diff --git a/abstract-interpreter.test.ts b/abstract-interpreter.test.ts
new file mode 100644
index 0000000..01e6cc0
--- /dev/null
+++ b/abstract-interpreter.test.ts
@@ -0,0 +1,190 @@
+/**
+ * Tests for abstract-interpreter.ts — interval domain + expression evaluation.
+ */
+
+import {
+  AbstractInterpreter,
+  Interval,
+  type VariableState,
+} from './abstract-interpreter';
+
+describe('Interval', () => {
+  test('fromValue creates a singleton interval', () => {
+    const i = Interval.fromValue(5n);
+    expect(i.min).toBe(5n);
+    expect(i.max).toBe(5n);
+  });
+
+  test('add widens bounds correctly', () => {
+    const a = new Interval(1n, 3n);
+    const b = new Interval(2n, 4n);
+    const r = a.add(b);
+    expect(r.min).toBe(3n);
+    expect(r.max).toBe(7n);
+  });
+
+  test('sub uses worst-case endpoints', () => {
+    const a = new Interval(10n, 20n);
+    const b = new Interval(1n, 5n);
+    const r = a.sub(b);
+    // min - maxOther .. max - minOther
+    expect(r.min).toBe(5n);
+    expect(r.max).toBe(19n);
+  });
+
+  test('mul considers all four endpoint products', () => {
+    const a = new Interval(-2n, 3n);
+    const b = new Interval(-4n, 5n);
+    const r = a.mul(b);
+    // products: 8, -10, -12, 15 → min -12, max 15
+    expect(r.min).toBe(-12n);
+    expect(r.max).toBe(15n);
+  });
+
+  test('mul of positive intervals stays positive', () => {
+    const a = new Interval(2n, 3n);
+    const b = new Interval(4n, 5n);
+    const r = a.mul(b);
+    expect(r.min).toBe(8n);
+    expect(r.max).toBe(15n);
+  });
+
+  test('isWithinBounds returns true when fully inside', () => {
+    const i = new Interval(0n, 100n);
+    expect(i.isWithinBounds(0n, AbstractInterpreter.U32_MAX)).toBe(true);
+  });
+
+  test('isWithinBounds returns false when max exceeds bound', () => {
+    const i = new Interval(0n, AbstractInterpreter.U32_MAX + 1n);
+    expect(i.isWithinBounds(0n, AbstractInterpreter.U32_MAX)).toBe(false);
+  });
+
+  test('isWithinBounds returns false when min is below bound', () => {
+    const i = new Interval(-1n, 10n);
+    expect(i.isWithinBounds(0n, AbstractInterpreter.U32_MAX)).toBe(false);
+  });
+
+  test('toString formats as [min, max]', () => {
+    expect(new Interval(1n, 2n).toString()).toBe('[1, 2]');
+  });
+});
+
+describe('AbstractInterpreter type bounds', () => {
+  test('U32_MAX is 2^32 - 1', () => {
+    expect(AbstractInterpreter.U32_MAX).toBe(4294967295n);
+  });
+
+  test('U64_MAX is 2^64 - 1', () => {
+    expect(AbstractInterpreter.U64_MAX).toBe(18446744073709551615n);
+  });
+
+  test('U128_MAX is 2^128 - 1', () => {
+    expect(AbstractInterpreter.U128_MAX).toBe(
+      340282366920938463463374607431768211455n,
+    );
+  });
+});
+
+describe('AbstractInterpreter.evaluateExpression', () => {
+  let interpreter: AbstractInterpreter;
+  let state: VariableState;
+
+  beforeEach(() => {
+    interpreter = new AbstractInterpreter();
+    state = new Map();
+  });
+
+  test('evaluates numeric literal', () => {
+    const r = interpreter.evaluateExpression('42', state);
+    expect(r).not.toBeNull();
+    expect(r!.min).toBe(42n);
+    expect(r!.max).toBe(42n);
+  });
+
+  test('trims whitespace around literal', () => {
+    const r = interpreter.evaluateExpression('  7  ', state);
+    expect(r!.min).toBe(7n);
+    expect(r!.max).toBe(7n);
+  });
+
+  test('resolves variable from state', () => {
+    state.set('x', new Interval(10n, 20n));
+    const r = interpreter.evaluateExpression('x', state);
+    expect(r!.min).toBe(10n);
+    expect(r!.max).toBe(20n);
+  });
+
+  test('returns null for unknown variable', () => {
+    expect(interpreter.evaluateExpression('unknown', state)).toBeNull();
+  });
+
+  test('returns null for empty input', () => {
+    expect(interpreter.evaluateExpression('', state)).toBeNull();
+    expect(interpreter.evaluateExpression('   ', state)).toBeNull();
+  });
+
+  test('returns null for malformed expression', () => {
+    expect(interpreter.evaluateExpression('1 +', state)).toBeNull();
+    expect(interpreter.evaluateExpression('+ 1', state)).toBeNull();
+    expect(interpreter.evaluateExpression('foo bar', state)).toBeNull();
+  });
+
+  test('adds two literals', () => {
+    const r = interpreter.evaluateExpression('3 + 5', state);
+    expect(r!.min).toBe(8n);
+    expect(r!.max).toBe(8n);
+  });
+
+  test('subtracts two literals', () => {
+    const r = interpreter.evaluateExpression('10 - 3', state);
+    expect(r!.min).toBe(7n);
+    expect(r!.max).toBe(7n);
+  });
+
+  test('multiplies two literals', () => {
+    const r = interpreter.evaluateExpression('4 * 5', state);
+    expect(r!.min).toBe(20n);
+    expect(r!.max).toBe(20n);
+  });
+
+  test('adds variable and literal', () => {
+    state.set('a', new Interval(1n, 2n));
+    const r = interpreter.evaluateExpression('a + 3', state);
+    expect(r!.min).toBe(4n);
+    expect(r!.max).toBe(5n);
+  });
+
+  test('multiplies two variables (interval product)', () => {
+    state.set('x', new Interval(2n, 3n));
+    state.set('y', new Interval(4n, 5n));
+    const r = interpreter.evaluateExpression('x * y', state);
+    expect(r!.min).toBe(8n);
+    expect(r!.max).toBe(15n);
+  });
+
+  test('detects potential u32 overflow via isWithinBounds', () => {
+    // 4000000000 + 4000000000 exceeds U32_MAX
+    const r = interpreter.evaluateExpression('4000000000 + 4000000000', state);
+    expect(r).not.toBeNull();
+    expect(r!.isWithinBounds(0n, AbstractInterpreter.U32_MAX)).toBe(false);
+  });
+
+  test('safe u32 addition stays within bounds', () => {
+    const r = interpreter.evaluateExpression('100 + 200', state);
+    expect(r!.isWithinBounds(0n, AbstractInterpreter.U32_MAX)).toBe(true);
+  });
+
+  test('large multiplication may exceed u64', () => {
+    const r = interpreter.evaluateExpression(
+      '18446744073709551615 * 2',
+      state,
+    );
+    expect(r).not.toBeNull();
+    expect(r!.isWithinBounds(0n, AbstractInterpreter.U64_MAX)).toBe(false);
+  });
+
+  test('returns null when one side of binary op is unknown', () => {
+    expect(interpreter.evaluateExpression('x + 1', state)).toBeNull();
+    expect(interpreter.evaluateExpression('1 + x', state)).toBeNull();
+  });
+});
diff --git a/scanner-engine/src/main.rs b/scanner-engine/src/main.rs
index ffbe6b8..5eb85a3 100644
--- a/scanner-engine/src/main.rs
+++ b/scanner-engine/src/main.rs
@@ -8,7 +8,6 @@ use std::{
     path::{Path, PathBuf},
     time::{SystemTime, UNIX_EPOCH},
 };
-use thiserror::Error;
 use walkdir::WalkDir;
 
 mod multisig_scanner;
@@ -32,30 +31,6 @@ struct ScanReport {
     report_hash: String,
 }
 
-/// Structured error type for all scanner-engine failure modes.
-/// Each variant maps to a distinct exit code and stderr format string.
-#[derive(Debug, Error)]
-pub enum ScannerError {
-    #[error("io error: {path}: {source}")]
-    IoError {
-        path: String,
-        #[source]
-        source: std::io::Error,
-    },
-    #[error("serialization failed: {0}")]
-    SerializationError(#[source] serde_json::Error),
-    #[error("report write failed: {path}: {source}")]
-    ReportWriteError {
-        path: String,
-        #[source]
-        source: std::io::Error,
-    },
-    #[error("invalid target: {path}: {reason}")]
-    InvalidTarget { path: String, reason: String },
-    #[error("report integrity check failed")]
-    IntegrityCheckFailed,
-}
-
 /// Static analysis rules applied to Soroban/Rust contract source files.
 const RULES: &[(&str, &str, &str)] = &[
     (r"unwrap\(\)", "UNSAFE_UNWRAP", "HIGH"),
@@ -221,16 +196,7 @@ fn main() {
     let (file_count, all_findings) = scan_target(&target, &rules);
     let governance_findings = scan_governance_target(&target);
 
-    // Serialize findings — exit 2 on failure, nothing written to stdout
-    let report_json = match serde_json::to_string_pretty(&all_findings) {
-        Ok(json) => json,
-        Err(e) => {
-            eprintln!("[scanner] ERROR: serialization failed: {}", e);
-            std::process::exit(2);
-        }
-    };
-    let hash = sha256_of(&report_json);
-
+    // Build report shell; hash filled after successful serialization.
     let combined_report = ScanReport {
         target: target.clone(),
         total_files: file_count,
@@ -239,7 +205,14 @@ fn main() {
         report_hash: String::new(),
     };
 
-    let report_json = serde_json::to_string_pretty(&combined_report).unwrap();
+    // Serialize findings — exit 2 on failure, nothing written to stdout
+    let report_json = match serde_json::to_string_pretty(&combined_report) {
+        Ok(json) => json,
+        Err(e) => {
+            eprintln!("[scanner] ERROR: serialization failed: {}", e);
+            std::process::exit(2);
+        }
+    };
     let hash = sha256_of(&report_json);
 
     let report = ScanReport {
@@ -263,7 +236,13 @@ fn main() {
     }
     eprintln!("[scanner] ZK state validation hook passed — scan state transition verified.");
 
-    let out = serde_json::to_string_pretty(&report).unwrap();
+    let out = match serde_json::to_string_pretty(&report) {
+        Ok(json) => json,
+        Err(e) => {
+            eprintln!("[scanner] ERROR: serialization failed: {}", e);
+            std::process::exit(2);
+        }
+    };
     println!("{}", out);
 
     // Write report to /reports directory — exit 3 on failure
@@ -297,7 +276,10 @@ fn main() {
     }
     eprintln!("[scanner] Report written to {}", report_path.display());
     eprintln!("[scanner] Report SHA-256: {}", report.report_hash);
-    eprintln!("[scanner] Governance findings: {}", report.governance_findings.len());
+    eprintln!(
+        "[scanner] Governance findings: {}",
+        report.governance_findings.len()
+    );
 
     // CRITICAL findings check — exit 1
     if report.findings.iter().any(|f| f.severity == "CRITICAL") {
@@ -354,7 +336,9 @@ mod tests {
         let post = sha256_of("[]");
         let mut hook = ZkStateValidationHook::new();
 
-        assert!(verify_scan_state_transition(&mut hook, &pre, &post, &scan_nullifier(&post)).is_ok());
+        assert!(
+            verify_scan_state_transition(&mut hook, &pre, &post, &scan_nullifier(&post)).is_ok()
+        );
     }
 
     #[test]
@@ -400,4 +384,4 @@ mod tests {
             Err(ZkStateError::NoOpTransition)
         );
     }
-}
+                        }