fix(dynamic): map unmappable function params/returns and type parameters to JSVAL

packages/compiler/src/frontend/lowering/lowerer.ts

@@ -771,6 +771,11 @@ export function dynFallbackType(L: Lowerer, node: ts.Node, t: ts.Type): IrType |
   if (t.flags & ts.TypeFlags.Void) return null;
   if (!isJsSourceFile(node.getSourceFile())) {
     if (t.flags & ts.TypeFlags.Any) return DYN;
+    // In --dynamic mode, `unknown` maps to the checked-dynamic type (same as
+    // `any`). This lets error handlers with `unknown`-typed catch bindings or
+    // parameters use instanceof Error, typeof checks, and dyn-compatible
+    // operations without SC2020 fences.
+    if (L.dynamic && (t.flags & ts.TypeFlags.Unknown)) return DYN;
     // TS single-call-signature function types: per-piece fallback, but
     // ONLY `any` pieces fall to dyn — any other unmappable piece keeps
     // the whole type's own fence.
@@ -6118,8 +6123,10 @@ export class Lowerer {
     // Marshalable CLOSURES cross as host functions — a record carrying
     // methods (the service-registry entry: `{ label, load: () =>
     // Promise<any>, defaultFallback: (cfg) => any }`) lifts field by
-    // field like any other.
+    // field like any other. In --dynamic mode, any function is liftable
+    // via jsMarshal (host function wrap) — the runtime handles type mismatches.
     if (t.kind === "func") {
+      if (this.dynamic) return true;
       return canMarshalTypedFuncIntoIsland(t, (id) => this.shapes.get(id), (id) => this.unions.get(id));
     }
     if (t.kind === "record") {

packages/compiler/src/frontend/ts7/checker.ts

@@ -1,4 +1,3 @@
-import { InternalCompilerError } from "../../errors.js";
 /* The checker facade: 5.9.3-shaped TypeChecker methods over 7.0.2's sync
  * client, built around the survey's feasibility verdict. Naive per-call use
  * of the 7.0.2 client costs 0.1-0.3 ms of IPC per query; the census counted
@@ -259,7 +258,7 @@ export class CheckerFacade {
 
   private requireProject(): Project {
     const project = this.options.project;
-    if (!project) throw new InternalCompilerError("CheckerFacade built without a project cannot resolve declarations");
+    if (!project) throw new Error("CheckerFacade built without a project cannot resolve declarations");
     return project;
   }
 
@@ -619,6 +618,14 @@ export class CheckerFacade {
     return base;
   }
 
+  /** Returns the base constraint of a TypeParameter, or undefined if none.
+   * Delegates directly to the raw checker — no memoization needed since this
+   * is only called in the constraint-fallback path (rare, uninstantiated
+   * generics) and the result is used only for JSVAL/null classification. */
+  getBaseConstraintOfType(type: Type): Type | undefined {
+    return this.raw.getBaseConstraintOfType(type);
+  }
+
   private intrinsic(name: string, fetch: () => Type): Type {
     let type = this.intrinsics.get(name);
     if (type === undefined) {