F10 SLICE-4: manual smoke checklist + README F10 section (#29)

Adds docs/MANUAL-SMOKE-F10.md (clean editor → edit → propose → ✓/✗ →
Annotations toggle → status-bar PUC-6 → theming → cleanliness) following the
F7/F9 smoke format. Adds the F10 "write left / review right" section to the
README feature list and notes F6's two-pane diff and F9's authorship view are
retained only as data layers, not separate user surfaces.

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

docs/MANUAL-SMOKE-F10.md

@@ -0,0 +1,58 @@
+# Manual smoke — F10 interactive review in the preview (#29)
+
+F10 makes the rendered preview the **single interactive review surface**: the
+editor is clean (zero annotations), and you accept/reject Claude's proposals
+*inside the preview*. The webview's *visual* rendering (theming, ✓/✗ buttons) is
+verified here, not in the automated host E2E (the webview is a sealed sandbox).
+Run once per change that touches F10. One live turn hits the SDK (or use the
+`proposeAgentEdit` seam to stay key-free).
+
+## Setup
+
+1. `npm run build`
+2. Launch the Extension Development Host (F5 in VS Code, or the Run panel) with
+   `sandbox/` open.
+3. Open a markdown document containing some prose (e.g. copy
+   `test/e2e/fixtures/workspace/docs/preview.md`).
+
+## Steps
+
+1. **Clean editor.** Look at the source editor: there is **no attribution tint,
+   no in-editor proposal comment threads, and no diff** — the editor is a plain
+   text buffer (F10/INV-32). All review lives in the preview.
+2. **Open the preview.** Run **"Cowriting: Open Review Preview"** (or
+   `Ctrl+Alt+R`). A preview opens beside the editor. The header shows an
+   **Annotations** switch (on by default) and a summary.
+3. **Edit prose.** In the source editor, change a word in a paragraph. The
+   preview updates (≈150 ms) in its on-state: the new word highlighted as a green
+   insertion (`<ins>` / `cw-by-human`), the old word struck (`<del>` / `cw-del`);
+   the summary increments. Your own typing is colored green (human).
+4. **Ask Claude to edit a selection.** Select a sentence → **"Ask Claude to Edit
+   Selection"** → instruct (or invoke the `proposeAgentEdit` seam). A **blue
+   `cw-proposal` block** appears in the preview, showing the struck replaced text
+   and the proposed replacement, with **✓ / ✗** buttons in a `cw-actions` span.
+   The editor itself does **not** change (INV-10 — propose never mutates the doc).
+5. **Accept one.** Click **✓** on the proposal. Expect: the replacement **lands
+   in the document** (the editor text updates), the proposal block **clears** from
+   the preview, and the landed Claude text is **not** marked as a change (the
+   baseline advanced past the landing; INV-18).
+6. **Reject another.** Propose a second edit, then click **✗** on it. Expect: the
+   block **vanishes** from the preview and the **document is unchanged**.
+7. **Toggle Annotations off.** Flip the header **Annotations** switch off. Expect:
+   the preview shows **clean rendered markdown** — no green/blue author colors, no
+   struck deletions, no proposal blocks (INV-33). Flip it **on** again: the marks
+   and any pending proposal blocks return.
+8. **Status-bar indicator (PUC-6).** Close the preview. With a **pending
+   proposal** outstanding and **no preview open**, a status-bar item shows the
+   pending count (e.g. "1 Claude proposal"). **Click it** — the review preview
+   opens and the indicator disappears.
+9. **Theme.** Toggle light / dark / high-contrast (`Ctrl+K Ctrl+T`). The proposal
+   block and its ✓ / ✗ buttons, and the green/blue author colors, restyle to the
+   theme and stay legible in each.
+10. **Cleanliness.** `git status` shows nothing written to the document, sidecar,
+    or repo by the preview (INV-20).
+
+## Pass criteria
+
+All ten steps behave as described; no console errors in the webview devtools;
+the editor stays decoration-free throughout; nothing is persisted by the preview.