docs(f8): manual smoke runbook + README hybrid-model/non-shareability note + plan

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

README.md

@@ -196,6 +196,33 @@ the manual smoke, not the sealed-sandbox E2E.
 Design: `vscode-cowriting-plugin-content/specs/coauthoring-rendered-preview.md`.
 Live smoke: [`docs/MANUAL-SMOKE-F7.md`](docs/MANUAL-SMOKE-F7.md).
 
+## F8 — Out-of-workspace authoring (Feature #25)
+
+"Ask Claude to Edit Selection" (and F2 threads / F3 attribution / F4
+propose-accept) now work on **any** document the editor shows — saved in the
+workspace folder, saved outside it, or untitled — matching the already-universal
+F6 diff and F7 preview. Authoring is no longer gated to in-workspace files, and
+the commands are live even with **no folder open**.
+
+Persistence is **hybrid** (one `SidecarStore` abstraction, routed per-document):
+
+- an **in-workspace** file keeps its committable `.threads/<repo-rel>.json`
+  sidecar, **byte-for-byte unchanged** (INV-2) — the only home the F5 cross-rung
+  contract ever sees;
+- an **out-of-workspace** file or **untitled** buffer stores its coauthoring
+  artifact in VS Code **global storage** keyed by `sha256(uri)` (the same home
+  and key F6's baseline uses, INV-19/24); untitled buffers are **in-memory
+  only** (lost on reload/save).
+
+A global-storage artifact is **not a committed file**, so it is **never
+cross-rung-shareable** (INV-25), and renaming/moving the file **orphans** its
+artifact (the key is the URI hash) — both stated as design contract, not
+discovered later. Routing leaves the in-workspace path untouched, so rollback is
+a plain PR revert with zero data migration.
+
+Design: `vscode-cowriting-plugin-content/specs/coauthoring-out-of-workspace.md`.
+Live smoke: [`docs/MANUAL-SMOKE-F8.md`](docs/MANUAL-SMOKE-F8.md).
+
 ## Develop
 
 - `npm run watch` — rebuild on change.

docs/MANUAL-SMOKE-F8.md

@@ -0,0 +1,45 @@
+# Manual smoke — F8 out-of-workspace authoring
+
+Confirms "Ask Claude to Edit Selection" (+ threads / attribution) work on a file
+**outside** the workspace folder and on an **untitled** buffer, while in-workspace
+authoring is unchanged. One live turn hits the SDK (the only LLM step).
+
+Spec: `vscode-cowriting-plugin-content/specs/coauthoring-out-of-workspace.md`.
+
+## Prereqs
+- Build: `npm run build`.
+- Launch the Extension Development Host (F5 in VS Code) with this repo's `sandbox/`
+  opened as the workspace folder.
+
+## A. Out-of-folder file (PUC-1)
+1. Open a markdown file from a DIFFERENT directory (outside `sandbox/`) — e.g. a
+   sibling repo, or `File > Open` a scratch file under `/tmp`.
+2. Select a sentence → Command Palette → **Cowriting: Ask Claude to Edit Selection**
+   → type an instruction → wait for the proposal (amber range + ✓/✗).
+3. Accept (✓). Expect: the text is replaced and shows the Claude attribution tint.
+4. Add a coauthoring thread on a selection (**Add Coauthoring Thread on Selection**).
+5. Close and reopen the file (or revert). Expect: the thread + attribution are
+   restored. There is **no** `.threads/` folder beside the file — its state lives
+   in VS Code global storage (`<globalStorage>/sidecars/<hash>.json`).
+
+## B. Untitled buffer (PUC-2)
+1. `File > New File` (don't save) → type a few sentences.
+2. Select → **Ask Claude to Edit Selection** → instruct → accept. Expect: it works
+   exactly like A, in-session.
+3. Reload the window (Developer: Reload Window). Expect: the untitled buffer's
+   coauthoring state is **gone** (in-memory only — documented limitation, §6.7).
+
+## C. In-workspace unchanged (PUC-3)
+1. Open a file UNDER `sandbox/`. Repeat the propose→accept→thread loop.
+2. Expect: a committable `sandbox/.threads/<path>.json` sidecar is written, exactly
+   as before F8 (byte-for-byte, INV-2).
+
+## D. Read-only view declines (PUC-5)
+1. Open a Git diff / Output view, select text, run **Ask Claude to Edit Selection**.
+2. Expect: a warning that this kind of document can't be edited (not "select some
+   text").
+
+## E. Folder-less (optional)
+1. Launch the EDH with **no folder** open. Open an untitled buffer or `File > Open`
+   any file. Repeat A/B. Expect: authoring works (every doc routes to global
+   storage); the commands are not stubbed.