CAPTURE: Disentangling Preference Drift from Memory Poisoning in Personalized LLM Agents

AuthorsS M Asif Hossain, Ruksat Khan Shayoni, Md Kishor Morol

arXiv 20262026

TL;DR

CAPTURE uses a continuous-time authenticity gate plus a multi-timescale ledger to disentangle genuine preference drift from poisoning, reaching 71.5% win rate and 11.5% poisoning on D-PREFGUARD.

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THE PROBLEM

Preference authenticity ambiguity breaks long term agents (recency and provenance rules provably fail)

CAPTURE targets the preference-authenticity ambiguity, where genuine preference changes and injected instructions look identical in a single turn.

When agents rely only on recency and provenance, CAPTURE proves any such rule must satisfy FUR(d) + RRL(d) ≥ 1 − δφ, so attackers can mimic legitimate updates and force errors.

HOW IT WORKS

CAPTURE: Continuous-time gate plus multi-timescale ledger

CAPTURE centers on a preference-hypothesis extractor, authenticity gate, multi-timescale ledger, quarantine, and safety-bounded selection with causal audit to infer whether updates are genuine.

You can think of CAPTURE like a layered memory system with a fast-decaying scratchpad, a medium-term notebook, and a slow-changing archive, all controlled by a timing-aware gate.

This design lets CAPTURE separate stable values from contextual and transient goals, ask clarifying questions when uncertain, and resist poisoning in ways a flat context window or simple recency filter cannot.

DIAGRAM

Continuous-time belief update and authenticity decision flow

This diagram shows how CAPTURE evolves its latent belief over time and decides whether to revise, scope, quarantine, or clarify on each event.

DIAGRAM

D-PREFGUARD evaluation pipeline for CAPTURE

This diagram shows how CAPTURE is evaluated on D-PREFGUARD tracks, with shared candidate pools and attack families.

PROCESS

How CAPTURE Handles a Longitudinal Episode

  1. 01

    Preference-hypothesis extraction

    CAPTURE uses the preference-hypothesis extractor to turn each event et into a structured tuple Ht with claim, direction, scope, timescale, confidence, and provenance, abstaining on roughly seven in ten events.

  2. 02

    The authenticity gate

    CAPTURE evolves a continuous-time latent belief ht with a neural differential equation and GRU update, then predicts one of six actions: retain, add, scope, revise, quarantine, or ask the user.

  3. 03

    Multi-timescale ledger

    CAPTURE writes hypotheses into a graph-structured ledger with stable, contextual, and transient layers, using fixed decay rates γs = 0.01, γc = 0.1, γg = 0.5 and a learned modulation σ(ht).

  4. 04

    Safety-bounded selection and causal audit

    CAPTURE’s safety-bounded selector scores candidates for personalized utility and safety risk, then the causal audit re-decodes without cited nodes to compute Inf(ni) and prune non-influential explanations.

KEY CONTRIBUTIONS

Key Contributions

  • 01

    Formalization of preference-authenticity ambiguity

    CAPTURE models memory updates as a continuous-time partially observable decision process and proves that any rule using only recency and provenance must satisfy FUR(d) + RRL(d) ≥ 1 − δφ against feasible adversaries.

  • 02

    CAPTURE architecture with continuous-time gate and ledger

    CAPTURE introduces a continuous-time authenticity gate plus a three-layer ledger with decay rates γs = 0.01, γc = 0.1, γg = 0.5, achieving 71.5% win rate and 11.5% poisoning on 480 held-out D-PREFGUARD episodes.

  • 03

    D-PREFGUARD benchmark for drift vs poisoning

    CAPTURE comes with D-PREFGUARD, 2,400 episodes across five tracks separating stationary behavior, four drift shapes, benign ambiguity, three contamination families, and safety conflicts, with 480 episodes held out for test.

RESULTS

By the Numbers

Win rate

71.5%

+2.2 over Sup. Transformer-∆t

Regret

0.27

0.02 lower than Sup. Transformer-∆t

Poison

11.5%

4.4 points lower than Sup. Transformer-∆t

Adher.

83.5%

1.4 points higher than Sup. Transformer-∆t

On the 480 held-out D-PREFGUARD episodes from 96 users, CAPTURE is evaluated with Qwen3-8B-Instruct and Llama-3.1-8B-Instruct backbones. These results show CAPTURE improves personalization win rate while reducing poisoning success compared to the supervision-matched Sup. Transformer-∆t baseline.

BENCHMARK

By the Numbers

On the 480 held-out D-PREFGUARD episodes from 96 users, CAPTURE is evaluated with Qwen3-8B-Instruct and Llama-3.1-8B-Instruct backbones. These results show CAPTURE improves personalization win rate while reducing poisoning success compared to the supervision-matched Sup. Transformer-∆t baseline.

BENCHMARK

Main comparison on D-PREFGUARD held-out episodes

Win rate (%) against the unpersonalized base model on 480 held-out D-PREFGUARD episodes.

KEY INSIGHT

The Counterintuitive Finding

Under an adaptive attacker, CAPTURE’s poisoning rate jumps from 11.5% to 24.7%, making Provenance-only marginally more secure at 22.1% despite being less adaptive.

This is counterintuitive because CAPTURE’s sophisticated gate and ledger beat Provenance-only under fixed attacks, yet exposing gradients lets attackers exploit CAPTURE more than simple provenance filters.

WHY IT MATTERS

What this unlocks for the field

CAPTURE shows that treating preference authenticity as a latent state with continuous-time dynamics and multi-timescale memory can jointly improve personalization and poisoning robustness.

Builders can now design agents that keep adapting over weeks while quantifying and bounding poisoning risk, instead of choosing between fast personalization and strict provenance filters.

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