fix(coding-agent): queued retry-drained skill prompts

Kept compaction-queued skill prompts in the agent queue during retry drains instead of allowing them to start a fresh turn after compaction unwinds.

packages/coding-agent/src/modes/skill-command.ts

@@ -26,6 +26,7 @@ interface ParsedSkillCommand {
 
 interface InvokeSkillCommandOptions {
 	propagateErrors?: boolean;
+	queueOnly?: boolean;
 }
 
 /** Built custom-message payload and delivery options for a `/skill:` command. */
@@ -97,7 +98,8 @@ export async function invokeSkillCommandFromText(
 	try {
 		const built = await buildSkillCommandPrompt(ctx, text, streamingBehavior);
 		if (!built) return false;
-		await ctx.session.promptCustomMessage(built.message, built.options);
+		const promptOptions = options?.queueOnly ? { ...built.options, queueOnly: true } : built.options;
+		await ctx.session.promptCustomMessage(built.message, promptOptions);
 		return true;
 	} catch (err) {
 		if (options?.propagateErrors) {

packages/coding-agent/src/modes/utils/ui-helpers.ts

@@ -668,7 +668,12 @@ export class UiHelpers {
 	}
 
 	async #deliverQueuedMessage(message: CompactionQueuedMessage): Promise<void> {
-		if (await invokeSkillCommandFromText(this.ctx, message.text, message.mode, { propagateErrors: true })) {
+		if (
+			await invokeSkillCommandFromText(this.ctx, message.text, message.mode, {
+				propagateErrors: true,
+				queueOnly: true,
+			})
+		) {
 			return;
 		}
 		if (this.ctx.isKnownSlashCommand(message.text)) {

packages/coding-agent/src/session/agent-session.ts

@@ -6526,7 +6526,10 @@ export class AgentSession {
 
 	async promptCustomMessage<T = unknown>(
 		message: Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
-		options?: Pick<PromptOptions, "streamingBehavior" | "toolChoice"> & { queueChipText?: string },
+		options?: Pick<PromptOptions, "streamingBehavior" | "toolChoice"> & {
+			queueChipText?: string;
+			queueOnly?: boolean;
+		},
 	): Promise<void> {
 		const textContent =
 			typeof message.content === "string"
@@ -6546,6 +6549,16 @@ export class AgentSession {
 			keywordNotices = this.#createMagicKeywordNotices(skillArgs);
 		}
 
+		if (options?.queueOnly) {
+			if (!options.streamingBehavior) {
+				throw new AgentBusyError();
+			}
+			for (const notice of keywordNotices) {
+				await this.#queueCustomMessage(notice, options.streamingBehavior);
+			}
+			await this.#queueCustomMessage(message, options.streamingBehavior, options.queueChipText);
+			return;
+		}
 		if (this.isStreaming) {
 			if (!options?.streamingBehavior) {
 				throw new AgentBusyError();
@@ -7111,6 +7124,40 @@ export class AgentSession {
 		}
 	}
 
+	/** Queue a custom message without starting a turn, matching steer/follow-up delivery. */
+	async #queueCustomMessage<T = unknown>(
+		message: Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+		deliverAs: "steer" | "followUp",
+		queueChipText?: string,
+	): Promise<void> {
+		const details =
+			queueChipText !== undefined
+				? ({
+						...((message.details && typeof message.details === "object" ? message.details : {}) as Record<
+							string,
+							unknown
+						>),
+						__queueChipText: queueChipText,
+					} as T)
+				: message.details;
+		const appMessage: CustomMessage<T> = {
+			role: "custom",
+			customType: message.customType,
+			content: message.content,
+			display: message.display,
+			details,
+			attribution: message.attribution ?? "agent",
+			timestamp: Date.now(),
+		};
+		const normalizedAppMessage = await this.#normalizeAgentMessageImages(appMessage);
+		if (deliverAs === "followUp") {
+			this.agent.followUp(normalizedAppMessage);
+		} else {
+			this.agent.steer(normalizedAppMessage);
+		}
+		this.#scheduleIdleQueueDrain();
+	}
+
 	/**
 	 * Send a custom message to the session. Creates a CustomMessageEntry.
 	 *

packages/coding-agent/test/input-controller-skill-queue.test.ts

@@ -42,7 +42,7 @@ type PromptCustomMessage = Mock<
 			attribution?: string;
 			details: SkillPromptDetails;
 		},
-		options?: { streamingBehavior?: "steer" | "followUp"; queueChipText?: string },
+		options?: { streamingBehavior?: "steer" | "followUp"; queueChipText?: string; queueOnly?: boolean },
 	) => Promise<void>
 >;
 
@@ -288,6 +288,24 @@ describe("compaction skill re-invocation", () => {
 		expect(steer).not.toHaveBeenCalled();
 		expect(followUp).not.toHaveBeenCalled();
 	});
+
+	it("queues retry-drained skills without appending them to session history", async () => {
+		const fixture = await createRealSession();
+		try {
+			const { ctx } = createCompactionDrainContext([{ text: "/skill:test-skill retry args", mode: "followUp" }]);
+			ctx.session = fixture.session;
+			const uiHelpers = new UiHelpers(ctx);
+
+			await uiHelpers.flushCompactionQueue({ willRetry: true });
+
+			expect(fixture.session.getQueuedMessages().followUp).toEqual(["/skill:test-skill retry args"]);
+			expect(fixture.session.messages).toEqual([]);
+		} finally {
+			await fixture.session.dispose();
+			fixture.authStorage.close();
+			fixture.tempDir.removeSync();
+		}
+	});
 });
 
 interface SessionFixture {