lang/el-compiler/src/codegen.el

@@ -610,6 +610,15 @@ fn cg_expr(expr: Map<String, Any>) -> String {
                         record_call(state_get("__cg_current_fn"), "temporal:instant_plus_instant")
                         return "0 /* TIME_TYPE_ERROR: Instant + Instant */"
                     }
+                    // A bare literal is a MAGNITUDE WITH NO AXIS. Duration + Int
+                    // was already refused because an Int carries no unit; adding
+                    // one to a POINT is worse, because it silently moves the
+                    // instant by an unspecified amount. The asymmetry had no
+                    // justification -- it was simply never written.
+                    if is_int_expr(right) {
+                        record_call(state_get("__cg_current_fn"), "temporal:instant_plus_int")
+                        return "0 /* TIME_TYPE_ERROR: Instant + Int */"
+                    }
                 }
                 if left_is_dur {
                     if right_is_inst {

lang/tests/native/test_compiler.el

@@ -967,3 +967,23 @@ test "test-keyword-is-still-reserved" {
     let out: String = compile_capture(src)
     assert str_contains(out, "int main"), "the suite still compiles, which requires test to remain a keyword"
 }
+
+// ── A bare literal is a magnitude with no axis ───────────────────────────────
+//
+// Duration + Int was already refused because an Int carries no unit. Adding one
+// to a POINT is worse: it moves the instant by an unspecified amount. The
+// asymmetry had no justification; it was simply never written.
+
+test "instant-plus-bare-int-is-refused" {
+    let src: String = "fn main() { let t: Instant = now() let u: Instant = t + 3 println(\"x\") }"
+    let out: String = compile_capture(src)
+    assert str_contains(out, "TIME_TYPE_ERROR: Instant + Int"), "3 of what?"
+}
+
+test "instant-plus-unit-suffix-is-allowed" {
+    // .hour supplies the axis, so the magnitude becomes a displacement.
+    let src: String = "fn main() { let t: Instant = now() let u: Instant = t + 1.hour println(\"x\") }"
+    let out: String = compile_capture(src)
+    assert str_contains(out, "el_instant_add_dur"), "a unit suffix makes it a Duration"
+    assert !str_contains(out, "TIME_TYPE_ERROR"), "and the addition is legal"
+}

lang/tools/check/temporal.rel

@@ -11,6 +11,7 @@
 #   <kind> means <message>
 
 instant_plus_instant   means Instant + Instant is not allowed — a point plus a point is not a point. Subtract them for a Duration, or add a Duration.
+instant_plus_int       means Instant + Int is not allowed — a bare literal is a magnitude with no axis. 3 of what? Adding it to a point moves the instant by an unspecified amount. Use a Duration.
 duration_plus_int      means Duration + Int is not allowed — an Int carries no unit. Use duration_seconds(n) or N.seconds.
 duration_minus_int     means Duration - Int is not allowed — an Int carries no unit.
 instant_cmp_duration   means Instant < Duration is not allowed — a point and a displacement are not on the same scale.