F4 SLICE-4: editSelection is propose-by-default — the turn ends in a proposal, the seam fires on accept (#12)

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

src/extension.ts

@@ -138,8 +138,9 @@ export function activate(context: vscode.ExtensionContext): CowritingApi | undef
     ),
   );
 
-  // F3 SLICE-5: the live turn (PUC-2) — selection + instruction → one
+  // F3 SLICE-5 → F4 SLICE-4: the live turn — selection + instruction → one
-  // claude-code SDK turn (liveTurn.ts, INV-8) → the applyAgentEdit seam (INV-9).
+  // 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;
@@ -163,8 +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(
@@ -174,24 +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).",
               );
             }
           },