feat: key fallback using agent models[] hierarchy, background tool modes, copy truncation

- Agent rate-limit fallback now iterates through agent's configured models[] in strict order
- Frontend sends agentModels with each /chat request; backend uses buildFallbackSequence()
- Emits notice event on fallback so chat shows which key failed and what's being tried next
- Child agents inherit parent's agentModels for fallback
- Added statusCode propagation from AI SDK errors for programmatic 429 detection
- Copy button truncates all tool results at 300 chars (was 200 for 4 specific tools)
- run_shell, summon, youtube_transcribe: background mode support
- summon: blocking mode by default with getResult callback

5 files changed, 82 insertions, 5 deletions

diff --git a/packages/core/src/agent/agent.ts b/packages/core/src/agent/agent.ts
index 6f1a5a4..bf9b22f 100644
--- a/packages/core/src/agent/agent.ts
+++ b/packages/core/src/agent/agent.ts
@@ -311,8 +311,15 @@ export class Agent {
 							allToolCalls.push(toolCall);
 							yield { type: "tool-call", toolCall };
 						} else if (event.type === "error") {
+							const errRecord = event.error as unknown as Record<string, unknown>;
+							const statusCode =
+								typeof errRecord.statusCode === "number" ? errRecord.statusCode : undefined;
 							const errorMsg = formatError(event.error, this.config);
-							yield { type: "error", error: errorMsg };
+							yield {
+								type: "error",
+								error: errorMsg,
+								...(statusCode !== undefined ? { statusCode } : {}),
+							};
 							this.status = "error";
 							yield { type: "status", status: "error" };
 							return;
@@ -471,8 +478,11 @@ export class Agent {
 
 			yield { type: "done", message: assistantMessage };
 		} catch (err) {
+			const errRecord = err as unknown as Record<string, unknown>;
+			const statusCode =
+				typeof errRecord.statusCode === "number" ? errRecord.statusCode : undefined;
 			const errorMsg = formatError(err, this.config);
-			yield { type: "error", error: errorMsg };
+			yield { type: "error", error: errorMsg, ...(statusCode !== undefined ? { statusCode } : {}) };
 			this.status = "error";
 			yield { type: "status", status: "error" };
 			return;
diff --git a/packages/core/src/tools/run-shell.ts b/packages/core/src/tools/run-shell.ts
index 6671c31..ec2db9c 100644
--- a/packages/core/src/tools/run-shell.ts
+++ b/packages/core/src/tools/run-shell.ts
@@ -54,6 +54,12 @@ export function createRunShellTool(
 		parameters: z.object({
 			command: z.string().describe("The shell command to execute"),
 			timeout: z.number().optional().describe("Timeout in milliseconds (default 2 minutes)"),
+			background: z
+				.boolean()
+				.optional()
+				.describe(
+					"If true, the command starts in the background and a job_id is returned immediately. Use the retrieve tool with the job_id to get the result later.",
+				),
 		}),
 		execute: async (
 			args: Record<string, unknown>,
@@ -61,6 +67,7 @@ export function createRunShellTool(
 		): Promise<string> => {
 			const command = args.command as string;
 			const timeout = (args.timeout as number | undefined) ?? DEFAULT_TIMEOUT;
+			const background = (args.background as boolean | undefined) ?? false;
 
 			const [shell, shellArgs] = getShell();
 			const child = spawn(shell, [...shellArgs, command], {
@@ -99,6 +106,23 @@ export function createRunShellTool(
 				});
 			});
 
+			// If background mode requested, register immediately and return job ID
+			if (background && shellStore) {
+				const jobId = shellStore.register({
+					command,
+					stdout,
+					stderr,
+					completion: completionPromise,
+				});
+				return [
+					`Command started in background.`,
+					`job_id: ${jobId}`,
+					`command: ${command}`,
+					``,
+					`Use the retrieve tool with this job_id to get the result when ready.`,
+				].join("\n");
+			}
+
 			const queueCallbacks = context?.queueCallbacks;
 
 			if (queueCallbacks && shellStore) {
diff --git a/packages/core/src/tools/summon.ts b/packages/core/src/tools/summon.ts
index 29f27d1..22ab35b 100644
--- a/packages/core/src/tools/summon.ts
+++ b/packages/core/src/tools/summon.ts
@@ -3,6 +3,9 @@ import type { ToolDefinition } from "../types/index.js";
 
 export interface SummonCallbacks {
 	spawn(options: { task: string; tools: string[]; workingDirectory?: string }): Promise<string>;
+	getResult(
+		agentId: string,
+	): Promise<{ status: "done"; result: string } | { status: "error"; error: string }>;
 }
 
 export function createSummonTool(
@@ -12,12 +15,15 @@ export function createSummonTool(
 	return {
 		name: "summon",
 		description: [
-			"Spawn a new child agent to work on a task independently. Returns immediately with an agent_id — does NOT wait for the child to finish.",
+			"Spawn a new child agent to work on a task independently.",
+			"",
+			"By default, blocks until the child agent finishes and returns the result directly.",
+			"Set background=true to return immediately with an agent_id instead — use retrieve to collect the result later.",
 			"",
 			"The child agent runs in its own tab visible to the user. Use the 'retrieve' tool with the returned agent_id to get the result when needed.",
 			"",
 			"Pattern for parallel work:",
-			"  1. Call summon multiple times to start several agents",
+			"  1. Call summon multiple times with background=true to start several agents",
 			"  2. Do your own work or wait",
 			"  3. Call retrieve for each agent_id to collect results",
 			"",
@@ -64,12 +70,19 @@ export function createSummonTool(
 				.describe(
 					"Absolute path for the child to work in. Defaults to the current working directory.",
 				),
+			background: z
+				.boolean()
+				.optional()
+				.describe(
+					"If true, returns immediately with an agent_id for later retrieval. If false (default), blocks until the child agent finishes and returns the result directly.",
+				),
 		}),
 		execute: async (args: Record<string, unknown>): Promise<string> => {
 			const task = args.task as string;
 			const tools = (args.tools as string[] | undefined) ?? ["read_file", "list_files", "todo"];
 			const workingDirectory =
 				(args.working_directory as string | undefined) ?? defaultWorkingDirectory;
+			const background = (args.background as boolean | undefined) ?? false;
 
 			try {
 				const agentId = await callbacks.spawn({
@@ -77,6 +90,16 @@ export function createSummonTool(
 					tools,
 					workingDirectory,
 				});
+
+				if (!background) {
+					// Block until the child agent completes
+					const result = await callbacks.getResult(agentId);
+					if (result.status === "done") {
+						return result.result;
+					}
+					return `Error from child agent: ${result.error}`;
+				}
+
 				return [
 					`Agent spawned successfully.`,
 					`agent_id: ${agentId}`,
diff --git a/packages/core/src/tools/youtube-transcribe.ts b/packages/core/src/tools/youtube-transcribe.ts
index ea8ed43..3a26d6f 100644
--- a/packages/core/src/tools/youtube-transcribe.ts
+++ b/packages/core/src/tools/youtube-transcribe.ts
@@ -141,17 +141,36 @@ export function createYoutubeTranscribeTool(
 		].join("\n"),
 		parameters: z.object({
 			url: z.string().describe("The YouTube video URL to fetch the transcript for."),
+			background: z
+				.boolean()
+				.optional()
+				.describe(
+					"If true, the transcription request starts in the background and a job_id is returned immediately. Use the retrieve tool with the job_id to get the transcript later.",
+				),
 		}),
 		execute: async (
 			args: Record<string, unknown>,
 			context?: ToolExecuteContext,
 		): Promise<string> => {
 			const url = args.url as string;
+			const background = (args.background as boolean | undefined) ?? false;
 			const queueCallbacks = context?.queueCallbacks;
 
 			try {
 				const pollPromise = pollUntilReady(url);
 
+				// If background mode requested, register immediately and return job ID
+				if (background && transcriptStore) {
+					const jobId = transcriptStore.register(url, pollPromise);
+					return [
+						`Transcript request started in background.`,
+						`job_id: ${jobId}`,
+						`url: ${url}`,
+						``,
+						`Use the retrieve tool with this job_id to get the transcript when ready.`,
+					].join("\n");
+				}
+
 				if (queueCallbacks && transcriptStore) {
 					const { promise: queuePromise, cancel: cancelQueueWait } =
 						queueCallbacks.waitForQueuedMessage();
diff --git a/packages/core/src/types/index.ts b/packages/core/src/types/index.ts
index c301822..b17a720 100644
--- a/packages/core/src/types/index.ts
+++ b/packages/core/src/types/index.ts
@@ -36,7 +36,8 @@ export type AgentEvent =
 	| { type: "tool-call"; toolCall: ToolCall }
 	| { type: "tool-result"; toolResult: ToolResult }
 	| { type: "shell-output"; data: string; stream: "stdout" | "stderr" }
-	| { type: "error"; error: string }
+	| { type: "error"; error: string; statusCode?: number }
+	| { type: "notice"; message: string }
 	| { type: "done"; message: ChatMessage }
 	| { type: "task-list-update"; tasks: TaskItem[] }
 	| { type: "config-reload" }