Safe, Persistent, and Evolving Agent Harness for Understanding Partially Observable Worlds
Authors’ abstract
Large language model agents can invoke tools fluently, but enterprise workflows demand more than selecting the right tools: actions must strictly comply with organizational policies, tool feedback often conceals hidden side effects under partial observability, and long-horizon tasks require persistent state tracking across multiple records. To address these challenges, we introduce E-Ledger, a multi-agent harness for safe and persistent execution. E-Ledger employs a code approval layer that checks every proposed action against policy before execution, and maintains a world ledger of verified hidden rules alongside evidence-backed dynamic state. Because hidden rules are typically unknown a priori, we further propose WorldAbduct, an abductive, world-model-driven harness evolution framework. WorldAbduct diagnoses execution trajectories across four complementary views (state consistency, world-observation gap, policy-gate correctness, and goal judgment) to hypothesize latent rules, and verifies them through targeted abductive interactions before integrating them into the ledger. On the enterprise benchmark World of Workflows, E-Ledger with WorldAbduct improves safe task completion across four LLM backbones, outperforming the strongest evolution baseline by 5--15 percentage points. Experiments in ScienceWorld and DiscoveryWorld further show that abductive harness evolution carries over to scientific environments. Our code is available at https://github.com/HKUST-KnowComp/E-LEDGER-WorldAbduct.
Paper
- Authors
- Yisen Gao, Yue Guo, Qing Zong, Yiwen Guo, Yangqiu Song
- Journal
- arXiv
- Publication date
- October 8, 2026
Transcript
You’re listening to “Safe, Persistent, and Evolving Agent Harness for Understanding Partially Observable Worlds,” by Yisen Gao and colleagues. Published in arXiv on October 8, 2026.
SAFE, PERSISTENT, AND EVOLVING AGENT H AR -NESS FOR UNDERSTANDING PARTIALLY OBSERVABLE WORLDS
Yisen Gao1, Yue Guo2, Qing Zong1, Yiwen Guo3∗, Yangqiu Song1 1The Hong Kong University of Science and Technology 2LIGHTSPEED 3Independent Researcher
ABSTRACT
Large language model agents can invoke tools fluently, but enterprise workflows demand more than selecting the right tools: actions must strictly comply with organizational policies, tool feedback often conceals hidden side effects under partial observability, and long-horizon tasks require persistent state tracking across multiple records. To address these challenges, we introduce E-Ledger, a multi-agent harness for safe and persistent execution. E-Ledger employs a code approval layer that checks every proposed action against policy before execution, and maintains a world ledger of verified hidden rules alongside evidence-backed dynamic state. Because hidden rules are typically unknown a priori, we further propose WorldAbduct, an abductive, world-model-driven harness evolution framework.
WorldAbduct diagnoses execution trajectories across four complementary views (state consistency, world-observation gap, policy-gate correctness, and goal judgment) to hypothesize latent rules, and verifies them through targeted abductive interactions before integrating them into the ledger. On the enterprise benchmark World of Workflows, E-Ledger with WorldAbduct improves safe task completion across four LLM backbones, outperforming the strongest evolution baseline by 5–15 percentage points. Experiments in ScienceWorld and Discov-eryWorld further show that abductive harness evolution carries over to scientific environments. Our code is available at the linked source.
1 INTRODUCTION
Large language model (LLM) agents increasingly complete multi-step tasks through tool use. By invoking APIs, databases, and software in-terfaces, they retrieve information, update records, and coordinate workflows. Enterprise applications extend these capabilities to incident management, employee administration, asset operations, and knowledge-base maintenance.
Enterprise workflows pose three interrelated challenges. First, actions are governed by strict policies, permissions, and approval requirements, so a locally plausible action may still be impermissi-ble. Whether an action is safe depends on record states, user permissions, and approval prerequisites. Second, the environment is only partially observable: tool responses reveal an interaction surface rather than the full transition dynamics, including hidden, cross-record, or delayed effects. Thus, a successful response does not necessarily confirm the resulting state, nor does an omitted field imply that it is absent or unchanged. Third, tasks require long-horizon state tracking across multiple objects, reads, and writes. Losing confirmed facts or outstanding subgoals can lead to repeated queries, incorrect actions, or premature termination. These challenges interact: in Fig.
1, a hidden priority change after assigning an asset to Alice makes a subsequent transfer violate policy. Safe execution therefore requires both persistent state tracking and knowledge of hidden transitions.
Directly deploying an agent in such enterprise environments remains unreliable. Previous work finds that agents often achieve low task-completion and safe-execution rates in enterprise environments: they not only fail to reach the requested end state, but can also violate constraints while attempting to do so. At the same time, agent harnesses have emerged as a promising way to augment a base agent with structured guidance, persistent state maintenance, verification, and control around its tool calls. Code-based harnesses further make environment reasoning and execution control explicit and executable, so that constraints are enforced by code rather than by the model’s own reasoning. For enterprise agents, this suggests combining policy checks with persistent state maintenance.
However, even a correctly implemented check is only as good as the state it receives: an unobserved side effect can make that state stale and an apparently compliant action unsafe. A harness must therefore also learn the world that lies behind the tool interface.
We introduce E-LEDGER, a safe and persistent harness that separates runtime control from environment-specific knowledge. It compiles known organizational policies into code and routes every proposed action through pre-execution approval. The code can permit an action, request evidence or an approval prerequisite, or block execution, so the model cannot bypass a known policy through its own reasoning. A complementary world ledger maintains static world knowledge of hidden rules and side effects, alongside dynamic world state recording evidence-backed changes to task-relevant entities and goals. Together, these layers make constraints, learned dynamics, and execution progress available throughout the workflow.
Much of this static knowledge, however, is unknown in advance. An action’s hidden effect may only become visible several steps later, when the observed state or outcome contradicts expectations. The agent must then identify the earlier trigger and decide whether the effect reflects a stable rule or an isolated event. Reliable attribution is essential for turning trajectories into reusable knowledge, especially when several actions could explain the same outcome.
To address these challenges, we propose WorldAbduct, a world-model-driven evolution strategy that uses abductive reasoning to recover hidden environment rules and improve E-LEDGER. The evolution process diagnoses execution trajectories from four complementary perspectives. State consistency keeps state predictions and the dynamic ledger aligned with observable tool feedback, helping the agent fit the part of the world it can directly observe. World-observation-gap analysis then focuses on the unobservable part of the world and seeks to recover hidden effects that are absent from the tool interface. Policy-gate correctness improves the enforcement of known constraints, while goal judgment helps the agent distinguish successful completion from premature termination.
The outputs of these four perspectives are then divided into two types: direct modifications to the harness, and hypotheses about hidden rules that require further validation. A dedicated abduction agent receives the latter hypotheses and designs targeted interactions to verify or revise them; only supported rules enter the static world layer. Our method achieves the highest safe task completion rate on the enterprise workflow benchmark WOW across four LLM backbones, and also performs strongly in the scientific discovery environments ScienceWorld and DiscoveryWorld. Our contributions can be summarized as:
• We introduce E-LEDGER, a safe and persistent enterprise agent harness that combines code-based policy enforcement with a world ledger layer that maintains static knowledge of hidden rules and dynamic state for task-relevant information.
• We propose WorldAbduct, a world-model-driven evolution method that uses four diagnostic views to fit the observable world and hypothesize unobservable hidden rules, then validates these hypotheses through abductive interaction to build a reusable world model.
• Experiments on the enterprise benchmark WOW show substantial improvements in both task completion and safety, and results on ScienceWorld and DiscoveryWorld show that the approach extends beyond enterprise workflows.
2 RELATED WORK
Enterprise Agents LLM agents increasingly complete multi-step tasks by interleaving reasoning with actions and observations from external tools. However, enterprise deployment introduces challenges beyond general tool use: actions operate over interconnected records, must obey organization-specific policies, and can trigger workflow side effects not revealed by an immediate tool response. WorkArena evaluates agents on common ServiceNow knowledge-work tasks, while the World of Workflows benchmark makes the additional challenge of hidden, cascading state changes explicit in partially observable workflows. These settings expose a gap between completing a visible interaction and establishing a safe final enterprise state.
Self-Evolving Agent Harnesses An agent harness is the external control layer around a base LLM model that organizes context, tools, memory, orchestration, and output handling. Rather than treat-ing this control layer as fixed, recent work lets it evolve with execution experience and task feedback. Some approaches convert failed attempts into natural-language guidance or use textual feedback to optimize components of a compound LLM system. Others distill trajectory experience across multiple control dimensions or iteratively improve harness code using traces and evaluations. Some systems further perform test-time adaptation Nie et al. (2026), using feedback from the current task to revise their control strategy online.
Another line of work Zhang et al. (2026); Dong et al. (2026) views the harness as a world model, evolving it to improve the agent’s understanding of environment dynamics and hidden state transitions. Our approach connects these two directions: four diagnostic views identify execution gaps, and targeted environment interactions test candidate hidden rules before the harness uses them for state tracking and policy approval.
3 METHOD 3.1 TASK DEFINITION
Following prior work, we model the task environment as a partially observable Markov decision process (POMDP). Each constraint-based task is defined by M = (U, P, S, A, T, O, Ω). Here, U denotes the user query, including the task description; P is the constraint policy; S is the complete enterprise database state; A is the discrete action space; T: S × A → S is the state-transition function; O is the space of tool responses; and Ω: S × A → O is the environment feedback function. At step t, the agent selects an action at ∈ A, consist-We define P (st, at) = 1 if at satisfies the policy at ing of an MCP tool and its parameters. state st, and P (st, at) = 0 otherwise. Under partial observability, the executing agent receives ot+1 = Ω(st, at) ∈ O, which may omit state changes, cross-record effects, or transition rules induced by its actions.
Let τ = (o0, a0, o1..., aL−1, oL) be a trajectory. We write CU (τ) = 1 when it reaches the requested goal or correctly identifies that the task cannot be completed safely, as required by WOW’s infeasible tasks (Appendix A.2). The objective is
L−1 Y J (τ) = CU (τ) P (st, at), t=0 where st+1 = T (st, at). Thus J (τ) = 1 denotes safe task success. Writing ht = (o0, a0, o1..., at−1, ot) for the available interaction history, the agent selects pθ,H (a | U, P, ht), at = arg max a∈A where θ denotes the model parameters and H the harness that organizes the history, world knowledge, and current task state.
3.2 MULTI-AGENT HARNESS ARCHITECTURE
As shown in Fig. 2, E-LEDGER is a multi-agent harness for partially observable environments. It maintains a world ledger for static hidden rules and dynamic task state, and at each interaction a task agent proposes an action, a policy-context agent supplies the evidence required for evaluation, a code-based approval layer checks it against organizational policies, and a state-tracking agent updates the ledger from the tool response.
World Ledger layer. To represent both hidden environment dynamics and task progress, the world ledger layer consists of static world knowledge WS and dynamic world state WD. WS stores hidden rules and tool-induced side effects that are absent from immediate tool feedback; for example, an asset change may also modify its priority. Formally, each rule is r: (a, s, c) −→ ∆s, where c is its applicability condition and ∆s is the induced state change. In contrast, WD maintains a global, schema-aligned store of task-relevant information for the current task, including identifiers, attributes, and relations extracted from tool feedback. It is updated incrementally after each interaction, preserving the state needed for long-horizon execution without reconstructing it from the entire trajectory.
Task agent. The task agent chooses an action from the user query, policy, available tools, static rules, dynamic ledger, and interaction history. It also predicts the resulting state change, which is retained for comparison with observations and subsequent evolution:
U, P, A, WS, W t ∆st) = Aθ (at, c D, ht, where at ∈ A is the proposed action and c ∆st is its predicted state change.
Code approval layer. To approve a proposed action using the relevant policy context, we compile each textual policy into an executable program Pcode and introduce a policy-context agent. Given the dynamic world state W t D, the policy-context agent extracts and binds the policy-relevant fields needed for approval, such as a target user’s active-incident count or an asset’s cost. The approval code then evaluates the proposed action at together with this extracted context, rather than relying on the task agent’s claims.
It returns one of four decisions: {execute, query, probe, block}. execute indicates that the action has passed approval and can be carried out. query or probe indicates that the available evidence is insufficient to determine whether the action complies with the policy, requiring additional information before approval. block indicates that the action violates the policy and must be replaced. Decisions other than execute are fed back to the task agent, which revises the proposed action accordingly. This approval process is non-bypassable.
Feedback and dynamic state update. After approval, the environment returns ot+1 = Ω(st, at). A response may confirm a creation or transfer without returning the resulting field values, or contain many irrelevant fields. The state-tracking agent Rθ interprets the response and extracts task-relevant updates: W t+1 W t = Rθ D, at, ot+1, WS. D
Applicable static rules help interpret indirect effects. Updates retain their supporting evidence, while conflicts and unresolved fields are recorded for subsequent verification. The task agent then acts on the updated ledger and interaction history.
3.3 WORLDABDUCT: ABDUCTIVE WORLD-MODEL-DRIVEN HARNESS EVOLUTION
The runtime above relies on static world knowledge WS, which is empty at initialization: hidden rules appear neither in the policy nor in immediate tool feedback. As shown at the bottom of Fig. 2, WorldAbduct addresses this gap through world-model-driven harness evolution. It analyzes each execution from four complementary perspectives and produces either direct harness updates or hiddenrule hypotheses. The latter are passed to a hiddenrule abduction agent for validation before entering the static world layer.
3.3.1 EVOLUTION PROPOSAL AGENT
The evolution proposal agent Eφ reads the task, policy, execution trajectory, task-agent predictions, tool feedback, and current harness. For each perspective, it identifies the corresponding gap and proposes the smallest appropriate harness update or hiddenrule hypothesis:
State consistency. State consistency first asks whether the agent can fit the part of the world that ∆st should agree with the task-is observable. At each step, the task agent’s predicted state change c relevant tool feedback ot+1. The state-tracking agent should record the same task-relevant facts in the ledger. It should not omit observable fields or add unrelated fields that are not supported by ot+1 or an applicable verified rule. Formally, the evolution proposal agent assesses this consistency at each step t:
∆st, ot+1, W t+1 c Js = Eφ D, WS.
World observation gap. State consistency helps the agent predict and record the observable world, but it cannot recover rules that never appear in the tool response. We therefore use the world observation gap objective to identify parts of the trajectory that may reveal the unobservable part. The evolution proposal agent focuses on state information that can change the outcome of the policy code. For example, if a knowledge asset has a flag that is false before an action and becomes true later, an earlier action may have triggered this change even if the relevant side effect was absent from the tool response. The agent identifies the actions that may have caused the change and formu-lates corresponding hiddenrule hypotheses for later validation. Its input is the complete trajectory, the executable policy code, and the dynamic world state: