docs(code-runtime-python): register the CPU-recheck and encoder-deps accepted residuals

Document the two remaining keep-current residuals in the python package README
Known Limitations (en + zh), per the review's accepted-resolution path:
- A trap-SIGXCPU program can exceed the soft CPU limit during settlement encoding
  and still report success (containment holds via hard +1s and wall clock; only
  the classification is degraded, because the recheck cannot meter mid-encode).
- The encoder's direct deps (_dump_scalar/_dump_string/json) resolve at call
  time, so a __main__ rebind after a legit return can downgrade success to
  exception; the value path's top-level deps are def-time bound, the transitive
  ones are an accepted residual.
Pairing re-recorded and consistent.

packages/code-runtime/code-runtime-python/README.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 packages/code-runtime/code-runtime-python/README.md
-README.md: b29121c892a820258f905f68f2ab8fbe78003198
-README.zh.md: 8e772c2dd5a09cc64769a4f1175f7c7bc334e3c5
+README.md: 180b0eec9bd5644bfb37086b9eb35cbe93d51672
+README.zh.md: 8a1468f56c62cc1b8544a05c4420270aa26dba31

packages/code-runtime/code-runtime-python/README.md

@@ -39,4 +39,6 @@ No direct invalidation; the named consumer owns any request-prefix changes.
 - **A descendant that calls `setsid()` / `start_new_session=True` escapes teardown.** Termination signals the child's process group with `kill(-pid)`; a descendant that moves itself into a fresh session is no longer in that group and no signal reaches it. If it also releases the inherited stdout/stderr/fd-3 pipes, the leader's `close` still settles the run, and after the `closeDeadline` bound the fiber goes quiescent while that orphan keeps running. This is the containment boundary, not a security one — model code has bash-equivalent trust, and a bash tool can `setsid` away just the same. Reaching such an orphan would require tracking every descendant pid (as the bash-local backend's process-inspector does) and is deferred; the process-group teardown reaps everything that stays in the group.
 - **A combined log-and-value peak is not modelled by the load gate.** Each budget is checked against `addressSpaceMb` on its own. A model daemon thread that keeps writing while the completion value is metered and framed can refill the log pending toward `maxLogBytes` during that window, so the two peaks add in a way no gate admits or rejects. A gate over `(maxLogBytes + maxValueBytes)` was considered and deferred: its discriminating case cannot be scheduled deterministically under `RLIMIT_AS`, so the gate would only prove its own arithmetic. When the combined peak is reached the run dies as `worker-exit` -- containment holds and only the failure classification is degraded.
 - **A 1-second dual-limit `ulimit -t 1` CPU overrun is reported as `worker-exit`, not a timeout.** When the host starts under a hard CPU limit equal to the soft (`ulimit -t N` sets both) and that limit is 1, `_clamped` cannot lower the soft to 0, so the kernel SIGKILLs the busy loop in the same tick and SIGXCPU is never delivered. The host classifies a CPU overrun only on `signal === 'SIGXCPU'`, so the overrun is reported as `worker-exit`. For a dual limit of 2 or more the soft is lowered by one unit, SIGXCPU fires, and the run is a timeout. Containment holds in both cases; only the classification is degraded.
+- **A program that traps SIGXCPU can exceed the soft CPU limit during settlement encoding and still report success.** The settlement CPU recheck runs before the completion value is flushed and encoded; a program that traps SIGXCPU (soft limit) and keeps burning past it through the build-and-encode window returns a result before `die_if_cpu_exhausted` re-checks, so the run reports success. Containment holds — the hard limit (soft + 1s) and the wall clock still bound it — and only the classification is degraded. The CPU recheck does not run mid-encode because doing so would have to meter the encode itself, and the encode is the path the budget already bounds.
+- **The encoder's direct dependencies resolve at call time.** `_encode_json_plain` reaches `_dump_scalar`/`_dump_string`/`json` via module-global lookup, so a program running as `__main__` that rebinds one of those names (e.g. `__main__._dump_scalar = boom`) after returning a legitimate value can make the encode throw and downgrade a success to `exception`. The value path's top-level `_check_done_value`/`_encode_json_plain` are bound as def-time defaults, but their transitive deps are not; this is an accepted residual for the same reason the analogous `_dump_*` helpers are not rebound in practice.
 - **A wide binding REPLY expands host-side state per member.** Resolutions cross through `snapshotJsonValue` in [`@deepseek-ai/dsh-session`](../../core/session/README.md), whose `walkJsonValue` pushes one task frame per member, and binding resolution carries no seam-level byte cap. A legitimate reply of several million elements can therefore exhaust the host heap. A cross-thread binding that the program joins with a synchronous `t.join()` can also deadlock: the joining thread blocks the main coroutine while the binding's reply still needs the pump to deliver it, so `await` never resumes until the wall clock. The property belongs to that shared walk, not to this backend -- the worker-thread backend consumes the same function -- so the fix belongs in `packages/core/session` where every consumer benefits.

packages/code-runtime/code-runtime-python/README.zh.md

@@ -39,4 +39,6 @@ host 与 CPython 子进程在子进程的 fd 3 上交换一个无版本号的 JS
 - **调用 `setsid()` ／ `start_new_session=True` 的后代会逃出 teardown。** 终止是用 `kill(-pid)` 向子进程的进程组发信号；一个把自己移入新会话的后代已不在该进程组内，任何信号都到不了它。若它同时释放了继承而来的 stdout／stderr／fd-3 管道，leader 的 `close` 仍会结算该次运行，在 `closeDeadline` 到界之后 fiber 变为完全停稳，而那个孤儿仍在运行。这是 containment 边界，而非安全边界——模型代码具有等同 bash 的信任级别，一个 bash 工具同样能 `setsid` 逃逸。要够到这样的孤儿需要追踪每一个后代 pid（如 bash-local 后端的 process-inspector 所做），此项已推迟；进程组 teardown 会回收所有留在组内的进程。
 - **日志与完成值的叠加峰值未被加载门建模。** 每项预算都是各自对照 `addressSpaceMb` 检查的。模型的 daemon 线程可以在完成值被计量并分帧的窗口内持续写入、把日志 pending 重填到接近 `maxLogBytes`，于是两个峰值以任何门都不曾放行也不曾拒绝的方式相加。对 `(maxLogBytes + maxValueBytes)` 设门的方案经评估后推迟：它的判别用例无法在 `RLIMIT_AS` 之下确定性地构造出来，因此该门只能证明自己的算术。叠加峰值被触及时该次运行死为 `worker-exit`——containment 仍然成立，只是失败分类失真。
 - **1 秒双限 `ulimit -t 1` 下的 CPU 超限会被报告为 `worker-exit`，而非超时。** 当宿主在一个硬 CPU 限制等于软限制（`ulimit -t N` 同时设置两者）且该限制为 1 的环境下启动时，`_clamped` 无法把软限制降到 0，因此内核在同一 tick 直接 SIGKILL 忙循环，SIGXCPU 永不送达。宿主只在 `signal === 'SIGXCPU'` 时把 CPU 超限分类为超时，因此该超限被报告为 `worker-exit`。当双限为 2 或更大时，软限制会被降低一个单位，SIGXCPU 触发，该次运行成为超时。两种情况 containment 都成立；只是分类被降级。
+- **一个 trap SIGXCPU 的程序可以在结算编码期间超过软 CPU 限制并仍报告成功。** 结算时的 CPU 复查在完成值被 flush 与编码之前运行；一个 trap SIGXCPU（软限制）并在构建与编码窗口内继续燃烧 CPU 的程序会在 `die_if_cpu_exhausted` 复查之前返回结果，因此该次运行报告成功。containment 成立——硬限制（软限制 + 1s）与墙钟仍会约束它——只是分类被降级。CPU 复查不在编码中途运行，因为那必须计量编码本身，而编码正是预算已经约束的路径。
+- **编码器的直接依赖在调用时解析。** `_encode_json_plain` 通过模块全局查找到达 `_dump_scalar`/`_dump_string`/`json`，因此以 `__main__` 运行的程序在返回合法值后重绑这些名字之一（例如 `__main__._dump_scalar = boom`）可以让编码抛出、把成功降级为 `exception`。值路径顶层的 `_check_done_value`/`_encode_json_plain` 被绑定为 def 期默认值，但其传递依赖没有；这是已接受的残余，原因与对应的 `_dump_*` 辅助函数在实践中不被重绑相同。
 - **宽 binding 回复会按成员展开宿主侧状态。** 回复经由 [`@deepseek-ai/dsh-session`](../../core/session/README.zh.md) 的 `snapshotJsonValue` 穿越，其 `walkJsonValue` 为每个成员压入一个任务帧，而 binding 回复在 seam 层没有字节上限。因此一个数百万元素的合法回复可以耗尽宿主堆。程序用同步的 `t.join()` 连接一个跨线程 binding 也会死锁：该线程阻塞主协程，而 binding 的回复仍需泵来投递，因此 `await` 直到墙钟才会恢复。该性质属于那个共享遍历，而不属于本后端——worker-thread 后端消费同一个函数——所以修复应落在 `packages/core/session`，让所有消费方一并受益。