feat(coding-agent): added subagent context passing and automatic tool injection for agent sessions

- Added getCompactContext() API to agent session for accessing parent conversation context.
- Implemented automatic submit_result tool injection for subagents with explicit tool lists.
- Added contextFile parameter to ExecutorOptions for passing parent conversation context to subagents.
- Enhanced subagent system prompt with conditional context file instructions and improved code formatting.
- Removed schema override notification from task summary prompt to simplify output.
- Implemented formatCompactContext() method to format conversation history for subagent consumption.

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

@@ -196,6 +196,8 @@ export interface ExecutorOptions {
 	sessionFile?: string | null;
 	persistArtifacts?: boolean;
 	artifactsDir?: string;
+	/** Path to parent conversation context file */
+	contextFile?: string;
 	eventBus?: EventBus;
 	contextFiles?: ContextFileEntry[];
 	skills?: Skill[];
@@ -948,6 +950,7 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 						agent: agent.systemPrompt,
 						worktree: worktree ?? "",
 						outputSchema: normalizedOutputSchema,
+						contextFile: options.contextFile,
 					}),
 				sessionManager,
 				hasUI: false,