Seat web.dev on the design council; record PWA backfill

docs/IMPLEMENTATION-PLAN.md

@@ -437,11 +437,13 @@ entries).
   `DONATE_URL` pending the real link).
 - **Offline/installable:** verify the SW + manifest give a working offline + installed app.
   **⏳ Remaining** — needs manual verification in a running/installed app.
-- **Council** — seat **web.dev** for the PWA/offline/storage surfaces none of the seated
+- **Council** — ~~seat **web.dev** for the PWA/offline/storage surfaces none of the seated
   members cover: the service-worker **update-available** prompt (`registerType: 'prompt'`),
   storage **persistence** (`navigator.storage.persist()`), and the quota **estimate**
-  (`StorageManager.estimate()`). **⏳ Remaining** (storage monitor is its consumer; seating
-  triggers a one-off backfill — see [`/council`](../.claude/skills/council/SKILL.md)).
+  (`StorageManager.estimate()`)~~ ✅ seated + backfilled (update-prompt toast + `persist()`
+  request; estimate already wired). **⏳ Remaining gap:** manifest ships no icons → not yet
+  installable (design-asset task). See [`/council`](../.claude/skills/council/SKILL.md) and
+  [arch 10](architecture/10-interaction-and-feedback.md).
 
 **Manual checks:** keyboard-only run-through; reload restores view from URL;
 offline reload works; install as standalone; reduced-motion honored. **⏳ Still owed**

docs/architecture/10-interaction-and-feedback.md

@@ -320,6 +320,20 @@ Datasets (⌘/Ctrl+K), or check the dataset name in your spec."_ — instead of
 must match the actual cause (NN/g #9, GOV.UK error-message). The thrown
 `DatasetNotFoundError` carries `datasetName` so the surface can name it.
 
+**Resolved — service-worker update prompt & persistent storage (web.dev seat).** The build
+uses `registerType: 'prompt'`, so a new service worker waits and never takes over a running
+session on its own — the app **must** tell the user, or "ask before updating" silently means
+"never update." `orchestration/pwa.ts` consumes `virtual:pwa-register` and surfaces
+`onNeedRefresh` as a **durable** (non-auto-dismissing) info toast with a **Reload** action
+that calls `updateSW()`; `onOfflineReady` is a transient success toast. Separately, browser
+storage is best-effort and evictable under pressure, which for a local-first workspace is data
+loss — so we request `navigator.storage.persist()` once at startup
+(`infrastructure/storage-persist`), feature-detected and silent on denial (Chromium decides
+automatically; nothing for the user to act on). _(Consulted via /council → web.dev, with the
+exact API from vite-plugin-pwa/Workbox; see `reference/principles/web-dev.md`. This bullet is
+the contract; cite it, not the source.) **Known gap:** the manifest ships no icons, so the app
+is not yet installable — a design-asset task, logged not passed._
+
 ## 6. Motion & accessibility as default
 
 Not features to add later — the baseline every surface is built on.