docs(runtime-tags): record that dynamic native tag var resume needs compiler work

Author: DylanPiercey

agent-feedback/bugs.md

@@ -146,10 +146,12 @@ The dynamic-tag change checks compare `renderer?.[RendererProp.Id] || renderer`
 
 ## Initialize tag variables for dynamic native tags
 
-`packages/runtime-tags/src/html/dynamic-tag.ts:146` | 2026-07-15 | impact:med | effort:med
+`packages/runtime-tags/src/html/dynamic-tag.ts:146` | 2026-07-15 | impact:med | effort:high
 
 The string-renderer branch of HTML `_dynamic_tag` never assigns `result` (the inline TODO calls this out), and the DOM branch creates the element but never sends its getter through the branch's `AccessorProp.TagVariable` callback (`dom/control-flow.ts:547`). Verified by adding `<${input.show && "div"}/el/><script>el().textContent = "set"</script>` to the `dynamic-tag-var` fixture: both CSR and SSR-resume left the `<div>` empty because `el` was never initialized, so its dependent effect never ran. Static native tags instead create a registered `_el(...)` getter; the dynamic-native path needs the equivalent getter tied to the created/resumed branch element in both runtimes.
 
+CSR is a runtime-only fix: push `() => childScope[AccessorProp.StartNode]` through the child scope's `TagVariable` callback right after the native branch is created in `dom/control-flow.ts`. SSR-resume is the hard part and needs the translator, not just the runtime. The native branch scope carries no state, so `_var`'s `writeScopePassive` `#TagVariable` slot is never serialized (the server fill contains only the parent scope); a dynamic _component_ tag var only resumes because its scope serializes anyway, carrying `{ "#TagVariable": _(1, "…/var") }`. So on resume there is no callback to invoke from the `BranchEndNativeTag` marker handler (`dom/resume.ts:232`). Runtime-only escapes don't exist: `_dynamic_tag` is never told a tag var is present (the compiler emits a separate `_var`), and forcing every tag var to serialize its scope actively regresses payload size for all of them. Delivering the getter across the dynamic boundary requires the compiler to serialize/reconstruct an element reference (a client-side `_el(id, accessor)` for the resumed branch element) — hence effort:high spanning compiler + runtime + serialization.
+
 ## Make conflicting load triggers for one shared asset deterministic
 
 `packages/runtime-tags/src/html/assets.ts:135` | 2026-07-15 | impact:med | effort:med