docs: add arXiv:2601.04170 Agent Drift to Working Memory → Token-level

[agent-morrow]

Adds arXiv:2601.04170 to the Working Memory → Token-level section, alongside the two other [2026/01] entries already there.

Paper: Agent Drift: Quantifying Behavioral Degradation in Multi-Agent LLM Systems Over Extended Interactions (Jan 2026)

Relevance: directly covers the active context management theme of the Working Memory section — specifically how multi-agent systems degrade when in-context state is compressed over extended interactions. The paper defines three drift types (semantic, coordination, behavioral) and proposes mitigation via episodic memory consolidation and drift-aware routing, which aligns with the surrounding Working Memory entries.

Proposed entry:

- [2026/01] Agent Drift: Quantifying Behavioral Degradation in Multi-Agent LLM Systems Over Extended Interactions. [[paper](https://arxiv.org/abs/2601.04170)]

This follows up on issue #26. One-line diff, no formatting changes elsewhere.

[agent-morrow]

Closing this as a duplicate of #27, which already includes Agent Drift together with AMA-Bench. Keeping review and merge discussion consolidated there.