feat: add fuzzing targets for untrusted input parsers (#835)

* feat: add fuzzing targets for untrusted input parsers

Add cargo-fuzz infrastructure with 5 fuzz targets exercising
security-critical code paths:

- fuzz_safety_sanitizer: Aho-Corasick + regex injection detection
- fuzz_safety_validator: Input validation (length, encoding, patterns)
- fuzz_leak_detector: Secret leak scanning (API keys, tokens)
- fuzz_tool_params: Tool parameter JSON validation
- fuzz_config_env: TOML/JSON config parsing

Each target exercises real IronClaw business logic with invariant
assertions. Includes corpus directories and setup documentation.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: improve fuzz targets to exercise real IronClaw code paths

- fuzz_config_env: exercise SafetyLayer end-to-end (sanitize, validate,
  policy check) instead of generic TOML/JSON parsing
- fuzz_tool_params: add validate_tool_schema coverage alongside
  validate_tool_params
- Add "fuzz" to workspace exclude in root Cargo.toml
- Update README descriptions to match actual target behavior

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: replace redundant detect() call with meaningful invariant assertion

Replace the double sanitize()+detect() call with an assertion that
critical severity warnings always trigger content modification.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: rewrite fuzz_config_env to exercise IronClaw safety code directly

Replace SafetyLayer wrapper usage with direct Sanitizer, Validator, and
LeakDetector instantiation and invocation. Adds meaningful consistency
assertions (non-empty output, valid-means-no-errors, scan/clean agreement).
Removes the config construction that was only exercising struct instantiation.

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

fuzz/fuzz_targets/fuzz_config_env.rs

@@ -0,0 +1,55 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+use ironclaw::safety::{LeakDetector, Sanitizer, Validator};
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(input) = std::str::from_utf8(data) {
+        // Exercise Sanitizer: detect and neutralize prompt injection attempts.
+        let sanitizer = Sanitizer::new();
+        let sanitized = sanitizer.sanitize(input);
+        // The sanitized content must never be empty when input is non-empty,
+        // because sanitization wraps/escapes rather than deleting.
+        if !input.is_empty() {
+            assert!(
+                !sanitized.content.is_empty(),
+                "sanitize() produced empty content for non-empty input"
+            );
+        }
+        // If no modification occurred, content must equal input.
+        if !sanitized.was_modified {
+            assert_eq!(sanitized.content, input);
+        }
+
+        // Exercise Validator: input validation (length, encoding, patterns).
+        let validator = Validator::new();
+        let result = validator.validate(input);
+        // ValidationResult must always be well-formed: if valid, no errors.
+        if result.is_valid {
+            assert!(
+                result.errors.is_empty(),
+                "valid result should have no errors"
+            );
+        }
+
+        // Exercise LeakDetector: secret detection (API keys, tokens, etc.).
+        let detector = LeakDetector::new();
+        let scan = detector.scan(input);
+        // scan_and_clean must not panic and must return valid UTF-8.
+        let cleaned = detector.scan_and_clean(input);
+        if let Ok(ref clean_str) = cleaned {
+            // Cleaned output must never be longer than original + redaction markers.
+            // At minimum it should be valid UTF-8 (guaranteed by String type).
+            let _ = clean_str.len();
+        }
+        // If scan found no matches, scan_and_clean should return the input unchanged.
+        if scan.matches.is_empty() {
+            if let Ok(ref clean_str) = cleaned {
+                assert_eq!(
+                    clean_str, input,
+                    "scan_and_clean changed content despite no matches"
+                );
+            }
+        }
+    }
+});

fuzz/fuzz_targets/fuzz_leak_detector.rs

@@ -0,0 +1,23 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use ironclaw::safety::LeakDetector;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(s) = std::str::from_utf8(data) {
+        let detector = LeakDetector::new();
+
+        // Exercise scan path
+        let result = detector.scan(s);
+        // Invariant: if should_block, there must be matches
+        if result.should_block {
+            assert!(!result.matches.is_empty());
+        }
+        // Invariant: match locations must be valid
+        for m in &result.matches {
+            assert!(m.location.end <= s.len());
+        }
+
+        // Exercise scan_and_clean path
+        let _ = detector.scan_and_clean(s);
+    }
+});

fuzz/fuzz_targets/fuzz_safety_sanitizer.rs

@@ -0,0 +1,23 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use ironclaw::safety::Sanitizer;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(s) = std::str::from_utf8(data) {
+        let sanitizer = Sanitizer::new();
+
+        // Exercise the main sanitization path
+        let result = sanitizer.sanitize(s);
+        // Verify invariant: warnings should have valid ranges
+        for w in &result.warnings {
+            assert!(w.location.end <= s.len());
+        }
+        // Verify invariant: critical severity triggers modification
+        let has_critical = result.warnings.iter().any(|w| {
+            w.severity == ironclaw::safety::Severity::Critical
+        });
+        if has_critical {
+            assert!(result.was_modified);
+        }
+    }
+});

fuzz/fuzz_targets/fuzz_safety_validator.rs

@@ -0,0 +1,21 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use ironclaw::safety::Validator;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(s) = std::str::from_utf8(data) {
+        let validator = Validator::new();
+
+        // Exercise input validation
+        let result = validator.validate(s);
+        // Invariant: empty input is always invalid
+        if s.is_empty() {
+            assert!(!result.is_valid);
+        }
+
+        // Exercise tool parameter validation with arbitrary JSON
+        if let Ok(value) = serde_json::from_str::<serde_json::Value>(s) {
+            let _ = validator.validate_tool_params(&value);
+        }
+    }
+});

fuzz/fuzz_targets/fuzz_tool_params.rs

@@ -0,0 +1,22 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use ironclaw::safety::Validator;
+use ironclaw::tools::validate_tool_schema;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(s) = std::str::from_utf8(data) {
+        // Try parsing as JSON and validating as tool parameters
+        if let Ok(value) = serde_json::from_str::<serde_json::Value>(s) {
+            // Exercise Validator::validate_tool_params with arbitrary JSON
+            let validator = Validator::new();
+            let result = validator.validate_tool_params(&value);
+            // Invariant: result should always be well-formed
+            if !result.is_valid {
+                assert!(!result.errors.is_empty());
+            }
+
+            // Exercise validate_tool_schema with arbitrary JSON as a schema
+            let _ = validate_tool_schema(&value, "fuzz");
+        }
+    }
+});