Feat/agent collaboration

[afjcjsbx]

📝 Description

This PR introduces a first-class internal Agent Collaboration Bus for PicoClaw.

It adds durable inter-agent communication with:

• per-agent mailboxes
• collaboration threads with isolated session history
• structured message envelopes and delivery state
• permission-aware routing between agents
• runtime observability events for message flow
• new internal tools: agent_request, agent_reply, and agent_inbox

It also routes synchronous delegate calls through the new collaboration runtime when available, while keeping existing multi-agent primitives backward-compatible.

🗣️ Type of Change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 📖 Documentation update
• ⚡ Code refactoring (no functional changes, no api changes)

🤖 AI Code Generation

• 🤖 Fully AI-generated (100% AI, 0% Human)
• 🛠️ Mostly AI-generated (AI draft, Human verified/modified)
• 👨‍💻 Mostly Human-written (Human lead, AI assisted or none)

🔗 Related Issue

Issue: #2929

📚 Technical Context (Skip for Docs)

• Reference URL: [Task] Add first-class agent-to-agent communication for cooperative workflows #2929
• Reasoning: The existing delegate / spawn / subagent flow worked well for one-shot delegation, but it did not provide a durable peer-to-peer communication layer between agents. This PR adds a collaboration bus scoped by target_agent_id + thread_id, persists mailbox/thread state, isolates collaboration history from user-facing sessions, enforces communication permissions, and emits runtime events for observability.

🧪 Test Environment

• Hardware:
• OS:
• Model/Provider:
• Channels:

📸 Evidence (Optional)

Click to view Logs/Screenshots

Validated with targeted tests and linting, including:

• go test ./pkg/collab ./pkg/config ./pkg/tools ./pkg/agent -run 'TestStore_PersistsThreadsMessagesAndMailboxes|TestCollaborationBus_|TestCollaborationSessionAliases_|TestDelegateTool_Execute_UsesCollaborationRuntimeWhenConfigured|TestAgentConfig_FullParse|TestAgentRegistry_CanCollaborate_RequiresSendAndReceive|TestAgentRegistry_CommunicationDefaults' -count=1
• golangci-lint run -E govet -E unused ./... --build-tags=goolm,stdjson

Key coverage includes:

• durable mailbox/thread persistence
• permission enforcement (allow_send_to / allow_receive_from)
• explicit replies and async durable replies
• thread isolation and anti-hijack checks
• closed-thread rejection
• delegate migration to the collaboration bus
• formatting/lint cleanup for the new code paths

☑️ Checklist

• My code/docs follow the style of this project.
• I have performed a self-review of my own changes.
• I have updated the documentation accordingly.