diff --git a/src/attributionController.ts b/src/attributionController.ts
index a9f4947..c3e7066 100644
--- a/src/attributionController.ts
+++ b/src/attributionController.ts
@@ -249,7 +249,7 @@ export class AttributionController implements vscode.Disposable {
     range: vscode.Range,
     newText: string,
     provenance: Provenance,
-    opts?: { expectedVersion?: number; turnId?: string },
+    opts?: { expectedVersion?: number; turnId?: string; landBaseline?: boolean },
   ): Promise<boolean> {
     if (!this.isTracked(document)) return false;
     if (opts?.expectedVersion !== undefined && document.version !== opts.expectedVersion) return false;
@@ -290,15 +290,25 @@ export class AttributionController implements vscode.Disposable {
         "(host minimized differently?) — the edit may be mis-attributed (INV-9).",
       );
     }
-    if (ok) {
-      // F6 (INV-18): a real machine landing — signal the baseline to advance so
-      // this text never shows as a change in the diff view. Fire regardless of
-      // attribution-match bookkeeping above; the landing happened either way.
+    if (ok && opts?.landBaseline !== false) {
+      // F6 (INV-18): a real machine landing — advance the baseline. F12 (INV-48)
+      // suppresses this for optimistic apply: the proposed text is in the buffer
+      // but the change stays PENDING (baseline at pre-proposal) until accept.
       this.applyEmitter.fire({ document });
     }
     return ok;
   }
 
+  /**
+   * F12/#64 (INV-51): fire the machine-landing signal WITHOUT applying text — used
+   * by finalize-in-place, where the proposed text already landed in the buffer via
+   * optimistic apply (`landBaseline:false`) and accept only needs to advance the
+   * F6 baseline so the now-accepted change stops reading as pending.
+   */
+  signalLanded(document: vscode.TextDocument): void {
+    if (this.isTracked(document)) this.applyEmitter.fire({ document });
+  }
+
   // ---- PUC-4: persistence on save ----------------------------------------------------
 
   private onDidSave(document: vscode.TextDocument): void {
diff --git a/test/e2e/suite/f12InlineDiff.test.ts b/test/e2e/suite/f12InlineDiff.test.ts
new file mode 100644
index 0000000..3a9c749
--- /dev/null
+++ b/test/e2e/suite/f12InlineDiff.test.ts
@@ -0,0 +1,48 @@
+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";
+
+const WS = process.env.E2E_WORKSPACE!;
+const settle = () => new Promise((r) => setTimeout(r, 400));
+
+async function getApi(): Promise<CowritingApi> {
+  const ext = vscode.extensions.getExtension("benstull.vscode-cowriting-plugin")!;
+  const api = (await ext.activate()) as CowritingApi;
+  assert.ok(api?.trackChangesPreviewController && api?.proposalController, "exports controllers");
+  return api;
+}
+
+async function freshDoc(rel: string, body: string): Promise<{ doc: vscode.TextDocument; key: string }> {
+  const abs = path.join(WS, rel);
+  fs.mkdirSync(path.dirname(abs), { recursive: true });
+  fs.writeFileSync(abs, body, "utf8");
+  const uri = vscode.Uri.file(abs);
+  const doc = await vscode.workspace.openTextDocument(uri);
+  await vscode.window.showTextDocument(doc);
+  await settle();
+  return { doc, key: uri.toString() };
+}
+
+suite("F12 inline diff — seam landBaseline (#64, INV-48)", () => {
+  test("applyAgentEdit with landBaseline:false applies text but does NOT advance the baseline", async () => {
+    const { doc, key } = await freshDoc("docs/f12-land.md", "# T\n\nalpha here.\n");
+    const api = await getApi();
+    await vscode.commands.executeCommand("cowriting.showTrackChangesPreview");
+    await settle();
+    const before = api.diffViewController.getBaseline(key)?.text ?? doc.getText();
+    const start = doc.getText().indexOf("alpha");
+    const ok = await api.attributionController.applyAgentEdit(
+      doc,
+      new vscode.Range(doc.positionAt(start), doc.positionAt(start + "alpha".length)),
+      "ALPHA",
+      { kind: "agent", id: "claude", agent: { sdk: "x", model: "m", sessionId: "s" } },
+      { landBaseline: false },
+    );
+    await settle();
+    assert.ok(ok, "edit applied");
+    assert.ok(doc.getText().includes("ALPHA"), "text in buffer");
+    assert.strictEqual(api.diffViewController.getBaseline(key)?.text ?? doc.getText(), before, "baseline unchanged");
+  });
+});