fix(tools): name the two bound SDK names and escape NEL

The static-stub sentence over-generalized: `tools` and `ToolCallError`
ARE bound at run time, and a model reading "everything below is a stub"
could stop catching `ToolCallError`. State the boundary and pin both
halves in the fixed-instruction assertions.

UNPRINTABLE missed U+0085: it is Cc but not ECMAScript whitespace, so
it survived the collapse and reached the docstring raw and invisible.
Add it and scope the docstring to Cc, since the `\xNN` escape cannot
address the Cf formatting characters that pass through by design.

Record the backend PR's two runtime contracts -- inject only `tools`
and `ToolCallError`, and bind the assembly-time language to the
request -- in the Agent Note and at requireCodeRuntime.

packages/core/tools/src/index.ts

@@ -836,6 +836,14 @@ export class ToolRegistry extends Service {
    * behind it — hostage to a code runtime existing even under `mode:
    * 'native'` (the loop's optional-backend idiom, same as
    * `sessionPersistence`).
+   *
+   * Assembly and `run_code` execution read separately, so the language is not
+   * bound to a request. Harmless while one published backend exists — both
+   * reads return the same flavor — but a reload that swapped in a second
+   * language between them would hand a program written against one SDK to the
+   * other. Binding it belongs to the PR that publishes that backend, which is
+   * also the first point it can be tested; recorded in the
+   * [language-dispatch note](../../../../.agents/notes/implemented/feature/2026-07-31-code-mode-language-dispatch.md).
    */
   private requireCodeRuntime(): CodeRuntime {
     const runtime = this.ctx.get('codeRuntime')