F4: document propose/accept — manual smoke, README, playground loop (#12)

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

README.md

@@ -12,7 +12,8 @@ catalog (a pure, key-free SDK call) in a notification and the
 "Cowriting (Cline SDK)" output channel.
 
 Features shipped so far: F2 region-anchored threads (Feature #4), F3 live
-human/Claude attribution (Feature #6).
+human/Claude attribution (Feature #6), F4 propose/accept diff flow
+(Feature #12).
 
 ## Architecture
 
@@ -67,13 +68,36 @@ Attribution" output channel) rather than silently moved or discarded.
 - **`Cowriting: Ask Claude to Edit Selection`** — select text → enter an
   instruction → a live `@cline/sdk` turn runs on the built-in `claude-code`
   provider (rides your local Claude Code Pro/Max login; the extension stores no
-  credentials). The replacement lands in the buffer as a Claude-attributed span.
+  credentials). As of F4 the turn ends in a **proposal** (see below); accepted
+  text lands as a Claude-attributed span.
 - **`Cowriting: Toggle Attribution`** — show/hide attribution decorations.
 - `cowriting.applyAgentEdit` _(palette-hidden)_ — the single machine-edit
   ingress seam. Tests drive this directly so CI requires no LLM.
 
 Design: `vscode-cowriting-plugin-content/specs/coauthoring-attribution.md`.
 
+## F4 — Propose/accept diff flow (Feature #12)
+
+Claude's edits arrive as **pending proposals** — propose-by-default, the
+document never changes without your say-so. A proposal renders two ways at
+once: an **amber tint** on the target range, and a "Claude proposes" comment
+thread showing a fenced `diff` of current → proposed text with two actions:
+
+- **✓ Accept Proposal** — applies the replacement through the `applyAgentEdit`
+  seam, so it lands Claude-attributed (F3) — and the proposal disappears.
+- **✗ Reject Proposal** — the document is untouched; the proposal disappears.
+
+Pending proposals persist git-natively in the same sidecar (`proposals[]`,
+sharing the F2/F3 `anchors` fingerprints), survive reload, and re-anchor as
+surrounding text changes. If the **target text itself** changes, the proposal
+goes **stale** (status-bar count, accept disabled — never applied by guess);
+undo the change and it becomes decidable again. `cowriting.proposeAgentEdit`
+_(palette-hidden)_ is the programmatic propose ingress E2E drives — no LLM in
+CI.
+
+Design: `vscode-cowriting-plugin-content/specs/coauthoring-propose-accept.md`.
+Live smoke: [`docs/MANUAL-SMOKE-F4.md`](docs/MANUAL-SMOKE-F4.md).
+
 ## Develop
 
 - `npm run watch` — rebuild on change.

docs/MANUAL-SMOKE-F3.md

@@ -1,5 +1,10 @@
 # F3 manual smoke — live `claude-code` turn (spec §6.8)
 
+> **As of F4 (#12)** the edit-selection turn ends in a **proposal** — the
+> direct-apply behavior in §2 step 4 now happens on **✓ Accept Proposal**. The
+> full propose→accept smoke is [`MANUAL-SMOKE-F4.md`](./MANUAL-SMOKE-F4.md);
+> §1's scripted smoke is unchanged (it drives the SDK turn only, no editor).
+
 The live turn is deliberately NOT in CI (unit + host E2E drive the seam). It
 gets this documented smoke, run once per machine that has Claude Code
 installed and signed in (Pro/Max). The extension itself holds no credentials
@@ -37,9 +42,9 @@ the model id, a non-empty `sessionId`, and exits 0.
   with a clear error (`runEditTurn` throws on any non-`completed` run
   status); in-editor, the command shows an error notification and NO edit is
   applied.
-- Buffer edited mid-turn: start an edit-selection turn, type elsewhere in the
+- Buffer edited mid-turn: superseded by F4 — the turn ends in a proposal, so a
-  document before it completes → warning notification "document changed", no
+  mid-turn edit can't race an application; the proposal simply renders where
-  partial application (stale `expectedVersion`, spec §6.9).
+  its target re-resolves (or stale if the target itself changed — F4 INV-11).
 
 ## Smoke log
 

docs/MANUAL-SMOKE-F4.md

@@ -0,0 +1,20 @@
+# Manual smoke — F4 propose/accept (live turn)
+
+Pre-req: Claude Code installed + signed in (the `claude-code` provider rides
+that login — the extension holds no credentials, INV-8). Run on a real machine,
+not CI.
+
+1. `npm run build`, then F5 (the EDH opens the committed `sandbox/` playground).
+2. Open `playground.md`, select a sentence → right-click → **Ask Claude to Edit
+   Selection** → give an instruction.
+3. ✅ A **proposal** appears: the selection gets an amber tint and a "Claude
+   proposes" comment thread shows a `diff` of current → proposed. **The document
+   text is unchanged** (INV-10).
+4. Click **✓ Accept Proposal** in the thread title. ✅ The replacement lands and
+   renders Claude-tinted (the F3 attribution substrate); the proposal disappears.
+5. Repeat with another selection and click **✗ Reject Proposal**. ✅ The document
+   is untouched; the proposal disappears.
+6. Propose again, then save and reload the window. ✅ The pending proposal is
+   restored at its re-resolved range.
+7. Failure path: edit the proposed-on text, then try Accept. ✅ Refused with a
+   warning ("target text changed"); undo your edit → Accept works.

sandbox/playground.md

@@ -8,8 +8,10 @@ open in your dev window (#8).
 Play here:
 
 1. Type a sentence below — it renders with the human left-border as you type.
-2. Highlight it → right-click → **Ask Claude to Edit Selection** — the
+2. Highlight it → right-click → **Ask Claude to Edit Selection** — Claude
-   replacement lands Claude-tinted.
+   **proposes** a diff (amber tint + a "Claude proposes" thread); click
+   **✓ Accept Proposal** and it lands Claude-tinted, or **✗ Reject Proposal**
+   to discard.
 3. Edit inside the tinted span — it splits character-precisely.
 4. Save, then peek at `sandbox/.threads/playground.md.json` — the git-native
    attribution record. Reopen the file: spans re-resolve.