v0.4.0 — SubagentStart/Stop HGP integration

What's New

SubagentStart / SubagentStop Hook Integration

• SubagentStart: Injects session root op_id into spawned subagent context via additionalContext
• SubagentStop: Records subagent HGP tool usage summary as a file-based handoff for hgp_get_context
• hgp_set_context: Register a session root op for propagation to subagents
• hgp_get_context: Retrieve session context and consume pending subagent summaries

Fixes

• Mode gating applied to hgp_set_context / hgp_get_context
• Summary filenames are now collision-resistant (UUID suffix)