fix(review): bound E2B readBytes at the seam, prove conditional-registration disposal, and align read_image contracts

- E2BFileSystem.readBytes now short-circuits on the stat size before any
  content transfer and streams the remote object, cancelling at the first
  chunk past the cap, honoring the seam's bounded-buffering contract; the
  fs-e2b README pair documents the new primitive.
- The tool-fs HMR test now proves the attachments-scoped registration:
  disposing the store withdraws read_image while read/write/edit stay,
  remounting restores it, and disposing the plugin withdraws everything.
- read_image caps reads at the smaller of maxImageBytes and
  maxMessageImageBytes, records an absent observation for a missing
  target like its sibling read, widens the mismatch remedy to cover
  out-of-family formats, and renames the gate's parameter to
  requestedPath; module/apply/registration JSDoc now match the shipped
  composition. zh terminology aligned; the examples manifest keeps its
  literal arrow.

packages/e2b/fs-e2b/README.md

@@ -9,6 +9,7 @@ E2B implementation of the [`@deepseek-ai/dsh-fs`](../../fs/fs/README.md) provide
 - **Remote identity and metadata** — relative paths resolve as POSIX paths against the caller cwd or `ctx.e2b.cwd`; GNU `realpath -mz` supplies canonical target identity without requiring the final file to exist, and ASCII/base64 plus strict NUL framing preserves newline and multibyte paths across the decoded SDK transport. `stat`, no-follow `lstat`, and stable one-level directory listings project E2B metadata into the filesystem seam; listings reuse returned metadata and resolve symbolic-link entries sequentially. Versions are opaque hashes of E2B metadata plus a per-write extended attribute.
 - **Execution-world paths** — canonical targets expose absolute POSIX process paths, percent-encoded `file:` URIs, and provider-owned containment checks, so generic subprocess consumers never parse E2B target ids or apply host path rules.
 - **UTF-8 reads** — whole reads and streamed reads preserve cross-chunk decoding, reject invalid UTF-8, and use the seam's 8192-byte NUL sample for binary detection. The model-facing tool still owns size selection and line windowing.
+- **Bounded raw-byte reads** — `readBytes` short-circuits on the stat size before any content transfer, then streams the remote object and cancels the stream at the first chunk past `maxBytes` (`FS_TOO_LARGE`), so neither an at-rest oversized file nor a post-stat grower is buffered whole in host memory. The empty-file quirk of the pinned SDK (content-length 0 returns `''` in stream format) yields an empty result.
 - **Atomic mutations** — writes create a random sibling staging directory, change it to mode `0700` before uploading content, and preserve an existing file's POSIX mode. Replacements publish through E2B's same-filesystem atomic rename. A guarded `createIfAbsent` publishes with remote `ln -T` instead, making the commit atomically no-replace even when a directory appears at the destination; metadata read from the staged file before that commit is projected to the target path for the returned version, so no fallible metadata request follows either commit point. E2B creates missing parent directories. Literal edits LF-normalize for matching, restore dominant CRLF storage, and serialize mutations per canonical target within the host process.
 - **Failures and cancellation** — E2B not-found, permission, abort, and other controller failures map to the existing `FsError` vocabulary. Cancellation is best-effort at earlier SDK request boundaries and checked immediately before publication. The signal is not forwarded into the rename or guarded-link commit, so cancellation cannot interrupt atomic publication or turn a committed write into a reported failure.