[Enhancement] Sub-agent spawning API for parallel task execution

[OneStepAt4time]

Summary

Claude Code has an AgentTool that spawns sub-agents with isolated context for parallel task execution. Aegis could expose a similar API, allowing orchestrators to run multiple CC sessions in parallel from a single parent session.

CC Reference

• src/tools/AgentTool/ — Sub-agent spawning tool
• src/services/tools/toolHooks.ts — Sub-agent lifecycle hooks
• src/types/hooks.ts — SubagentStart, SubagentStop hook events
• src/state/AppState.ts — Sub-agent state tracking

CC Architecture

• AgentTool: spawns a new CC process with isolated context, parent context summary, and task prompt
• Sub-agent lifecycle hooks: SubagentStart (before spawn), SubagentStop (after completion)
• Context isolation: sub-agents get a summary of parent context, not full transcript
• Parallel execution: multiple sub-agents can run simultaneously
• Result aggregation: parent session receives sub-agent output when complete

Current Aegis Gap

• Aegis creates independent sessions via POST /v1/sessions
• No concept of parent-child session relationships
• No way to spawn a session from within another session
• No context sharing or result aggregation between related sessions

Proposed Implementation

1. Add parentId field to session creation — links sessions hierarchically
2. Add POST /v1/sessions/:id/spawn — spawn child session with parent context summary
3. Track sub-agent state: pending, running, completed, failed
4. GET /v1/sessions/:id/children — list child sessions with status
5. Hook events: SubagentStart, SubagentStop for lifecycle management
6. Future: automatic context summarization from parent to child

Priority

P2 — key differentiator for multi-agent orchestration

[OneStepAt4time]

🔧 Starting work on this. ETA: ~20 min per issue. Separate PRs targeting v2.7.0.

[OneStepAt4time]

Resolved by PR #943 (merged in release 2.7.0 on 2026-04-03).