refactor(agent): make harness resources explicit

packages/agent/docs/agent-harness.md

@@ -16,13 +16,17 @@ Harness config is the latest runtime configuration set by the application or ext
 - thinking level
 - tools
 - active tool names
-- resources or resource provider
+- resources
 - system prompt or system prompt provider
 
 Getters return harness config. They do not return the snapshot used by an in-flight provider request.
 
 Setters update harness config immediately, including while a turn is in flight. Changes affect the next turn snapshot, not the currently running provider request.
 
+`setResources()` accepts concrete resources and emits `resources_update` with shallow-copied resources. Applications own loading/reloading resources from disk or other sources and should call `setResources()` with new values.
+
+`getResources()` returns shallow-copied current resources. It is a live config read, not the last turn snapshot.
+
 ### Turn snapshot
 
 A turn snapshot is the concrete state used for one LLM turn. It is created by `createTurnState()` and contains:
@@ -35,7 +39,9 @@ A turn snapshot is the concrete state used for one LLM turn. It is created by `c
 - all tools
 - active tools
 
-Static option values are used directly. Provider callbacks are invoked once per `createTurnState()` call. All logic for that turn uses the same snapshot.
+Static option values are used directly. System-prompt provider callbacks are invoked once per `createTurnState()` call. All logic for that turn uses the same snapshot.
+
+Resource arrays are shallow-copied when a snapshot is created. Individual skill and prompt-template objects are not deep-copied.
 
 ### Session
 
@@ -116,6 +122,8 @@ The low-level loop converts harness `ThinkingLevel` to provider `reasoning` at t
 
 No state refresh is needed on `agent_end` except flushing leftover pending session writes and clearing the operation phase. The exact `settled` event timing is still under review.
 
+If the system-prompt callback throws while starting `prompt`, `skill`, or `promptFromTemplate`, the operation throws and the harness returns to idle. If it throws from the save-point snapshot created by `prepareNextTurn`, the low-level agent run records an assistant error message.
+
 ## Hooks and events
 
 Current hooks receive only the event payload. There is no extension context object yet.

packages/agent/src/harness/agent-harness.ts

@@ -38,7 +38,7 @@ export class AgentHarness {
 	private steerQueue: UserMessage[] = [];
 	private followUpQueue: UserMessage[] = [];
 	private pendingSessionWrites: PendingSessionWrite[] = [];
-	private resources?: AgentHarnessOptions["resources"];
+	private resources: AgentHarnessResources;
 	private systemPrompt: AgentHarnessOptions["systemPrompt"];
 	private getApiKeyAndHeaders?: AgentHarnessOptions["getApiKeyAndHeaders"];
 	private tools = new Map<string, AgentTool>();
@@ -57,7 +57,7 @@ export class AgentHarness {
 		});
 		this.env = options.env;
 		this.session = options.session;
-		this.resources = options.resources;
+		this.resources = options.resources ?? {};
 		this.systemPrompt = options.systemPrompt;
 		this.getApiKeyAndHeaders = options.getApiKeyAndHeaders;
 		for (const tool of this.agent.state.tools) {
@@ -165,7 +165,7 @@ export class AgentHarness {
 
 	private async createTurnState(): Promise<AgentHarnessTurnState> {
 		const context = await this.session.buildContext();
-		const resources = typeof this.resources === "function" ? await this.resources() : (this.resources ?? {});
+		const resources = this.getResources();
 		const tools = [...this.tools.values()];
 		const activeTools = this.activeToolNames
 			.map((name) => this.tools.get(name))
@@ -578,8 +578,19 @@ export class AgentHarness {
 		this.agent.followUpMode = mode;
 	}
 
+	getResources(): AgentHarnessResources {
+		return {
+			skills: this.resources.skills?.slice(),
+			promptTemplates: this.resources.promptTemplates?.slice(),
+		};
+	}
+
 	async setResources(resources: AgentHarnessResources): Promise<void> {
-		this.resources = resources;
+		this.resources = {
+			skills: resources.skills?.slice(),
+			promptTemplates: resources.promptTemplates?.slice(),
+		};
+		await this.emitOwn({ type: "resources_update", resources: this.getResources() });
 	}
 
 	async setTools(tools: AgentTool[], activeToolNames?: string[]): Promise<void> {

packages/agent/src/harness/types.ts

@@ -410,6 +410,11 @@ export interface ThinkingLevelSelectEvent {
 	previousLevel: ThinkingLevel;
 }
 
+export interface ResourcesUpdateEvent {
+	type: "resources_update";
+	resources: AgentHarnessResources;
+}
+
 export type AgentHarnessOwnEvent =
 	| QueueUpdateEvent
 	| SavePointEvent
@@ -426,7 +431,8 @@ export type AgentHarnessOwnEvent =
 	| SessionBeforeTreeEvent
 	| SessionTreeEvent
 	| ModelSelectEvent
-	| ThinkingLevelSelectEvent;
+	| ThinkingLevelSelectEvent
+	| ResourcesUpdateEvent;
 
 export type AgentHarnessEvent = AgentEvent | AgentHarnessOwnEvent;
 
@@ -481,6 +487,7 @@ export type AgentHarnessEventResultMap = {
 	session_tree: undefined;
 	model_select: undefined;
 	thinking_level_select: undefined;
+	resources_update: undefined;
 	queue_update: undefined;
 	save_point: undefined;
 	abort: undefined;
@@ -565,7 +572,11 @@ export interface AgentHarnessOptions {
 	env: ExecutionEnv;
 	session: Session;
 	tools?: AgentTool[];
-	resources?: AgentHarnessResources | (() => AgentHarnessResources | Promise<AgentHarnessResources>);
+	/**
+	 * Concrete resources available to explicit invocation methods and system-prompt callbacks.
+	 * Applications own loading/reloading resources and should call `setResources()` with new values.
+	 */
+	resources?: AgentHarnessResources;
 	systemPrompt?:
 		| string
 		| ((context: {

packages/agent/test/harness/factory.test.ts

@@ -35,4 +35,30 @@ describe("harness factories", () => {
 		expect(harness.agent.steeringMode).toBe("one-at-a-time");
 		expect(harness.agent.followUpMode).toBe("one-at-a-time");
 	});
+
+	it("updates and reads concrete resources", async () => {
+		const session = createSession(new InMemorySessionStorage());
+		const env = new NodeExecutionEnv({ cwd: process.cwd() });
+		const model = getModel("anthropic", "claude-sonnet-4-5");
+		const harness = createAgentHarness({ env, session, model });
+		const skill = {
+			name: "inspect",
+			description: "Inspect things",
+			content: "Use inspection tools.",
+			filePath: "/skills/inspect/SKILL.md",
+		};
+		const resources = { skills: [skill], promptTemplates: [{ name: "review", content: "Review $1" }] };
+		const updates: unknown[] = [];
+		harness.subscribe((event) => {
+			if (event.type === "resources_update") updates.push(event.resources);
+		});
+
+		await harness.setResources(resources);
+		const resolved = harness.getResources();
+
+		expect(updates).toEqual([resources]);
+		expect(resolved).toEqual(resources);
+		expect(resolved.skills).not.toBe(resources.skills);
+		expect(resolved.promptTemplates).not.toBe(resources.promptTemplates);
+	});
 });