diff --git a/src/proposalController.ts b/src/proposalController.ts
index 139c096..6ae714b 100644
--- a/src/proposalController.ts
+++ b/src/proposalController.ts
@@ -22,6 +22,8 @@ export interface RenderedProposal {
   id: string;
   /** true → resolves exactly, decidable; false → stale/orphaned (INV-11). */
   pending: boolean;
+  /** always false — proposals are decide-only, no reply input (INV-12). */
+  canReply: boolean;
   turnId?: string;
   range: { start: number; end: number };
 }
@@ -252,6 +254,11 @@ export class ProposalController implements vscode.Disposable {
         author: { name: proposal.author.id },
       },
     ]);
+    // Proposals are decide-only (INV-12): ✓ accept / ✗ reject in the title
+    // bar. Without this, VS Code renders its default "Reply…" input with no
+    // submit command wired — a dead end. Discussion belongs in a regular
+    // coauthoring thread; proposal discussion trails are deferred (spec §1.7).
+    vsThread.canReply = false;
     vsThread.label = pending
       ? "Pending proposal"
       : "⚠ Stale proposal (target text changed or missing) — accept disabled";
@@ -315,12 +322,13 @@ export class ProposalController implements vscode.Disposable {
     const state = this.docs.get(docPath);
     if (!state) return [];
     const out: RenderedProposal[] = [];
-    for (const [id] of state.vsThreads) {
+    for (const [id, vsThread] 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),
+        canReply: vsThread.canReply !== false,
         turnId: p.turnId,
         range: { start: off.start, end: off.end },
       });
diff --git a/test/e2e/suite/proposals.test.ts b/test/e2e/suite/proposals.test.ts
index 0ba7c9c..19d4e61 100644
--- a/test/e2e/suite/proposals.test.ts
+++ b/test/e2e/suite/proposals.test.ts
@@ -74,6 +74,7 @@ suite("F4 propose/accept (host E2E — programmatic ingress, no LLM)", () => {
     assert.strictEqual(rendered.length, 1);
     assert.strictEqual(rendered[0].pending, true);
     assert.strictEqual(rendered[0].turnId, "turn-p1");
+    assert.strictEqual(rendered[0].canReply, false, "proposals are decide-only — no dead reply input (INV-12)");
     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);