refactor(brief): move the action lifecycle into the machine (RD-12)

The action lifecycle (Idle | Busy | Failed) lived in an imperative
store-level signal, set from ten call sites outside the reducer. The
reducer could not enforce which action transitions are legal.

Add `action` to `BriefState.Loaded`, driven by three new messages
(ActionStarted, ActionFinished, ActionFailed) and handled in `reduce`.
Replace every `actionState.set(...)` call in `brief.store.ts` with the
matching `dispatch`. `BriefLoaded` resets `action` to Idle, so a fresh
load clears a stale action error instead of letting it outlive the
reload.

`busy` and `lastError` stay as `computed`s on the store with a
byte-identical public signature — they are the render seam for four
components and two page templates, and the union belongs in the
machine, not the components. `revealBigNummer` still sets only
`Failed`, never `Busy` — an existing asymmetry, not changed here.
`SaveState`, `org-template.store.ts`, and `pendingPublish` are out of
scope (RD-13, RD-14).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/ssp/src/app/brief/application/brief.store.ts

@@ -1,7 +1,7 @@
 import { Injectable, computed, inject, signal } from '@angular/core';
 import { Result } from '@shared/kernel/fp';
 import { createStore } from '@shared/application/store';
-import { ActionState, SaveState } from '@shared/application/action-state';
+import { SaveState } from '@shared/application/action-state';
 import { createHistory } from '@shared/application/history';
 import { createDebouncedSave } from '@shared/application/debounced-save';
 import { fromLoadLifecycle } from '@shared/application/remote-data';
@@ -41,11 +41,16 @@ export class BriefStore implements PendingSave {
 
   readonly model = this.store.model;
 
-  private actionState = signal<ActionState>({ tag: 'Idle' });
-  readonly busy = computed(() => this.actionState().tag === 'Busy');
+  /** The one-shot action lifecycle now lives on the machine's `Loaded.action` (RD-12);
+      these stay as plain `computed`s so the render seam (four `busy = input(...)`
+      components, two page templates) keeps a byte-identical boolean/string API. */
+  readonly busy = computed(() => {
+    const s = this.model();
+    return s.tag === 'Loaded' && s.action.tag === 'Busy';
+  });
   readonly lastError = computed(() => {
-    const s = this.actionState();
-    return s.tag === 'Failed' ? s.error : null;
+    const s = this.model();
+    return s.tag === 'Loaded' && s.action.tag === 'Failed' ? s.action.error : null;
   });
 
   /** Surfaced autosave state for the indicator + aria-live region. */
@@ -212,7 +217,9 @@ export class BriefStore implements PendingSave {
     if (r.ok) {
       this.saveState.set({ tag: 'Saved' });
     } else {
-      this.actionState.set({ tag: 'Failed', error: r.error });
+      // The autosave failure legitimately surfaces in two places: the small save
+      // indicator below (kept as-is) and the action error line (RD-12).
+      this.store.dispatch({ tag: 'ActionFailed', error: r.error });
       this.saveState.set({ tag: 'Error' });
     }
   }
@@ -224,19 +231,19 @@ export class BriefStore implements PendingSave {
 
   /** Demo "start over": recreate the brief server-side and load the fresh view. */
   async resetDemo() {
-    this.actionState.set({ tag: 'Busy' });
+    this.store.dispatch({ tag: 'ActionStarted' });
     this.debouncedSave.cancel();
     const r = await this.adapter.reset();
     this.saveState.set({ tag: 'Idle' });
     if (r.ok) {
-      this.actionState.set({ tag: 'Idle' });
+      this.store.dispatch({ tag: 'ActionFinished' });
       this.orgTemplate.set(r.value.orgTemplate);
       this.caseContext.set(r.value.caseContext);
       this.history.clear();
       this.rejectionSnapshot.set(null);
       this.store.dispatch({ tag: 'BriefLoaded', ...r.value });
     } else {
-      this.actionState.set({ tag: 'Failed', error: r.error });
+      this.store.dispatch({ tag: 'ActionFailed', error: r.error });
     }
   }
 
@@ -249,13 +256,13 @@ export class BriefStore implements PendingSave {
       letter in a new tab via `BLOB_PRESENTER.open` — see its doc comment for why the
       object URL is never revoked. */
   async previewLetter() {
-    this.actionState.set({ tag: 'Busy' });
+    this.store.dispatch({ tag: 'ActionStarted' });
     const r = await this.previewAdapter.preview();
     if (!r.ok) {
-      this.actionState.set({ tag: 'Failed', error: r.error });
+      this.store.dispatch({ tag: 'ActionFailed', error: r.error });
       return;
     }
-    this.actionState.set({ tag: 'Idle' });
+    this.store.dispatch({ tag: 'ActionFinished' });
     this.blobPresenter.open(r.value);
   }
 
@@ -269,7 +276,8 @@ export class BriefStore implements PendingSave {
   async revealBigNummer() {
     const r = await this.revealAdapter.reveal(true);
     if (!r.ok) {
-      this.actionState.set({ tag: 'Failed', error: r.error });
+      // Never sets Busy — an existing asymmetry (RD-12), not fixed here.
+      this.store.dispatch({ tag: 'ActionFailed', error: r.error });
       return;
     }
     this.caseContext.update((c) => (c ? { ...c, bigNummer: r.value } : c));
@@ -278,15 +286,15 @@ export class BriefStore implements PendingSave {
   // A transition: flush any pending save, call the server (authoritative), then mirror
   // the returned status through the pure reducer's guarded transition.
   private async transition(action: () => Promise<Result<string, BriefView>>) {
-    this.actionState.set({ tag: 'Busy' });
+    this.store.dispatch({ tag: 'ActionStarted' });
     this.debouncedSave.cancel();
     await this.flushSave();
     const r = await action();
     if (!r.ok) {
-      this.actionState.set({ tag: 'Failed', error: r.error });
+      this.store.dispatch({ tag: 'ActionFailed', error: r.error });
       return;
     }
-    this.actionState.set({ tag: 'Idle' });
+    this.store.dispatch({ tag: 'ActionFinished' });
     this.applyServerStatus(r.value);
   }