fix(subagent-session-spawning): resolved subagent parent id propagation

- Forwarded `parentAgentId` through task and eval launch paths when spawning subagents.
- Mapped `parentAgentId` to `parentId` in `createAgentSession`.
- Passed each caller's session `getAgentId` (or `MAIN_AGENT_ID`) as the parent for spawned agents.

packages/coding-agent/src/task/executor.ts

@@ -351,6 +351,12 @@ export interface ExecutorOptions {
 	parentTelemetry?: AgentTelemetryConfig;
 	/** Skills to autoload via sendCustomMessage before the first prompt */
 	autoloadSkills?: Skill[];
+	/**
+	 * Registry id of the spawning agent, recorded as this subagent's parent.
+	 * Forwarded verbatim to the SDK; the executor never derives it (the spawner
+	 * passes its own `getAgentId()`).
+	 */
+	parentAgentId?: string;
 }
 
 function parseStringifiedJson(value: unknown): unknown {
@@ -2021,6 +2027,7 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 				parentHindsightSessionState: options.parentHindsightSessionState,
 				parentMnemopiSessionState: options.parentMnemopiSessionState,
 				parentTaskPrefix: id,
+				parentAgentId: options.parentAgentId,
 				agentId: id,
 				agentDisplayName: subagentDisplayName,
 				enableLsp: lspEnabled,

packages/coding-agent/src/task/index.ts

@@ -46,7 +46,7 @@ import "../tools/review";
 import type { AsyncJobManager } from "../async";
 import type { LocalProtocolOptions } from "../internal-urls";
 import { loadOverallPlanReference } from "../plan-mode/plan-handoff";
-import { AgentRegistry } from "../registry/agent-registry";
+import { AgentRegistry, MAIN_AGENT_ID } from "../registry/agent-registry";
 import { generateCommitMessage } from "../utils/commit-message-generator";
 import * as git from "../utils/git";
 import { type DiscoveryResult, discoverAgents, getAgent } from "./discovery";
@@ -1300,6 +1300,7 @@ export class TaskTool implements AgentTool<TaskToolSchemaInstance, TaskToolDetai
 				parentMnemopiSessionState: this.session.getMnemopiSessionState?.(),
 				parentTelemetry: this.session.getTelemetry?.(),
 				parentEvalSessionId,
+				parentAgentId: this.session.getAgentId?.() ?? MAIN_AGENT_ID,
 			};
 
 			const runTask = async (): Promise<SingleResult> => {