research(memory): collaborative memory with multi-agent access control (CollabMem)

[bug-ops]

Summary

Two-tier memory (private + shared) with immutable provenance tracking and dynamic bipartite-graph access control for multi-user/multi-agent scenarios. Enables safe cross-agent knowledge transfer without permission leaks.

Source: arXiv 2505.18279 — Collaborative Memory: Multi-User Memory Sharing in LLM Agents with Dynamic Access Control
Alireza Rezazadeh et al., Accenture Center for Advanced AI. Published 2025-05-23.

Key Results

• Bipartite graph encodes user ↔ agent ↔ resource permissions, updated dynamically
• Each fragment carries immutable provenance: contributing agent, accessed resource, timestamp
• Retrospective permission checks: can revoke access to historical fragments
• Significant overhead reduction vs. per-user context duplication

Applicability to Zeph

Current gap: Zeph's SQLite+Qdrant memory has no per-agent or per-user boundaries. Subagent memory writes go into the same key_facts / episodes tables as the root agent. A malicious subagent could pollute root agent memory.

Integration points:

1. A2A multi-agent: incoming A2A agent sessions should have scoped memory access — read shared pool, write only to their private scope
2. Subagents: each spawned subagent gets a memory scope bound to its task; on completion, root agent promotes approved facts to shared memory
3. ACP multi-session: IDE sessions share a read-only knowledge base but write to session-private memory

Schema changes: Add memory_scope column to key_facts + episodes; MemoryAccessPolicy struct maps agent_id → (read_scopes, write_scope).

Complements: #1608 (episodic-to-semantic promotion), #2603.10062 memory architecture vision paper.

Implementation Sketch

• MemoryScope { public, private(agent_id), shared(session_id) } enum
• SemanticMemory::search() accepts scope filter; save() tags with agent_id scope
• Config: [memory.access_control] enabled = false, default_scope = "public"
• Migration: add scope TEXT NOT NULL DEFAULT 'public' to relevant tables