diff --git a/package.json b/package.json
index e94f3a4..be51ccf 100644
--- a/package.json
+++ b/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"
         }
       ]
     }
diff --git a/src/extension.ts b/src/extension.ts
index f99eaf1..58c4d7c 100644
--- a/src/extension.ts
+++ b/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);
@@ -102,6 +113,31 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
     ),
   );
 
+  // The propose ingress as a command (spec §6.4): records a pending proposal,
+  // 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: the live turn (PUC-2) — selection + instruction → one
   // claude-code SDK turn (liveTurn.ts, INV-8) → the applyAgentEdit seam (INV-9).
   context.subscriptions.push(
@@ -172,12 +208,13 @@ 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 {