docs(code-runtime): sync Agent Note and public JSDoc with the shipped seam

- Agent Note: correct the stale worker-adoption paragraph — the worker
  consumes the seam constants directly by name (no RESERVED_WORDS /
  RESERVED_ERROR_PROPERTIES re-alias) — and describe DUNDER_MEMBER as
  `__x__` (non-empty middle).
- types.ts: document RESERVED_BINDING_GLOBALS on CodeBindingNamespace.global
  (names like `__dsh_main__` pass the identifier rule but are still refused)
  and the non-empty-middle dunder rule on memberNameProperty; propagate to
  the type-equiv derivative docs (both languages, re-recorded).

packages/code-runtime/code-runtime/src/types.ts

@@ -32,9 +32,9 @@ export interface CodeBindingErrorClass {
   name: string
   /**
    * Non-empty own property for the member name. The portable exclusion set is
-   * `RESERVED_ERROR_MEMBERS` plus dunder-form names (`__*__`), enforced
-   * identically by every backend; any other name — identifiers or not — is
-   * accepted everywhere.
+   * `RESERVED_ERROR_MEMBERS` plus dunder-form names (`__x__`, non-empty
+   * middle), enforced identically by every backend; any other name —
+   * identifiers or not — is accepted everywhere.
    */
   memberNameProperty: string
 }
@@ -52,7 +52,10 @@ export interface CodeBindingNamespace {
    * identifier subset `[A-Za-z_][A-Za-z0-9_]*` and no language's reserved
    * words, so the same namespace list works against every backend regardless
    * of `language` — a JS-only spelling like `$tools` is rejected by design,
-   * not just by the Python backend.
+   * not just by the Python backend. Names that satisfy the identifier rule but
+   * name a backend-owned slot (`RESERVED_BINDING_GLOBALS`: `console`,
+   * `__dsh_main__`, `__builtins__`, `__name__`, `__debug__`) are also refused
+   * everywhere, since some backend seeds that slot in the program's namespace.
    */
   global: string
   /** The callable members, keyed by the exact name the program calls. */