extend source and target calculi with observable tick effects + add invariant checks for relation preservation and target arity/shape

test/invariants.ml

@@ -57,6 +57,18 @@ let () =
   assert_true
     "expected strictness shift witness"
     (strict.failure_mode = Audit.Strictness_shift);
+  let effect_audit = Audit.audit_case (find_case "effect-elision-breaks-observation") in
+  assert_true
+    "expected effect shift witness"
+    (effect_audit.failure_mode = Audit.Effect_shift);
+  assert_true
+    "expected unsafe effect rewrite to emit effect observation obligation"
+    (has_obligation Pipeline.Effect_observation effect_audit.compiled.obligations);
+  assert_true
+    "expected effect trace invariant failure"
+    (List.exists
+       (fun result -> result.Audit.kind = Audit.Effect_trace && not result.Audit.passed)
+       effect_audit.Audit.invariants);
   let generated = Gen.sample_terms ~count:80 ~max_depth:4 () in
   List.iter
     (fun specimen ->
@@ -84,7 +96,7 @@ let () =
     "expected unsupported worker-wrapper source shape to be rejected"
     (fun () ->
        Pipeline.compile
-         { Pipeline.default_flags with unsafe_repr_eq = false; unsafe_strict_unroll = false }
+         { Pipeline.default_flags with unsafe_repr_eq = false; unsafe_strict_unroll = false; unsafe_effect_drop = false }
          (Types.TArrow (Types.TPair (Types.TInt, Types.TBool), Types.TPair (Types.TInt, Types.TBool)))
          (Source.Lam
             ( "p",