compat(nestjs): .prototype of a capturing class expression is undefined — tslib __decorate crashes @nestjs/common module init

[TheHypnoo]

Context

I'm running a NestJS compatibility probe to map the current Perry → NestJS state, using the existing tests/release/packages/nestjs-hello fixture (@nestjs/common + @nestjs/core + @nestjs/platform-express 11.1.x, compiled via perry.compilePackages). After #4872 the fixture links (42.1 MB executable), but the binary dies during module init, before the server starts:

TypeError: Cannot convert undefined or null to object
    at <anonymous>

Reproduced today on main (6378dbd). This is "Wall 2" in the fixture's WALLS.md, previously bisected to @nestjs/common/services/logger.service.js: tsc's class-decorator output calls Object.getOwnPropertyDescriptor(Logger.prototype, "error") inside tslib.__decorate, and Logger.prototype reads as undefined while typeof Logger is "function".

Minimal repro (no node_modules)

const r = (function () {
    var L_1: any;
    let L: any = (L_1 = class L {
        get gi() { return L_1.staticRef; } // member captures outer var → ClassExprFresh
        e(m: any) { return m; }
    });
    return [typeof L, typeof L.prototype];
})();
console.log(JSON.stringify(r));

	Node (--experimental-strip-types)	Perry (main, 6378dbd)
output	["function","object"]	["function","undefined"]

Trigger matrix (narrows WALLS.md)

The trigger is any class member capturing an outer variable — not just getters:

variant	Node	Perry
class expr, no capture	object	object ✓
plain method captures outer var	object	undefined
getter captures outer var	object	undefined
Object.getOwnPropertyDescriptor(L.prototype, "error") (tslib __decorate shape)	descriptor object	throws Cannot convert undefined or null to object ← the exact NestJS crash

Root cause / fix direction

A capturing member routes the class through the ClassExprFresh lowering (captured_args: [LocalGet(..)] in HIR), and .prototype access on a ClassExprFresh value is not wired. The fix needs to give ClassExprFresh values a live .prototype object — and since tslib's __decorate then mutates it via Object.defineProperty, instances must observe the decorated methods (a read-only snapshot prototype is not enough).

This is the single remaining blocker between "links" and "boots" for the NestJS hello fixture; once fixed, the next wall (if any) surfaces at runtime.