feat(fs): add a minimal read_image tool over the attachment and fs seams

The model reads a PNG/JPEG/WebP/GIF file, the bytes commit through the
durable attachment lifecycle, and the tool result carries the real
ImageBlock so the image enters context from the next request onward.
FileSystem gains a bounded readBytes primitive (local + E2B providers);
registration is conditional on the attachment store, and a strict
execution gate refuses routes that do not declare image input, so a
text route's durable history stays free of image blocks. llm-replay
models may declare inputModalities, letting keyless ACP snapshots pin
both the sha256-referenced success and the verbatim refusal.

Supersedes the withdrawn route-scoped design of PR #598; the decision
record is .agents/notes/implemented/feature/2026-08-10-minimal-read-image-tool.md.

packages/fs/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/fs/README.md
-README.md: 62d3febde82e013ace054a9e6242147c1756b0d1
-README.zh.md: 137c1e8da1014bf7dda7c4bf2e667aca6d2f51b5
+README.md: 4e3a37b997c9d377ebb3795f61f9070a8a9c38ea
+README.zh.md: 50551d3752acf4ffc12ae40c711c9289fd4d87d7

packages/fs/fs/README.md

@@ -2,7 +2,7 @@
 
 English | [中文](README.zh.md)
 
-The **`FileSystem`** (`ctx.fs`) defines the storage primitives in one execution world — resolve paths, expose canonical process paths and file URIs, test containment, read whole or streaming text, inspect/list metadata, write atomically, and apply a literal edit — without saying HOW. Both mutations take their version guard **optionally**, so `ctx.fs` on its own is a complete, unconstrained text-storage seam. This package also owns the `fs/*` policy event vocabulary the tool dispatches and the policy plugin listens for.
+The **`FileSystem`** (`ctx.fs`) defines the storage primitives in one execution world — resolve paths, expose canonical process paths and file URIs, test containment, read whole or streaming text, read bounded raw bytes, inspect/list metadata, write atomically, and apply a literal edit — without saying HOW. Both mutations take their version guard **optionally**, so `ctx.fs` on its own is a complete, unconstrained storage seam. This package also owns the `fs/*` policy event vocabulary the tool dispatches and the policy plugin listens for.
 
 This package owns the Service Definition and provider contract layer of the four-layer filesystem stack, split so each concern can evolve (and be swapped) independently (see [the capability-seam Agent Note](../../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md), [the filesystem capability-seam Agent Note](../../../.agents/notes/implemented/architecture/2026-06-17-filesystem-capability-seam.md), [the split-the-filesystem-seam Agent Note](../../../.agents/notes/implemented/simplification/2026-06-26-fsspec-style-fs-seam.md), and [the file-context event-gate Agent Note](../../../.agents/notes/implemented/architecture/2026-06-26-file-context-as-event-gate.md)):
 
@@ -17,7 +17,7 @@ This package owns the Service Definition and provider contract layer of the four
 
 ## Service API (`ctx.fs`)
 
-A backend subclasses `FileSystem` and implements eleven primitives.
+A backend subclasses `FileSystem` and implements twelve primitives.
 
 | Member | Semantics |
 |---|---|
@@ -29,6 +29,7 @@ A backend subclasses `FileSystem` and implements eleven primitives.
 | `lstat(path, opts?, signal?)` | Return `FsPathInfo` metadata without following the final path component when it is a symlink. This is path-shaped so consumers can reject repository-owned symlinks before `resolve` follows them into a target. |
 | `readText(target, signal?)` | Read the whole regular text file as one decoded string. Owns regular-file checks, UTF-8 decoding, binary/NUL rejection (`FS_NOT_TEXT`). |
 | `streamText(target, signal?)` | Stream the same text as decoded chunks for large files (cross-chunk UTF-8 decoding stays here); consumers that need a byte ceiling enforce it while consuming the stream. |
+| `readBytes(target, signal, maxBytes)` | Read a complete regular file as raw bytes with no decoding or binary rejection. `maxBytes` is required and bounds the complete content at this seam: a known or discovered overflow fails with `FS_TOO_LARGE` instead of truncating or buffering without a bound. |
 | `listDir(target, signal?)` | List direct directory children in stable name order. Returns entry names, entry types, resolved child targets, and cheap metadata (`version`/file `size` when available); never reads file contents. Missing targets throw `FS_NOT_FOUND`, non-directories throw `FS_NOT_DIRECTORY`, permission failures throw `FS_PERMISSION_DENIED`, and other backend I/O failures throw `FS_IO_ERROR`. Broken/disappeared children may be returned as `other` without metadata; child permission/IO failures fail the whole listing with the same structured codes. |
 | `writeText(target, content, expected?, signal?)` | Atomic create/replace. `expected` is OPTIONAL: omit ⇒ unconditional create-or-overwrite; supply an `FsWriteIntent` (`createIfAbsent`/`replaceIfVersion`) to guard. `createIfAbsent` must perform a no-replace publication so a creator racing the initial probe is preserved. |
 | `editText(target, edit, expected?, signal?)` | Literal edit. `expected` is OPTIONAL: omit ⇒ unconditional edit of the current content; supply `{ version }` to guard (verified BEFORE matching). A missing target reports `FS_STALE_VERSION` either way. Applies and writes atomically — one mutation critical section. |
@@ -59,7 +60,7 @@ No direct invalidation; the named consumer owns any request-prefix changes.
 
 ## Known Limitations and Deferred Work
 
-- **Text-only by contract** — backends reject binary/non-UTF-8 content with `FS_NOT_TEXT`; binary-safe operations are a deliberate deferral of [the tool-schemas Agent Note](../../../.agents/notes/implemented/feature/2026-06-17-filesystem-tool-schemas.md).
-- **Eleven primitives only** — no delete, rename/move, copy, or watch; `listDir` is single-level, with recursion, globbing, pagination, and search out of scope per [the directory-listing Agent Note](../../../.agents/notes/archived/architecture/2026-07-03-filesystem-directory-listing-seam.md).
+- **Text-only mutations by contract** — text reads and both mutations reject binary/non-UTF-8 content with `FS_NOT_TEXT`; `readBytes` is the one raw-byte primitive, and binary-safe mutations remain a deliberate deferral of [the tool-schemas Agent Note](../../../.agents/notes/implemented/feature/2026-06-17-filesystem-tool-schemas.md).
+- **Twelve primitives only** — no delete, rename/move, copy, or watch; `listDir` is single-level, with recursion, globbing, pagination, and search out of scope per [the directory-listing Agent Note](../../../.agents/notes/archived/architecture/2026-07-03-filesystem-directory-listing-seam.md).
 - **No IO deadline** — the seam arms no timeout; cancellation is a best-effort optional `AbortSignal` per primitive (the deliberate [fs-family stance](../README.md)).
 - **Resolve-then-operate costs a remote backend two round-trips per tool call** — folding or caching resolution is left to such a backend.

packages/fs/fs/README.zh.md

@@ -2,7 +2,7 @@
 
 [English](README.md) | 中文
 
-**`FileSystem`**（`ctx.fs`）定义同一个执行世界中的存储原语，包括解析路径、公开规范化进程路径与文件 URI、检查包含关系、完整或流式读取文本、检查／列出元数据、原子写入和应用字面量编辑，但不规定实现方式。两个变更操作都**可选** 接收版本防护，因此 `ctx.fs` 本身就是完整且不受约束的文本存储 seam。本包还拥有由工具分派、政策插件监听的 `fs/*` 政策事件词汇。
+**`FileSystem`**（`ctx.fs`）定义同一个执行世界中的存储原语，包括解析路径、公开规范化进程路径与文件 URI、检查包含关系、完整或流式读取文本、有界读取原始字节、检查／列出元数据、原子写入和应用字面量编辑，但不规定实现方式。两个变更操作都**可选** 接收版本防护，因此 `ctx.fs` 本身就是完整且不受约束的存储 seam。本包还拥有由工具分派、政策插件监听的 `fs/*` 政策事件词汇。
 
 本包是四层文件系统栈中的提供方约定层；该拆分使每个关注点可以独立演进和替换（见[能力 seam Agent Note](../../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md)、[文件系统能力 seam Agent Note](../../../.agents/notes/implemented/architecture/2026-06-17-filesystem-capability-seam.md)、[拆分文件系统 seam Agent Note](../../../.agents/notes/implemented/simplification/2026-06-26-fsspec-style-fs-seam.md)和[文件上下文事件门禁 Agent Note](../../../.agents/notes/implemented/architecture/2026-06-26-file-context-as-event-gate.md)）：
 
@@ -17,7 +17,7 @@
 
 ## 服务 API（`ctx.fs`）
 
-后端继承 `FileSystem` 并实现十一个原语。
+后端继承 `FileSystem` 并实现十二个原语。
 
 | 成员 | 语义 |
 |---|---|
@@ -29,6 +29,7 @@
 | `lstat(path, opts?, signal?)` | 当最后一个路径组件是符号链接时，不跟随该组件，返回 `FsPathInfo` 元数据。该方法采用路径形态，使消费方能在 `resolve` 跟随仓库所有的符号链接进入目标前拒绝它。 |
 | `readText(target, signal?)` | 把整个普通文本文件读取为一个解码后的字符串。负责普通文件检查、UTF-8 解码和二进制/NUL 拒绝（`FS_NOT_TEXT`）。 |
 | `streamText(target, signal?)` | 为大文件按解码后的分片流式读取相同文本（跨分片 UTF-8 解码仍由此处负责）；需要字节上限的消费方在消费流时执行该上限。 |
+| `readBytes(target, signal, maxBytes)` | 把完整普通文件按原始字节读出，不做解码或二进制拒绝。`maxBytes` 为必填，在该 seam 上限制完整内容：已知或读取中发现的超限以 `FS_TOO_LARGE` 失败，而不是截断或无界缓冲。 |
 | `listDir(target, signal?)` | 按稳定名称顺序列出直接子项。返回条目名称、条目类型、解析后的子目标和低成本元数据（若可用则包括 `version`/文件 `size`）；绝不读取文件内容。缺失目标抛出 `FS_NOT_FOUND`，非目录抛出 `FS_NOT_DIRECTORY`，权限失败抛出 `FS_PERMISSION_DENIED`，其他后端 I/O 失败抛出 `FS_IO_ERROR`。损坏/消失的子项可以作为无元数据的 `other` 返回；子项权限/I/O 失败会使用相同结构化代码使整个列表失败。 |
 | `writeText(target, content, expected?, signal?)` | 原子创建/替换。`expected` 是可选的：省略 ⇒ 无条件创建或覆盖；提供 `FsWriteIntent`（`createIfAbsent`/`replaceIfVersion`）⇒ 添加防护。`createIfAbsent` 必须以不替换的方式发布，使初始探测后抢先创建的文件得到保留。 |
 | `editText(target, edit, expected?, signal?)` | 字面量编辑。`expected` 是可选的：省略 ⇒ 无条件编辑当前内容；提供 `{ version }` ⇒ 添加防护，并在匹配之前校验。无论哪种情况，目标缺失都报告 `FS_STALE_VERSION`。应用和写入以原子方式完成，使用同一个变更临界区。 |
@@ -59,7 +60,7 @@
 
 ## 已知限制与延期工作
 
-- **约定只支持文本**：后端以 `FS_NOT_TEXT` 拒绝二进制/非 UTF-8 内容；二进制安全操作是[工具 schema Agent Note](../../../.agents/notes/implemented/feature/2026-06-17-filesystem-tool-schemas.md)有意延期的工作。
-- **只有十一个原语**：没有删除、重命名/移动、复制或监视；`listDir` 只支持一层，递归、glob、分页和搜索不在范围内，见[目录列出 Agent Note](../../../.agents/notes/archived/architecture/2026-07-03-filesystem-directory-listing-seam.md)。
+- **变更操作约定只支持文本**：文本读取和两个变更操作都以 `FS_NOT_TEXT` 拒绝二进制/非 UTF-8 内容；`readBytes` 是唯一的原始字节原语，二进制安全的变更操作仍是[工具 schema Agent Note](../../../.agents/notes/implemented/feature/2026-06-17-filesystem-tool-schemas.md)有意延期的工作。
+- **只有十二个原语**：没有删除、重命名/移动、复制或监视；`listDir` 只支持一层，递归、glob、分页和搜索不在范围内，见[目录列出 Agent Note](../../../.agents/notes/archived/architecture/2026-07-03-filesystem-directory-listing-seam.md)。
 - **没有 I/O deadline**：该 seam 不启动超时；取消只是每个原语上尽力而为的可选 `AbortSignal`（见有意采用的 [fs 能力族立场](../README.md)）。
 - **先解析后操作使远程后端每次工具调用需要两次往返**：折叠或缓存解析由这种后端自行决定。

packages/fs/fs/src/index.ts

@@ -186,6 +186,18 @@ export abstract class FileSystem extends Service {
    */
   abstract streamText(target: FsTarget, signal?: AbortSignal): Promise<AsyncIterable<string>>
 
+  /**
+   * Read the whole regular file as raw bytes with no decoding or binary
+   * rejection. The bound lives at this seam so a backend can never buffer an
+   * unbounded file: a target known or discovered to exceed `maxBytes` fails
+   * with `FS_TOO_LARGE` instead of returning a truncated result.
+   * @param target - the resolved target to read.
+   * @param signal - aborts the read.
+   * @param maxBytes - inclusive byte cap on the complete content.
+   * @returns the full raw content, at most `maxBytes` long.
+   */
+  abstract readBytes(target: FsTarget, signal: AbortSignal | undefined, maxBytes: number): Promise<Uint8Array>
+
   /**
    * List direct children of a directory in stable name order. Returns resolved
    * child targets plus cheap metadata only; never reads file contents.

packages/fs/fs/src/types.ts

@@ -176,6 +176,7 @@ export type FsErrorCode =
   | 'FS_NOT_DIRECTORY'
   | 'FS_NOT_TEXT'
   | 'FS_NOT_REGULAR_FILE'
+  | 'FS_TOO_LARGE'
   | 'FS_PERMISSION_DENIED'
   | 'FS_SANDBOX_DENIED'
   | 'FS_IO_ERROR'

packages/fs/fs/tests/service.spec.ts

@@ -50,6 +50,13 @@ class FakeFileSystem extends FileSystem {
     const content = await this.readText(target)
     return (async function* () { yield content })()
   }
+  override async readBytes(target: FsTarget, _signal: AbortSignal | undefined, maxBytes: number): Promise<Uint8Array> {
+    const bytes = new TextEncoder().encode(await this.readText(target))
+    if (bytes.length > maxBytes) {
+      throw new FsError(`too large: ${target.displayPath}`, 'FS_TOO_LARGE')
+    }
+    return bytes
+  }
   override async listDir(target: FsTarget): Promise<FsDirEntry[]> {
     if (target.targetKey !== 'skills') throw new FsError(`not a directory: ${target.displayPath}`, 'FS_NOT_DIRECTORY')
     return [
@@ -112,6 +119,16 @@ describe('FileSystem provider seam', () => {
     expect(streamed).toBe(await fs.readText(target))
   })
 
+  it('readBytes returns raw content and enforces the byte cap with FS_TOO_LARGE', async () => {
+    const ctx = new Context()
+    await ctx.plugin(FakeFileSystem)
+    const fs = ctx.fs as FakeFileSystem
+    fs.files.set('a.bin', 'hi')
+    const target = await fs.resolve('a.bin')
+    expect(await fs.readBytes(target, undefined, 2)).toEqual(new TextEncoder().encode('hi'))
+    await expect(fs.readBytes(target, undefined, 1)).rejects.toMatchObject({ code: 'FS_TOO_LARGE' })
+  })
+
   it('listDir returns child entry targets without reading file content', async () => {
     const ctx = new Context()
     await ctx.plugin(FakeFileSystem)