docs(spec): spell the acted_as slot forms as the approvals changesets do, and say what absent cannot prove

Claude-Session: https://claude.ai/code/session_01YDt3PzwfrkuFzUBF89WPmM
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/21458-spec-approval-action-acted-as.md

@@ -8,8 +8,8 @@ Clause-②: yes
 
 **What it declares.** One optional string member on `ApprovalActionRow` in `@objectstack/spec/contracts`, the row type of an approval request's action log (`IApprovalService.listActions`, served at `GET /api/v1/approvals/requests/:id/actions` and typed by the client SDK):
 
-- `acted_as?: string` is the slot the action was admitted under, in the slot's stored spelling as it stood in the request's `pending_approvers`: a `position:<p>` address (or its older `role:<p>` spelling), an email, or a user id.
+- `acted_as?: string` is the slot the action was admitted under, in the slot's stored spelling as it stood in the request's `pending_approvers`: a `position:<name>` address (or `role:<name>`, the deprecated pre-rename spelling), an email, or a user id.
 - It is never a person. The person who acted is `actor_id`, which under ADR-0118 D1 holds a `sys_user` id or nothing. A slot addressed by a user id carries that id in `acted_as` as the slot's address, which makes no claim about who acted.
-- Absent means the action was not admitted through a slot (a submitter's own action, a system action, or an admin override, which `via_override` marks), or the row was written before the slot was recorded. Absent reads as "not recorded", not as "no slot".
+- Absent means the action was not admitted through a slot (a submitter's own action, a system action, or an admin override, which `via_override` marks), or the row was written before the slot was recorded. So absent alone never proves that no slot was involved.
 
 **What moves for consumers.** Nothing in this package writes the member, and every existing export and member is unchanged: a row without `acted_as` conforms exactly as before. The approvals service is its producer, and that package's own changeset states when `listActions` starts returning it. Until then every row omits it, which is the member's declared absent case. A client that renders the action log can show `acted_as` beside the actor's name as the capacity the actor acted in.

packages/spec/src/contracts/approval-service.ts

@@ -516,8 +516,9 @@ export interface ApprovalActionRow {
   /**
    * The pending-approver slot this action was taken as: the slot's address in
    * its stored spelling, exactly as it stood in the request's
-   * `pending_approvers` when the action was admitted — a `position:<p>`
-   * address (or its older `role:<p>` spelling), an email, or a user id.
+   * `pending_approvers` when the action was admitted — a `position:<name>`
+   * address (or `role:<name>`, the deprecated pre-rename spelling), an email,
+   * or a user id.
    *
    * "Who acted" and "as which slot" are two facts. One holder of a position
    * can act for it, and one person can hold several slots, so the slot is
@@ -531,8 +532,8 @@ export interface ApprovalActionRow {
    * Absent means one of two things, and this member alone does not tell them
    * apart: the action was not admitted through a slot (a submitter's own
    * action, a system action, or an admin override — see `via_override`), or
-   * the row was written before the slot was recorded — "not recorded", which
-   * is not the same claim as "no slot".
+   * the row was written before the slot was recorded. So absent alone never
+   * proves that no slot was involved: "not recorded" is not the same claim.
    */
   acted_as?: string;
 }