feat(views,surface-host): Extensions sidebar view — auto-expanded surfaces + tables

views (new feature):
- pure panel-stack reducer + thin generic ViewSidebar (dropdown picker + add/remove),
  switches on view KIND, never a surface id

Extensions view (composition root):
- folds frontend modules + backend surfaces into one "Extensions" view
- frontend module list AGGREGATED from each feature's public `manifest` export
  (can't drift); no per-module version (FE features are internal to dispatch-web)
- surfaces are AUTO-SUBSCRIBED on catalog + rendered expanded (no catalog buttons)

surface-host:
- consecutive `stat` fields coalesce into one aligned label/value table (StatTable)
- generic custom-field renderer: dispatch on rendererId === "table" → SurfaceTable
  (pure parseTablePayload), so a backend `custom`/table field renders generically
- shared presentational components/Table.svelte (used by both, neither feature
  depends on the other)

store:
- auto-subscribe every catalog entry, unsubscribe vanished ones, re-subscribe all
  on reconnect; expose all received specs via `surfaces` (drops single-selection)

backend-handoff: CR-1 — emit Loaded Extensions as a custom/table field; notes
what's already covered FE-side (renderer shipped, stat-table fallback works).

1 files changed, 55 insertions, 0 deletions

diff --git a/src/features/views/logic/panels.test.ts b/src/features/views/logic/panels.test.ts
new file mode 100644
index 0000000..edd7d9e
--- /dev/null
+++ b/src/features/views/logic/panels.test.ts
@@ -0,0 +1,55 @@
+import { describe, expect, it } from "vitest";
+import { addPanel, initialPanels, removePanel, selectKind } from "./panels";
+
+describe("view panels reducer", () => {
+	it("seeds one empty panel by default", () => {
+		const s = initialPanels();
+		expect(s.panels).toHaveLength(1);
+		expect(s.panels[0]?.kind).toBeNull();
+	});
+
+	it("seeds a panel per provided kind, in order, with unique ids", () => {
+		const s = initialPanels(["surfaces", null]);
+		expect(s.panels.map((p) => p.kind)).toEqual(["surfaces", null]);
+		expect(new Set(s.panels.map((p) => p.id)).size).toBe(2);
+	});
+
+	it("addPanel appends an empty panel with a fresh id", () => {
+		const seed = initialPanels(["surfaces"]);
+		const s = addPanel(seed);
+		expect(s.panels).toHaveLength(2);
+		expect(s.panels[1]?.kind).toBeNull();
+		expect(s.panels[1]?.id).not.toBe(s.panels[0]?.id);
+	});
+
+	it("addPanel can seed a kind", () => {
+		const s = addPanel(initialPanels([null]), "surfaces");
+		expect(s.panels[1]?.kind).toBe("surfaces");
+	});
+
+	it("removePanel drops the matching id only", () => {
+		const seed = initialPanels(["surfaces", null]);
+		const firstId = seed.panels[0]?.id ?? -1;
+		const s = removePanel(seed, firstId);
+		expect(s.panels).toHaveLength(1);
+		expect(s.panels[0]?.kind).toBeNull();
+	});
+
+	it("selectKind updates only the targeted panel", () => {
+		const seed = initialPanels([null, null]);
+		const targetId = seed.panels[1]?.id ?? -1;
+		const s = selectKind(seed, targetId, "surfaces");
+		expect(s.panels[0]?.kind).toBeNull();
+		expect(s.panels[1]?.kind).toBe("surfaces");
+	});
+
+	it("is pure — never mutates the input state", () => {
+		const seed = initialPanels(["surfaces"]);
+		const snapshot = JSON.stringify(seed);
+		const id = seed.panels[0]?.id ?? -1;
+		addPanel(seed);
+		removePanel(seed, id);
+		selectKind(seed, id, null);
+		expect(JSON.stringify(seed)).toBe(snapshot);
+	});
+});