diff --git a/README.md b/README.md
index 362701b..c7fd4e6 100644
--- a/README.md
+++ b/README.md
@@ -132,26 +132,32 @@ record per the contract; git push/pull is the transport, no re-homing ever.
 
 Design: `vscode-cowriting-plugin-content/specs/coauthoring-cross-rung-format.md`.
 
-## F6 — Diff-view toggle (Feature #17)
+## F6 — Diff-view toggle (Feature #17, #19)
 
-**Cmd/Ctrl-Alt-D** (or **Cowriting: Toggle Diff View**) flips a tracked
-document into a native `vscode.diff` against a **coauthoring baseline** — the
-readonly baseline on the left, your **live, editable** document on the right
-(so you keep writing inside the diff; toggling again closes it). The diff
-answers "what did *I* change?" in one keystroke instead of git archaeology.
+**`Ctrl+Alt+D`** (the same chord on macOS — not `Cmd`; or **Cowriting: Toggle
+Diff View**) flips the focused document into a native `vscode.diff` against a
+**coauthoring baseline** — the readonly baseline on the left, your **live,
+editable** document on the right (so you keep writing inside the diff; toggling
+again closes it). The diff answers "what did *I* change?" in one keystroke
+instead of git archaeology.
 
+- **Works on any file (#19):** any document you can edit — a file inside or
+  outside the workspace folder, or an **untitled** scratch buffer. Only a
+  non-text-editor focus warns. (Untitled buffers diff in-memory; saving makes
+  the baseline persist.)
 - **Machine-factored baseline (INV-18):** the baseline initializes when a doc
-  is first tracked and **advances automatically at every machine landing**
-  (every successful `applyAgentEdit` seam apply — INV-9). So text Claude landed
-  never shows as a change; everything the diff shows is operator-authored by
+  is first seen and **advances automatically at every machine landing** (every
+  successful `applyAgentEdit` seam apply — INV-9). So text Claude landed never
+  shows as a change; everything the diff shows is operator-authored by
   construction — no attribution filtering.
 - **Pin on demand:** **Cowriting: Pin Diff Baseline to Now** resets the
   baseline to the current buffer for a deliberate "review my next pass" epoch;
   the diff tab title names the epoch (`opened` / `Claude landed` / `pinned`).
 - **Pure view, repo-free (INV-19):** the baseline snapshot lives in VS Code
-  workspace storage, **never** the repo — `.threads/`, the cross-rung contract
-  (INV-14..17), and `SCHEMA_VERSION` are untouched. Storage-unavailable
-  degrades to in-memory baselines + one warning.
+  **global** extension storage, keyed by a hash of the document URI, **never**
+  the repo — `.threads/`, the cross-rung contract (INV-14..17), and
+  `SCHEMA_VERSION` are untouched. Storage-unavailable degrades to in-memory
+  baselines + one warning.
 - **No LLM in CI:** host E2E (`test/e2e/suite/diffView.test.ts`) drives the same
   programmatic seam ingress (propose + accept) the F4 suite uses.
 
diff --git a/docs/MANUAL-SMOKE-F6.md b/docs/MANUAL-SMOKE-F6.md
index f3279fe..e619a14 100644
--- a/docs/MANUAL-SMOKE-F6.md
+++ b/docs/MANUAL-SMOKE-F6.md
@@ -6,10 +6,11 @@ rest of F6 needs no credentials and no network.
 
 1. `npm run build`, launch the extension (F5 in VS Code opens the committed
    `sandbox/` playground), open `playground.md`.
-2. Edit a sentence by hand, then **Cmd/Ctrl-Alt-D** (or run **Cowriting: Toggle
-   Diff View**). ✅ A diff opens: the readonly baseline on the left, your live
-   document on the right; the tab title reads `playground.md — my changes since
-   opened <time>`. Your hand edit shows as a change.
+2. Edit a sentence by hand, then **`Ctrl+Alt+D`** (same chord on macOS — not
+   `Cmd`; or run **Cowriting: Toggle Diff View**). ✅ A diff opens: the readonly
+   baseline on the left, your live document on the right; the tab title reads
+   `playground.md — my changes since opened <time>`. Your hand edit shows as a
+   change.
 3. Keep typing **in the diff's right pane**. ✅ Editing continues in place;
    decorations/threads still work. Toggle again. ✅ The diff tab closes and the
    normal editor is back.
@@ -21,6 +22,9 @@ rest of F6 needs no credentials and no network.
    now); the title reads `pinned <time>`. Type → your changes show against the
    pin.
 6. Reload the window (Developer: Reload Window). ✅ Toggle: the baseline is the
-   same as before the reload (persisted in workspace storage, not the repo —
-   INV-19; `git status` shows nothing new).
-7. Toggle on a file outside the workspace folder. ✅ A warning, no diff.
+   same as before the reload (persisted in **global** extension storage, not the
+   repo — INV-19; `git status` shows nothing new).
+7. **Any file (#19):** open a file from *outside* the `sandbox/` folder, or a
+   new untitled buffer (`Cmd/Ctrl+N`), edit it, and `Ctrl+Alt+D`. ✅ The diff
+   opens there too — untitled buffers show `(unsaved)` in the title and diff
+   in-memory. Toggle with focus on a non-editor (e.g. the terminal) → warning.
diff --git a/src/baselineStore.ts b/src/baselineStore.ts
index 44b0d33..4980aff 100644
--- a/src/baselineStore.ts
+++ b/src/baselineStore.ts
@@ -1,10 +1,12 @@
 /**
  * BaselineStore — load/save one diff-view baseline JSON per document (F6 §6.3).
  * The CoauthorStore shape (src/store.ts): vscode-free (Node fs only, unit-
- * testable), one file per docPath. INV-19: the storage dir is VS Code's
- * per-workspace extension storage, NEVER the repo — so the baseline can never
- * be committed, merged, or read by another rung, and the sidecar / cross-rung
- * contract (INV-14..17) are untouched by construction.
+ * testable), one file per storage key. INV-19: the storage dir is VS Code's
+ * per-extension GLOBAL storage, NEVER the repo — so the baseline can never be
+ * committed, merged, or read by another rung. F6 works on *any* file, so the
+ * key is a hash of the document URI (the controller derives it), not a
+ * workspace-relative path; an untitled buffer has no durable identity and is
+ * never persisted here (in-memory only — see DiffViewController).
  */
 import * as fs from "node:fs";
 import * as path from "node:path";
@@ -12,7 +14,8 @@ import * as path from "node:path";
 export type BaselineReason = "opened" | "machine-landing" | "pinned";
 
 export interface Baseline {
-  docPath: string;
+  /** the document URI (the identity the key is derived from) — for round-trip/debug. */
+  uri: string;
   /** full document text captured at the epoch (from the buffer, not disk — §6.3). */
   text: string;
   capturedAt: string;
@@ -20,23 +23,23 @@ export interface Baseline {
 }
 
 export class BaselineStore {
-  /** @param storageDir absolute VS Code workspace-storage dir (context.storageUri.fsPath). */
+  /** @param storageDir absolute VS Code GLOBAL-storage dir (context.globalStorageUri.fsPath). */
   constructor(private readonly storageDir: string) {}
 
-  /** `<storageDir>/baselines/<repo-relative-docPath>.json` (§6.3). */
-  baselinePath(docPath: string): string {
-    return path.join(this.storageDir, "baselines", `${docPath}.json`);
+  /** `<storageDir>/baselines/<key>.json` — `key` is a filesystem-safe hash (§6.3). */
+  baselinePath(key: string): string {
+    return path.join(this.storageDir, "baselines", `${key}.json`);
   }
 
-  load(docPath: string): Baseline | null {
-    const p = this.baselinePath(docPath);
+  load(key: string): Baseline | null {
+    const p = this.baselinePath(key);
     if (!fs.existsSync(p)) return null;
     return JSON.parse(fs.readFileSync(p, "utf8")) as Baseline;
   }
 
   /** Newest epoch wins — overwrite in place, no history (state-not-history, the F3/F4 precedent). */
-  save(docPath: string, baseline: Baseline): void {
-    const p = this.baselinePath(docPath);
+  save(key: string, baseline: Baseline): void {
+    const p = this.baselinePath(key);
     fs.mkdirSync(path.dirname(p), { recursive: true });
     fs.writeFileSync(p, JSON.stringify(baseline, null, 2) + "\n", "utf8");
   }
diff --git a/src/diffViewController.ts b/src/diffViewController.ts
index 1d61fb7..cb5c904 100644
--- a/src/diffViewController.ts
+++ b/src/diffViewController.ts
@@ -1,14 +1,21 @@
 /**
  * DiffViewController — F6 diff-view toggle (spec §6.2/§6.4). Owns the baseline
- * lifecycle (initialize at first track / advance at every machine landing / pin
+ * lifecycle (initialize at first sight / advance at every machine landing / pin
  * on demand), serves the baseline as a readonly `cowriting-baseline:` virtual
  * document, and toggles a native vscode.diff (baseline left, the LIVE document
  * right). A pure view: never mutates the document, sidecar, or attribution
- * state (INV-19). Baselines persist via the vscode-free BaselineStore; if
- * storage is unavailable the controller degrades to in-memory baselines + one
- * warning (reload survival is lost; the toggle still works) — §6.5 PUC-5.
+ * state (INV-19).
+ *
+ * F6 works on ANY text document, not just workspace files — it needs no
+ * `.threads/` sidecar, only a stable doc identity + a storage home. So it has
+ * its OWN diffable predicate (any `file:` or `untitled:` doc), decoupled from
+ * F2's workspace `isTracked`. Persistable docs (`file:`) keep their baseline in
+ * VS Code's per-extension GLOBAL storage keyed by a hash of the document URI;
+ * untitled buffers have no durable identity, so their baseline is in-memory
+ * only (lost on reload) — the same degrade the storage-unavailable path uses.
  */
 import * as path from "node:path";
+import { createHash } from "node:crypto";
 import * as vscode from "vscode";
 import { BaselineStore, type Baseline, type BaselineReason } from "./baselineStore";
 
@@ -16,20 +23,17 @@ export const BASELINE_SCHEME = "cowriting-baseline";
 
 export class DiffViewController implements vscode.Disposable {
   private readonly disposables: vscode.Disposable[] = [];
-  /** Source of truth for the content provider; mirrors what the store persists. */
+  /** Source of truth for the content provider, keyed by `document.uri.toString()`. */
   private readonly baselines = new Map<string, Baseline>();
   private readonly onDidChangeEmitter = new vscode.EventEmitter<vscode.Uri>();
   private storageWarned = false;
 
-  constructor(
-    private readonly store: BaselineStore | null,
-    private readonly rootDir: string,
-  ) {
+  constructor(private readonly store: BaselineStore | null) {
     const provider: vscode.TextDocumentContentProvider = {
       onDidChange: this.onDidChangeEmitter.event,
       provideTextDocumentContent: (uri) => {
-        const docPath = this.docPathFromBaselineUri(uri);
-        return this.baselines.get(docPath)?.text ?? "";
+        // The baseline URI carries the real document URI in its query (see baselineUri).
+        return this.baselines.get(uri.query)?.text ?? "";
       },
     };
     this.disposables.push(
@@ -41,37 +45,49 @@ export class DiffViewController implements vscode.Disposable {
       vscode.commands.registerCommand("cowriting.pinDiffBaseline", () =>
         this.pinCommand(vscode.window.activeTextEditor),
       ),
+      // F6 captures a baseline for any diffable doc the moment it is first seen,
+      // independent of the workspace gate (so "opened" is the open-time text).
+      vscode.workspace.onDidOpenTextDocument((d) => this.ensureBaseline(d)),
     );
+    for (const d of vscode.workspace.textDocuments) this.ensureBaseline(d);
   }
 
-  // ---- tracking / uri helpers --------------------------------------------------------
+  // ---- diffability / identity --------------------------------------------------------
 
-  private isTracked(document: vscode.TextDocument): boolean {
-    return document.uri.scheme === "file" && document.uri.fsPath.startsWith(this.rootDir);
+  /** Any text document F6 can diff: a saved file OR an unsaved buffer. */
+  private isDiffable(document: vscode.TextDocument): boolean {
+    return document.uri.scheme === "file" || document.uri.scheme === "untitled";
   }
-  private docPathOf(uri: vscode.Uri): string {
-    return vscode.workspace.asRelativePath(uri, false);
+  /** Only `file:` docs have a durable identity to persist a baseline against. */
+  private isPersistable(document: vscode.TextDocument): boolean {
+    return document.uri.scheme === "file";
   }
-  /** The readonly virtual-doc URI whose content the provider serves for this doc. */
-  private baselineUri(docPath: string): vscode.Uri {
-    return vscode.Uri.from({ scheme: BASELINE_SCHEME, path: "/" + docPath });
+  /** In-memory map key — the full document URI. */
+  private uriKey(document: vscode.TextDocument): string {
+    return document.uri.toString();
   }
-  private docPathFromBaselineUri(uri: vscode.Uri): string {
-    return uri.path.replace(/^\//, "");
+  /** Filesystem-safe storage key for a persistable doc: sha256 of its URI. */
+  private storageKey(uriKey: string): string {
+    return createHash("sha256").update(uriKey).digest("hex");
+  }
+  /** The readonly virtual-doc URI; its query carries the real document URI. */
+  private baselineUri(document: vscode.TextDocument): vscode.Uri {
+    const name = path.basename(document.uri.path) || "untitled";
+    return vscode.Uri.from({ scheme: BASELINE_SCHEME, path: "/" + name, query: this.uriKey(document) });
   }
 
   // ---- baseline lifecycle (§6.4) -----------------------------------------------------
 
-  /** First sight of a tracked doc: load the stored baseline, else capture `opened`. */
+  /** First sight of a diffable doc: load the stored baseline, else capture `opened`. */
   ensureBaseline(document: vscode.TextDocument): void {
-    if (!this.isTracked(document)) return;
-    const docPath = this.docPathOf(document.uri);
-    if (this.baselines.has(docPath)) return;
-    if (this.store) {
+    if (!this.isDiffable(document)) return;
+    const key = this.uriKey(document);
+    if (this.baselines.has(key)) return;
+    if (this.store && this.isPersistable(document)) {
       try {
-        const stored = this.store.load(docPath);
+        const stored = this.store.load(this.storageKey(key));
         if (stored) {
-          this.baselines.set(docPath, stored);
+          this.baselines.set(key, stored);
           return;
         }
       } catch {
@@ -83,35 +99,30 @@ export class DiffViewController implements vscode.Disposable {
 
   /** Machine landing (INV-18): re-capture so landed text never shows as a change. */
   advance(document: vscode.TextDocument): void {
-    if (!this.isTracked(document)) return;
+    if (!this.isDiffable(document)) return;
     this.capture(document, "machine-landing");
   }
 
   /** Human pin: baseline := now; the open diff visibly empties (left = right). */
   pin(document: vscode.TextDocument): void {
-    if (!this.isTracked(document)) return;
+    if (!this.isDiffable(document)) return;
     this.capture(document, "pinned");
   }
 
-  /** Capture buffer text at this epoch, persist, and refresh any open diff's left side. */
+  /** Capture buffer text at this epoch, persist (if persistable), refresh any open diff. */
   private capture(document: vscode.TextDocument, reason: BaselineReason): void {
-    const docPath = this.docPathOf(document.uri);
-    const baseline: Baseline = {
-      docPath,
-      text: document.getText(),
-      capturedAt: new Date().toISOString(),
-      reason,
-    };
-    this.baselines.set(docPath, baseline);
-    if (this.store) {
+    const key = this.uriKey(document);
+    const baseline: Baseline = { uri: key, text: document.getText(), capturedAt: new Date().toISOString(), reason };
+    this.baselines.set(key, baseline);
+    if (this.store && this.isPersistable(document)) {
       try {
-        this.store.save(docPath, baseline);
+        this.store.save(this.storageKey(key), baseline);
       } catch {
         this.warnStorageOnce();
       }
     }
     // An open diff re-requests the left side when its baseline URI changes.
-    this.onDidChangeEmitter.fire(this.baselineUri(docPath));
+    this.onDidChangeEmitter.fire(this.baselineUri(document));
   }
 
   private warnStorageOnce(): void {
@@ -122,44 +133,21 @@ export class DiffViewController implements vscode.Disposable {
     );
   }
 
-  // ---- commands (toggle implemented in SLICE-3, Task 4) ------------------------------
-
-  private pinCommand(editor: vscode.TextEditor | undefined): void {
-    if (!editor || !this.isTracked(editor.document)) {
-      void vscode.window.showWarningMessage("Cowriting: open a tracked workspace document to pin its diff baseline.");
-      return;
-    }
-    this.pin(editor.document);
-  }
-
-  // ---- test-facing surface (§6.4) ----------------------------------------------------
-
-  getBaseline(docPath: string): { text: string; reason: BaselineReason; capturedAt: string } | undefined {
-    const b = this.baselines.get(docPath);
-    return b ? { text: b.text, reason: b.reason, capturedAt: b.capturedAt } : undefined;
-  }
-  /** Absolute on-disk path of this doc's persisted baseline, or undefined if in-memory. */
-  baselineFilePath(docPath: string): string | undefined {
-    return this.store?.baselinePath(docPath);
-  }
-
   // ---- toggle UX (§6.5 PUC-1) --------------------------------------------------------
 
   /**
-   * If this doc's baseline diff is the active/open tab → close it and reveal the
-   * normal editor; if the active editor is a tracked doc with no diff open →
-   * open vscode.diff (baseline left, the live document right). Untracked → warn,
-   * no diff.
+   * If this doc's baseline diff is open → close it and reveal the normal editor;
+   * else open vscode.diff (baseline left, the live document right). Warns only
+   * when there is no active text editor (or a non-diffable scheme).
    */
   private async toggle(editor: vscode.TextEditor | undefined): Promise<void> {
-    if (!editor || !this.isTracked(editor.document)) {
+    if (!editor || !this.isDiffable(editor.document)) {
       void vscode.window.showWarningMessage(
-        "Cowriting: open a tracked workspace document to toggle its diff view.",
+        "Cowriting: focus a text editor to toggle its diff view.",
       );
       return;
     }
     const document = editor.document;
-    const docPath = this.docPathOf(document.uri);
     const openTab = this.findDiffTab(document.uri);
     if (openTab) {
       await vscode.window.tabGroups.close(openTab);
@@ -167,11 +155,13 @@ export class DiffViewController implements vscode.Disposable {
       return;
     }
     this.ensureBaseline(document);
-    const baseline = this.baselines.get(docPath)!;
-    const title = `${path.basename(docPath)} — my changes since ${this.epochLabel(baseline)}`;
+    const baseline = this.baselines.get(this.uriKey(document))!;
+    const name = path.basename(document.uri.path) || "untitled";
+    const unsaved = this.isPersistable(document) ? "" : " (unsaved)";
+    const title = `${name} — my changes since ${this.epochLabel(baseline)}${unsaved}`;
     await vscode.commands.executeCommand(
       "vscode.diff",
-      this.baselineUri(docPath),
+      this.baselineUri(document),
       document.uri,
       title,
       { preview: false },
@@ -208,12 +198,28 @@ export class DiffViewController implements vscode.Disposable {
     }
   }
 
-  /**
-   * Test-facing (§6.4): is this doc's baseline diff currently open in any tab
-   * group? The diff's `modified` side is the document's own file: URI.
-   */
-  isDiffOpen(docPath: string): boolean {
-    return this.findDiffTab(vscode.Uri.file(path.join(this.rootDir, docPath))) !== undefined;
+  private pinCommand(editor: vscode.TextEditor | undefined): void {
+    if (!editor || !this.isDiffable(editor.document)) {
+      void vscode.window.showWarningMessage("Cowriting: focus a text editor to pin its diff baseline.");
+      return;
+    }
+    this.pin(editor.document);
+  }
+
+  // ---- test-facing surface (§6.4) ----------------------------------------------------
+
+  getBaseline(uriString: string): { text: string; reason: BaselineReason; capturedAt: string } | undefined {
+    const b = this.baselines.get(uriString);
+    return b ? { text: b.text, reason: b.reason, capturedAt: b.capturedAt } : undefined;
+  }
+  /** Is this doc's baseline diff currently open in any tab group? */
+  isDiffOpen(uriString: string): boolean {
+    return this.findDiffTab(vscode.Uri.parse(uriString)) !== undefined;
+  }
+  /** Absolute on-disk path of this doc's persisted baseline, or undefined (untitled/in-memory). */
+  baselineFilePath(uriString: string): string | undefined {
+    if (!this.store || vscode.Uri.parse(uriString).scheme !== "file") return undefined;
+    return this.store.baselinePath(this.storageKey(uriString));
   }
 
   dispose(): void {
diff --git a/src/extension.ts b/src/extension.ts
index 3cb27a2..bf9965f 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -44,6 +44,18 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
     }),
   );
 
+  // --- F6: diff-view toggle (Features #17 + #19) — workspace-INDEPENDENT ---
+  // F6 works on ANY diffable doc (file or untitled), so it is constructed
+  // regardless of whether a folder is open, and its commands are always live
+  // (never stubbed). Baseline lives in VS Code's per-extension GLOBAL storage
+  // (always present), never the repo (INV-19). The machine-landing advance is
+  // wired in the with-root branch below (landings only occur on workspace files
+  // through the seam). The controller self-wires baseline capture on open.
+  const baselineStorageDir = context.globalStorageUri?.fsPath;
+  const baselineStore = baselineStorageDir ? new BaselineStore(baselineStorageDir) : null;
+  const diffViewController = new DiffViewController(baselineStore);
+  context.subscriptions.push(diffViewController);
+
   // --- F2: region-anchored threads (Feature #4) ---
   const root = vscode.workspace.workspaceFolders?.[0]?.uri.fsPath;
   if (!root) {
@@ -66,11 +78,12 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
       "cowriting.acceptProposal",
       "cowriting.rejectProposal",
       "cowriting.proposeAgentEdit",
-      "cowriting.toggleDiffView",
-      "cowriting.pinDiffBaseline",
     ]) {
       context.subscriptions.push(vscode.commands.registerCommand(command, stub));
     }
+    // F6 (toggleDiffView / pinDiffBaseline) is NOT stubbed here — it works
+    // without a folder (on untitled buffers and out-of-folder files); its real
+    // commands were registered above by DiffViewController.
     return undefined;
   }
   const store = new CoauthorStore(root);
@@ -88,14 +101,10 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
   const proposalController = new ProposalController(store, attributionController, root, versionGuard);
   context.subscriptions.push(proposalController);
 
-  // --- F6: diff-view toggle (Feature #17) ---
-  // Baseline lives in VS Code workspace storage, never the repo (INV-19).
-  // storageUri can be undefined in odd host states → in-memory fallback (§6.5).
-  const storageDir = context.storageUri?.fsPath;
-  const baselineStore = storageDir ? new BaselineStore(storageDir) : null;
-  const diffViewController = new DiffViewController(baselineStore, root);
-  context.subscriptions.push(diffViewController);
+  // --- F6 machine-landing wiring (with-root only) ---
   // The seam's single machine-landing signal advances the baseline (INV-18).
+  // The seam fires only on workspace files, so this wiring belongs here; the
+  // DiffViewController itself was constructed above (workspace-independent).
   context.subscriptions.push(
     attributionController.onDidApplyAgentEdit((e) => diffViewController.advance(e.document)),
   );
@@ -245,7 +254,6 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
       threadController.renderAll(doc);
       attributionController.loadAll(doc);
       proposalController.renderAll(doc);
-      diffViewController.ensureBaseline(doc);
     }
   };
   vscode.workspace.textDocuments.forEach(renderIfOpen);
diff --git a/test/baselineStore.test.ts b/test/baselineStore.test.ts
index ed7b516..22af488 100644
--- a/test/baselineStore.test.ts
+++ b/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");
+  });
 });
diff --git a/test/e2e/suite-no-workspace/noWorkspace.test.ts b/test/e2e/suite-no-workspace/noWorkspace.test.ts
index e2aecb7..b6c1cb5 100644
--- a/test/e2e/suite-no-workspace/noWorkspace.test.ts
+++ b/test/e2e/suite-no-workspace/noWorkspace.test.ts
@@ -28,8 +28,6 @@ suite("no-workspace activation (#8)", () => {
       "cowriting.acceptProposal",
       "cowriting.rejectProposal",
       "cowriting.proposeAgentEdit",
-      "cowriting.toggleDiffView",
-      "cowriting.pinDiffBaseline",
     ]) {
       assert.ok(all.includes(command), `${command} is registered`);
     }
@@ -39,4 +37,26 @@ suite("no-workspace activation (#8)", () => {
     await vscode.commands.executeCommand("cowriting.editSelection");
     await vscode.commands.executeCommand("cowriting.createThread");
   });
+
+  // F6 (#19) is workspace-INDEPENDENT: its commands are real (not stubs) even
+  // with no folder open, and the toggle works on an untitled buffer.
+  test("F6 toggle works with no folder open (untitled buffer)", async () => {
+    const all = await vscode.commands.getCommands(true);
+    assert.ok(all.includes("cowriting.toggleDiffView"), "toggleDiffView registered");
+    assert.ok(all.includes("cowriting.pinDiffBaseline"), "pinDiffBaseline registered");
+    const untitled = await vscode.workspace.openTextDocument({ content: "no-folder scratch\n", language: "markdown" });
+    await vscode.window.showTextDocument(untitled);
+    await new Promise((r) => setTimeout(r, 300));
+    await vscode.commands.executeCommand("cowriting.toggleDiffView");
+    await new Promise((r) => setTimeout(r, 300));
+    const opened = vscode.window.tabGroups.all.some((g) =>
+      g.tabs.some(
+        (t) =>
+          t.input instanceof vscode.TabInputTextDiff &&
+          t.input.original.scheme === "cowriting-baseline" &&
+          t.input.modified.toString() === untitled.uri.toString(),
+      ),
+    );
+    assert.ok(opened, "a cowriting-baseline diff opened for the untitled buffer with no folder");
+  });
 });
diff --git a/test/e2e/suite/diffView.test.ts b/test/e2e/suite/diffView.test.ts
index 2cc27e6..d694633 100644
--- a/test/e2e/suite/diffView.test.ts
+++ b/test/e2e/suite/diffView.test.ts
@@ -1,11 +1,13 @@
 import * as assert from "assert";
 import * as fs from "fs";
+import * as os from "os";
 import * as path from "path";
 import * as vscode from "vscode";
 import type { CowritingApi } from "../../../src/extension";
 
 const WS = process.env.E2E_WORKSPACE!;
 const DOC_REL = "docs/diffview.md";
+const docUri = () => vscode.Uri.file(path.join(WS, DOC_REL)).toString();
 
 async function openDoc(): Promise<vscode.TextDocument> {
   const uri = vscode.Uri.file(path.join(WS, DOC_REL));
@@ -22,16 +24,17 @@ async function getApi(): Promise<CowritingApi> {
 const settle = () => new Promise((r) => setTimeout(r, 300));
 
 // Order-dependent (F2–F4 pattern): later tests consume earlier state. Owns
-// docs/diffview.md exclusively.
-suite("F6 diff-view toggle (host E2E — programmatic seam ingress, no LLM)", () => {
+// docs/diffview.md exclusively. F6 works on ANY file (#19), so the last two
+// tests use an out-of-workspace file and an untitled buffer.
+suite("F6 diff-view toggle (host E2E — any file, programmatic seam ingress, no LLM)", () => {
   const TARGET = "A target sentence Claude will rewrite via the seam.";
   const REPLACEMENT = "A SENTENCE CLAUDE REWROTE via the seam.";
 
   test("opening a tracked doc captures an `opened` baseline equal to the buffer (INV-18)", async () => {
     const doc = await openDoc();
+    await getApi();
     const api = await getApi();
-    // renderIfOpen on open already called ensureBaseline; assert it captured.
-    const baseline = api.diffViewController.getBaseline(DOC_REL);
+    const baseline = api.diffViewController.getBaseline(docUri());
     assert.ok(baseline, "baseline captured on first sight");
     assert.strictEqual(baseline!.reason, "opened");
     assert.strictEqual(baseline!.text, doc.getText(), "baseline = open-time buffer");
@@ -39,11 +42,10 @@ suite("F6 diff-view toggle (host E2E — programmatic seam ingress, no LLM)", ()
 
   test("toggle opens a diff tab (original scheme cowriting-baseline) over the live doc (PUC-1)", async () => {
     const api = await getApi();
-    assert.strictEqual(api.diffViewController.isDiffOpen(DOC_REL), false, "no diff open yet");
+    assert.strictEqual(api.diffViewController.isDiffOpen(docUri()), false, "no diff open yet");
     await vscode.commands.executeCommand("cowriting.toggleDiffView");
     await settle();
-    assert.strictEqual(api.diffViewController.isDiffOpen(DOC_REL), true, "diff tab open");
-    // The active tab is a TextDiff whose original is the baseline scheme.
+    assert.strictEqual(api.diffViewController.isDiffOpen(docUri()), true, "diff tab open");
     const active = vscode.window.tabGroups.activeTabGroup.activeTab;
     assert.ok(active && active.input instanceof vscode.TabInputTextDiff, "active tab is a diff");
     assert.strictEqual(
@@ -56,12 +58,12 @@ suite("F6 diff-view toggle (host E2E — programmatic seam ingress, no LLM)", ()
   test("typing leaves the baseline unchanged while the buffer diverges", async () => {
     const doc = await openDoc();
     const api = await getApi();
-    const before = api.diffViewController.getBaseline(DOC_REL)!.text;
+    const before = api.diffViewController.getBaseline(docUri())!.text;
     const edit = new vscode.WorkspaceEdit();
     edit.insert(doc.uri, new vscode.Position(0, 0), "OPERATOR ADDED LINE\n");
     assert.ok(await vscode.workspace.applyEdit(edit), "operator edit applied");
     await settle();
-    assert.strictEqual(api.diffViewController.getBaseline(DOC_REL)!.text, before, "baseline unchanged by typing");
+    assert.strictEqual(api.diffViewController.getBaseline(docUri())!.text, before, "baseline unchanged by typing");
     assert.notStrictEqual(doc.getText(), before, "buffer diverged");
   });
 
@@ -82,7 +84,7 @@ suite("F6 diff-view toggle (host E2E — programmatic seam ingress, no LLM)", ()
     assert.ok(id, "propose returns an id");
     assert.ok(await api.proposalController.acceptById(DOC_REL, id!), "accept applies via the seam");
     await settle();
-    const baseline = api.diffViewController.getBaseline(DOC_REL)!;
+    const baseline = api.diffViewController.getBaseline(docUri())!;
     assert.strictEqual(baseline.reason, "machine-landing", "baseline advanced on the landing");
     assert.ok(baseline.text.includes(REPLACEMENT), "landed text is in the baseline (won't show as a change)");
     assert.ok(!baseline.text.includes(TARGET), "old target gone from the baseline too");
@@ -97,7 +99,7 @@ suite("F6 diff-view toggle (host E2E — programmatic seam ingress, no LLM)", ()
     assert.ok(await vscode.workspace.applyEdit(edit));
     await settle();
     assert.notStrictEqual(
-      api.diffViewController.getBaseline(DOC_REL)!.text,
+      api.diffViewController.getBaseline(docUri())!.text,
       doc.getText(),
       "operator changes show against the advanced baseline",
     );
@@ -108,59 +110,82 @@ suite("F6 diff-view toggle (host E2E — programmatic seam ingress, no LLM)", ()
     const api = await getApi();
     await vscode.commands.executeCommand("cowriting.pinDiffBaseline");
     await settle();
-    const baseline = api.diffViewController.getBaseline(DOC_REL)!;
+    const baseline = api.diffViewController.getBaseline(docUri())!;
     assert.strictEqual(baseline.reason, "pinned");
     assert.strictEqual(baseline.text, doc.getText(), "pinned baseline == current buffer (diff empties)");
   });
 
-  test("the baseline is persisted on disk under the storage dir with the expected content (PUC-4)", async () => {
+  test("the baseline is persisted in GLOBAL storage, never the repo (PUC-4, INV-19)", async () => {
+    await openDoc();
     const api = await getApi();
-    const p = api.diffViewController.baselineFilePath(DOC_REL);
-    assert.ok(p, "storage-backed baseline path is available");
+    const p = api.diffViewController.baselineFilePath(docUri());
+    assert.ok(p, "storage-backed baseline path is available for a file: doc");
     assert.ok(fs.existsSync(p!), `baseline file exists at ${p}`);
     const onDisk = JSON.parse(fs.readFileSync(p!, "utf8"));
-    assert.strictEqual(onDisk.docPath, DOC_REL);
+    assert.strictEqual(onDisk.uri, docUri(), "baseline records the document URI");
     assert.strictEqual(onDisk.reason, "pinned", "last epoch (pin) persisted");
-    assert.strictEqual(onDisk.text, api.diffViewController.getBaseline(DOC_REL)!.text, "on-disk == in-memory");
-    // INV-19: nothing leaked into the repo's .threads sidecar tree.
+    assert.strictEqual(onDisk.text, api.diffViewController.getBaseline(docUri())!.text, "on-disk == in-memory");
+    // INV-19: baseline lives under the extension's storage dir, not the repo.
     assert.ok(!p!.includes(`${path.sep}.threads${path.sep}`), "baseline is NOT in the sidecar tree");
+    assert.ok(!p!.startsWith(WS + path.sep), "baseline is NOT under the workspace folder");
+    assert.ok(p!.includes(`${path.sep}baselines${path.sep}`), "baseline lives under <globalStorage>/baselines/");
   });
 
   test("toggle again closes the diff tab and reveals the normal editor (PUC-1)", async () => {
     const api = await getApi();
-    if (!api.diffViewController.isDiffOpen(DOC_REL)) {
+    if (!api.diffViewController.isDiffOpen(docUri())) {
+      await openDoc();
       await vscode.commands.executeCommand("cowriting.toggleDiffView");
       await settle();
     }
-    assert.strictEqual(api.diffViewController.isDiffOpen(DOC_REL), true, "diff open before close");
+    assert.strictEqual(api.diffViewController.isDiffOpen(docUri()), true, "diff open before close");
     await vscode.commands.executeCommand("cowriting.toggleDiffView");
     await settle();
-    assert.strictEqual(api.diffViewController.isDiffOpen(DOC_REL), false, "diff tab closed");
-    // "Normal editor is back": the file is the active text editor, and no
-    // baseline-diff tab for it remains in any group.
+    assert.strictEqual(api.diffViewController.isDiffOpen(docUri()), false, "diff tab closed");
     assert.strictEqual(
       vscode.window.activeTextEditor?.document.uri.toString(),
-      vscode.Uri.file(path.join(WS, DOC_REL)).toString(),
+      docUri(),
       "the normal editor for the doc is active after closing the diff",
     );
   });
 
-  test("toggling on an untracked doc warns and opens no diff (PUC-5)", async () => {
-    await getApi();
-    const untracked = await vscode.workspace.openTextDocument({ content: "scratch", language: "markdown" });
-    await vscode.window.showTextDocument(untracked);
+  test("toggle works on a file OUTSIDE the workspace folder, persisted in global storage (#19)", async () => {
+    const api = await getApi();
+    const outsideDir = fs.mkdtempSync(path.join(os.tmpdir(), "cowriting-outside-"));
+    const outsidePath = path.join(outsideDir, "outside.md");
+    fs.writeFileSync(outsidePath, "# Outside the workspace\n\nThe operator edits this too.\n", "utf8");
+    const outsideUri = vscode.Uri.file(outsidePath);
+    const doc = await vscode.workspace.openTextDocument(outsideUri);
+    await vscode.window.showTextDocument(doc);
     await settle();
+    // Captured on open even though it is NOT under the workspace folder.
+    const baseline = api.diffViewController.getBaseline(outsideUri.toString());
+    assert.ok(baseline, "baseline captured for an out-of-folder file");
+    assert.strictEqual(baseline!.reason, "opened");
     await vscode.commands.executeCommand("cowriting.toggleDiffView");
     await settle();
-    // No baseline-diff tab for an untitled doc anywhere.
-    const anyDiff = vscode.window.tabGroups.all.some((g) =>
-      g.tabs.some(
-        (t) =>
-          t.input instanceof vscode.TabInputTextDiff &&
-          t.input.original.scheme === "cowriting-baseline" &&
-          t.input.modified.toString() === untracked.uri.toString(),
-      ),
-    );
-    assert.strictEqual(anyDiff, false, "no diff opened for the untracked doc");
+    assert.strictEqual(api.diffViewController.isDiffOpen(outsideUri.toString()), true, "diff opens for the outside file");
+    const fp = api.diffViewController.baselineFilePath(outsideUri.toString());
+    assert.ok(fp && fs.existsSync(fp), "outside-file baseline persisted in global storage");
+    assert.ok(!fp!.startsWith(WS + path.sep), "not under the workspace folder");
+    // close it so it doesn't bleed into the untitled test's active-tab checks
+    await vscode.commands.executeCommand("cowriting.toggleDiffView");
+    await settle();
+    fs.rmSync(outsideDir, { recursive: true, force: true });
+  });
+
+  test("toggle works on an UNTITLED buffer, baseline in-memory only (#19)", async () => {
+    const api = await getApi();
+    const untitled = await vscode.workspace.openTextDocument({ content: "scratch line\n", language: "markdown" });
+    await vscode.window.showTextDocument(untitled);
+    await settle();
+    const key = untitled.uri.toString();
+    assert.strictEqual(untitled.uri.scheme, "untitled", "it really is an untitled buffer");
+    const baseline = api.diffViewController.getBaseline(key);
+    assert.ok(baseline, "untitled buffer got an in-memory baseline");
+    assert.strictEqual(api.diffViewController.baselineFilePath(key), undefined, "untitled is NOT persisted to disk");
+    await vscode.commands.executeCommand("cowriting.toggleDiffView");
+    await settle();
+    assert.strictEqual(api.diffViewController.isDiffOpen(key), true, "diff opens for the untitled buffer");
   });
 });