Test 2: parse YAML and list keys
+            let script2 = format!(
+                "echo '{}' | yaml keys 2>/dev/null; true",
+                yaml_doc.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script2).await;
+
+            // Test 3: parse YAML and get type
+            let script3 = format!(
+                "echo '{}' | yaml type 2>/dev/null; true",
+                yaml_doc.replace('\'', "'\\''"),
+            );
+            let _ = bash.exec(&script3).await;
+        });
+    }
+});