docs(protocol): show the required plan object in the v2 migration checklist (#2763)

* docs(protocol): show the required plan object in the v2 migration checklist

Wrap the checklist's plan_update literal in the required plan object.

* docs(protocol): include sessionUpdate discriminator in v2 plan checklist literal

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

Author: PerryLink

docs/protocol/v2/migration.mdx

@@ -918,7 +918,7 @@ See [Errors](/protocol/v2/error).
 7. **Terminal output.** Add `terminal` content references for Agent-owned display terminals. Send `terminal_update` for command, absolute cwd, size, snapshots, and exit state. Send independently base64-encoded `terminal_output_chunk` values for live bytes. Do not expect Client control methods or capability negotiation.
 8. **Diffs.** Replace `oldText`/`newText` with `changes` (+ `fileType`/`mimeType` where known) and provide `patch` in `git_patch` format whenever feasible. If a tool's input describes an edit only as a snippet, read the file somewhere the tool waits on, before it can run, or send no diff until the change is done (see [Edits known only as a snippet](#edits-known-only-as-a-snippet)).
 9. **Permissions.** Put prompt copy in required `title` (+ optional `description`). Use the `tool_call` subject for tool-call state and the `command` subject for a command, required absolute cwd, and optional tool-call/terminal associations. Treat a `cancelled` outcome as "don't proceed with this operation", not as the turn ending.
-10. **Plans.** Send `plan_update` with `{ "type": "items", "planId": ..., "entries": [...] }`.
+10. **Plans.** Send `plan_update` with `{ "sessionUpdate": "plan_update", "plan": { "type": "items", "planId": ..., "entries": [...] } }`.
 11. **Modes and config options.** Drop `session/set_mode`, `modes`, and `current_mode_update`. Expose the same state as config options with `category: "mode"` and emit `config_option_update`. Rename option `id` to `configId` and group `group` to `groupId`, and require the `type` discriminator (`"id"` or `"boolean"`) on `session/set_config_option`.
 12. **Replay.** Handle `replayFrom` on `session/resume`. Replay history as ordinary `session/update` notifications when asked, current-state snapshots such as terminal `output` are fine. When the Client may already hold an entity's `_meta`, remove stale keys explicitly, since an `_meta` object no longer replaces them. Start chunked messages with an empty-content update. Remove `session/load`.
 13. **Client file and terminal methods.** Remove all `fs/*` and `terminal/*` calls. The new terminal content is Agent-owned display state, not a Client resource.