feat(editor): EditorProposalController — optimistic apply + decorations + CodeLens (#64)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/e2e/suite/f11Toolbar.test.ts

@@ -99,8 +99,9 @@ suite("F11 preview toolbar (host E2E — message → seam wiring, no LLM)", () =
       "The quick RED fox jumps over the lazy CAT.",
       "the block proposal carries the whole rewritten paragraph",
     );
-    // INV-10: proposing never mutates the document.
-    assert.ok(doc.getText().includes("brown fox") && doc.getText().includes("lazy dog"), "document unchanged by propose");
+    // F12 (INV-48): EditorProposalController optimistically applies the proposed text,
+    // so after settle the buffer has the replacement. The proposal is still pending.
+    assert.ok(doc.getText().includes("RED fox") && doc.getText().includes("lazy CAT"), "F12 optimistic-apply: proposed text in buffer");
     void key;
   });
 
@@ -129,7 +130,9 @@ suite("F11 preview toolbar (host E2E — message → seam wiring, no LLM)", () =
     assert.ok(view, "the proposal is live");
     assert.strictEqual(view!.replacement, "The REWRITTEN paragraph from Claude.", "carries the turn replacement");
     assert.strictEqual(view!.replaced, target, "replaces exactly the selected range");
-    assert.ok(doc.getText().includes(target), "document unchanged by propose (INV-10)");
+    // F12 (INV-48): the EditorProposalController optimistically applies, so the buffer
+    // now has the replacement. `view.replaced` still records the original target text.
+    assert.ok(doc.getText().includes("The REWRITTEN paragraph from Claude."), "F12 optimistic-apply: proposed text in buffer");
     void key;
   });