Add snippet-library search, sort, empty states, storage monitor (M6, §02/§09D)

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

@@ -236,6 +236,45 @@ relative date and size), in a fixed-width leading slot so it never shifts adjace
 _(Consulted via /council → GOV.UK Tag, Carbon status-indicator-pattern, APG. This bullet is the
 contract; cite it, not the external source.)_
 
+**Resolved — library search (Carbon active-search).** The snippet-library search (spec
+§02) is an **unlabelled active-search input** pinned above the list: `type="search"` with a
+leading magnifier and `aria-label="Search snippets"` (no visible label — the icon +
+placeholder name it), filtering the list on **each keystroke** (no Search button, no results
+page). A **clear (✕)** appears only when the box is non-empty; it empties the box **and
+returns focus to the input** (NN/g #3 user control). Matching is case-insensitive substring
+across **name + comment + draft spec text** (the pure `snippetMatchesQuery` in
+`core/snippet-sort.ts`). Search affects **visibility only** — it never changes
+`activeSnippetId` or any data. A **polite `aria-live` region announces the result count,
+including no results** (Carbon: _"always include the number of results, including no
+results"_); it stays silent for the default unfiltered list. _(Consulted via /council →
+Carbon search/active-search, NN/g #3. This bullet is the contract; cite it, not the source.)_
+
+**Resolved — library sort (APG menu-button + NN/g recognition).** The Sort control (spec
+§02) reuses the **disclosure popover** primitive (the settings-popover model above), **not**
+an ARIA menu — but its trigger shows the **current state for recognition** ("Sort: Modified
+↓"), per NN/g #6 (recognition over recall), instead of a bare gear. Fields are **Modified /
+Created / Name / Size**; the active field shows a **direction arrow** (↓ desc / ↑ asc) in both
+the trigger and the field row, and the arrow's meaning is mirrored into the field's
+`aria-label` ("Modified, descending") so it isn't carried by the glyph alone. **Selection
+model** (spec §02): re-selecting the **active** field flips direction; selecting a
+**different** field switches to it and **resets to descending** — encapsulated in
+`SnippetStore.setSort` and tested in core. APG disclosure keyboard/focus is inherited from
+the shared popover (Enter/Space open; **Esc closes and returns focus to the trigger**; outside
+click closes; one open at a time). Field+direction **persist across sessions** (ux-prefs;
+default Modified/desc); search is **not** persisted (it's a transient view narrowing).
+_(Consulted via /council → WAI-ARIA APG disclosure + menu-button, NN/g #6. This bullet is the
+contract; cite it, not the source.)_
+
+**Resolved — the two library empty states (Carbon's two types).** The snippet list owes
+**two distinct empty states** (Carbon empty-state types), chosen by cause and never conflated:
+(a) a **genuinely empty library** (first run) is **positive and concise and guides to the
+Create action** — title "No snippets yet" + a one-line nudge to create one; (b) **no search
+matches** says "No snippets match your search" + a hint to try a different term. Both are
+plain-language and minimal (NN/g aesthetic-and-minimalist; §3 empty ≠ error). The library
+derives **which** to show from whether a query is active, not from the raw count alone.
+_(Consulted via /council → Carbon empty-state, NN/g. This bullet is the contract; cite it,
+not the source.)_
+
 **Resolved — one live region per shared message.** When the same error feeds two surfaces
 (the §1 "one producer, two subscribers" case — render errors via `PreviewStore`), exactly
 **one** subscriber is the live region (`role="alert"` on the editor, where focus is); the