fix(session): admit ownerless continuation before selection

packages/coding-agent/CHANGELOG.md

@@ -26,6 +26,7 @@
 - Post-merge repair for #4542: `CHAT_DAEMON_GENERATIONS.discord` 64→65 and `.slack` 67→68 so the `SessionRouter` initial attachment replay change is generation-fenced for already-running Discord and Slack daemons. The semantic guard manifest is regenerated with the corrected generation and declaration digests.
 - Cursor split responses now preserve canonical provider order across pre-admission artifact spilling, so a server-side tool result cannot be persisted after the assistant continuation that follows it. The canonical admission reservation is owned by each emission's own handler, so a host bridge or replay emitting the same `message_end` event object twice can no longer overwrite the reservation and deadlock every later canonical admission (#4536).
 - Uncontended canonical `message_end` admissions no longer cost a microtask: the admission lane keeps a synchronous fast path when its predecessor slot is already released, restoring synchronous visibility of persisted appends for external emitters (successor-finalization and deep-interview continuation flows) while FIFO admission still holds under a genuinely in-flight predecessor (#4536).
+- SDK `session.prompt`/`steer` dispatches that arrive while a default-model selection already owns the admission fence are now preserved as queued work instead of failing: the shared ingress awaits the selection fence, keeps same-session prompt entry fail-fast, and only private scheduled continuations (auto-compaction/queue continuation) bypass the fence with an explicit reentry capability. Queued dispatches reserve follow-up order before durable acceptance so a later plain prompt cannot overtake an earlier follow-up behind the same fence, and continuations parked behind a pending selection fence are tracked as settlement work so `waitForIdle` cannot report completion while the continuation is still waiting (#4519).
 - Default-model selection now reserves a causal fence before credential probing, so an already accepted prompt preflight cannot be overtaken and a selection accepted first blocks later prompt preflight through durable publication. The fence does not hold session admission across `waitForIdle`, allowing inherited auto-compaction continuations to obtain prompt admission; same-session reentrancy still fails fast, successor sessions remain protected, and disposal deterministically drains accepted selections while rejecting queued prompts without unhandled rejections (#4519).
 - Ordinary sessions no longer import or execute Claude Code and Codex directory hooks as competing runtime authorities. Runtime hook discovery is fail-closed to canonical native `.gjc/hooks/` providers while explicit configured paths, constrained plugin hooks, and foreign-provider import/diagnostic discovery remain available (#4516).
 - Telegram/Slack/Discord outbound publications no longer freeze after a session-host rehost. A rehosted fleet re-attaches every session in one reconcile pass, and each attachment's initial `event_replay` was awaited inside the serialized `#reconcileTail`, so one slow replay (up to its full retry budget) wedged all later reconciles and the sends funneling through them; leases and inbound polling stayed green while delivery died until daemon restart. Reconcile-driven attachments now publish immediately and run initial replay on the attachment's ready tail (matching the reconnect path); `start()` still drains those tails so bootstrap callers observe replay completion. Replay ordering, generation fences, cross-session isolation, and provider hooks are unchanged (#4527).

packages/coding-agent/src/extensibility/extensions/loader.ts

@@ -242,9 +242,12 @@ class ConcreteExtensionAPI implements ExtensionAPI, IExtensionRuntime {
 		content: string | (TextContent | ImageContent)[],
 		options?: {
 			deliverAs?: "steer" | "followUp";
+			queuedAtDispatch?: boolean;
 			onPreflightAccepted?: () => void;
 			onPreflightAcceptCommit?: () => void | Promise<void>;
+			onQueuedPromoted?: () => void;
 			preflightSignal?: AbortSignal;
+			sdkRunToken?: string;
 		},
 	): Promise<void> {
 		return Promise.resolve(this.runtime.sendUserMessage(content, options));

packages/coding-agent/src/extensibility/extensions/runner.ts

@@ -207,7 +207,7 @@ export class ExtensionRunner {
 	#isIdleFn: () => boolean = () => true;
 	#getActivePromptHandleFn: () => string | undefined = () => undefined;
 	#waitForIdleFn: () => Promise<void> = async () => {};
-	#abortFn: () => void = () => {};
+	#abortFn: () => void | Promise<void> = () => {};
 	#abortPromptAndWaitFn: NonNullable<ExtensionContextActions["abortPromptAndWait"]> = async () => {
 		throw new Error("abortPromptAndWait binding is unavailable");
 	};

packages/coding-agent/src/extensibility/extensions/types.ts

@@ -369,7 +369,7 @@ export interface ExtensionContext {
 	/** Stable resource ownership identifier for the active prompt run. */
 	getActivePromptHandle(): string | undefined;
 	/** Abort the current agent operation */
-	abort(): void;
+	abort(): void | Promise<void>;
 	/** Abort and prove whether resources for a specific prompt settled. */
 	abortPromptAndWait?(handle: string, options: { graceMs: number }): Promise<RunSettlementProof>;
 	/** Whether there are queued messages waiting */
@@ -1186,8 +1186,11 @@ export interface ExtensionAPI {
 		content: string | (TextContent | ImageContent)[],
 		options?: {
 			deliverAs?: "steer" | "followUp";
+			/** Internal SDK signal preserving a busy dispatch across async admission fences. */
+			queuedAtDispatch?: boolean;
 			onPreflightAccepted?: () => void;
 			onPreflightAcceptCommit?: () => void | Promise<void>;
+			onQueuedPromoted?: () => void;
 			preflightSignal?: AbortSignal;
 			/** Internal SDK correlation owner for an exact queued follow-up. */
 			sdkRunToken?: string;
@@ -1505,7 +1508,7 @@ export interface ExtensionContextActions {
 	isIdle: () => boolean;
 	/** Stable resource ownership identifier for the active prompt run. */
 	getActivePromptHandle?: () => string | undefined;
-	abort: () => void;
+	abort: () => void | Promise<void>;
 	abortPromptAndWait?: (handle: string, options: { graceMs: number }) => Promise<RunSettlementProof>;
 
 	hasPendingMessages: () => boolean;

packages/coding-agent/src/sdk/host/session-runtime.test.ts

@@ -434,6 +434,7 @@ describe("SessionSdkSessionRuntime", () => {
 		const cwd = await mkdtemp(path.join(os.tmpdir(), "gjc-sdk-unwind-promoted-"));
 		let idle = true;
 		let promoted: (() => void) | undefined;
+		const queuedDispositions: boolean[] = [];
 		const handlers = new Map<string, (event: unknown, ctx: ExtensionContext) => Promise<void> | void>();
 		const api = {
 			on(event: string, handler: (event: unknown, ctx: ExtensionContext) => Promise<void> | void) {
@@ -446,10 +447,12 @@ describe("SessionSdkSessionRuntime", () => {
 							onPreflightAccepted?: () => void;
 							onPreflightAcceptCommit?: () => void;
 							onQueuedPromoted?: () => void;
+							queuedAtDispatch?: boolean;
 					  }
 					| undefined,
 			) =>
 				Promise.resolve(options?.onPreflightAcceptCommit?.()).then(() => {
+					queuedDispositions.push(options?.queuedAtDispatch === true);
 					promoted = options?.onQueuedPromoted;
 					options?.onPreflightAccepted?.();
 					return {};
@@ -509,6 +512,7 @@ describe("SessionSdkSessionRuntime", () => {
 			idle = false;
 			prompt("conn-b", "unwind-b");
 			await waitResponse("unwind-b");
+			expect(queuedDispositions).toEqual([false, true]);
 			expect(promoted).toBeDefined();
 			// The unwind continuation promotes the queued steer to its own run: the
 			// correlation hook fires before agent_start...

packages/coding-agent/src/sdk/host/session-runtime.ts

@@ -1317,6 +1317,7 @@ function createControlSurface(
 			onPreflightAcceptCommit: () => Promise<void>;
 			/** Fired when a queued submission (steering or follow-up) is promoted to its own run (SDK ownership correlation). */
 			onQueuedPromoted: () => void;
+			queuedAtDispatch: boolean;
 		}) => Promise<unknown>,
 		acceptedFields?: () => Record<string, unknown>,
 		allowCompletionFallback = false,
@@ -1392,6 +1393,7 @@ function createControlSurface(
 					// created at promotion so the submitting connection can
 					// terminal-abort that turn (review threads P1/P2).
 					onQueuedPromoted: () => onPromotedTurn?.(kind, correlation, requesterConnectionId),
+					queuedAtDispatch,
 				}),
 			);
 			void submission.then(
@@ -2316,10 +2318,10 @@ function createControlSurface(
 	};
 	return {
 		prompt: async (text, images, clientRef) =>
-			submit("prompt", clientRef, options =>
+			submit("prompt", clientRef, ({ queuedAtDispatch, ...options }) =>
 				api.sendUserMessage(
 					typeof images === "undefined" ? text : ([{ type: "text", text }, ...(images as never[])] as never),
-					options,
+					queuedAtDispatch ? { ...options, queuedAtDispatch: true } : options,
 				),
 			),
 		steer: async (text, clientRef) => {
@@ -2355,7 +2357,7 @@ function createControlSurface(
 		},
 		abortTerminal: terminalAbort,
 		abortAndPrompt: async text => {
-			ctx.abort();
+			await ctx.abort();
 			return await submit("prompt", undefined, options => api.sendUserMessage(text, options));
 		},
 		answerAsk: unavailable("ask.answer"),