feat(f6): diff-view toggle on any file — global storage, untitled in-memory (#19)

F6 no longer requires a workspace file. It gets its own diffable predicate
(any file: or untitled:) decoupled from F2 isTracked, keys baselines by a
sha256 of the document URI, and stores them in VS Code GLOBAL storage
(context.globalStorageUri) — always present, never the repo (INV-19). Untitled
buffers have no durable identity → in-memory baseline only (lost on reload).

DiffViewController is now constructed before the workspace-root check and its
commands are always live (never stubbed) — the machine-landing advance wiring
stays in the with-root branch since the seam only fires on workspace files.
BaselineStore generalized to key-by-hash (Baseline.docPath → uri).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/baselineStore.test.ts

@@ -13,41 +13,49 @@ afterEach(() => {
   fs.rmSync(dir, { recursive: true, force: true });
 });
 
-function sample(docPath = "notes/chapter-1.md"): Baseline {
-  return { docPath, text: "hello\nworld\n", capturedAt: "2026-06-11T00:00:00.000Z", reason: "opened" };
+const KEY = "a1b2c3"; // a stand-in for the controller's sha256(uri) key
+
+function sample(uri = "file:///ws/notes/chapter-1.md"): Baseline {
+  return { uri, text: "hello\nworld\n", capturedAt: "2026-06-11T00:00:00.000Z", reason: "opened" };
 }
 
 describe("BaselineStore", () => {
-  it("returns null for a document with no baseline", () => {
-    expect(new BaselineStore(dir).load("notes/chapter-1.md")).toBeNull();
+  it("returns null for a key with no baseline", () => {
+    expect(new BaselineStore(dir).load(KEY)).toBeNull();
   });
 
-  it("computes the baseline path as baselines/<docPath>.json", () => {
+  it("computes the baseline path as baselines/<key>.json", () => {
     const store = new BaselineStore(dir);
-    expect(store.baselinePath("notes/chapter-1.md")).toBe(
-      path.join(dir, "baselines", "notes", "chapter-1.md.json"),
-    );
+    expect(store.baselinePath(KEY)).toBe(path.join(dir, "baselines", "a1b2c3.json"));
   });
 
-  it("save then load round-trips the baseline (including nested docPaths)", () => {
+  it("save then load round-trips the baseline (including the uri identity)", () => {
     const store = new BaselineStore(dir);
     const b = sample();
-    store.save(b.docPath, b);
-    expect(store.load(b.docPath)).toEqual(b);
+    store.save(KEY, b);
+    expect(store.load(KEY)).toEqual(b);
   });
 
   it("overwrites in place: the newest epoch wins, no history kept", () => {
     const store = new BaselineStore(dir);
-    store.save("d.md", { docPath: "d.md", text: "v1", capturedAt: "2026-06-11T00:00:00.000Z", reason: "opened" });
-    store.save("d.md", { docPath: "d.md", text: "v2", capturedAt: "2026-06-11T00:01:00.000Z", reason: "pinned" });
-    expect(store.load("d.md")).toEqual({ docPath: "d.md", text: "v2", capturedAt: "2026-06-11T00:01:00.000Z", reason: "pinned" });
+    store.save(KEY, { uri: "untitled:Untitled-1", text: "v1", capturedAt: "2026-06-11T00:00:00.000Z", reason: "opened" });
+    store.save(KEY, { uri: "untitled:Untitled-1", text: "v2", capturedAt: "2026-06-11T00:01:00.000Z", reason: "pinned" });
+    expect(store.load(KEY)).toEqual({ uri: "untitled:Untitled-1", text: "v2", capturedAt: "2026-06-11T00:01:00.000Z", reason: "pinned" });
   });
 
   it("writes pretty JSON with a trailing newline", () => {
     const store = new BaselineStore(dir);
-    const b = sample("d.md");
-    store.save("d.md", b);
-    const raw = fs.readFileSync(store.baselinePath("d.md"), "utf8");
+    const b = sample();
+    store.save(KEY, b);
+    const raw = fs.readFileSync(store.baselinePath(KEY), "utf8");
     expect(raw).toBe(JSON.stringify(b, null, 2) + "\n");
   });
+
+  it("distinct keys are independent files (no collision)", () => {
+    const store = new BaselineStore(dir);
+    store.save("k1", sample("file:///a.md"));
+    store.save("k2", sample("file:///b.md"));
+    expect(store.load("k1")!.uri).toBe("file:///a.md");
+    expect(store.load("k2")!.uri).toBe("file:///b.md");
+  });
 });