F3 SLICE-3/4 review fixes: counted self-writes, persist deletion-to-empty, render all visible editors (#6)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/store.test.ts

@@ -88,4 +88,22 @@ describe("CoauthorStore", () => {
     });
     expect(Object.keys(store.load("d.md")!.anchors)).toEqual([]);
   });
+
+  it("consumeSelfWrite counts multiple writes to the same sidecar (double-save suppression)", () => {
+    const store = new CoauthorStore(root);
+    store.update("d.md", (a) => {
+      a.anchors["a_t"] = { fingerprint: { text: "t", before: "", after: "", lineHint: 0 } };
+      a.threads.push({ id: "t1", anchorId: "a_t", status: "open", messages: [] });
+    });
+    store.update("d.md", (a) => {
+      a.attributions.push({
+        id: "at1", anchorId: "a_t", author: { kind: "human", id: "ben" },
+        createdAt: "2026-06-10T00:00:00.000Z", updatedAt: "2026-06-10T00:00:00.000Z",
+      });
+    });
+    const p = store.sidecarPath("d.md");
+    expect(store.consumeSelfWrite(p)).toBe(true);
+    expect(store.consumeSelfWrite(p)).toBe(true);
+    expect(store.consumeSelfWrite(p)).toBe(false);
+  });
 });