Closes #8793

Summary

Fix is_top_level() in crates/rolldown_ecmascript_utils/src/scope.rs which incorrectly treated scopes with ScopeFlags::StrictMode as "top-level" (eagerly evaluated during module evaluation).

Root Cause

is_top_level() determines whether the current AST position executes eagerly during module evaluation (as opposed to being deferred inside a function). It checks that all scopes in the stack are "transparent" — i.e., Top, ClassStaticBlock, or empty block scopes.

The bug was that ScopeFlags::StrictMode was included in the transparency check via intersects:

flag.intersects(ScopeFlags::Top | ScopeFlags::StrictMode | ScopeFlags::ClassStaticBlock)

StrictMode is a modifier flag inherited by child scopes, not a scope boundary indicator. An arrow function with "use strict" gets scope flags like Arrow | Function | StrictMode — the intersects(StrictMode) check made this appear "transparent", so code inside the arrow function was incorrectly considered top-level.

How This Causes Colliding Variable Names

Given this input:

// index.js (entry)
import { Pb as He } from "./chunk.js";
console.log(() => { "use strict"; return 0 })
var Ub = ["open", "opening", "toggle"];
console.log(class {
  constructor() { console.log(Ub); }
  static p = He({});
})

The chain of failure:

1. is_top_level() returns true inside the arrow function — because its StrictMode flag matches the intersects check
2. Scanner detects return 0 as a top-level return — top-level return is only valid in CommonJS, so the module gets ExportsKind::CommonJs
3. Module gets CJS-wrapped — its code is placed inside a __commonJSMin(() => { ... }) closure
4. Deconfliction skips local variables in CJS-wrapped modules — because their code runs in a nested closure, not at chunk root scope. So the local var Ub (array) is NOT registered in the root scope renamer
5. Cross-chunk import gets name Ub — since the local var Ub wasn't registered, no conflict is detected, and the imported function keeps the name Ub
6. Collision at runtime — static p = Ub({}) resolves to the local array ["open", "opening", "toggle"] instead of the imported function, causing TypeError: Ub is not a function

Fix

flag.is_top() || flag.contains(ScopeFlags::ClassStaticBlock) || flag.is_block()

This correctly handles all cases:

• Top scope + StrictMode (ESM modules): Top after stripping → transparent ✓
• Block scope + StrictMode: empty after stripping → transparent ✓
• Arrow/function + StrictMode: Arrow|Function after stripping → NOT transparent ✓

Test plan

• Added reproduction test case in crates/rolldown/tests/rolldown/issues/8793/
• All 1645 integration tests pass
• rolldown_ecmascript_utils unit tests pass

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