Preserve barrel side effects when rewriting deep imports

[NullVoxPopuli-ai-agent]

Summary

Fixes the failing smoke tests on #21350 with a 5-line change in @glimmer/runtime. No lint-rule changes.

The failure (Cannot read properties of null (reading 'syscall') in AppendOpcodes.evaluate) was a real correctness issue — not a flake. After the lint autofix replaced barrel imports with deep imports, nothing imported @glimmer/runtime/index.ts anymore, and that index's import './lib/bootstrap'; was the only thing loading the opcode handler files. Each lib/compiled/opcodes/*.ts registers handlers via top-level APPEND_OPCODES.add(...), so when the bootstrap chain stopped, 28 of 90 handlers stayed unregistered — opcodes those handlers cover ({{on}}, dynamic helpers, etc.) hit null.syscall at evaluation.

Approach

Own the bootstrap from the file that actually consumes registered handlers — lib/vm/low-level.ts, where evaluateSyscall calls APPEND_OPCODES.evaluate(...). Any deep-import path that uses the VM (directly or transitively) now triggers bootstrap; consumers that don't need the VM don't pay for opcode handlers in their bundle. Removed the equivalent side-effect import from the package barrel since it's now redundant.

I considered solving this in the lint rule (detect side-effect imports in barrels and re-emit import 'BARREL'; to preserve them) — pushed up an earlier version of this PR doing exactly that. But adding bare side-effect imports of whole barrels back undoes the whole tree-shaking point of #21350. Better to put the trigger where the demand actually is.

Verified

I built dist/dev from each version and counted top-level APPEND_OPCODES.add(...) calls in chunks that are actually loaded:

Branch	reachable adds	trapped adds
origin/main	90	0
nvp/remove-barrel-imports	62	28 stuck in unused @glimmer/runtime/index.js
this PR	90	0

The 90 handlers in this PR's dist/dev are reachable from @ember/-internals/glimmer/index.js → setup-registry-...js → render-...js (28 adds, plus a side-effect import './untouchable-this-...js' for the other 62).

Note for reviewers

Two other barrel-only side effects in this PR's diff that might be worth a follow-up:

• @glimmer/validator/index.ts has a globalThis-based duplicate-package guard. It becomes dormant under deep imports — silent corruption is now possible if two copies ship. Move the registration check into a shared leaf module (e.g. lib/meta.ts) to keep it firing.
• @ember/object/index.ts runs class EmberObject extends CoreObject.extend(Observable) at module load. This one's actually fine: import EmberObject from '@ember/object' is a default import, which the rule's kept mechanism preserves on the barrel. Anyone using EmberObject still triggers the extension.

Test plan

• pnpm lint clean
• pnpm build:js succeeds
• All 90 APPEND_OPCODES.add(...) calls reachable from @ember/-internals/glimmer/index.js in dist/dev
• pnpm test:node passes
• pnpm type-check:internals reports same 10 pre-existing errors as the base branch
• Smoke tests in CI

🤖 Generated with Claude Code