refactor(code-runtime): address seam review — drop worker aliases, tighten dunder

- Worker consumes PORTABLE_RESERVED_WORDS / RESERVED_ERROR_MEMBERS by
  their seam names directly, dropping the local re-alias (symmetry with
  the other two imported constants).
- Split the reserved-vs-duplicate diagnostics: a backend-owned global now
  reports "reserved binding global", not the misleading "duplicate".
- DUNDER_MEMBER uses `__.+__` so a bare `__` (empty middle, not a real
  CPython dunder) is not matched; add coverage.
- Worker misuse tests add `a$b` (second-char `$`) and `lambda` (Python
  keyword) so the identifier narrowing and reserved-word adoption are
  each pinned directly, not only transitively.
- Clarify the seam JSDoc (dunder-vs-explicit-set wording, Python backend
  is a later stack PR) and record in the Agent Note the obligation to
  widen RESERVED_BINDING_GLOBALS when the bootstrap seeds more globals.

.agents/notes/implemented/architecture/2026-07-31-code-runtime-portable-identifier-seam.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write .agents/notes/implemented/architecture/2026-07-31-code-runtime-portable-identifier-seam.md
-2026-07-31-code-runtime-portable-identifier-seam.md: a24a2c03c937a7d569528504b5bd5fba812009a2
-2026-07-31-code-runtime-portable-identifier-seam.zh.md: 1bef607e31a5820ba849f09eb7ae4cc781c45a84
+2026-07-31-code-runtime-portable-identifier-seam.md: bd1876fc459dc85bb5d9f42ac04f4cc801d6398a
+2026-07-31-code-runtime-portable-identifier-seam.zh.md: 2fd5e97c562d1e51cbad906cd37998b8ffccc58a

.agents/notes/implemented/architecture/2026-07-31-code-runtime-portable-identifier-seam.md

@@ -27,6 +27,8 @@ The constants live at the seam even though only one backend ships in this PR: th
 
 This PR delivers only the seam extension and the worker's adoption of it. No Python backend, `py-types` renderer, or Code Mode language dispatch ships here — they are later PRs in the stack that depend on these exports. The seam README's worker-only wording is left unchanged for the same reason: linking to a `dsh-code-runtime-python` README that does not yet exist would break the dead-link gate.
 
+`RESERVED_BINDING_GLOBALS` currently encodes the not-yet-merged Python bootstrap's concrete design: it seeds exactly `__builtins__`/`__name__` and wraps the program under `__dsh_main__`. The Python-backend PR that seeds any additional module global (`__doc__`, `__loader__`, `__spec__`, `__file__`, `__package__`, …) MUST widen this set in the same change, exactly as adding a language widens `PORTABLE_RESERVED_WORDS` — a name the bootstrap seeds but the set omits is the portability split this contract exists to prevent.
+
 ## Alternatives considered
 
 **Each backend declares its own exclusions.** Rejected: it makes the portability promise per-backend. A binding list the caller tested on the worker could be refused by Python, which is exactly the split the seam exists to prevent.

.agents/notes/implemented/architecture/2026-07-31-code-runtime-portable-identifier-seam.zh.md

@@ -27,6 +27,8 @@ seam 同时把可移植标识符子集收窄为 `[A-Za-z_][A-Za-z0-9_]*`（记
 
 本 PR 只交付 seam 扩展与 worker 对它的采用。这里不交付任何 Python 后端、`py-types` 渲染器或 Code Mode 的语言分发——它们是本 stack 中依赖这些导出的后续 PR。seam README 中仅描述 worker 的措辞保持不变，理由相同：链接到一个尚不存在的 `dsh-code-runtime-python` README 会破坏死链 gate。
 
+`RESERVED_BINDING_GLOBALS` 当前编码了尚未合并的 Python bootstrap 的具体设计：它恰好 seed `__builtins__`/`__name__`，并把程序包装在 `__dsh_main__` 之下。任何 seed 额外模块 global（`__doc__`、`__loader__`、`__spec__`、`__file__`、`__package__` 等）的 Python 后端 PR 必须在同一改动中扩宽此集合，正如新增一门语言即扩宽 `PORTABLE_RESERVED_WORDS`——bootstrap 会 seed 却不在集合中的名称，正是本契约要防止的可移植性分裂。
+
 ## Alternatives considered
 
 **每个后端声明自己的排除集。** 拒绝：这让可移植承诺变成逐后端成立。调用方在 worker 上测过的绑定列表可能被 Python 拒绝，而这正是 seam 存在要防止的分裂。