spec/metadata-protocol: a draft change written through the MCP build door is recorded as by: 'copilot'; draftChanges cannot say "an MCP agent (OAuth client X) on behalf of user Y" (cloud#3302 item 5) #27176

Filing gate: ① a product defect with a named location. cloud#3302 item 5 (maintainer-directed, the 2026-10-27 MCP build batch) is not met because of a missing value in MetadataAuthoringSurfaceSchema (packages/spec/src/api/protocol.zod.ts:490).

维护者速读

cloud 的 MCP build 入口（cloud#3302 / cloud#3345）让开发者自己的 agent 通过 /api/v1/mcp 写草稿，由人在 Studio「变更」里发布。卡片第 5 项要求发布的人能看到「哪个入口、哪个 OAuth 客户端、代表谁」写了这条草稿。框架现在的草稿逐键来源 draftChanges（#24298）只有 copilot / studio / api 三种来源和 actor，MCP 写入只能记成 copilot，没有客户端。本卡补上来源值和客户端归属，并让 Studio 变更抽屉显示它。

Facts (objectstack main, read 2026-10-28)

• MetadataAuthoringSurfaceSchema = z.enum(['copilot', 'studio', 'api']) is at protocol.zod.ts:490. draftChanges[].by is that enum, and actor is the acting user (metadata-protocol / spec: a draft carries no per-field provenance (which surface changed which key, and when), so Studio cannot mark a copilot's draft change with the ruled 草稿 chip and 来源 line #24298).
• copilot is stated only by an in-process AI tool calling the save, never by a remote caller (protocol.zod.ts:~1000). The cloud MCP door's tools are in-process AI tools, so their saves record by: 'copilot'. That is indistinguishable from the in-app chat.
• The execution context already carries the OAuth performer for the /mcp door: performedByClientId (ADR-0090 D10 rule 4, kernel/execution-context.zod.ts:298-315). It is attribution only, and it is recorded in sys_audit_log, but not in draftChanges.
• cloud side (cloud#3345): /meta/_drafts updatedBy is the token user, which is asserted. The tool context carries authoringDoor: 'mcp' and mcpPrincipal { userId, clientId, organizationId }, ready to pass into the save.

Done looks like

1. The draft save can record, in-process only, that a change came through the MCP door and which OAuth client performed it: a new surface value (for example mcp) and an optional client attribution on the draftChanges entry. The exact shape is the spec owner's call. It stays refused from ?surface= over HTTP, the way copilot is.
2. Studio's changes drawer and properties source line render it, for example 「由 MCP 客户端 代表 作为草稿加入」, in all locales.
3. A follow-up cloud half (cloud#3302 stays open, Blocked-by: this card) passes surface and the client from the MCP door's tool context into saveMetaItem.

Out of scope

Who may write through the door (cloud#3299 and #3303), and any change to authorization. This card is attribution only.

Dedup: #24298 (closed; the per-key provenance this extends), #26587 (closed; consent copy for metadata:write). There is no open card on draft attribution for MCP.

Reader: the spec/metadata-protocol lane plus Studio (ui). Routed domain:cloud by involvement (pm-dispatch #26972).