diff --git a/PLAN.md b/PLAN.md
index e4bccf0..63ce27e 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -3,7 +3,7 @@
 A Rust-flavored, C-targeting language - built pipeline-first.
 
 **Implementation language:** Rust  
-**Code generation target:** x86-64 (AT&T / Intel syntax `.s` → assembled via GAS or NASM)
+**Code generation target:** Native object files (`.o`) via Cranelift JIT/AOT
 
 ## Phase 1 - Lexer
 
@@ -25,23 +25,25 @@ A Rust-flavored, C-targeting language - built pipeline-first.
 
 ## Phase 3 - Semantic Analysis
 
-- [ ] Implement scope-aware symbol table
-- [ ] Name resolution pass - resolve all `Ident` nodes to their declarations
-- [ ] Type inference / checking for `int` and `bool`
-- [ ] Validate function return types match declared signature
-- [ ] Error on use-before-declaration and undeclared symbols
-- [ ] Unit-test: ill-typed programs produce correct diagnostics
+- [x] Implement scope-aware symbol table (environment)
+- [x] Name resolution pass - resolve all `Ident` nodes to their declarations
+- [x] Hindley-Milner type inference (unification, type variables, occurs check)
+- [x] Integer literal sizing and unary minus type promotion logic
+- [x] Translate untyped AST directly into a fully-typed AST (Typed AST)
+- [x] Validate function return types match declared signature
+- [x] Error on use-before-declaration, undeclared symbols, and type mismatches
+- [x] Unit-test: HM unification, type mappings, and ill-typed program diagnostics
 
-## Phase 4 - x86-64 Code Generation
+## Phase 4 - Code Generation via Cranelift
 
-- [ ] Design a simple intermediate representation (linear IR, or use AST directly)
-- [ ] Implement stack-frame layout for local variables
-- [ ] Emit System V AMD64 ABI-compliant function prologues / epilogues
-- [ ] Codegen for arithmetic & comparison expressions
-- [ ] Codegen for function calls (argument passing via registers)
-- [ ] Codegen for `return` statements
-- [ ] Output `.s` file, assemble with NASM / GAS
-- [ ] End-to-end test: compile a simple `fn` → run → correct exit code
+- [x] Integrate `cranelift-codegen`, `cranelift-frontend`, and `cranelift-object`
+- [x] Implement CLI with `clap` (`--emit-ir` flag, input/output files)
+- [x] Map Typed AST types (`Ty`) to Cranelift IR types
+- [x] Lower functions, parameters, and variable definitions to Cranelift IR
+- [x] Codegen for arithmetic, unary operations, and `return` statements
+- [x] Run built-in optimization passes (constant folding, e-graphs, DCE)
+- [x] Output System V AMD64 ABI-compliant `.o` machine code files
+- [x] End-to-end test: compile a simple `fn` → link via `gcc` → run → correct exit code
 
 ## Planned Features (Backlog)
 
diff --git a/e2e.sh b/e2e.sh
new file mode 100755
index 0000000..301d57a
--- /dev/null
+++ b/e2e.sh
@@ -0,0 +1,56 @@
+#!/bin/bash
+
+# Exit immediately if a command exits with a non-zero status.
+set -e
+
+# --- Helper Function ---
+run_test() {
+    local src_file="$1"
+    local expected_code="$2"
+    local base_name
+    base_name=$(basename "$src_file" .src)
+    local obj_file="tests/$base_name.o"
+    local exec_file="tests/$base_name"
+
+    echo "--- Running test: $src_file ---"
+
+    # 1. Compile the source file using our compiler
+    echo "  [1/4] Compiling..."
+    cargo run --release -- "$src_file" -o "$obj_file" > /dev/null 2>&1
+
+    # 2. Link the object file with the system linker (gcc)
+    echo "  [2/4] Linking with gcc..."
+    gcc "$obj_file" -o "$exec_file"
+
+    # 3. Run the executable
+    echo "  [3/4] Running..."
+    set +e
+    ./"$exec_file"
+    local actual_code=$?
+    set -e
+
+    # 4. Check the exit code
+    echo "  [4/4] Verifying exit code..."
+    if [ "$actual_code" -eq "$expected_code" ]; then
+        echo "SUCCESS: Exit code is $actual_code as expected."
+    else
+        echo "FAILURE: Expected exit code $expected_code, but got $actual_code."
+        exit 1
+    fi
+
+    # Clean up generated files
+    rm "$obj_file" "$exec_file"
+    echo "------------------------------------"
+    echo
+}
+
+# --- Test Cases ---
+
+# Test a simple positive return value.
+run_test "tests/return_42.src" 42
+
+# Test a negative return value. Shell exit codes are unsigned 8-bit integers,
+# so -69 (i8) wraps around to 187.
+run_test "tests/return_neg_69.src" 187
+
+echo "All end-to-end tests passed!"
\ No newline at end of file
diff --git a/tests/return_42.src b/tests/return_42.src
new file mode 100644
index 0000000..f356e2d
--- /dev/null
+++ b/tests/return_42.src
@@ -0,0 +1,3 @@
+fn main() -> i32 {
+    return 42;
+}
\ No newline at end of file
diff --git a/tests/return_neg_69.src b/tests/return_neg_69.src
new file mode 100644
index 0000000..2eaeebc
--- /dev/null
+++ b/tests/return_neg_69.src
@@ -0,0 +1,3 @@
+fn main() -> i8 {
+    return -69;
+}
\ No newline at end of file