diff --git a/SPEC.md b/SPEC.md
index cd3be18..a53de48 100644
--- a/SPEC.md
+++ b/SPEC.md
@@ -60,6 +60,7 @@ This document reflects the implementation that ships in this repository today (`
   - Reader hooks: `set-token-hook` installs a word that receives each token (pushed as a `Token` object) and must leave a truthy handled flag; `clear-token-hook` disables it. `libs/fn.sl`'s `extend-syntax` demonstrates rewriting `foo(1, 2)` into ordinary word calls.
   - Prelude/BSS control: `prelude-clear`, `prelude-append`, `prelude-set`, `bss-clear`, `bss-append`, `bss-set` let user code override the `_start` stub or `.bss` layout.
   - Definition helpers: `emit-definition` injects a `word ... end` definition on the fly (used by the struct macro). `parse-error` raises a custom diagnostic.
+  - Assertions: `static_assert` is a compile-time-only primitive that pops a condition and raises `ParseError("static assertion failed at <path>:<line>:<column>")` when the value is zero/false.
 - **Text macros** – `macro` is an immediate word implemented in Python; it prevents nesting by tracking active recordings and registers expansion tokens with `$n` substitution.
 - **Python bridges** – `:py name { ... } ;` executes once during parsing. The body may define `macro(ctx: MacroContext)` (with helpers such as `next_token`, `emit_literal`, `inject_tokens`, `new_label`, and direct `parser` access) and/or `intrinsic(builder: FunctionEmitter)` to emit assembly directly. The `fn` DSL (`libs/fn.sl`) and other syntax layers are ordinary `:py` blocks.
 
@@ -76,10 +77,10 @@ This document reflects the implementation that ships in this repository today (`
 - **`mem.sl`** – `alloc`/`free` wrappers around `mmap`/`munmap` plus a byte-wise `memcpy` used by higher-level utilities.
 - **`io.sl`** – `read_file`, `write_file`, `read_stdin`, `write_buf`, `ewrite_buf`, `putc`, `puti`, `puts`, `eputs`, and a smart `print` that detects `(addr,len)` pairs located inside the default `.data` region.
 - **`utils.sl`** – String and number helpers (`strcmp`, `strconcat`, `strlen`, `digitsN>num`, `toint`, `count_digits`, `tostr`).
-- **`arr.sl`** – Dynamically sized qword arrays with `arr_new`, `arr_len`, `arr_cap`, `arr_data`, `arr_push`, `arr_pop`, `arr_reserve`, `arr_free`.
+- **`arr.sl`** – Dynamically sized qword arrays with `arr_new`, `arr_len`, `arr_cap`, `arr_data`, `arr_push`, `arr_pop`, `arr_reserve`, `arr_free`; built-in static-array sorting via `arr_sort`/`arr_sorted`; and dynamic-array sorting via `dyn_arr_sort`/`dyn_arr_sorted`.
 - **`float.sl`** – SSE-based double-precision arithmetic (`f+`, `f-`, `f*`, `f/`, `fneg`, comparisons, `int>float`, `float>int`, `fput`, `fputln`).
 - **`linux.sl`** – Auto-generated syscall macros (one constant block per entry in `syscall_64.tbl`) plus the `syscallN` helpers implemented purely in assembly so the file can be used in isolation.
-- **`debug.sl`** – Diagnostics such as `dump`, `rdump`, and `int3`.
+- **`debug.sl`** – Diagnostics and checks such as `dump`, `rdump`, `int3`, runtime `assert` (prints `assertion failed` and exits with code 1), `assert_msg` (message + condition; exits with message when false), `abort` (prints `abort` and exits with code 1), and `abort_msg` (prints caller-provided message and exits with code 1).
 - **`stdlib.sl`** – Convenience aggregator that imports `core`, `mem`, `io`, and `utils` so most programs can simply `import stdlib/stdlib.sl`.
 
 ## 9. Testing and Usage Patterns
diff --git a/main.py b/main.py
index 0c89cb1..5d1881d 100644
--- a/main.py
+++ b/main.py
@@ -1433,6 +1433,7 @@ class CompileTimeVM:
         self._dl_handles: List[Any] = []  # ctypes.CDLL handles
         self._dl_func_cache: Dict[str, Any] = {}  # name → ctypes callable
         self._ct_libs: List[str] = []  # library names from -l flags
+        self.current_location: Optional[SourceLocation] = None
 
     def reset(self) -> None:
         self.stack.clear()
@@ -1443,6 +1444,7 @@ class CompileTimeVM:
         self._list_capture_stack.clear()
         self.r12 = 0
         self.r13 = 0
+        self.current_location = None
 
     def invoke(self, word: Word, *, runtime_mode: bool = False, libs: Optional[List[str]] = None) -> None:
         self.reset()
@@ -2194,8 +2196,14 @@ class CompileTimeVM:
         if defn._begin_pairs is None:
             defn._begin_pairs = self._begin_pairs(defn.body)
         self._resolve_words_in_body(defn)
-        if self.runtime_mode and defn._merged_runs is None:
-            defn._merged_runs = self._find_mergeable_runs(defn)
+        if self.runtime_mode:
+            # Merged JIT runs are a performance optimization, but have shown
+            # intermittent instability on some environments. Keep them opt-in.
+            if os.environ.get("L2_CT_MERGED_JIT", "0") == "1":
+                if defn._merged_runs is None:
+                    defn._merged_runs = self._find_mergeable_runs(defn)
+            else:
+                defn._merged_runs = {}
         return defn._label_positions, defn._for_pairs, defn._begin_pairs
 
     def _find_mergeable_runs(self, defn: Definition) -> Dict[int, Tuple[int, str]]:
@@ -2387,9 +2395,11 @@ class CompileTimeVM:
 
         n_nodes = len(nodes)
         ip = 0
+        prev_location = self.current_location
         try:
             while ip < n_nodes:
                 node = nodes[ip]
+                self.current_location = node.loc
                 kind = node.op
 
                 if kind == "word":
@@ -2627,6 +2637,7 @@ class CompileTimeVM:
 
                 raise ParseError(f"unsupported compile-time op {node!r}")
         finally:
+            self.current_location = prev_location
             self.loop_stack = prev_loop_stack
 
     def _label_positions(self, nodes: Sequence[Op]) -> Dict[str, int]:
@@ -4579,6 +4590,23 @@ def _ct_parse_error(vm: CompileTimeVM) -> None:
     raise ParseError(message)
 
 
+def _ct_static_assert(vm: CompileTimeVM) -> None:
+    condition = vm._resolve_handle(vm.pop())
+    if isinstance(condition, bool):
+        ok = condition
+    elif isinstance(condition, int):
+        ok = condition != 0
+    else:
+        raise ParseError(
+            f"static_assert expects integer/boolean condition, got {type(condition).__name__}"
+        )
+    if not ok:
+        loc = vm.current_location
+        if loc is not None:
+            raise ParseError(f"static assertion failed at {loc.path}:{loc.line}:{loc.column}")
+        raise ParseError("static assertion failed")
+
+
 def _ct_lexer_new(vm: CompileTimeVM) -> None:
     separators = vm.pop_str()
     vm.push(SplitLexer(vm.parser, separators))
@@ -4902,6 +4930,7 @@ def _register_compile_time_primitives(dictionary: Dictionary) -> None:
         word_use_l2.immediate = True
     register("emit-definition", _ct_emit_definition, compile_only=True)
     register("parse-error", _ct_parse_error, compile_only=True)
+    register("static_assert", _ct_static_assert, compile_only=True)
 
     register("lexer-new", _ct_lexer_new, compile_only=True)
     register("lexer-pop", _ct_lexer_pop, compile_only=True)
diff --git a/stdlib/arr.sl b/stdlib/arr.sl
index b47af22..670fba1 100644
--- a/stdlib/arr.sl
+++ b/stdlib/arr.sl
@@ -127,3 +127,112 @@ end
 word arr_set
     arr_data swap 8 * + swap !
 end
+
+#dyn_arr_clone [* | dyn_arr] -> [* | dyn_arr_copy]
+word dyn_arr_clone
+    dup arr_len
+    dup arr_new
+
+    dup arr_data
+    3 pick arr_data
+    3 pick
+    arr_copy_elements
+
+    dup >r
+    swap !
+    drop
+    r>
+end
+
+#arr_item_ptr [*, i | arr] -> [* | ptr]
+word arr_item_ptr
+    swap 8 * swap 8 + +
+end
+
+#arr_get [*, i | arr] -> [* | x]
+# Get element from built-in static array
+word arr_get_static
+    arr_item_ptr @
+end
+
+#arr_set [*, x, i | arr] -> [*]
+# Set element in built-in static array
+word arr_set_static
+    arr_item_ptr swap !
+end
+
+#arr_sort [* | arr] -> [* | arr]
+# Sort built-in static array in-place in ascending order
+word arr_sort
+    dup >r
+    dup arr_to_dyn
+    dyn_arr_sort
+    dup arr_data
+    r@ 8 +
+    swap
+    r@ @
+    arr_copy_elements
+    arr_free
+    rdrop
+end
+
+#dyn_arr_sort [* | dyn_arr] -> [* | dyn_arr]
+:asm dyn_arr_sort {
+    mov rbx, [r12]          ; arr
+    mov rcx, [rbx]          ; len
+    cmp rcx, 1
+    jle .done
+
+    dec rcx                 ; outer = len - 1
+.outer:
+    xor rdx, rdx            ; j = 0
+
+.inner:
+    cmp rdx, rcx
+    jge .next_outer
+
+    mov r8, [rbx + 16]      ; data ptr
+    lea r9, [r8 + rdx*8]    ; &data[j]
+    mov r10, [r9]           ; a = data[j]
+    mov r11, [r9 + 8]       ; b = data[j+1]
+    cmp r10, r11
+    jle .no_swap
+
+    mov [r9], r11
+    mov [r9 + 8], r10
+
+.no_swap:
+    inc rdx
+    jmp .inner
+
+.next_outer:
+    dec rcx
+    jnz .outer
+
+.done:
+    ret
+}
+;
+
+#arr_clone [* | arr] -> [* | arr_copy]
+# Clone built-in static array (len header + payload)
+word arr_clone
+    dup @ 1 +
+    dup 8 * alloc
+    dup >r
+    rot rot
+    arr_copy_elements
+    r>
+end
+
+#arr_sorted [* | arr] -> [* | arr_sorted]
+word arr_sorted
+    arr_clone
+    arr_sort
+end
+
+#dyn_arr_sorted [* | dyn_arr] -> [* | dyn_arr_sorted]
+word dyn_arr_sorted
+    dyn_arr_clone
+    dyn_arr_sort
+end
diff --git a/stdlib/debug.sl b/stdlib/debug.sl
index 917633e..db3e914 100644
--- a/stdlib/debug.sl
+++ b/stdlib/debug.sl
@@ -70,3 +70,32 @@ end
 }
 ;
 
+#abort [*] -> [*]
+word abort
+	"abort" eputs
+	1 exit
+end
+
+#abort_msg [* | msg] -> [*]
+word abort_msg
+	eputs
+	1 exit
+end
+
+#assert [* | cond] -> [*]
+word assert
+	if
+	else
+		"assertion failed" abort_msg
+	end
+end
+
+#assert_msg [*, msg | cond] -> [*]
+word assert_msg
+	if
+		2drop
+	else
+		abort_msg
+	end
+end
+
diff --git a/tests/arr_dynamic.expected b/tests/arr_dynamic.expected
index e3b1791..f5c2cba 100644
--- a/tests/arr_dynamic.expected
+++ b/tests/arr_dynamic.expected
@@ -21,4 +21,19 @@
 6
 7
 8
-9
\ No newline at end of file
+9
+1
+2
+3
+3
+1
+2
+1
+2
+3
+4
+6
+9
+4
+9
+6
diff --git a/tests/arr_dynamic.sl b/tests/arr_dynamic.sl
index ea0b59c..721c4a7 100644
--- a/tests/arr_dynamic.sl
+++ b/tests/arr_dynamic.sl
@@ -56,4 +56,44 @@ word main
 
     # free list allocation: bytes = (len + 1) * 8
     dup @ 1 + 8 * free
+
+    # dyn_arr_sorted (copy) should not mutate source
+    5 arr_new
+    3 swap arr_push
+    1 swap arr_push
+    2 swap arr_push
+
+    dup dyn_arr_sorted
+    dup 0 swap arr_get puti cr
+    dup 1 swap arr_get puti cr
+    dup 2 swap arr_get puti cr
+    arr_free
+
+    dup 0 swap arr_get puti cr
+    dup 1 swap arr_get puti cr
+    dup 2 swap arr_get puti cr
+
+    # dyn_arr_sort (alias) sorts in place
+    dyn_arr_sort
+    dup 0 swap arr_get puti cr
+    dup 1 swap arr_get puti cr
+    dup 2 swap arr_get puti cr
+    arr_free
+
+    # dyn_arr_sorted (alias) returns a sorted copy
+    5 arr_new
+    4 swap arr_push
+    9 swap arr_push
+    6 swap arr_push
+
+    dup dyn_arr_sorted
+    dup 0 swap arr_get puti cr
+    dup 1 swap arr_get puti cr
+    dup 2 swap arr_get puti cr
+    arr_free
+
+    dup 0 swap arr_get puti cr
+    dup 1 swap arr_get puti cr
+    dup 2 swap arr_get puti cr
+    arr_free
 end
diff --git a/tests/arr_static_sort.expected b/tests/arr_static_sort.expected
new file mode 100644
index 0000000..889105e
--- /dev/null
+++ b/tests/arr_static_sort.expected
@@ -0,0 +1,10 @@
+1
+2
+3
+4
+5
+7
+9
+9
+5
+7
diff --git a/tests/arr_static_sort.sl b/tests/arr_static_sort.sl
new file mode 100644
index 0000000..f7261c6
--- /dev/null
+++ b/tests/arr_static_sort.sl
@@ -0,0 +1,29 @@
+import ../stdlib/stdlib.sl
+import ../stdlib/io.sl
+import ../stdlib/arr.sl
+
+word free_static
+    dup @ 1 + 8 * free
+end
+
+word main
+    [ 4 1 3 2 ] dup arr_sort
+    dup 0 swap arr_get_static puti cr
+    dup 1 swap arr_get_static puti cr
+    dup 2 swap arr_get_static puti cr
+    dup 3 swap arr_get_static puti cr
+    free_static
+
+    [ 9 5 7 ] dup arr_sorted
+    dup 0 swap arr_get_static puti cr
+    dup 1 swap arr_get_static puti cr
+    dup 2 swap arr_get_static puti cr
+
+    swap
+    dup 0 swap arr_get_static puti cr
+    dup 1 swap arr_get_static puti cr
+    dup 2 swap arr_get_static puti cr
+
+    free_static
+    free_static
+end
diff --git a/tests/assert_msg_fail.expected b/tests/assert_msg_fail.expected
new file mode 100644
index 0000000..e69de29
diff --git a/tests/assert_msg_fail.meta.json b/tests/assert_msg_fail.meta.json
new file mode 100644
index 0000000..ada3abb
--- /dev/null
+++ b/tests/assert_msg_fail.meta.json
@@ -0,0 +1,3 @@
+{
+  "expected_exit": 1
+}
diff --git a/tests/assert_msg_fail.sl b/tests/assert_msg_fail.sl
new file mode 100644
index 0000000..e3fb5ca
--- /dev/null
+++ b/tests/assert_msg_fail.sl
@@ -0,0 +1,6 @@
+import stdlib/debug.sl
+
+word main
+    "boom msg" 0 assert_msg
+    0
+end
diff --git a/tests/assert_msg_fail.stderr b/tests/assert_msg_fail.stderr
new file mode 100644
index 0000000..c7f6e1d
--- /dev/null
+++ b/tests/assert_msg_fail.stderr
@@ -0,0 +1 @@
+boom msg
diff --git a/tests/debug_assert.expected b/tests/debug_assert.expected
new file mode 100644
index 0000000..f351add
--- /dev/null
+++ b/tests/debug_assert.expected
@@ -0,0 +1,2 @@
+debug assert ok
+assert_msg ok
diff --git a/tests/debug_assert.sl b/tests/debug_assert.sl
new file mode 100644
index 0000000..4f5814d
--- /dev/null
+++ b/tests/debug_assert.sl
@@ -0,0 +1,10 @@
+import stdlib/debug.sl
+import stdlib/io.sl
+
+word main
+    1 assert
+    2 2 == assert
+    "should not print" 1 assert_msg
+    "debug assert ok" puts
+    "assert_msg ok" puts
+end
diff --git a/tests/static_assert.expected b/tests/static_assert.expected
new file mode 100644
index 0000000..8c0d5d5
--- /dev/null
+++ b/tests/static_assert.expected
@@ -0,0 +1 @@
+static assert ok
diff --git a/tests/static_assert.sl b/tests/static_assert.sl
new file mode 100644
index 0000000..39deb57
--- /dev/null
+++ b/tests/static_assert.sl
@@ -0,0 +1,12 @@
+import stdlib/debug.sl
+import stdlib/io.sl
+
+word ct_checks
+    1 static_assert
+    2 3 < static_assert
+end
+compile-time ct_checks
+
+word main
+    "static assert ok" puts
+end