diff --git a/config/prompts/manager/SYSTEM.md b/config/prompts/manager/SYSTEM.md
index 37760896..f003a583 100644
--- a/config/prompts/manager/SYSTEM.md
+++ b/config/prompts/manager/SYSTEM.md
@@ -38,6 +38,10 @@ build software under a human operator's merge gate.
 - The operator can read your live session but cannot answer in it. To get human
   input you MUST post to a channel. A post is ASYNC and NON-BLOCKING: post your
   question, keep working, the answer arrives later.
+- The operator READS THE CHANNEL, NOT YOUR SESSION LOG. Every answer to the
+  operator, and every status they need to see, MUST be posted to a channel
+  (`comms_post_message`) — a reply left only in your working session is
+  invisible to them.
 - Delivery: a regular message lands at the START of your next turn (read with
   `comms_list_messages`); an @mention that names you reaches you MID-TURN as a
   steer. End turns often anyway — a foreground wait makes you deaf to
diff --git a/packages/compass-agent/src/agent.test.ts b/packages/compass-agent/src/agent.test.ts
index c09e6bad..cc817dc6 100644
--- a/packages/compass-agent/src/agent.test.ts
+++ b/packages/compass-agent/src/agent.test.ts
@@ -1803,6 +1803,27 @@ describe("formatDeliversForPrompt — coalescing format (SEA-1310 §8)", () => {
 		expect(out.match(/^Topic /gm)).toHaveLength(1);
 		expect(out.indexOf("one")).toBeLessThan(out.indexOf("two"));
 	});
+
+	// RIG-2664: the coalesced prompt carries ONE reply-in-channel cue for the
+	// whole batch, naming the topic + comms_post, so the model posts its answer
+	// back to the channel instead of only narrating it into its session.
+	test("appends a single reply-in-channel cue naming the topic and comms_post", () => {
+		const batch = [
+			deliverMsg("m1", "alpha msg", "t-alpha"),
+			deliverMsg("m2", "beta msg", "t-beta"),
+		];
+		const out = formatDeliversForPrompt(batch);
+
+		expect(out).toContain("comms_post");
+		expect(out).toContain("t-alpha");
+		expect(out).toContain("t-beta");
+		// One cue for the whole batch, not one per message/topic.
+		expect(out.match(/comms_post/g)).toHaveLength(1);
+		// The cue trails the topic sections.
+		expect(out.indexOf("Topic t-beta:")).toBeLessThan(
+			out.indexOf("comms_post"),
+		);
+	});
 });
 
 describe("formatAskAnswerForPrompt — answer render (RIG-1509)", () => {
diff --git a/packages/compass-agent/src/agent.ts b/packages/compass-agent/src/agent.ts
index d3c527bb..86409cd2 100644
--- a/packages/compass-agent/src/agent.ts
+++ b/packages/compass-agent/src/agent.ts
@@ -811,6 +811,16 @@ export class CompassAgent {
 // text stays greppable in its section. A blank text (a message with no text
 // blocks) still contributes its slot so a section is a faithful 1:1 with its
 // group.
+//
+// RIG-2664: the coalesced prompt ends with ONE reply-in-channel cue for the
+// whole batch (not per message — the batch is already grouped by topic). A
+// delivered message arrived from an operator/peer over a channel, and the
+// operator READS THE CHANNEL, NOT THIS SESSION TRANSCRIPT: a reply the model
+// only narrates into its own turn is invisible to whoever asked. The cue names
+// the batch's topics so the model knows it must post back with
+// `comms_post_message` to answer, closing the gap that a bare
+// `Topic <id>:\n<text>` digest left open
+// (unlike Cotal, which cues an in-channel reply on every delivery).
 export function formatDeliversForPrompt(batch: readonly Message[]): string {
 	const groups = new Map<string, string[]>();
 	for (const msg of batch) {
@@ -823,10 +833,15 @@ export function formatDeliversForPrompt(batch: readonly Message[]): string {
 		if (existing) existing.push(text);
 		else groups.set(msg.topicId, [text]);
 	}
-	return Array.from(
+	const sections = Array.from(
 		groups,
 		([topicId, texts]) => `Topic ${topicId}:\n${texts.join("\n\n")}`,
-	).join("\n\n");
+	);
+	const topics = Array.from(groups.keys()).join(", ");
+	sections.push(
+		`This arrived from an operator or peer over a channel — the operator reads the channel, not this session transcript. To answer, you MUST post back with comms_post_message to the relevant topic (${topics}); replying only in this turn is invisible to them.`,
+	);
+	return sections.join("\n\n");
 }
 
 // Render an inbound `AskAnswerControl` against the questions the model asked