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, 47 insertions, 0 deletions

diff --git a/src/features/surface-host/logic/table.test.ts b/src/features/surface-host/logic/table.test.ts
new file mode 100644
index 0000000..e55b3f7
--- /dev/null
+++ b/src/features/surface-host/logic/table.test.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from "vitest";
+import { parseTablePayload } from "./table";
+
+describe("parseTablePayload", () => {
+	it("parses a well-formed table payload", () => {
+		const data = parseTablePayload({
+			columns: ["Name", "Version"],
+			rows: [
+				["alpha", "1.0"],
+				["beta", "2.3"],
+			],
+		});
+		expect(data).toEqual({
+			columns: ["Name", "Version"],
+			rows: [
+				["alpha", "1.0"],
+				["beta", "2.3"],
+			],
+		});
+	});
+
+	it("coerces numeric and boolean cells to strings", () => {
+		const data = parseTablePayload({
+			columns: ["k", "n", "b"],
+			rows: [["x", 42, true]],
+		});
+		expect(data?.rows[0]).toEqual(["x", "42", "true"]);
+	});
+
+	it("accepts an empty rows array", () => {
+		expect(parseTablePayload({ columns: ["A"], rows: [] })).toEqual({ columns: ["A"], rows: [] });
+	});
+
+	it.each([
+		["null", null],
+		["a number", 7],
+		["a string", "nope"],
+		["missing columns", { rows: [] }],
+		["missing rows", { columns: ["A"] }],
+		["non-string column", { columns: [1], rows: [] }],
+		["row that is not an array", { columns: ["A"], rows: ["x"] }],
+		["cell of unsupported type", { columns: ["A"], rows: [[{ nested: true }]] }],
+		["non-finite numeric cell", { columns: ["A"], rows: [[Number.NaN]] }],
+	])("returns null for invalid payload: %s", (_label, payload) => {
+		expect(parseTablePayload(payload)).toBeNull();
+	});
+});