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.

package.json

@@ -30,11 +30,17 @@
       { "command": "cowriting.reopenThread", "title": "Reopen Thread", "category": "Cowriting" },
       { "command": "cowriting.toggleAttribution", "title": "Toggle Attribution", "category": "Cowriting" },
       { "command": "cowriting.applyAgentEdit", "title": "Apply Agent Edit (internal seam)", "category": "Cowriting" },
-      { "command": "cowriting.editSelection", "title": "Ask Claude to Edit Selection", "category": "Cowriting" }
+      { "command": "cowriting.editSelection", "title": "Ask Claude to Edit Selection", "category": "Cowriting" },
+      { "command": "cowriting.acceptProposal", "title": "✓ Accept Proposal", "category": "Cowriting" },
+      { "command": "cowriting.rejectProposal", "title": "✗ Reject Proposal", "category": "Cowriting" },
+      { "command": "cowriting.proposeAgentEdit", "title": "Propose Agent Edit (internal seam)", "category": "Cowriting" }
     ],
     "menus": {
       "commandPalette": [
-        { "command": "cowriting.applyAgentEdit", "when": "false" }
+        { "command": "cowriting.applyAgentEdit", "when": "false" },
+        { "command": "cowriting.proposeAgentEdit", "when": "false" },
+        { "command": "cowriting.acceptProposal", "when": "false" },
+        { "command": "cowriting.rejectProposal", "when": "false" }
       ],
       "editor/context": [
         {
@@ -61,6 +67,16 @@
           "command": "cowriting.reopenThread",
           "group": "inline",
           "when": "commentController == cowriting.threads && commentThread =~ /^resolved$/"
+        },
+        {
+          "command": "cowriting.acceptProposal",
+          "group": "inline@1",
+          "when": "commentController == cowriting.proposals && commentThread =~ /^pending$/"
+        },
+        {
+          "command": "cowriting.rejectProposal",
+          "group": "inline@2",
+          "when": "commentController == cowriting.proposals"
         }
       ]
     }

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.

src/attributionController.ts

@@ -146,6 +146,26 @@ export class AttributionController implements vscode.Disposable {
       return;
     }
     const s = this.state(docPath);
+    // One applyEdit = one change event, but the host may deliver a seam edit
+    // as SEVERAL minimal hunks (word-level diffing). Match the EVENT's net
+    // effect against the registry; on a hit the agent owns its FULL intended
+    // replacement (INV-9) — apply it as ONE algebra edit, not per hunk.
+    const hit = this.pending.matchEvent(
+      docPath,
+      e.contentChanges.map((c) => ({
+        start: c.rangeOffset,
+        end: c.rangeOffset + c.rangeLength,
+        newLength: c.text.length,
+      })),
+    );
+    if (hit) {
+      const full = hit.full ?? { start: hit.start, end: hit.end, newLength: hit.newText.length };
+      s.spans = applyChange(s.spans, full, hit.provenance, {
+        newId: () => newId("at"),
+        now: () => new Date().toISOString(),
+        turnId: hit.turnId,
+      });
+    } else {
       // Sort descending by offset so earlier changes don't invalidate later offsets
       // (VS Code's order is undocumented; defensive sort is the safe guarantee).
       for (const change of [...e.contentChanges].sort((a, b) => b.rangeOffset - a.rangeOffset)) {
@@ -154,17 +174,12 @@ export class AttributionController implements vscode.Disposable {
           end: change.rangeOffset + change.rangeLength,
           newLength: change.text.length,
         };
-      const hit = this.pending.match(docPath, { start: edit.start, end: edit.end, text: change.text });
+        s.spans = applyChange(s.spans, edit, this.currentAuthor(), {
-      const author = hit ? hit.provenance : this.currentAuthor();
-      // On a seam hit, attribute the agent's FULL intended replacement (the
-      // registered edit is diff-minimized for transport only): same delta,
-      // wider span — the agent owns every char it asserted (INV-9).
-      s.spans = applyChange(s.spans, hit?.full ?? edit, author, {
           newId: () => newId("at"),
           now: () => new Date().toISOString(),
-        turnId: hit?.turnId,
         });
       }
+    }
     if (s.spans.length > 0) s.hadAttributions = true;
     this.render(e.document);
   }

src/extension.ts

@@ -3,12 +3,15 @@ import { fetchSdkSummary } from "./cline";
 import { CoauthorStore } from "./store";
 import { ThreadController } from "./threadController";
 import { AttributionController } from "./attributionController";
+import { ProposalController } from "./proposalController";
+import { buildFingerprint } from "./anchorer";
 
 const CHANNEL_NAME = "Cowriting (Cline SDK)";
 
 export interface CowritingApi {
   threadController: ThreadController;
   attributionController: AttributionController;
+  proposalController: ProposalController;
 }
 
 export function activate(context: vscode.ExtensionContext): CowritingApi | undefined {
@@ -55,6 +58,9 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
       "cowriting.editSelection",
       "cowriting.toggleAttribution",
       "cowriting.applyAgentEdit",
+      "cowriting.acceptProposal",
+      "cowriting.rejectProposal",
+      "cowriting.proposeAgentEdit",
     ]) {
       context.subscriptions.push(vscode.commands.registerCommand(command, stub));
     }
@@ -68,6 +74,10 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
   const attributionController = new AttributionController(store, root);
   context.subscriptions.push(attributionController);
 
+  // --- F4: propose/accept (Feature #12) ---
+  const proposalController = new ProposalController(store, attributionController, root);
+  context.subscriptions.push(proposalController);
+
   // One SHARED sidecar watcher for both controllers; self-writes are
   // suppressed centrally in the store (the sidecar is co-owned).
   const watcher = vscode.workspace.createFileSystemWatcher("**/.threads/**/*.json");
@@ -75,6 +85,7 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
     if (store.consumeSelfWrite(uri.fsPath)) return;
     threadController.handleExternalSidecarChange(uri);
     attributionController.handleExternalSidecarChange(uri);
+    proposalController.handleExternalSidecarChange(uri);
   };
   watcher.onDidChange(onSidecar);
   watcher.onDidCreate(onSidecar);
@@ -102,8 +113,34 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
     ),
   );
 
-  // F3 SLICE-5: the live turn (PUC-2) — selection + instruction → one
+  // The propose ingress as a command (spec §6.4): records a pending proposal,
-  // claude-code SDK turn (liveTurn.ts, INV-8) → the applyAgentEdit seam (INV-9).
+  // NEVER touches the document (INV-10) — for the host E2E harness.
+  context.subscriptions.push(
+    vscode.commands.registerCommand(
+      "cowriting.proposeAgentEdit",
+      (args: {
+        uri: string; start: number; end: number; newText: string;
+        model?: string; sessionId?: string; turnId?: string; instruction?: string;
+      }) => {
+        const doc = vscode.workspace.textDocuments.find((d) => d.uri.toString() === args.uri);
+        if (!doc) return Promise.resolve(undefined);
+        const fp = buildFingerprint(doc.getText(), { start: args.start, end: args.end });
+        const provenance = {
+          kind: "agent" as const,
+          id: "claude",
+          agent: { sdk: "@cline/sdk", model: args.model ?? "sonnet", sessionId: args.sessionId ?? "" },
+        };
+        return proposalController.propose(doc, fp, args.newText, provenance, {
+          turnId: args.turnId,
+          instruction: args.instruction,
+        });
+      },
+    ),
+  );
+
+  // F3 SLICE-5 → F4 SLICE-4: the live turn — selection + instruction → one
+  // claude-code SDK turn (liveTurn.ts, INV-8) → a PENDING PROPOSAL (F4,
+  // INV-10); the applyAgentEdit seam (INV-9) now fires only on accept.
   context.subscriptions.push(
     vscode.commands.registerCommand("cowriting.editSelection", async () => {
       const editor = vscode.window.activeTextEditor;
@@ -127,8 +164,13 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
       }
       const document = editor.document;
       const selection = editor.selection;
-      const expectedVersion = document.version;
       const selectedText = document.getText(selection);
+      // Capture the anchor BEFORE the turn (spec §6.5 PUC-1): mid-turn edits
+      // can't skew it — the proposal renders wherever the target re-resolves.
+      const fp = buildFingerprint(document.getText(), {
+        start: document.offsetAt(selection.start),
+        end: document.offsetAt(selection.end),
+      });
       const turnId = `turn-${Date.now().toString(36)}`;
       try {
         await vscode.window.withProgress(
@@ -138,24 +180,32 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
             const turn = await runEditTurn(instruction, selectedText);
             if (turn.replacement === "") {
               void vscode.window.showWarningMessage(
-                "Cowriting: Claude returned an empty replacement — nothing was applied.",
+                "Cowriting: Claude returned an empty replacement — nothing was proposed.",
               );
               return;
             }
-            const ok = await attributionController.applyAgentEdit(
+            if (turn.replacement === selectedText) {
+              void vscode.window.showInformationMessage(
+                "Cowriting: Claude proposed no change to the selection.",
+              );
+              return;
+            }
+            // F4 (INV-10): the turn ends in a PROPOSAL, not a buffer mutation.
+            // The seam now fires only on accept (ProposalController, INV-9).
+            const id = await proposalController.propose(
               document,
-              new vscode.Range(selection.start, selection.end),
+              fp,
               turn.replacement,
               {
                 kind: "agent",
                 id: "claude",
                 agent: { sdk: "@cline/sdk", model: turn.model, sessionId: turn.sessionId },
               },
-              { expectedVersion, turnId },
+              { turnId, instruction },
             );
-            if (!ok) {
+            if (id) {
-              void vscode.window.showWarningMessage(
+              void vscode.window.showInformationMessage(
-                "Cowriting: the edit could not be applied (the document changed during the turn, or the editor rejected the edit) — nothing was changed.",
+                "Cowriting: Claude proposed an edit — review the diff at the highlighted range (✓ accept / ✗ reject).",
               );
             }
           },
@@ -172,12 +222,13 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
     if (doc.uri.scheme === "file" && doc.uri.fsPath.startsWith(root)) {
       threadController.renderAll(doc);
       attributionController.loadAll(doc);
+      proposalController.renderAll(doc);
     }
   };
   vscode.workspace.textDocuments.forEach(renderIfOpen);
   context.subscriptions.push(vscode.workspace.onDidOpenTextDocument(renderIfOpen));
 
-  return { threadController, attributionController };
+  return { threadController, attributionController, proposalController };
 }
 
 export function deactivate(): void {

src/model.ts

@@ -61,6 +61,22 @@ export interface AttributionRecord {
   turnId?: string;
 }
 
+/** F4 (spec §6.3, INV-13): a PENDING machine edit — state, not history. */
+export interface Proposal {
+  id: string;
+  /** shared anchors map; fingerprint.text IS the exact target text (INV-11). */
+  anchorId: string;
+  /** the full proposed text for the anchored range. */
+  replacement: string;
+  author: Provenance;
+  /** ISO-8601. */
+  createdAt: string;
+  /** groups N proposals born of one live turn. */
+  turnId?: string;
+  /** what the human asked for (review context). */
+  instruction?: string;
+}
+
 export interface Artifact {
   schemaVersion: number;
   /** repo-relative path; the sidecar key. */
@@ -70,8 +86,8 @@ export interface Artifact {
   threads: Thread[];
   /** F3 fills this (spec §6.3, INV-4): typed attribution records anchored via anchors[]. */
   attributions: AttributionRecord[];
-  /** F4 extension point — reuses anchors[] + provenance; not in F2. */
+  /** F4 (spec §6.3, INV-13): pending proposals on shared anchors[] + Provenance. */
-  proposals: unknown[];
+  proposals: Proposal[];
 }
 
 export function emptyArtifact(docPath: string): Artifact {
@@ -139,7 +155,15 @@ export function serializeArtifact(a: Artifact): string {
       updatedAt: at.updatedAt,
       ...(at.turnId !== undefined ? { turnId: at.turnId } : {}),
     })),
-    proposals: a.proposals,
+    proposals: a.proposals.map((p) => ({
+      id: p.id,
+      anchorId: p.anchorId,
+      replacement: p.replacement,
+      author: serializeProvenance(p.author),
+      createdAt: p.createdAt,
+      ...(p.turnId !== undefined ? { turnId: p.turnId } : {}),
+      ...(p.instruction !== undefined ? { instruction: p.instruction } : {}),
+    })),
   };
   return JSON.stringify(canonical, null, 2) + "\n";
 }

src/pendingEdits.ts

@@ -67,17 +67,28 @@ export class PendingEditRegistry {
   }
 
   /**
-   * Find-and-consume the registration exactly matching a change event
+   * Find-and-consume the registration matching a change EVENT's net effect.
-   * (same doc, same replaced range, same inserted text). Null → human edit.
+   * The host may deliver one applied WorkspaceEdit as SEVERAL minimal hunks
+   * (word-level diffing — observed on the F4 accept path), so per-hunk
+   * equality misses real seam edits and they fall through as "human typing".
+   * A pending edit matches an event when EVERY hunk lies inside its full
+   * pre-edit range and the event's net length delta equals the edit's
+   * (one applyEdit = one change event, so a seam event is never mixed with
+   * human hunks). Null → human edit.
    */
-  match(docPath: string, change: { start: number; end: number; text: string }): PendingEdit | null {
+  matchEvent(
-    const i = this.pending.findIndex(
+    docPath: string,
-      (p) =>
+    changes: ReadonlyArray<{ start: number; end: number; newLength: number }>,
-        p.docPath === docPath &&
+  ): PendingEdit | null {
-        p.start === change.start &&
+    if (changes.length === 0) return null;
-        p.end === change.end &&
+    const i = this.pending.findIndex((p) => {
-        p.newText === change.text,
+      if (p.docPath !== docPath) return false;
-    );
+      const full = p.full ?? { start: p.start, end: p.end, newLength: p.newText.length };
+      const delta = full.newLength - (full.end - full.start);
+      const eventDelta = changes.reduce((d, c) => d + (c.newLength - (c.end - c.start)), 0);
+      if (delta !== eventDelta) return false;
+      return changes.every((c) => c.start >= full.start && c.end <= full.end);
+    });
     if (i === -1) return null;
     const [hit] = this.pending.splice(i, 1);
     return hit;

src/proposalController.ts

@@ -0,0 +1,332 @@
+/**
+ * ProposalController — the editor-facing layer for F4 (spec
+ * coauthoring-propose-accept §6.2). Owns the proposal lifecycle: the propose
+ * ingress (INV-10: NEVER mutates the document), persistence at propose time,
+ * resolve-or-flag on load/external change (INV-11 — a proposal's anchor is
+ * immutable for its life: no save-time re-fingerprint, unlike threads),
+ * rendering (second Comments controller + amber pending-range decoration),
+ * and the human-only accept/reject gestures (INV-12). Accept drives the seam
+ * (AttributionController.applyAgentEdit, INV-9) so accepted text lands
+ * Claude-attributed with zero new attribution code.
+ */
+import * as vscode from "vscode";
+import { CoauthorStore } from "./store";
+import { emptyArtifact, type Artifact, type Fingerprint, type Proposal, type Provenance } from "./model";
+import { resolve, shift, type OffsetRange } from "./anchorer";
+import { addProposal, proposalBody, removeProposal } from "./proposalModel";
+import type { AttributionController } from "./attributionController";
+
+/** Test-facing snapshot of what is currently rendered for a document. */
+export interface RenderedProposal {
+  id: string;
+  /** true → resolves exactly, decidable; false → stale/orphaned (INV-11). */
+  pending: boolean;
+  turnId?: string;
+  range: { start: number; end: number };
+}
+
+interface DocState {
+  docPath: string;
+  uri: vscode.Uri;
+  artifact: Artifact;
+  vsThreads: Map<string, vscode.CommentThread>;
+  /** proposal id -> live offset range (within-session optimization, INV-3). */
+  live: Map<string, OffsetRange>;
+  /** proposal ids whose anchor did not resolve at last render (stale/orphaned). */
+  unresolved: Set<string>;
+}
+
+const PENDING_DECO: vscode.DecorationRenderOptions = {
+  backgroundColor: "rgba(245, 158, 11, 0.18)",
+  overviewRulerColor: "rgba(245, 158, 11, 0.8)",
+  overviewRulerLane: vscode.OverviewRulerLane.Right,
+};
+
+export class ProposalController implements vscode.Disposable {
+  private readonly controller: vscode.CommentController;
+  private readonly disposables: vscode.Disposable[] = [];
+  private readonly docs = new Map<string, DocState>(); // keyed by docPath
+  private readonly pendingType = vscode.window.createTextEditorDecorationType(PENDING_DECO);
+  private readonly statusItem = vscode.window.createStatusBarItem(vscode.StatusBarAlignment.Right, 89);
+
+  constructor(
+    private readonly store: CoauthorStore,
+    private readonly attribution: AttributionController,
+    private readonly rootDir: string,
+  ) {
+    // No commentingRangeProvider: humans never open proposal threads by hand —
+    // proposals are born of machine turns only (INV-12 keeps decisions human).
+    this.controller = vscode.comments.createCommentController("cowriting.proposals", "Claude Proposals");
+    this.disposables.push(this.controller, this.pendingType, this.statusItem);
+    this.disposables.push(
+      vscode.commands.registerCommand("cowriting.acceptProposal", (t: vscode.CommentThread) => this.acceptThread(t)),
+      vscode.commands.registerCommand("cowriting.rejectProposal", (t: vscode.CommentThread) => this.rejectThread(t)),
+      vscode.workspace.onDidChangeTextDocument((e) => this.onDidChange(e)),
+    );
+  }
+
+  private isTracked(document: vscode.TextDocument): boolean {
+    return document.uri.scheme === "file" && document.uri.fsPath.startsWith(this.rootDir);
+  }
+  private docPathOf(uri: vscode.Uri): string {
+    return vscode.workspace.asRelativePath(uri, false);
+  }
+  private ensureState(document: vscode.TextDocument): DocState {
+    const docPath = this.docPathOf(document.uri);
+    let state = this.docs.get(docPath);
+    if (!state) {
+      state = {
+        docPath,
+        uri: document.uri,
+        artifact: this.store.load(docPath) ?? emptyArtifact(docPath),
+        vsThreads: new Map(),
+        live: new Map(),
+        unresolved: new Set(),
+      };
+      this.docs.set(docPath, state);
+    }
+    return state;
+  }
+
+  // ---- PUC-1: the propose ingress (INV-10) -----------------------------------------
+
+  /**
+   * Record + render a pending proposal. The fingerprint is built by the CALLER
+   * at gesture time (editSelection captures it BEFORE the turn, so mid-turn
+   * edits can't skew the anchor). Never touches the document.
+   */
+  async propose(
+    document: vscode.TextDocument,
+    fp: Fingerprint,
+    replacement: string,
+    author: Provenance,
+    opts?: { turnId?: string; instruction?: string },
+  ): Promise<string | undefined> {
+    if (!this.isTracked(document)) return undefined;
+    const docPath = this.docPathOf(document.uri);
+    let proposalId: string | undefined;
+    this.store.update(docPath, (a) => {
+      proposalId = addProposal(a, fp, replacement, author, opts).proposalId;
+    });
+    this.renderAll(document);
+    return proposalId;
+  }
+
+  // ---- PUC-2/PUC-3: accept / reject (INV-11/INV-12) ----------------------------------
+
+  /** Accept by proposal id (test-facing twin of the thread-menu gesture). */
+  async acceptById(docPath: string, proposalId: string): Promise<boolean> {
+    const hit = this.byId(docPath, proposalId);
+    return hit ? this.accept(hit.state, hit.proposal) : false;
+  }
+  /** Reject by proposal id (test-facing twin of the thread-menu gesture). */
+  rejectById(docPath: string, proposalId: string): boolean {
+    const hit = this.byId(docPath, proposalId);
+    if (!hit) return false;
+    this.reject(hit.state, hit.proposal);
+    return true;
+  }
+
+  private async acceptThread(vsThread: vscode.CommentThread): Promise<void> {
+    const hit = this.byThread(vsThread);
+    if (hit) await this.accept(hit.state, hit.proposal);
+  }
+  private rejectThread(vsThread: vscode.CommentThread): void {
+    const hit = this.byThread(vsThread);
+    if (hit) this.reject(hit.state, hit.proposal);
+  }
+
+  private async accept(state: DocState, proposal: Proposal): Promise<boolean> {
+    const document = this.openDoc(state);
+    if (!document) return false;
+    // INV-11: the fingerprint-guard — exact re-resolve at decision time.
+    const fp = state.artifact.anchors[proposal.anchorId]?.fingerprint;
+    const resolved = fp ? resolve(document.getText(), fp) : "orphaned";
+    if (resolved === "orphaned") {
+      void vscode.window.showWarningMessage(
+        "Cowriting: this proposal's target text changed or is missing — undo to restore it, or reject to discard (it is never applied by guess).",
+      );
+      this.renderAll(document);
+      return false;
+    }
+    const range = new vscode.Range(document.positionAt(resolved.start), document.positionAt(resolved.end));
+    // No awaits between resolve and the seam call: document.version is current.
+    const ok = await this.attribution.applyAgentEdit(document, range, proposal.replacement, proposal.author, {
+      expectedVersion: document.version,
+      turnId: proposal.turnId,
+    });
+    if (!ok) {
+      void vscode.window.showWarningMessage(
+        "Cowriting: the editor rejected the accept — the proposal is still pending.",
+      );
+      return false;
+    }
+    this.store.update(state.docPath, (a) => removeProposal(a, proposal.id));
+    this.renderAll(document);
+    return true;
+  }
+
+  private reject(state: DocState, proposal: Proposal): void {
+    this.store.update(state.docPath, (a) => removeProposal(a, proposal.id));
+    const document = this.openDoc(state);
+    if (document) this.renderAll(document);
+  }
+
+  // ---- PUC-4: load / external change / resolve-or-flag --------------------------------
+
+  /** Load + (re)render every pending proposal at its resolved anchor (or flagged). */
+  renderAll(document: vscode.TextDocument): void {
+    if (!this.isTracked(document)) return;
+    const docPath = this.docPathOf(document.uri);
+    const state = this.ensureState(document);
+    state.artifact = this.store.load(docPath) ?? emptyArtifact(docPath);
+    for (const vsThread of state.vsThreads.values()) vsThread.dispose();
+    state.vsThreads.clear();
+    state.live.clear();
+    state.unresolved.clear();
+    const text = document.getText();
+    for (const proposal of state.artifact.proposals) {
+      const fp = state.artifact.anchors[proposal.anchorId]?.fingerprint;
+      const resolved = fp ? resolve(text, fp) : "orphaned";
+      if (resolved === "orphaned") {
+        const line = fp ? Math.min(fp.lineHint, Math.max(0, document.lineCount - 1)) : 0;
+        const off = document.offsetAt(new vscode.Position(line, 0));
+        this.renderProposal(document, state, proposal, { start: off, end: off }, false);
+      } else {
+        this.renderProposal(document, state, proposal, resolved, true);
+      }
+    }
+    this.renderDecorations(document, state);
+    this.renderStatus(state);
+  }
+
+  /** Shared-watcher entry point (extension.ts): a sidecar changed externally. */
+  handleExternalSidecarChange(uri: vscode.Uri): void {
+    for (const state of this.docs.values()) {
+      if (this.store.sidecarPath(state.docPath) === uri.fsPath) {
+        const doc = vscode.workspace.textDocuments.find((d) => this.docPathOf(d.uri) === state.docPath);
+        if (doc) this.renderAll(doc);
+      }
+    }
+  }
+
+  private onDidChange(e: vscode.TextDocumentChangeEvent): void {
+    const state = this.docs.get(this.docPathOf(e.document.uri));
+    if (!state || state.live.size === 0) return;
+    for (const change of e.contentChanges) {
+      const edit = { start: change.rangeOffset, end: change.rangeOffset + change.rangeLength, newLength: change.text.length };
+      for (const [id, range] of state.live) {
+        const next = shift(range, edit);
+        state.live.set(id, next);
+        const vsThread = state.vsThreads.get(id);
+        if (vsThread && !state.unresolved.has(id)) {
+          vsThread.range = new vscode.Range(e.document.positionAt(next.start), e.document.positionAt(next.end));
+        }
+      }
+    }
+    // Live shift keeps the UI following; staleness is judged at decision time
+    // (accept re-resolves, INV-11) and at the next renderAll.
+    this.renderDecorations(e.document, state);
+  }
+
+  // ---- rendering -----------------------------------------------------------------------
+
+  private renderProposal(
+    document: vscode.TextDocument,
+    state: DocState,
+    proposal: Proposal,
+    offsets: OffsetRange,
+    pending: boolean,
+  ): void {
+    const fp = state.artifact.anchors[proposal.anchorId]?.fingerprint;
+    const range = new vscode.Range(document.positionAt(offsets.start), document.positionAt(offsets.end));
+    const vsThread = this.controller.createCommentThread(document.uri, range, [
+      {
+        body: new vscode.MarkdownString(proposalBody(fp?.text ?? "", proposal)),
+        mode: vscode.CommentMode.Preview,
+        author: { name: proposal.author.id },
+      },
+    ]);
+    vsThread.label = pending
+      ? "Pending proposal"
+      : "⚠ Stale proposal (target text changed or missing) — accept disabled";
+    vsThread.contextValue = pending ? "pending" : "unresolved";
+    vsThread.collapsibleState = pending
+      ? vscode.CommentThreadCollapsibleState.Expanded
+      : vscode.CommentThreadCollapsibleState.Collapsed;
+    state.vsThreads.set(proposal.id, vsThread);
+    state.live.set(proposal.id, offsets);
+    if (!pending) state.unresolved.add(proposal.id);
+  }
+
+  private renderDecorations(document: vscode.TextDocument, state: DocState): void {
+    const ranges: vscode.Range[] = [];
+    for (const [id, off] of state.live) {
+      if (state.unresolved.has(id)) continue;
+      ranges.push(new vscode.Range(document.positionAt(off.start), document.positionAt(off.end)));
+    }
+    for (const editor of vscode.window.visibleTextEditors) {
+      if (editor.document === document) editor.setDecorations(this.pendingType, ranges);
+    }
+  }
+
+  private renderStatus(state: DocState): void {
+    const n = state.unresolved.size;
+    if (n === 0) {
+      this.statusItem.hide();
+      return;
+    }
+    this.statusItem.text = `$(warning) ${n} stale proposal${n === 1 ? "" : "s"}`;
+    this.statusItem.tooltip =
+      "Cowriting: proposals whose target text changed or is missing — undo to restore, or reject";
+    this.statusItem.show();
+  }
+
+  // ---- lookups ----------------------------------------------------------------------------
+
+  private openDoc(state: DocState): vscode.TextDocument | undefined {
+    return vscode.workspace.textDocuments.find((d) => this.docPathOf(d.uri) === state.docPath);
+  }
+  private byThread(vsThread: vscode.CommentThread): { state: DocState; proposal: Proposal } | undefined {
+    for (const state of this.docs.values()) {
+      for (const [id, t] of state.vsThreads) {
+        if (t === vsThread) {
+          const proposal = state.artifact.proposals.find((p) => p.id === id);
+          if (proposal) return { state, proposal };
+        }
+      }
+    }
+    return undefined;
+  }
+  private byId(docPath: string, proposalId: string): { state: DocState; proposal: Proposal } | undefined {
+    const state = this.docs.get(docPath);
+    const proposal = state?.artifact.proposals.find((p) => p.id === proposalId);
+    return state && proposal ? { state, proposal } : undefined;
+  }
+
+  // ---- test-facing surface ------------------------------------------------------------------
+
+  getRendered(docPath: string): RenderedProposal[] {
+    const state = this.docs.get(docPath);
+    if (!state) return [];
+    const out: RenderedProposal[] = [];
+    for (const [id] of state.vsThreads) {
+      const p = state.artifact.proposals.find((x) => x.id === id)!;
+      const off = state.live.get(id)!;
+      out.push({
+        id,
+        pending: !state.unresolved.has(id),
+        turnId: p.turnId,
+        range: { start: off.start, end: off.end },
+      });
+    }
+    return out;
+  }
+  getStaleCount(docPath: string): number {
+    return this.docs.get(docPath)?.unresolved.size ?? 0;
+  }
+
+  dispose(): void {
+    for (const d of this.disposables) d.dispose();
+  }
+}

src/proposalModel.ts

@@ -0,0 +1,47 @@
+/**
+ * proposalModel — pure helpers over the F4 `proposals[]` section (spec §6.3,
+ * INV-13: pending-only). Mirrors threadModel.ts: vscode-free mutations against
+ * an Artifact, used inside CoauthorStore.update() by ProposalController.
+ * The diff body is PRESENTATION ONLY — the truth is fingerprint.text →
+ * replacement (INV-11); a whole-range -/+ rendering, not an LCS diff (§6.7).
+ */
+import { newId, type Artifact, type Fingerprint, type Proposal, type Provenance } from "./model";
+
+export function addProposal(
+  artifact: Artifact,
+  fp: Fingerprint,
+  replacement: string,
+  author: Provenance,
+  opts?: { turnId?: string; instruction?: string },
+): { proposalId: string; anchorId: string } {
+  const anchorId = newId("a");
+  const proposalId = newId("pr");
+  artifact.anchors[anchorId] = { fingerprint: fp };
+  artifact.proposals.push({
+    id: proposalId,
+    anchorId,
+    replacement,
+    author,
+    createdAt: new Date().toISOString(),
+    ...(opts?.turnId !== undefined ? { turnId: opts.turnId } : {}),
+    ...(opts?.instruction !== undefined ? { instruction: opts.instruction } : {}),
+  });
+  return { proposalId, anchorId };
+}
+
+/** Remove a pending proposal (accept and reject both end here — INV-13). */
+export function removeProposal(artifact: Artifact, proposalId: string): boolean {
+  const before = artifact.proposals.length;
+  artifact.proposals = artifact.proposals.filter((p) => p.id !== proposalId);
+  return artifact.proposals.length < before;
+}
+
+/** Markdown comment body: instruction header + fenced whole-range diff. */
+export function proposalBody(targetText: string, p: Proposal): string {
+  const header = p.instruction ? `**Claude proposes** — _${p.instruction}_` : "**Claude proposes**";
+  const diffLines = [
+    ...targetText.split("\n").map((l) => `- ${l}`),
+    ...p.replacement.split("\n").map((l) => `+ ${l}`),
+  ].join("\n");
+  return `${header}\n\n\`\`\`diff\n${diffLines}\n\`\`\`\n\n✓ Accept applies this replacement · ✗ Reject discards it`;
+}

src/store.ts

@@ -61,8 +61,8 @@ export class CoauthorStore {
    * Read-modify-write for sidecar co-ownership (spec F3 §6.2): each controller
    * mutates only its own section against a FRESH load, so ThreadController and
    * AttributionController never clobber each other. After the mutation, anchors
-   * referenced by neither threads nor attributions are pruned (proposals are
+   * referenced by no thread, attribution, OR proposal are pruned (threads,
-   * still empty in F3 — revisit in F4). `mutate` MUST be synchronous: the
+   * attributions, and proposals all keep their anchors — F4). `mutate` MUST be synchronous: the
    * read-modify-write (and the self-write mark) completes within this call.
    */
   update(docPath: string, mutate: (artifact: Artifact) => void): Artifact {
@@ -71,6 +71,7 @@ export class CoauthorStore {
     const referenced = new Set<string>([
       ...artifact.threads.map((t) => t.anchorId),
       ...artifact.attributions.map((a) => a.anchorId),
+      ...artifact.proposals.map((p) => p.anchorId),
     ]);
     for (const id of Object.keys(artifact.anchors)) {
       if (!referenced.has(id)) delete artifact.anchors[id];

test/e2e/fixtures/workspace/docs/proposal.md

@@ -0,0 +1,9 @@
+# Proposal fixture
+
+A stable opening paragraph.
+
+The propose target sentence lives here.
+
+A second target for coexistence checks.
+
+A stable closing paragraph.

test/e2e/suite-no-workspace/noWorkspace.test.ts

@@ -25,6 +25,9 @@ suite("no-workspace activation (#8)", () => {
       "cowriting.editSelection",
       "cowriting.toggleAttribution",
       "cowriting.applyAgentEdit",
+      "cowriting.acceptProposal",
+      "cowriting.rejectProposal",
+      "cowriting.proposeAgentEdit",
     ]) {
       assert.ok(all.includes(command), `${command} is registered`);
     }

test/e2e/suite/proposals.test.ts

@@ -0,0 +1,163 @@
+import * as assert from "assert";
+import * as fs from "fs";
+import * as path from "path";
+import * as vscode from "vscode";
+import type { CowritingApi } from "../../../src/extension";
+import type { Artifact } from "../../../src/model";
+
+const WS = process.env.E2E_WORKSPACE!;
+const DOC_REL = "docs/proposal.md";
+
+function sidecarPath(): string {
+  return path.join(WS, ".threads", "docs", "proposal.md.json");
+}
+function readSidecar(): Artifact {
+  return JSON.parse(fs.readFileSync(sidecarPath(), "utf8")) as Artifact;
+}
+async function openDoc(): Promise<vscode.TextDocument> {
+  const uri = vscode.Uri.file(path.join(WS, DOC_REL));
+  const doc = await vscode.workspace.openTextDocument(uri);
+  await vscode.window.showTextDocument(doc);
+  return doc;
+}
+async function getApi(): Promise<CowritingApi> {
+  const ext = vscode.extensions.getExtension("benstull.vscode-cowriting-plugin")!;
+  const api = (await ext.activate()) as CowritingApi;
+  assert.ok(api?.proposalController, "extension exports proposalController");
+  return api;
+}
+async function proposeViaCommand(
+  doc: vscode.TextDocument,
+  target: string,
+  newText: string,
+  turnId: string,
+): Promise<string> {
+  const start = doc.getText().indexOf(target);
+  assert.ok(start >= 0, `fixture contains "${target}"`);
+  const id = await vscode.commands.executeCommand<string>("cowriting.proposeAgentEdit", {
+    uri: doc.uri.toString(),
+    start,
+    end: start + target.length,
+    newText,
+    model: "sonnet",
+    sessionId: "e2e-prop",
+    turnId,
+    instruction: "e2e instruction",
+  });
+  assert.ok(id, "propose returns the proposal id");
+  return id!;
+}
+async function externalWriteAndReload(uri: vscode.Uri, content: string): Promise<vscode.TextDocument> {
+  fs.writeFileSync(uri.fsPath, content, "utf8");
+  const doc = await vscode.workspace.openTextDocument(uri);
+  await vscode.window.showTextDocument(doc);
+  await vscode.commands.executeCommand("workbench.action.files.revert");
+  return doc;
+}
+const settle = () => new Promise((r) => setTimeout(r, 300));
+
+// Tests are ORDER-DEPENDENT (F2/F3 pattern): later tests consume earlier state.
+// This suite OWNS docs/proposal.md; threads owns docs/sample.md, attribution
+// owns docs/attrib.md — fixtures stay disjoint.
+suite("F4 propose/accept (host E2E — programmatic ingress, no LLM)", () => {
+  const TARGET = "The propose target sentence lives here.";
+  const REPLACEMENT = "PROPOSED-BY-CLAUDE replacement sentence.";
+
+  test("propose records + renders a pending proposal and does NOT touch the document (INV-10)", async () => {
+    const doc = await openDoc();
+    const api = await getApi();
+    const before = doc.getText();
+    await proposeViaCommand(doc, TARGET, REPLACEMENT, "turn-p1");
+    await settle();
+    assert.strictEqual(doc.getText(), before, "document text unchanged (INV-10)");
+    const rendered = api.proposalController.getRendered(DOC_REL);
+    assert.strictEqual(rendered.length, 1);
+    assert.strictEqual(rendered[0].pending, true);
+    assert.strictEqual(rendered[0].turnId, "turn-p1");
+    const art = readSidecar();
+    assert.strictEqual(art.proposals.length, 1, "proposal persisted at propose time");
+    assert.strictEqual(art.anchors[art.proposals[0].anchorId].fingerprint.text, TARGET);
+  });
+
+  test("accept applies via the seam: text replaced, Claude-attributed, proposal removed (INV-9/11/13)", async () => {
+    const doc = await openDoc();
+    const api = await getApi();
+    const id = api.proposalController.getRendered(DOC_REL)[0].id;
+    const ok = await api.proposalController.acceptById(DOC_REL, id);
+    assert.strictEqual(ok, true, "accept applies");
+    await settle();
+    assert.ok(doc.getText().includes(REPLACEMENT), "replacement landed");
+    assert.ok(!doc.getText().includes(TARGET), "target gone");
+    const spans = api.attributionController.getSpans(DOC_REL);
+    const agent = spans.find((s) => s.turnId === "turn-p1");
+    assert.ok(agent, `accepted text is Claude-attributed with the proposal's turnId — got spans: ${JSON.stringify(spans)}`);
+    assert.strictEqual(agent!.authorKind, "agent");
+    assert.strictEqual(api.proposalController.getRendered(DOC_REL).length, 0, "proposal gone (INV-13)");
+    assert.strictEqual(readSidecar().proposals.length, 0, "removed from the sidecar");
+  });
+
+  test("reject leaves the document untouched and removes the proposal (PUC-3)", async () => {
+    const doc = await openDoc();
+    const api = await getApi();
+    const before = doc.getText();
+    const id = await proposeViaCommand(doc, "A second target for coexistence checks.", "WOULD-BE replacement.", "turn-p2");
+    await settle();
+    assert.strictEqual(api.proposalController.rejectById(DOC_REL, id), true);
+    await settle();
+    assert.strictEqual(doc.getText(), before, "document untouched");
+    assert.strictEqual(api.proposalController.getRendered(DOC_REL).length, 0);
+    assert.strictEqual(readSidecar().proposals.length, 0);
+  });
+
+  test("a pending proposal persists, survives reload, and re-anchors after an external move (PUC-4)", async () => {
+    let doc = await openDoc();
+    const api = await getApi();
+    const anchor = "A stable closing paragraph.";
+    await proposeViaCommand(doc, anchor, "A PROPOSED closing paragraph.", "turn-p3");
+    await settle();
+    const uri = vscode.Uri.file(path.join(WS, DOC_REL));
+    doc = await externalWriteAndReload(uri, "PREPENDED LINE\n\n" + doc.getText());
+    await settle();
+    api.proposalController.renderAll(doc);
+    const rendered = api.proposalController.getRendered(DOC_REL);
+    assert.strictEqual(rendered.length, 1, "proposal survived reload");
+    assert.strictEqual(rendered[0].pending, true, "still decidable");
+    const moved = doc.getText().indexOf(anchor);
+    assert.strictEqual(rendered[0].range.start, moved, "re-anchored after the move");
+  });
+
+  test("editing the target text makes the proposal stale: flagged, accept refused, doc untouched (INV-11)", async () => {
+    let doc = await openDoc();
+    const api = await getApi();
+    const id = api.proposalController.getRendered(DOC_REL)[0].id;
+    const mangled = doc.getText().replace("A stable closing paragraph.", "A reworded closing paragraph.");
+    doc = await externalWriteAndReload(vscode.Uri.file(path.join(WS, DOC_REL)), mangled);
+    await settle();
+    api.proposalController.renderAll(doc);
+    assert.strictEqual(api.proposalController.getStaleCount(DOC_REL), 1, "flagged stale");
+    const before = doc.getText();
+    const ok = await api.proposalController.acceptById(DOC_REL, id);
+    assert.strictEqual(ok, false, "accept refused (INV-11)");
+    assert.strictEqual(doc.getText(), before, "document untouched");
+    assert.strictEqual(readSidecar().proposals.length, 1, "proposal still pending (recoverable)");
+    // discard the husk so later tests see a clean sidecar
+    assert.strictEqual(api.proposalController.rejectById(DOC_REL, id), true);
+  });
+
+  test("multiple pending proposals coexist and are decidable out of order (PUC-5)", async () => {
+    const doc = await openDoc();
+    const api = await getApi();
+    const id1 = await proposeViaCommand(doc, "A stable opening paragraph.", "An ACCEPTED opening paragraph.", "turn-p4");
+    const id2 = await proposeViaCommand(doc, "PROPOSED-BY-CLAUDE replacement sentence.", "A REPLACED-AGAIN sentence.", "turn-p5");
+    await settle();
+    assert.strictEqual(api.proposalController.getRendered(DOC_REL).length, 2);
+    // decide the SECOND first, then the first — order independence
+    assert.strictEqual(await api.proposalController.acceptById(DOC_REL, id2), true);
+    await settle();
+    assert.strictEqual(await api.proposalController.acceptById(DOC_REL, id1), true);
+    await settle();
+    assert.ok(doc.getText().includes("An ACCEPTED opening paragraph."));
+    assert.ok(doc.getText().includes("A REPLACED-AGAIN sentence."));
+    assert.strictEqual(api.proposalController.getRendered(DOC_REL).length, 0);
+  });
+});

test/pendingEdits.test.ts

@@ -8,26 +8,53 @@ const AGENT: Provenance = {
 };
 
 describe("PendingEditRegistry (INV-9)", () => {
-  it("matches and consumes an exact registration", () => {
+  it("matches and consumes a single-hunk event equal to the registration", () => {
     const reg = new PendingEditRegistry();
-    reg.register({ docPath: "d.md", start: 3, end: 7, newText: "new", provenance: AGENT, turnId: "t1" });
+    reg.register({
-    const hit = reg.match("d.md", { start: 3, end: 7, text: "new" });
+      docPath: "d.md", start: 3, end: 7, newText: "new", provenance: AGENT, turnId: "t1",
-    expect(hit?.turnId).toBe("t1");
+      full: { start: 3, end: 7, newLength: 3 },
-    expect(reg.match("d.md", { start: 3, end: 7, text: "new" })).toBeNull();
     });
-  it("does not match a different doc, range, or text (human typing stays human)", () => {
+    const hit = reg.matchEvent("d.md", [{ start: 3, end: 7, newLength: 3 }]);
+    expect(hit?.turnId).toBe("t1");
+    expect(reg.matchEvent("d.md", [{ start: 3, end: 7, newLength: 3 }])).toBeNull();
+  });
+  it("matches a HOST-SPLIT event: several hunks inside the full range with the same net delta", () => {
+    // The host word-diffs one applied replace into multiple minimal hunks
+    // (observed on F4 accept) — per-hunk equality misses; net-effect matches.
+    const reg = new PendingEditRegistry();
+    reg.register({
+      docPath: "d.md", start: 10, end: 50, newText: "x".repeat(45), provenance: AGENT, turnId: "t2",
+      full: { start: 10, end: 50, newLength: 45 },
+    });
+    const hit = reg.matchEvent("d.md", [
+      { start: 12, end: 20, newLength: 9 },
+      { start: 25, end: 30, newLength: 6 },
+      { start: 40, end: 48, newLength: 11 },
+    ]);
+    expect(hit?.turnId).toBe("t2");
+  });
+  it("does not match a different doc, hunks outside the full range, or a different delta", () => {
+    const reg = new PendingEditRegistry();
+    reg.register({
+      docPath: "d.md", start: 3, end: 7, newText: "new", provenance: AGENT,
+      full: { start: 3, end: 7, newLength: 3 },
+    });
+    expect(reg.matchEvent("other.md", [{ start: 3, end: 7, newLength: 3 }])).toBeNull();
+    expect(reg.matchEvent("d.md", [{ start: 3, end: 8, newLength: 4 }])).toBeNull();
+    expect(reg.matchEvent("d.md", [{ start: 3, end: 7, newLength: 4 }])).toBeNull();
+    expect(reg.matchEvent("d.md", [])).toBeNull();
+  });
+  it("falls back to the minimized range when no full extent was registered", () => {
     const reg = new PendingEditRegistry();
     reg.register({ docPath: "d.md", start: 3, end: 7, newText: "new", provenance: AGENT });
-    expect(reg.match("other.md", { start: 3, end: 7, text: "new" })).toBeNull();
+    expect(reg.matchEvent("d.md", [{ start: 3, end: 7, newLength: 3 }])).not.toBeNull();
-    expect(reg.match("d.md", { start: 3, end: 8, text: "new" })).toBeNull();
-    expect(reg.match("d.md", { start: 3, end: 7, text: "neww" })).toBeNull();
   });
   it("unregister removes a failed application", () => {
     const reg = new PendingEditRegistry();
     const p = { docPath: "d.md", start: 0, end: 0, newText: "x", provenance: AGENT };
     reg.register(p);
     reg.unregister(p);
-    expect(reg.match("d.md", { start: 0, end: 0, text: "x" })).toBeNull();
+    expect(reg.matchEvent("d.md", [{ start: 0, end: 0, newLength: 1 }])).toBeNull();
   });
   it("unregister reports whether the registration was still pending", () => {
     const reg = new PendingEditRegistry();
@@ -35,7 +62,7 @@ describe("PendingEditRegistry (INV-9)", () => {
     reg.register(p);
     expect(reg.unregister(p)).toBe(true);
     reg.register(p);
-    reg.match("d.md", { start: 0, end: 0, text: "x" });
+    reg.matchEvent("d.md", [{ start: 0, end: 0, newLength: 1 }]);
     expect(reg.unregister(p)).toBe(false);
   });
 });

test/proposalModel.test.ts

@@ -0,0 +1,107 @@
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { describe, expect, it } from "vitest";
+import {
+  emptyArtifact,
+  serializeArtifact,
+  type Artifact,
+  type Proposal,
+} from "../src/model";
+import { CoauthorStore } from "../src/store";
+import { addProposal, proposalBody, removeProposal } from "../src/proposalModel";
+
+const agent = {
+  kind: "agent" as const,
+  id: "claude",
+  agent: { sdk: "@cline/sdk", model: "sonnet", sessionId: "s1" },
+};
+
+describe("Proposal model (spec §6.3, INV-13)", () => {
+  it("serializes proposals with stable field order and survives a round-trip", () => {
+    const a = emptyArtifact("docs/x.md");
+    a.anchors["a_1"] = {
+      fingerprint: { text: "old text", before: "", after: "", lineHint: 0 },
+    };
+    const p: Proposal = {
+      id: "pr_1",
+      anchorId: "a_1",
+      replacement: "new text",
+      author: agent,
+      createdAt: "2026-06-10T00:00:00.000Z",
+      turnId: "turn-1",
+      instruction: "tighten",
+    };
+    a.proposals.push(p);
+    const reloaded = JSON.parse(serializeArtifact(a)) as Artifact;
+    expect(reloaded.proposals).toHaveLength(1);
+    expect(reloaded.proposals[0]).toEqual(p);
+    // optional fields are OMITTED (not null) when absent
+    const bare: Proposal = {
+      id: "pr_2", anchorId: "a_1", replacement: "r", author: agent,
+      createdAt: "2026-06-10T00:00:00.000Z",
+    };
+    a.proposals.push(bare);
+    const again = JSON.parse(serializeArtifact(a)) as Artifact;
+    expect("turnId" in again.proposals[1]).toBe(false);
+    expect("instruction" in again.proposals[1]).toBe(false);
+    // serialization is byte-stable (INV-2)
+    expect(serializeArtifact(again)).toBe(serializeArtifact(a));
+  });
+});
+
+describe("CoauthorStore prune with proposals (spec §6.3)", () => {
+  it("retains anchors referenced only by proposals; prunes them after removal", () => {
+    const dir = mkdtempSync(join(tmpdir(), "cowriting-prune-"));
+    try {
+      const store = new CoauthorStore(dir);
+      store.update("docs/x.md", (a) => {
+        a.anchors["a_p"] = {
+          fingerprint: { text: "t", before: "", after: "", lineHint: 0 },
+        };
+        a.proposals.push({
+          id: "pr_1", anchorId: "a_p", replacement: "r", author: agent,
+          createdAt: "2026-06-10T00:00:00.000Z",
+        });
+      });
+      expect(store.load("docs/x.md")!.anchors["a_p"]).toBeDefined();
+      store.update("docs/x.md", (a) => {
+        a.proposals = a.proposals.filter((p) => p.id !== "pr_1");
+      });
+      expect(store.load("docs/x.md")!.anchors["a_p"]).toBeUndefined();
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  });
+});
+
+describe("proposalModel helpers (spec §6.4)", () => {
+  const fp = { text: "old line one\nold line two", before: "", after: "", lineHint: 3 };
+
+  it("addProposal creates the anchor + pending record; removeProposal deletes by id", () => {
+    const a = emptyArtifact("docs/x.md");
+    const { proposalId, anchorId } = addProposal(a, fp, "new line", agent, {
+      turnId: "turn-9", instruction: "shorten",
+    });
+    expect(a.anchors[anchorId].fingerprint).toEqual(fp);
+    expect(a.proposals).toHaveLength(1);
+    expect(a.proposals[0].id).toBe(proposalId);
+    expect(a.proposals[0].replacement).toBe("new line");
+    expect(a.proposals[0].turnId).toBe("turn-9");
+    expect(a.proposals[0].instruction).toBe("shorten");
+    expect(removeProposal(a, proposalId)).toBe(true);
+    expect(a.proposals).toHaveLength(0);
+    expect(removeProposal(a, proposalId)).toBe(false);
+  });
+
+  it("proposalBody renders instruction + a fenced unified diff of old → new", () => {
+    const a = emptyArtifact("docs/x.md");
+    addProposal(a, fp, "new only line", agent, { instruction: "merge the lines" });
+    const body = proposalBody(fp.text, a.proposals[0]);
+    expect(body).toContain("**Claude proposes** — _merge the lines_");
+    expect(body).toContain("```diff");
+    expect(body).toContain("- old line one");
+    expect(body).toContain("- old line two");
+    expect(body).toContain("+ new only line");
+  });
+});