fix(fs): persist read window offset in the read card meta

An empty read window (byte cap below the first selected line: `lines: []`
with `totalLines > 0`) dropped `offset` from the persisted presentation
meta, so a replayed read card could not report where the window starts or
where a continuation resumes. Carry `offset` on `FsReadMeta`,
`ReadResultView`, and the `presentationMeta` projection, and validate it in
`readMetaFromMeta` (1-based integer; the first line number may not fall
below it). Re-record the ACP fixtures and the cordis api catalog.

Also correct the Note's `parallel-file-reads` golden path
(examples/tui-agent -> apps/cli) and record the pre-card replay-degradation
tradeoff in the Decision section.

.agents/notes/implemented/feature/2026-07-30-web-read-card.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/feature/2026-07-30-web-read-card.md
-2026-07-30-web-read-card.md: 7d517beb359eec17948ea312b0478604cf92a49b
-2026-07-30-web-read-card.zh.md: bfcc17e782a6a1caf0f775875264839af357be0d
+2026-07-30-web-read-card.md: 509fc866737be6f9f05a02aed02324f3a337e936
+2026-07-30-web-read-card.zh.md: aec170fd2180af58102d8079118339cdef55a4c4

.agents/notes/implemented/feature/2026-07-30-web-read-card.md

@@ -14,9 +14,9 @@ The structured data cannot be recovered downstream. A tool result on the wire ca
 
 Add a fourth `card` tag, `read`, to the [render-intent union](../architecture/2026-07-02-tool-render-intent-union.md) — result-side only. `ToolResultView` gains `ReadResultView { card: 'read'; title?; path; lines: ReadFileLine[]; totalLines; lang?; content? }`; `ReadFileLine { number; text }` is the shared line unit. `ToolCallView` is untouched: the pending state stays a `GenericCallView` (`kind: 'read'`) because a call carries no file content until `execute` returns, so there is nothing structured to show at call time. This diverges from the bash terminal card, which tags both sides — a terminal call already carries its command and cwd at call time, a read call carries neither content nor total, so tagging the call side would add an empty variant.
 
-The read tool projects the structured window through `output.presentationMeta`, the same persisted channel write/edit use for their applied-diff hunks ([canonical tool output contract](../architecture/2026-07-20-canonical-tool-output-contract.md)). `presentationMeta` runs once for a top-level surface call, returns `{ path, lines, totalLines, lang? }` as JSON the session validates and stores on the result's `meta`, and `presentResult` narrows that meta back into the `ReadResultView` on both live and replay paths. Without this channel the line array and total would be unreachable: the raw output object is not on the wire, and re-parsing the `N: text` text is lossy and fragile against the truncation footer.
+The read tool projects the structured window through `output.presentationMeta`, the same persisted channel write/edit use for their applied-diff hunks ([canonical tool output contract](../architecture/2026-07-20-canonical-tool-output-contract.md)). `presentationMeta` runs once for a top-level surface call, returns `{ path, offset, lines, totalLines, lang? }` as JSON the session validates and stores on the result's `meta`, and `presentResult` narrows that meta back into the `ReadResultView` on both live and replay paths. `offset` (the 1-based first line the window requested) rides along because a byte cap below the first selected line yields an empty `lines` array with a positive `totalLines`; without the persisted `offset` a replayed card of such a window could not report where it starts or where a continuation resumes, and the last-line and re-parse fallbacks are both lossy. Without this channel the line array and total would be unreachable: the raw output object is not on the wire, and re-parsing the `N: text` text is lossy and fragile against the truncation footer.
 
-`presentResult` returns `undefined` — the generic fallback — whenever the meta is absent or malformed (`readMetaFromMeta` narrows it defensively, so a replay of an older logged result never throws), whenever the result is an error, and whenever the single text block is not the read envelope. On the success path it carries `content` (the envelope-stripped text) alongside the structured fields, so a UI without the read capability, including the current TUI, renders the file text through the generic/default card arm exactly as before. The TUI's `renderBody` switch (`packages/ui/tui/src/components/transcript.ts`) is not `assertNever`-exhaustive: `terminal` and `diff` have arms and everything else falls through to the generic arm, which reads `view.content`. That default arm alone was not enough: `render()` sets `genericContent` — and with it the dim-Markdown `dimBody` treatment — on a separate gate that was `card === 'generic'` only, so a `read` card would have kept the text but lost its dim styling. The gate now admits `card: 'read'` too, taking `content` down the same dim-Markdown path, so a read renders in the TUI exactly as it did before the read card existed. Beyond that one gate the TUI needs no read-specific code.
+`presentResult` returns `undefined` — the generic fallback — whenever the meta is absent or malformed (`readMetaFromMeta` narrows it defensively, so a replay of an older logged result never throws), whenever the result is an error, and whenever the single text block is not the read envelope. A pre-card logged result — a valid read envelope with no persisted `meta`, recorded before this card existed — takes that same `undefined` path deliberately: the client falls back to the raw `result.content`, so it shows the enveloped `<path>/<type>/<content>` text rather than the envelope-stripped generic card the old presenter returned. This is the accepted degradation under the [pre-release stance](../../../CLAUDE.md): reject the old on-disk format rather than add an envelope-stripping compatibility branch, since this PR re-records every published fixture and the session format promises no backward compatibility. On the success path `presentResult` carries `content` (the envelope-stripped text) alongside the structured fields, so a UI without the read capability, including the current TUI, renders the file text through the generic/default card arm exactly as before. The TUI's `renderBody` switch (`packages/ui/tui/src/components/transcript.ts`) is not `assertNever`-exhaustive: `terminal` and `diff` have arms and everything else falls through to the generic arm, which reads `view.content`. That default arm alone was not enough: `render()` sets `genericContent` — and with it the dim-Markdown `dimBody` treatment — on a separate gate that was `card === 'generic'` only, so a `read` card would have kept the text but lost its dim styling. The gate now admits `card: 'read'` too, taking `content` down the same dim-Markdown path, so a read renders in the TUI exactly as it did before the read card existed. Beyond that one gate the TUI needs no read-specific code.
 
 ### Language hint derivation
 
@@ -40,7 +40,7 @@ The read tool now computes `presentationMeta` for every top-level read, a small
 
 ## Testing
 
-`packages/fs/tool-fs/tests/read-render.spec.ts` unit-tests `langFromPath` (known extensions case-insensitively, extension read after the last segment and last dot, and the `undefined` cases: dotfile, extensionless, trailing dot, unknown) and `readMetaFromMeta` (a well-formed narrow with and without `lang`, and every rejection: non-object, array, missing or wrong-typed `path`/`totalLines`/`lines`, a malformed line entry, a non-string `lang`, and — because the function narrows the opaque persisted `meta` boundary — the semantically invalid paths a well-typed replayed JSON can still carry: a line `number` that is not a 1-based integer (`0`, `1.5`, `NaN`, `Infinity`), a `totalLines` that is not a non-negative integer (`-1`, `1.5`, `NaN`), and lines whose numbers duplicate, decrease, or exceed `totalLines`). `packages/fs/tool-fs/tests/tools.spec.ts` pins the tool wiring: `execute` attaches the structured window (with and without a `lang` hint) as `meta`, `presentResult` narrows it into a `card: 'read'` view carrying the envelope-stripped `content`, and the decline paths (error result, non-single-text content, malformed envelope with valid meta, and valid envelope with absent or malformed meta) all fall back to `undefined`. Both changed source files hold per-file 100% coverage. This PR carries the snapshot evidence for the persisted meta and the extended union, not for a new rendered view: the re-recorded ACP session fixtures (`fs-read`, `fs-read-window`, `fs-edit`, `fs-policy-reject`, `fs-write-overwrite`, `parallel-tool-calls`, `workspace-context`, `workspace-edit`) pin the persisted read `meta` (with `{{cwd}}`-tokenized paths), and `cordis-inspect-jsdoc` pins the four-member `ToolResultView` union. The keyless snapshot and assembled-application transcript for the rendered read card belong to the follow-up Web PR that consumes the view, since this PR adds no new product-user-visible rendering — the TUI routes the read card through its existing generic dim-Markdown fallback (`transcript.ts` treats `card: 'read'` like `card: 'generic'`), so its output is unchanged. The `apps/cli` `parallel-file-reads` terminal golden (`examples/tui-agent/tests/snapshots/parallel-file-reads/terminal.expected.txt`) pins exactly that: a real replay executes the read tool, renders it through the new `card: 'read'` gate, and the golden's dim-Markdown rows are byte-for-byte what a generic read produced before this card existed.
+`packages/fs/tool-fs/tests/read-render.spec.ts` unit-tests `langFromPath` (known extensions case-insensitively, extension read after the last segment and last dot, and the `undefined` cases: dotfile, extensionless, trailing dot, unknown) and `readMetaFromMeta` (a well-formed narrow with and without `lang`, and every rejection: non-object, array, missing or wrong-typed `path`/`totalLines`/`lines`, a malformed line entry, a non-string `lang`, and — because the function narrows the opaque persisted `meta` boundary — the semantically invalid paths a well-typed replayed JSON can still carry: an `offset` that is not a 1-based integer, a first line `number` below `offset`, a line `number` that is not a 1-based integer (`0`, `1.5`, `NaN`, `Infinity`), a `totalLines` that is not a non-negative integer (`-1`, `1.5`, `NaN`), and lines whose numbers duplicate, decrease, or exceed `totalLines`; it also narrows an empty window at a positive `offset` (a byte cap below the first selected line). `packages/fs/tool-fs/tests/tools.spec.ts` pins the tool wiring: `execute` attaches the structured window (with and without a `lang` hint) as `meta`, `presentResult` narrows it into a `card: 'read'` view carrying the envelope-stripped `content`, and the decline paths (error result, non-single-text content, malformed envelope with valid meta, and valid envelope with absent or malformed meta) all fall back to `undefined`. Both changed source files hold per-file 100% coverage. This PR carries the snapshot evidence for the persisted meta and the extended union, not for a new rendered view: the re-recorded ACP session fixtures (`fs-read`, `fs-read-window`, `fs-edit`, `fs-policy-reject`, `fs-write-overwrite`, `parallel-tool-calls`, `workspace-context`, `workspace-edit`) pin the persisted read `meta` (with `{{cwd}}`-tokenized paths), and `cordis-inspect-jsdoc` pins the four-member `ToolResultView` union. The keyless snapshot and assembled-application transcript for the rendered read card belong to the follow-up Web PR that consumes the view, since this PR adds no new product-user-visible rendering — the TUI routes the read card through its existing generic dim-Markdown fallback (`transcript.ts` treats `card: 'read'` like `card: 'generic'`), so its output is unchanged. The `apps/cli` `parallel-file-reads` terminal golden (`apps/cli/tests/snapshots/parallel-file-reads/terminal.expected.txt`) pins exactly that: a real replay executes the read tool, renders it through the new `card: 'read'` gate, and the golden's dim-Markdown rows are byte-for-byte what a generic read produced before this card existed.
 
 ## Related
 

.agents/notes/implemented/feature/2026-07-30-web-read-card.zh.md

@@ -14,9 +14,9 @@ Status: implemented
 
 给[渲染意图 union](../architecture/2026-07-02-tool-render-intent-union.md) 新增第四个 `card` 标签 `read`——仅在结果侧。`ToolResultView` 增加 `ReadResultView { card: 'read'; title?; path; lines: ReadFileLine[]; totalLines; lang?; content? }`；`ReadFileLine { number; text }` 是共享的行单元。`ToolCallView` 不动：待定状态仍是 `GenericCallView`（`kind: 'read'`），因为一次调用在 `execute` 返回前不携带文件内容，调用时没有可展示的结构。这与 bash 终端 card 不同——终端 card 两侧都打标签，因为终端调用在调用时已携带命令和 cwd，而 read 调用既无内容也无总数，给调用侧打标签只会新增一个空变体。
 
-read 工具通过 `output.presentationMeta` 投影结构化窗口，这与 write/edit 用来投影其应用 diff hunk 的持久化通道相同（[规范化工具输出契约](../architecture/2026-07-20-canonical-tool-output-contract.md)）。`presentationMeta` 对一次顶层 surface 调用运行一次，返回 `{ path, lines, totalLines, lang? }` 作为会话校验并存储在结果 `meta` 上的 JSON，`presentResult` 在 live 和回放路径上都把该 meta 收窄回 `ReadResultView`。没有这个通道，行数组和总数就无法触及：原始输出对象不在线上，而重新解析 `N: text` 文本既有损又对截断脚注脆弱。
+read 工具通过 `output.presentationMeta` 投影结构化窗口，这与 write/edit 用来投影其应用 diff hunk 的持久化通道相同（[规范化工具输出契约](../architecture/2026-07-20-canonical-tool-output-contract.md)）。`presentationMeta` 对一次顶层 surface 调用运行一次，返回 `{ path, offset, lines, totalLines, lang? }` 作为会话校验并存储在结果 `meta` 上的 JSON，`presentResult` 在 live 和回放路径上都把该 meta 收窄回 `ReadResultView`。`offset`（窗口请求的 1-based 起始行）一并携带，是因为当字节上限低于首个选中行时，窗口会返回空的 `lines` 数组而 `totalLines` 为正；没有持久化的 `offset`，这类窗口的回放 card 就无法报告它从哪行开始、或续读应从哪行继续，而末行推断与文本重解析两种兜底都有损。没有这个通道，行数组和总数就无法触及：原始输出对象不在线上，而重新解析 `N: text` 文本既有损又对截断脚注脆弱。
 
-`presentResult` 在以下情况返回 `undefined`——即 generic 回退：meta 缺失或畸形（`readMetaFromMeta` 防御性收窄它，因此回放旧的已记录结果永不抛错）、结果是错误、以及单个文本块不是 read 信封。在成功路径上，它在结构化字段之外携带 `content`（剥信封后的文本），因此不具备 read 能力的 UI（包括当前的 TUI）通过 generic/default card 分支渲染文件文本，与之前完全一致。TUI 的 `renderBody` switch（`packages/ui/tui/src/components/transcript.ts`）不是 `assertNever` 穷尽的：`terminal` 和 `diff` 有分支，其余都落入 generic 分支，该分支读取 `view.content`。仅有该默认分支还不够：`render()` 在一个独立门控上设置 `genericContent`（连同 dim-Markdown 的 `dimBody` 处理），该门控原先只判 `card === 'generic'`，因此 `read` card 虽保留文本却会丢失 dim 样式。现在该门控也接纳 `card: 'read'`，让 `content` 走同一条 dim-Markdown 路径，因此 read 在 TUI 中的渲染与 read card 出现之前完全一致。除这一处门控外，TUI 无需 read 专属代码。
+`presentResult` 在以下情况返回 `undefined`——即 generic 回退：meta 缺失或畸形（`readMetaFromMeta` 防御性收窄它，因此回放旧的已记录结果永不抛错）、结果是错误、以及单个文本块不是 read 信封。本 card 出现之前记录的结果——信封合法但无持久化 `meta`——有意走同一条 `undefined` 路径：客户端回退到原始 `result.content`，因此显示带 `<path>/<type>/<content>` 信封的原文，而非旧展示器返回的剥信封 generic card。这是 [pre-release 立场](../../../CLAUDE.md)下接受的降级：拒绝旧的磁盘格式，而非加一个剥信封的兼容分支——本 PR 已重录全部已发布 fixtures，且 session 格式不承诺向后兼容。在成功路径上，`presentResult` 在结构化字段之外携带 `content`（剥信封后的文本），因此不具备 read 能力的 UI（包括当前的 TUI）通过 generic/default card 分支渲染文件文本，与之前完全一致。TUI 的 `renderBody` switch（`packages/ui/tui/src/components/transcript.ts`）不是 `assertNever` 穷尽的：`terminal` 和 `diff` 有分支，其余都落入 generic 分支，该分支读取 `view.content`。仅有该默认分支还不够：`render()` 在一个独立门控上设置 `genericContent`（连同 dim-Markdown 的 `dimBody` 处理），该门控原先只判 `card === 'generic'`，因此 `read` card 虽保留文本却会丢失 dim 样式。现在该门控也接纳 `card: 'read'`，让 `content` 走同一条 dim-Markdown 路径，因此 read 在 TUI 中的渲染与 read card 出现之前完全一致。除这一处门控外，TUI 无需 read 专属代码。
 
 ### 语言提示推导
 
@@ -40,7 +40,7 @@ read 工具现在为每次顶层 read 计算 `presentationMeta`，这是对已
 
 ## Testing
 
-`packages/fs/tool-fs/tests/read-render.spec.ts` 单测 `langFromPath`（已知扩展名的大小写不敏感、扩展名在最后一段与最后一个点之后读取、以及 `undefined` 各情况：dotfile、无扩展名、结尾的点、未知）与 `readMetaFromMeta`（含与不含 `lang` 的良构收窄，以及每种拒绝：非对象、数组、缺失或类型错误的 `path`/`totalLines`/`lines`、畸形行项、非字符串 `lang`，以及——因为该函数收窄持久化的 opaque `meta` 边界——良构类型的回放 JSON 仍可能携带的语义无效路径：不是 1-based 整数的行 `number`（`0`、`1.5`、`NaN`、`Infinity`）、不是非负整数的 `totalLines`（`-1`、`1.5`、`NaN`）、以及行号重复、递减或超过 `totalLines` 的情况）。`packages/fs/tool-fs/tests/tools.spec.ts` 固定工具接线：`execute` 把结构化窗口（含与不含 `lang` 提示）作为 `meta` 附上、`presentResult` 把它收窄为携带剥信封 `content` 的 `card: 'read'` 视图、以及各拒绝路径（错误结果、非单文本内容、meta 有效但信封畸形、信封有效但 meta 缺失或畸形）都回退到 `undefined`。两个改动的源文件保持逐文件 100% 覆盖率。本 PR 携带的是持久化 meta 与扩展后联合类型的快照证据，而非新渲染视图的证据：重录的 ACP session fixtures（`fs-read`、`fs-read-window`、`fs-edit`、`fs-policy-reject`、`fs-write-overwrite`、`parallel-tool-calls`、`workspace-context`、`workspace-edit`）钉住持久化的读取 `meta`（含 `{{cwd}}` 令牌化路径），`cordis-inspect-jsdoc` 钉住四成员的 `ToolResultView` 联合类型。已渲染读取 card 的 keyless 快照与组装应用 transcript 属于消费该视图的后续 Web PR，因为本 PR 不新增任何面向产品用户可见的渲染——TUI 通过其现有的通用 dim-Markdown 回退路由读取 card（`transcript.ts` 把 `card: 'read'` 当作 `card: 'generic'` 处理），因此其输出保持不变。`apps/cli` 的 `parallel-file-reads` 终端 golden（`examples/tui-agent/tests/snapshots/parallel-file-reads/terminal.expected.txt`）正钉住这一点:一次真实回放执行 read 工具、经新的 `card: 'read'` 门渲染，golden 的 dim-Markdown 行与本 card 出现前 generic read 所产出的逐字节一致。
+`packages/fs/tool-fs/tests/read-render.spec.ts` 单测 `langFromPath`（已知扩展名的大小写不敏感、扩展名在最后一段与最后一个点之后读取、以及 `undefined` 各情况：dotfile、无扩展名、结尾的点、未知）与 `readMetaFromMeta`（含与不含 `lang` 的良构收窄，以及每种拒绝：非对象、数组、缺失或类型错误的 `path`/`totalLines`/`lines`、畸形行项、非字符串 `lang`，以及——因为该函数收窄持久化的 opaque `meta` 边界——良构类型的回放 JSON 仍可能携带的语义无效路径：不是 1-based 整数的 `offset`、小于 `offset` 的首行 `number`、不是 1-based 整数的行 `number`（`0`、`1.5`、`NaN`、`Infinity`）、不是非负整数的 `totalLines`（`-1`、`1.5`、`NaN`）、以及行号重复、递减或超过 `totalLines` 的情况；并且收窄正 `offset` 处的空窗口（字节上限低于首个选中行））。`packages/fs/tool-fs/tests/tools.spec.ts` 固定工具接线：`execute` 把结构化窗口（含与不含 `lang` 提示）作为 `meta` 附上、`presentResult` 把它收窄为携带剥信封 `content` 的 `card: 'read'` 视图、以及各拒绝路径（错误结果、非单文本内容、meta 有效但信封畸形、信封有效但 meta 缺失或畸形）都回退到 `undefined`。两个改动的源文件保持逐文件 100% 覆盖率。本 PR 携带的是持久化 meta 与扩展后联合类型的快照证据，而非新渲染视图的证据：重录的 ACP session fixtures（`fs-read`、`fs-read-window`、`fs-edit`、`fs-policy-reject`、`fs-write-overwrite`、`parallel-tool-calls`、`workspace-context`、`workspace-edit`）钉住持久化的读取 `meta`（含 `{{cwd}}` 令牌化路径），`cordis-inspect-jsdoc` 钉住四成员的 `ToolResultView` 联合类型。已渲染读取 card 的 keyless 快照与组装应用 transcript 属于消费该视图的后续 Web PR，因为本 PR 不新增任何面向产品用户可见的渲染——TUI 通过其现有的通用 dim-Markdown 回退路由读取 card（`transcript.ts` 把 `card: 'read'` 当作 `card: 'generic'` 处理），因此其输出保持不变。`apps/cli` 的 `parallel-file-reads` 终端 golden（`apps/cli/tests/snapshots/parallel-file-reads/terminal.expected.txt`）正钉住这一点：一次真实回放执行 read 工具、经新的 `card: 'read'` 门渲染，golden 的 dim-Markdown 行与本 card 出现前 generic read 所产出的逐字节一致。
 
 ## Related
 

examples/acp-agent/tests/snapshots/fs-edit/session.jsonl

@@ -14,7 +14,7 @@
 {"type":"assistant/chunk","seq":68,"time":1783352086057,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
 {"type":"assistant/message","seq":69,"time":1783352086059,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to:\n1. Read config.txt in the current directory\n2. Use the edit tool to replace DEBUG with RELEASE\n3. Reply with exactly \"DONE\"\n\nLet me start by reading the file."},{"type":"tool-call","id":"call_00_S6krdIDHoSCGWv7WnXX97617","name":"read","arguments":"{\"file_path\": \"config.txt\"}"}],"source":{"kind":"model","provider":"deepseek","model":"deepseek-v4-flash"},"id":"36ebf262-429c-4398-abbc-a197e2522f1d"},"usage":{"inputTokens":2900,"outputTokens":91,"cacheReadTokens":0,"reasoningTokens":46}},"sourceEventSeqs":[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68],"surfaceOp":"append"}
 {"type":"tool/call","seq":70,"time":1783352086059,"data":{"turn":1,"step":1,"callId":"call_00_S6krdIDHoSCGWv7WnXX97617","name":"read","arguments":"{\"file_path\": \"config.txt\"}"}}
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examples/acp-agent/tests/snapshots/fs-policy-reject/session.jsonl

@@ -27,7 +27,7 @@
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+{"type":"tool/result","seq":146,"time":1783611705579,"data":{"turn":1,"step":2,"message":{"source":{"kind":"tool","callId":"call_00_tfr0gdIclW92oIEgi7NF0891"},"content":[{"type":"tool-result","toolCallId":"call_00_tfr0gdIclW92oIEgi7NF0891","content":[{"type":"text","text":"<path>{{cwd}}/settings.txt</path>\n<type>file</type>\n<content>\n1: color: blue\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"fade9382-14c7-47e3-8da4-286008d7e9b8"},"meta":{"path":"{{cwd}}/settings.txt","offset":1,"lines":[{"number":1,"text":"color: blue"}],"totalLines":1}},"sourceEventSeqs":[145],"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/fs-read-window/session.jsonl

@@ -14,7 +14,7 @@
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 {"type":"assistant/message","seq":91,"time":1783352101348,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to use the read tool with offset 5 and limit 4 to read lines 5 through 8 of big.txt in the current directory. Then reply with exactly the single word DONE.\n\nLet me first check the current directory, then read the file."},{"type":"tool-call","id":"call_00_GIZwZS9a7vhWTFCIc7Z35497","name":"read","arguments":"{\"file_path\": \"big.txt\", \"offset\": 5, \"limit\": 4}"}],"source":{"kind":"model","provider":"deepseek","model":"deepseek-v4-flash"},"id":"5620412c-8fae-4d17-aac4-0801f3b02461"},"usage":{"inputTokens":2894,"outputTokens":133,"cacheReadTokens":0,"reasoningTokens":56}},"sourceEventSeqs":[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90],"surfaceOp":"append"}
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-{"type":"tool/result","seq":93,"time":1783352101353,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_00_GIZwZS9a7vhWTFCIc7Z35497"},"content":[{"type":"tool-result","toolCallId":"call_00_GIZwZS9a7vhWTFCIc7Z35497","content":[{"type":"text","text":"<path>{{cwd}}/big.txt</path>\n<type>file</type>\n<content>\n5: line five\n6: line six\n7: line seven\n8: line eight\n\n(Showing lines 5-8 of 10. Use offset=9 to continue.)\n</content>"}],"isError":false}],"role":"user","id":"02513672-93cb-4f70-9ee7-ad19542a5f6b"},"meta":{"path":"{{cwd}}/big.txt","lines":[{"number":5,"text":"line five"},{"number":6,"text":"line six"},{"number":7,"text":"line seven"},{"number":8,"text":"line eight"}],"totalLines":10}},"sourceEventSeqs":[92],"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/fs-read/session.jsonl

@@ -14,7 +14,7 @@
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 {"type":"assistant/message","seq":53,"time":1783352073708,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to read the file greeting.txt using the read tool (not bash), then reply with exactly the single word \"DONE\"."},{"type":"tool-call","id":"call_00_hHPZCcivsIkXAGS9jTGy8417","name":"read","arguments":"{\"file_path\": \"greeting.txt\"}"}],"source":{"kind":"model","provider":"deepseek","model":"deepseek-v4-flash"},"id":"5452254c-4843-458c-9732-12fe8b7c1468"},"usage":{"inputTokens":2882,"outputTokens":75,"cacheReadTokens":0,"reasoningTokens":29}},"sourceEventSeqs":[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52],"surfaceOp":"append"}
 {"type":"tool/call","seq":54,"time":1783352073709,"data":{"turn":1,"step":1,"callId":"call_00_hHPZCcivsIkXAGS9jTGy8417","name":"read","arguments":"{\"file_path\": \"greeting.txt\"}"}}
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examples/acp-agent/tests/snapshots/fs-write-overwrite/session.jsonl

@@ -14,7 +14,7 @@
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 {"type":"assistant/message","seq":65,"time":1783352093617,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to:\n1. Read data.txt using the read tool\n2. Replace its entire contents with exactly \"replaced\" using the write tool\n3. Reply with exactly \"DONE\""},{"type":"tool-call","id":"call_00_n4eRJuGoxNR07svgNtk82243","name":"read","arguments":"{\"file_path\": \"data.txt\"}"}],"source":{"kind":"model","provider":"deepseek","model":"deepseek-v4-flash"},"id":"00272d0c-8ed0-436a-8d10-4a7091447dfe"},"usage":{"inputTokens":2899,"outputTokens":87,"cacheReadTokens":0,"reasoningTokens":42}},"sourceEventSeqs":[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64],"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/parallel-tool-calls/session.jsonl

@@ -15,8 +15,8 @@
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+{"type":"tool/result","seq":17,"time":0,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_read_b"},"content":[{"type":"tool-result","toolCallId":"call_read_b","content":[{"type":"text","text":"<path>{{cwd}}/b.txt</path>\n<type>file</type>\n<content>\n1: beta\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"49a6bffd-3a0e-490e-bf49-e9d3e6370f83"},"meta":{"path":"{{cwd}}/b.txt","offset":1,"lines":[{"number":1,"text":"beta"}],"totalLines":1}},"sourceEventSeqs":[15],"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/workspace-context/session.jsonl

@@ -12,7 +12,7 @@
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+{"type":"tool/result","seq":13,"time":1784903339813,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_workspace_read"},"content":[{"type":"tool-result","toolCallId":"call_workspace_read","content":[{"type":"text","text":"<path>{{cwd}}/nested/task.txt</path>\n<type>file</type>\n<content>\n1: snapshot task\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"9027e8f1-572e-45f2-9c92-c78227adc42a"},"meta":{"path":"{{cwd}}/nested/task.txt","offset":1,"lines":[{"number":1,"text":"snapshot task"}],"totalLines":1}},"sourceEventSeqs":[12],"surfaceOp":"append"}
 {"type":"user/message","seq":14,"time":1784903339813,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: nested/AGENTS.md\n\nThese instructions apply to work under `nested`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nNested snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","changes":[{"action":"set","scope":"nested\u0000AGENTS.md","path":"nested/AGENTS.md","digest":"c446df9a85c7e73a3055f394a4822a19ac9ead5a"}]},"role":"user","id":"939dbe9f-7df8-48af-b36c-3b546fd5d95e"},"surfaceOp":"append"}
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@@ -23,7 +23,7 @@
 {"type":"assistant/chunk","seq":21,"time":1784903339821,"data":{"turn":1,"step":2,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
 {"type":"assistant/message","seq":22,"time":1784903339821,"data":{"turn":1,"step":2,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_workspace_delimiter_read","name":"read","arguments":"{\"file_path\":\"scope</system-reminder>/task.txt\"}"}],"source":{"kind":"model","provider":"deepseek","model":"deepseek-v4-flash"},"id":"a9d0e5a8-e1ae-4b09-933d-882400f5f13a"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[17,18,19,20,21],"surfaceOp":"append"}
 {"type":"tool/call","seq":23,"time":1785233046380,"data":{"turn":1,"step":2,"callId":"call_workspace_delimiter_read","name":"read","arguments":"{\"file_path\":\"scope</system-reminder>/task.txt\"}"}}
-{"type":"tool/result","seq":24,"time":1785233046389,"data":{"turn":1,"step":2,"message":{"source":{"kind":"tool","callId":"call_workspace_delimiter_read"},"content":[{"type":"tool-result","toolCallId":"call_workspace_delimiter_read","content":[{"type":"text","text":"<path>{{cwd}}/scope</system-reminder>/task.txt</path>\n<type>file</type>\n<content>\n1: delimiter path snapshot task\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"31c9f547-39d5-4fd8-903a-2b4625fb3b8e"},"meta":{"path":"{{cwd}}/scope</system-reminder>/task.txt","lines":[{"number":1,"text":"delimiter path snapshot task"}],"totalLines":1}},"sourceEventSeqs":[23],"surfaceOp":"append"}
+{"type":"tool/result","seq":24,"time":1785233046389,"data":{"turn":1,"step":2,"message":{"source":{"kind":"tool","callId":"call_workspace_delimiter_read"},"content":[{"type":"tool-result","toolCallId":"call_workspace_delimiter_read","content":[{"type":"text","text":"<path>{{cwd}}/scope</system-reminder>/task.txt</path>\n<type>file</type>\n<content>\n1: delimiter path snapshot task\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"31c9f547-39d5-4fd8-903a-2b4625fb3b8e"},"meta":{"path":"{{cwd}}/scope</system-reminder>/task.txt","offset":1,"lines":[{"number":1,"text":"delimiter path snapshot task"}],"totalLines":1}},"sourceEventSeqs":[23],"surfaceOp":"append"}
 {"type":"user/message","seq":25,"time":1785233046389,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: scope<\\/system-reminder>/AGENTS.md\n\nThese instructions apply to work under `scope<\\/system-reminder>`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nDelimiter path snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","changes":[{"action":"set","scope":"scope</system-reminder>\u0000AGENTS.md","path":"scope</system-reminder>/AGENTS.md","digest":"38803cd13e2dff9105ba5fbbc703fe27e989e26e"}]},"role":"user","id":"149d4be0-a33b-4478-be5a-8d1e4f9ec7cc"},"surfaceOp":"append"}
 {"type":"step/end","seq":26,"time":1785233046389,"data":{"turn":1,"step":2}}
 {"type":"step/start","seq":27,"time":1785233046397,"data":{"turn":1,"step":3}}

examples/acp-agent/tests/snapshots/workspace-edit/session.jsonl

@@ -14,7 +14,7 @@
 {"type":"assistant/chunk","seq":78,"time":1783352265489,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
 {"type":"assistant/message","seq":79,"time":1783352265491,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to:\n1. Read the file greeting.txt\n2. Append the word WORLD as a second line\n3. Read the file back with cat to confirm\n4. Reply with DONE\n\nLet me start by reading the file to see its contents."},{"type":"tool-call","id":"call_00_OjRFB4zvxu6UALDjytZD0978","name":"read","arguments":"{\"file_path\": \"greeting.txt\"}"}],"source":{"kind":"model","provider":"deepseek","model":"deepseek-v4-flash"},"id":"3f154ea9-6cf0-4d0a-a478-503962bfe8e1"},"usage":{"inputTokens":2918,"outputTokens":101,"cacheReadTokens":0,"reasoningTokens":55}},"sourceEventSeqs":[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78],"surfaceOp":"append"}
 {"type":"tool/call","seq":80,"time":1783352265491,"data":{"turn":1,"step":1,"callId":"call_00_OjRFB4zvxu6UALDjytZD0978","name":"read","arguments":"{\"file_path\": \"greeting.txt\"}"}}
-{"type":"tool/result","seq":81,"time":1783352265504,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_00_OjRFB4zvxu6UALDjytZD0978"},"content":[{"type":"tool-result","toolCallId":"call_00_OjRFB4zvxu6UALDjytZD0978","content":[{"type":"text","text":"<path>{{cwd}}/greeting.txt</path>\n<type>file</type>\n<content>\n1: hello\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"59ffbde4-d450-4564-a907-beeec29af0d0"},"meta":{"path":"{{cwd}}/greeting.txt","lines":[{"number":1,"text":"hello"}],"totalLines":1}},"sourceEventSeqs":[80],"surfaceOp":"append"}
+{"type":"tool/result","seq":81,"time":1783352265504,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_00_OjRFB4zvxu6UALDjytZD0978"},"content":[{"type":"tool-result","toolCallId":"call_00_OjRFB4zvxu6UALDjytZD0978","content":[{"type":"text","text":"<path>{{cwd}}/greeting.txt</path>\n<type>file</type>\n<content>\n1: hello\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"59ffbde4-d450-4564-a907-beeec29af0d0"},"meta":{"path":"{{cwd}}/greeting.txt","offset":1,"lines":[{"number":1,"text":"hello"}],"totalLines":1}},"sourceEventSeqs":[80],"surfaceOp":"append"}
 {"type":"step/end","seq":82,"time":1783352265504,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":83,"time":1783352265505,"data":{"turn":1,"step":2}}
 {"type":"assistant/chunk","seq":84,"time":1783352266385,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -2101,7 +2101,7 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'ReadResultView',
-    declaration: 'export interface ReadResultView {\n    card: \'read\';\n    title?: string;\n    path: string;\n    lines: ReadFileLine[];\n    totalLines: number;\n    lang?: string;\n    content?: ContentBlock[];\n}',
+    declaration: 'export interface ReadResultView {\n    card: \'read\';\n    title?: string;\n    path: string;\n    offset: number;\n    lines: ReadFileLine[];\n    totalLines: number;\n    lang?: string;\n    content?: ContentBlock[];\n}',
   },
   {
     name: 'ReasoningBlock',

packages/core/tools/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/core/tools/README.md
-README.md: bff80e34d8b8a03424263ae978fe43c143bcb4fa
-README.zh.md: 9d141cdfe91f14420bcd5a394b8bbd5871407b42
+README.md: dc3d059c1ce16f11cb0650e266762eb6d7466e34
+README.zh.md: 8d1ee0139b2d311fed07a0673cd772222ae22032

packages/core/tools/README.md

@@ -108,7 +108,7 @@ Optional `isConcurrencySafe(args)` receives typed, softly validated arguments. E
 Tools optionally own pure `presentCall()` and `presentResult()` render intents, so UIs do not special-case tool names:
 
 - Call views are `{ card: 'generic', title, kind?, rawInput?, content?, locations? }`, `{ card: 'terminal', title, description?, cwd? }`, or `{ card: 'diff', title, diffs, locations? }`.
-- Result views are `{ card: 'generic', title?, content? }`, `{ card: 'terminal', title?, output?, exitCode?, signal? }`, `{ card: 'diff', title?, diffs }`, or `{ card: 'read', title?, path, lines, totalLines, lang?, content? }` (a completed file read → a line-numbered, optionally syntax-highlighted code view; `lines` is `{ number, text }[]` keeping each file line number, and `content` is the envelope-stripped text a UI without read support falls back to).
+- Result views are `{ card: 'generic', title?, content? }`, `{ card: 'terminal', title?, output?, exitCode?, signal? }`, `{ card: 'diff', title?, diffs }`, or `{ card: 'read', title?, path, offset, lines, totalLines, lang?, content? }` (a completed file read → a line-numbered, optionally syntax-highlighted code view; `offset` is the 1-based first line the window requested, kept even when `lines` is empty; `lines` is `{ number, text }[]` keeping each file line number, and `content` is the envelope-stripped text a UI without read support falls back to).
 
 Returning `undefined` selects generic fallback. Presenters depend only on their arguments and the durable result because UIs call them during live streaming and log replay. `output.presentationMeta(args, value)` derives JSON metadata for direct surface calls; that metadata persists with `tool/result` and returns to `presentResult`, while the canonical value itself remains execution-local and is never replayed. Nested Code dispatches do not compute metadata. `defineTool` soft-validates older logged arguments and falls back instead of crashing replay. `dsh-tool-bash` and `dsh-tool-fs` are the reference implementations; the [canonical-output Agent Note](../../../.agents/notes/implemented/architecture/2026-07-20-canonical-tool-output-contract.md) owns the value/presentation split and the [render-intent Agent Note](../../../.agents/notes/implemented/architecture/2026-07-02-tool-render-intent-union.md) owns card vocabulary.
 

packages/core/tools/README.zh.md

@@ -108,7 +108,7 @@ ctx.tools.register(defineTool({
 工具可以选择拥有纯 `presentCall()` 和 `presentResult()` 呈现意图，使 UI 无需特殊处理工具名称：
 
 - 调用视图为 `{ card: 'generic', title, kind?, rawInput?, content?, locations? }`、`{ card: 'terminal', title, description?, cwd? }` 或 `{ card: 'diff', title, diffs, locations? }`。
-- 结果视图为 `{ card: 'generic', title?, content? }`、`{ card: 'terminal', title?, output?, exitCode?, signal? }`、`{ card: 'diff', title?, diffs }` 或 `{ card: 'read', title?, path, lines, totalLines, lang?, content? }`（已完成的文件读取→带行号、可选语法高亮的代码视图；`lines` 是 `{ number, text }[]`，保留每一行的文件行号，`content` 是无读取能力的 UI 回退时使用的去信封文本）。
+- 结果视图为 `{ card: 'generic', title?, content? }`、`{ card: 'terminal', title?, output?, exitCode?, signal? }`、`{ card: 'diff', title?, diffs }` 或 `{ card: 'read', title?, path, offset, lines, totalLines, lang?, content? }`（已完成的文件读取→带行号、可选语法高亮的代码视图；`offset` 是窗口请求的 1-based 起始行，即使 `lines` 为空也保留；`lines` 是 `{ number, text }[]`，保留每一行的文件行号，`content` 是无读取能力的 UI 回退时使用的去信封文本）。
 
 返回 `undefined` 会选择通用回退。呈现器只依赖其参数和持久结果，因为 UI 会在实时流式输出和日志回放期间调用它们。`output.presentationMeta(args, value)` 为直接接口调用派生 JSON 元数据；该元数据随 `tool/result` 持久化并传回 `presentResult`，而规范值本身仍只存在于执行局部，绝不会回放。嵌套 Code 分发不会计算元数据。`defineTool` 会软验证较旧的日志参数并回退，而不会使回放崩溃。`dsh-tool-bash` 与 `dsh-tool-fs` 是参考实现；[规范输出 Agent Note](../../../.agents/notes/implemented/architecture/2026-07-20-canonical-tool-output-contract.md) 规定值／呈现拆分，[呈现意图 Agent Note](../../../.agents/notes/implemented/architecture/2026-07-02-tool-render-intent-union.md) 规定卡片词汇。
 

packages/core/tools/src/presentation.ts

@@ -207,6 +207,12 @@ export interface ReadResultView {
   title?: string
   /** The read file's path (the model-facing path; the bridge relativizes it). */
   path: string
+  /**
+   * The 1-based first line the window requested, preserved even when `lines` is
+   * empty (a byte cap below the first selected line yields an empty window) so a
+   * UI knows where the window starts and where a continuation resumes.
+   */
+  offset: number
   /** The returned window's lines, in file order, each keeping its file line number. */
   lines: ReadFileLine[]
   /** Exact total line count in the file, so a UI can show a "showing N of M" affordance. */

packages/fs/tool-fs/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/fs/tool-fs/README.md
-README.md: 9e72ed53324d5f5efeaf659427c02d826221425c
-README.zh.md: aa94a7f6144b6cc6da34b059f5699312737d38a2
+README.md: c00b59fed06249e6d9479c4a809cdf7d78f93239
+README.zh.md: f90fbb36391c1388ab0f6836daa2a9061d046be6

packages/fs/tool-fs/README.md

@@ -34,7 +34,7 @@ All keys are optional; the defaults are the shipped read caps.
 
 Field names are snake_case to match Claude Code and existing harness tool schemas.
 
-Canonical successes are `read` → `{ path, offset, lines: [{ number, text }], totalLines }`, `write` → `{ path, operation: 'create' | 'update', before: string | null, after }`, and `edit` → `{ path, before, after }`. Native renderers preserve the line-numbered read and mutation acknowledgements below. `write`/`edit` derive replayable diff-card metadata, and `read` derives a replayable read-card window `{ path, lines, totalLines, lang? }`, from these canonical values; the canonical values themselves are execution-local and are not added to `tool/result`, only the derived presentation metadata is persisted.
+Canonical successes are `read` → `{ path, offset, lines: [{ number, text }], totalLines }`, `write` → `{ path, operation: 'create' | 'update', before: string | null, after }`, and `edit` → `{ path, before, after }`. Native renderers preserve the line-numbered read and mutation acknowledgements below. `write`/`edit` derive replayable diff-card metadata, and `read` derives a replayable read-card window `{ path, offset, lines, totalLines, lang? }`, from these canonical values; the canonical values themselves are execution-local and are not added to `tool/result`, only the derived presentation metadata is persisted.
 
 ## The tool is the executor; policy is an event gate
 

packages/fs/tool-fs/README.zh.md

@@ -34,7 +34,7 @@ await ctx.plugin(ToolFs)                                  // this package — re
 
 字段名使用 snake_case，与 Claude Code 和现有 harness 工具 schema 一致。
 
-规范成功值分别为：`read` → `{ path, offset, lines: [{ number, text }], totalLines }`，`write` → `{ path, operation: 'create' | 'update', before: string | null, after }`，`edit` → `{ path, before, after }`。原生渲染器会保留下方带行号的读取结果和变更确认。`write`/`edit` 从这些规范值派生可回放的 diff 卡片元数据，`read` 派生可回放的读取卡片窗口 `{ path, lines, totalLines, lang? }`；规范值本身仅限于本次执行，不会添加到 `tool/result`，只有派生出的呈现元数据会被持久化。
+规范成功值分别为：`read` → `{ path, offset, lines: [{ number, text }], totalLines }`，`write` → `{ path, operation: 'create' | 'update', before: string | null, after }`，`edit` → `{ path, before, after }`。原生渲染器会保留下方带行号的读取结果和变更确认。`write`/`edit` 从这些规范值派生可回放的 diff 卡片元数据，`read` 派生可回放的读取卡片窗口 `{ path, offset, lines, totalLines, lang? }`；规范值本身仅限于本次执行，不会添加到 `tool/result`，只有派生出的呈现元数据会被持久化。
 
 ## 工具就是执行器；策略是事件门禁
 

packages/fs/tool-fs/src/read-render.ts

@@ -220,6 +220,8 @@ export function langFromPath(path: string): string | undefined {
 export interface FsReadMeta {
   /** The read file's model-facing path. */
   path: string
+  /** The 1-based first line the window requested, kept even when `lines` is empty. */
+  offset: number
   /** The returned window's lines, each keeping its file line number. */
   lines: FileTextLine[]
   /** Exact total line count in the file. */
@@ -245,24 +247,26 @@ function isFileTextLine(value: unknown): value is FileTextLine {
  * Malformed metadata returns `undefined` so presentation can fall back to the
  * generic text card instead of throwing during replay. Beyond shape, the
  * semantic contract of a read window is enforced against replayed JSON that is
- * well-typed but out of range: `totalLines` must be a non-negative integer, each
- * line number must be a 1-based integer, the line numbers must strictly increase,
- * and no line number may exceed `totalLines`. Any violation declines to the
- * generic fallback rather than emitting a card that misnumbers or overcounts.
+ * well-typed but out of range: `offset` must be a 1-based integer, `totalLines`
+ * must be a non-negative integer, each line number must be a 1-based integer no
+ * less than `offset`, the line numbers must strictly increase, and no line number
+ * may exceed `totalLines`. Any violation declines to the generic fallback rather
+ * than emitting a card that misnumbers or overcounts.
  * @param meta - result metadata.
  * @returns the validated read window, or `undefined` for absent, malformed, or semantically invalid data.
  */
 export function readMetaFromMeta(meta: unknown): FsReadMeta | undefined {
   if (typeof meta !== 'object' || meta === null || Array.isArray(meta)) return undefined
-  const { path, lines, totalLines, lang } = meta as Record<string, unknown>
-  if (typeof path !== 'string' || typeof totalLines !== 'number') return undefined
+  const { path, offset, lines, totalLines, lang } = meta as Record<string, unknown>
+  if (typeof path !== 'string' || typeof totalLines !== 'number' || typeof offset !== 'number') return undefined
+  if (!Number.isInteger(offset) || offset < 1) return undefined
   if (!Number.isInteger(totalLines) || totalLines < 0) return undefined
   if (!Array.isArray(lines) || !lines.every(isFileTextLine)) return undefined
   if (lang !== undefined && typeof lang !== 'string') return undefined
-  let previous = 0
+  let previous = offset - 1
   for (const { number } of lines) {
     if (number <= previous || number > totalLines) return undefined
     previous = number
   }
-  return { path, lines, totalLines, ...lang === undefined ? {} : { lang } }
+  return { path, offset, lines, totalLines, ...lang === undefined ? {} : { lang } }
 }

packages/fs/tool-fs/src/read.ts

@@ -125,6 +125,7 @@ export function applyReadTool(ctx: Context, caps: ReadToolCaps): void {
         const lang = langFromPath(value.path)
         return {
           path: value.path,
+          offset: value.offset,
           lines: value.lines.map(({ number, text }) => ({ number, text })),
           totalLines: value.totalLines,
           ...lang === undefined ? {} : { lang },
@@ -186,6 +187,7 @@ export function applyReadTool(ctx: Context, caps: ReadToolCaps): void {
       return {
         card: 'read',
         path: meta.path,
+        offset: meta.offset,
         lines: meta.lines,
         totalLines: meta.totalLines,
         ...meta.lang === undefined ? {} : { lang: meta.lang },

packages/fs/tool-fs/tests/read-render.spec.ts

@@ -151,14 +151,19 @@ describe('langFromPath', () => {
 })
 
 describe('readMetaFromMeta', () => {
-  const good = { path: '/abs/a.ts', lines: [{ number: 1, text: 'x' }], totalLines: 1, lang: 'ts' }
+  const good = { path: '/abs/a.ts', offset: 1, lines: [{ number: 1, text: 'x' }], totalLines: 1, lang: 'ts' }
 
   it('narrows a well-formed read meta, with and without a lang hint', () => {
     expect(readMetaFromMeta(good)).toEqual(good)
-    const noLang = { path: '/abs/a', lines: [], totalLines: 0 }
+    const noLang = { path: '/abs/a', offset: 1, lines: [], totalLines: 0 }
     expect(readMetaFromMeta(noLang)).toEqual(noLang)
   })
 
+  it('narrows an empty window at a positive offset (byte cap below the first selected line)', () => {
+    const empty = { path: '/abs/a', offset: 5, lines: [], totalLines: 9 }
+    expect(readMetaFromMeta(empty)).toEqual(empty)
+  })
+
   it('returns undefined for absent, non-object, or array meta', () => {
     expect(readMetaFromMeta(undefined)).toBeUndefined()
     expect(readMetaFromMeta(null)).toBeUndefined()
@@ -168,6 +173,7 @@ describe('readMetaFromMeta', () => {
 
   it('returns undefined when a field is missing or the wrong type (defensive narrowing)', () => {
     expect(readMetaFromMeta({ ...good, path: 5 })).toBeUndefined()
+    expect(readMetaFromMeta({ ...good, offset: '1' })).toBeUndefined()
     expect(readMetaFromMeta({ ...good, totalLines: '1' })).toBeUndefined()
     expect(readMetaFromMeta({ ...good, lines: 'nope' })).toBeUndefined()
     expect(readMetaFromMeta({ ...good, lines: [{ number: '1', text: 'x' }] })).toBeUndefined()
@@ -176,6 +182,17 @@ describe('readMetaFromMeta', () => {
     expect(readMetaFromMeta({ ...good, lang: 5 })).toBeUndefined()
   })
 
+  it('rejects an offset that is not a 1-based integer', () => {
+    expect(readMetaFromMeta({ ...good, offset: 0 })).toBeUndefined()
+    expect(readMetaFromMeta({ ...good, offset: 1.5 })).toBeUndefined()
+    expect(readMetaFromMeta({ ...good, offset: NaN })).toBeUndefined()
+    expect(readMetaFromMeta({ ...good, offset: Infinity })).toBeUndefined()
+  })
+
+  it('rejects a first line number below offset', () => {
+    expect(readMetaFromMeta({ ...good, offset: 2, lines: [{ number: 1, text: 'x' }], totalLines: 2 })).toBeUndefined()
+  })
+
   it('rejects a line number that is not a 1-based integer', () => {
     expect(readMetaFromMeta({ ...good, lines: [{ number: 0, text: 'x' }], totalLines: 1 })).toBeUndefined()
     expect(readMetaFromMeta({ ...good, lines: [{ number: 1.5, text: 'x' }], totalLines: 2 })).toBeUndefined()
@@ -190,7 +207,7 @@ describe('readMetaFromMeta', () => {
   })
 
   it('rejects lines that do not strictly increase or exceed totalLines', () => {
-    const twoLines = { path: '/abs/a', lang: 'ts' }
+    const twoLines = { path: '/abs/a', offset: 1, lang: 'ts' }
     // Duplicate line numbers.
     expect(readMetaFromMeta({ ...twoLines, lines: [{ number: 1, text: 'a' }, { number: 1, text: 'b' }], totalLines: 2 })).toBeUndefined()
     // Out-of-order line numbers.

packages/fs/tool-fs/tests/tools.spec.ts

@@ -329,6 +329,7 @@ describe('read tool', () => {
     // The extension drives the lang hint; the window rides on persisted meta.
     expect(result.meta).toEqual({
       path: '/abs/a.ts',
+      offset: 1,
       lines: [{ number: 1, text: 'const x = 1' }, { number: 2, text: 'const y = 2' }],
       totalLines: 2,
       lang: 'ts',
@@ -337,6 +338,7 @@ describe('read tool', () => {
     expect(view).toEqual({
       card: 'read',
       path: '/abs/a.ts',
+      offset: 1,
       lines: [{ number: 1, text: 'const x = 1' }, { number: 2, text: 'const y = 2' }],
       totalLines: 2,
       lang: 'ts',
@@ -349,7 +351,7 @@ describe('read tool', () => {
     fs.files.set('key:notes', 'plain')
     const result = await call(ctx, 'read', { file_path: 'notes' })
     if (result.isError) throw new Error('expected read success')
-    expect(result.meta).toEqual({ path: '/abs/notes', lines: [{ number: 1, text: 'plain' }], totalLines: 1 })
+    expect(result.meta).toEqual({ path: '/abs/notes', offset: 1, lines: [{ number: 1, text: 'plain' }], totalLines: 1 })
   })
 })
 
@@ -485,7 +487,7 @@ describe('tool-owned presentation (pure presentCall)', () => {
     // The structured line data rides on persisted meta (the raw output object is
     // not on the wire); presentResult narrows it and appends the stripped text as
     // the no-capability `content` fallback.
-    const meta = { path: '/tmp/a.ts', lines: [{ number: 1, text: 'hello' }], totalLines: 1, lang: 'ts' }
+    const meta = { path: '/tmp/a.ts', offset: 1, lines: [{ number: 1, text: 'hello' }], totalLines: 1, lang: 'ts' }
     expect(await presentResult('read', { file_path: 'a.ts' }, {
       content: [{ type: 'text', text: '<path>/tmp/a.ts</path>\n<type>file</type>\n<content>\n1: hello\n\n(End of file - total 1 lines)\n</content>' }],
       isError: false,
@@ -493,6 +495,7 @@ describe('tool-owned presentation (pure presentCall)', () => {
     })).toEqual({
       card: 'read',
       path: '/tmp/a.ts',
+      offset: 1,
       lines: [{ number: 1, text: 'hello' }],
       totalLines: 1,
       lang: 'ts',
@@ -502,10 +505,11 @@ describe('tool-owned presentation (pure presentCall)', () => {
     expect(await presentResult('read', { file_path: 'notes' }, {
       content: [{ type: 'text', text: '<path>/tmp/notes</path>\n<type>file</type>\n<content>\nbody\n</content>' }],
       isError: false,
-      meta: { path: '/tmp/notes', lines: [{ number: 1, text: 'body' }], totalLines: 1 },
+      meta: { path: '/tmp/notes', offset: 1, lines: [{ number: 1, text: 'body' }], totalLines: 1 },
     })).toEqual({
       card: 'read',
       path: '/tmp/notes',
+      offset: 1,
       lines: [{ number: 1, text: 'body' }],
       totalLines: 1,
       content: [{ type: 'text', text: 'body' }],