docs(notes): record model-facing error remedy decision

The tool-fs error wrapper decision: guarded-mutation failures gain their recovery instruction at the model boundary while the provider messages and structured codes stay unchanged; includes the deleted-target fail-closed corner.
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+# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
+# 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/feature/2026-08-03-fs-tool-error-remedy.md
+2026-08-03-fs-tool-error-remedy.md: f227c31365725652b130e097d70c79d3daab3684
+2026-08-03-fs-tool-error-remedy.zh.md: 11acd0cf48924833ced91591d5ea1424735969cd
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+# Agent Note: Guarded-mutation errors append the recovery instruction at the model boundary
+
+Status: implemented
+
+English | [中文](2026-08-03-fs-tool-error-remedy.zh.md)
+
+## Problem
+
+Guarded `write` and `edit` failures reach the model with messages that state the condition but not the only correct recovery: `FS_STALE_VERSION` ("file changed since it was read") and `FS_NOT_OBSERVED` ("edit requires reading … first"). The model must guess that the recovery is a re-read (or a first read) followed by a retry, and the retry/permission/UI layers that route on the structured code see the same message text. The provider-owned messages are part of the storage seam's machine-oriented vocabulary ([filesystem capability seam](../architecture/2026-06-17-filesystem-capability-seam.md)), so the remedy cannot live there without leaking model-facing wording into every consumer of `FsError`.
+
+## Decision
+
+`dsh-tool-fs` owns a model-facing error wrapper, `remediateFsError` in `src/error.ts`, applied in `write.ts` and `edit.ts` after the sandbox denial mapping. It appends the recovery instruction to the two guarded-mutation codes and passes everything else through untouched:
+
+- `FS_STALE_VERSION` (including a missing edit target, which shares the stale code) gains `— re-read the file, then retry`.
+- `FS_NOT_OBSERVED` gains `— read the file, then retry`.
+
+The structured `FsError` code is preserved so retry/permission/UI layers keep routing on it, and the original error chains as `cause`. Provider messages stay machine-oriented and unchanged.
+
+In `edit.ts` the `fs/edit-intent` waterfall now sits inside the same `try` as the provider mutation, so the policy plugin's `FS_NOT_OBSERVED` refusal thrown from the intent slot also receives the remedy — both refusal paths reach the model with the same recovery wording.
+
+## Alternatives considered
+
+- **Append the remedy to the provider messages in `dsh-fs` / `dsh-fs-local`.** Rejected because those messages are machine-oriented seam vocabulary consumed by retry, permission, and UI layers as well as the model surface; model-facing wording belongs at the model boundary, where `dsh-tool-fs` already owns result formatting ([filesystem capability seam](../architecture/2026-06-17-filesystem-capability-seam.md)).
+- **Add the recovery to prompt guidance instead.** Rejected because the failure arrives mid-task; a static instruction does not reliably reach the retry decision, while the error message is present exactly when the model must act.
+- **Signal the remedy with a new `FsError` code.** Rejected because the two failures are the same conditions retry layers already handle; splitting the code would fork routing on identical semantics.
+
+## Consequences
+
+Model-visible text for the two codes changes; the `fs-policy-reject` keyless snapshot is re-recorded, and the READMEs of `dsh-tool-fs` and `dsh-fs-policy` pin the exact appended text. Unit tests cover the wrapper directly (remedy text, code preservation, cause chaining, passthrough of other codes and non-`FsError` values) and the assembled tool paths assert the remedy reaches the model for both codes.
+
+The remedy is not a promise: a deleted observed target cannot be unblocked, because re-reading a missing file fails with `FS_NOT_FOUND` and records no observation. That dead end is pinned fail-closed in the integration tests — the retried mutation fails identically until the target exists again and is freshly observed.
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+# Agent Note: Guarded-mutation errors append the recovery instruction at the model boundary
+
+Status: implemented
+
+[English](2026-08-03-fs-tool-error-remedy.md) | 中文
+
+## Problem
+
+受防护的 `write` 与 `edit` 失败以只陈述条件、不给出唯一正确恢复方式的消息到达模型：`FS_STALE_VERSION`（"file changed since it was read"）与 `FS_NOT_OBSERVED`（"edit requires reading … first"）。模型必须自行猜测恢复方式是重新读取（或首次读取）后重试，而基于结构化错误码路由的重试/权限/UI 层看到的也是同一段消息文本。提供方拥有的消息属于存储接缝的面向机器词汇（[filesystem capability seam](../architecture/2026-06-17-filesystem-capability-seam.md)），因此恢复指令不能放在那里，否则会把面向模型的措辞泄漏给 `FsError` 的每个消费者。
+
+## Decision
+
+`dsh-tool-fs` 拥有一个面向模型的错误包装 `remediateFsError`（位于 `src/error.ts`），在 `write.ts` 与 `edit.ts` 中于沙箱拒绝映射之后应用。它为两个受防护变更错误码追加恢复指令，其余错误原样透传：
+
+- `FS_STALE_VERSION`（包括缺失的编辑目标——它与陈旧错误共用同一错误码）追加 `— re-read the file, then retry`。
+- `FS_NOT_OBSERVED` 追加 `— read the file, then retry`。
+
+结构化 `FsError` 错误码保持不变，使重试/权限/UI 层继续基于它路由；原始错误作为 `cause` 链入。提供方消息保持面向机器且不变。
+
+在 `edit.ts` 中，`fs/edit-intent` waterfall 现在与提供方变更位于同一个 `try` 内，因此策略插件从 intent 槽抛出的 `FS_NOT_OBSERVED` 拒绝也会获得恢复指令——两条拒绝路径都以相同的恢复措辞到达模型。
+
+## Alternatives considered
+
+- **在 `dsh-fs` / `dsh-fs-local` 的提供方消息中追加恢复指令。** 被拒绝：这些消息是面向机器的接缝词汇，除模型表面外还被重试、权限与 UI 层消费；面向模型的措辞应位于模型边界，即 `dsh-tool-fs` 已经拥有结果格式化之处（[filesystem capability seam](../architecture/2026-06-17-filesystem-capability-seam.md)）。
+- **改为在提示词引导中加入恢复方式。** 被拒绝：失败发生在任务中途；静态指令无法可靠地影响重试决策，而错误消息恰好在模型必须行动时出现。
+- **用新的 `FsError` 错误码表达恢复指令。** 被拒绝：这两种失败本就是重试层已处理的相同条件；拆分错误码会让语义相同的路由分叉。
+
+## Consequences
+
+两个错误码的模型可见文本发生变化；`fs-policy-reject` 无密钥快照被重新录制，`dsh-tool-fs` 与 `dsh-fs-policy` 的 README 逐字固定追加后的文本。单元测试直接覆盖包装器（恢复指令文本、错误码保留、cause 链、其他错误码与非 `FsError` 值的透传），组装后的工具路径断言两个错误码的恢复指令都到达模型。
+
+恢复指令不是承诺：已删除的观察目标无法被解除阻塞，因为重新读取缺失文件会以 `FS_NOT_FOUND` 失败且不记录观察。这一死胡同在集成测试中以 fail-closed 方式固定——在目标重新存在并被新鲜观察之前，重试的变更以相同方式失败。