Fallback Rehydration: Recovering Partial Agents Through Contextual Policy Inference

Mechanism

Fallback rehydration begins with the detection of a primary-instance fault. Detection is performed by a liveness oracle that observes the primary's commit stream against the bounded scheduling-latency parameter of the execution graph manager. When the oracle determines that the primary has not committed an admissible scheduled node within its latency bound, the oracle emits a fault declaration into the graph as a first-class event. The fault declaration names the primary instance, the last node the primary committed, and the wall-clock time at which the bound was exceeded. The declaration is not a recommendation; it is the authoritative record that the primary has ceased to make progress, and downstream rehydration logic refers to it by hash to anchor its own work.

A fallback instance, having observed the fault declaration, initiates rehydration by traversing the durable lineage from the last node attributed to the primary back to the most recent node whose state envelope is fully reconstructible from durable storage alone. Reconstructibility requires that all of the node's predecessors be present in durable storage, that all referenced policies be resolvable by hash, and that all referenced field values be either inlined or fetchable from a content-addressed object store. The traversal is bounded by the depth of the durable lineage; in practice it terminates at a checkpoint node, which is a node whose envelope was previously and explicitly committed as a recovery anchor.

Once a recovery anchor is identified, the fallback instance computes the rehydrated state by replaying, in lineage order, every admissible node from the anchor forward. Replay is deterministic: each node's transformation is a pure function of its inputs, its policies, and its predecessors, all of which are bound by hash. The fallback computes each node's output, compares the output's hash to the hash recorded by the primary in the durable graph, and proceeds to the next node only if the hashes match. A mismatch is itself a fault, recorded as a divergence event, and rehydration halts at the divergence so that an auditor can determine whether the primary or the fallback computed correctly.

Cryptographic binding of the rehydration is achieved by the fact that every node the fallback replays is referenced by the same content-addressed hash as the corresponding node in the primary's graph. The fallback does not produce a new history; it adopts the existing history. The first node the fallback originates after rehydration completes references, by hash, the last successfully replayed node, so that the durable graph contains a single continuous lineage spanning the primary's work and the fallback's continuation. There is no fork, no merge, and no period during which two parallel histories must be reconciled.

Audit is enforced by the requirement that the fallback instance write a rehydration event into the durable graph before originating any new node. The rehydration event names the fault declaration that authorized the rehydration, the recovery anchor from which replay began, the sequence of replayed node hashes, and the fallback instance's own identity. The event is itself subject to admissibility evaluation: the platform refuses to admit a rehydration event whose authorizing fault declaration is missing, whose anchor is not a valid checkpoint, or whose replayed hashes do not match the durable record. A fallback that attempts to skip the audit event cannot proceed because subsequent nodes it originates will fail admissibility for lack of a valid predecessor lineage.

Contextual policy inference enters the mechanism when the rehydrated state references policies that have evolved since the original execution. The platform resolves each policy reference against the policy version recorded at the time of the original node's commit, not against the current policy version, so that replay is faithful to the conditions under which the original work was authorized. A policy that has been revoked since the original commit is treated as historically valid for replay purposes but invalid for any new work the fallback originates; the boundary between historical and prospective policy validity is the rehydration event itself.

Operating Parameters

The liveness-oracle latency bound is the principal tunable parameter of the rehydration mechanism. A short bound minimizes recovery time but increases the rate of spurious fault declarations under transient network conditions; a long bound is robust against transients but extends the period during which downstream consumers must wait for progress. Operators select the bound based on the loss function of the surrounding application, with no impact on rehydration correctness.

Checkpoint frequency is a tunable parameter that trades durable-storage cost against recovery time. A frequent checkpoint policy means that recovery anchors are close to the fault, minimizing replay cost; an infrequent checkpoint policy means that fewer envelopes are stored explicitly, reducing storage cost. Checkpoints are themselves graph nodes, so the historical checkpoint frequency is recoverable from the graph and may be adjusted retroactively in the sense that future checkpoints reference past nodes.

The set of fallback instances eligible to rehydrate after a given fault is governed by a policy node referenced by the fault declaration. The policy may name specific instances, name a quorum of instances any of which may proceed, or name a leader-election protocol whose outcome determines the rehydrating instance. The platform admits any such policy provided that the policy is itself a valid graph node and that the rehydrating instance is named by the policy's outcome.

Replay parallelism is bounded by the partial order of the lineage. Independent nodes may be replayed concurrently; dependent nodes are replayed in lineage order. The bound is a structural property of the graph, not a tunable parameter, but the implementer may choose how aggressively to exploit available parallelism within the bound.

Alternative Embodiments

Fallback rehydration may be embodied with the durable lineage stored in a single append-only log, in a federated set of partition-local logs, or in a fully replicated log maintained by a Byzantine-fault-tolerant consensus protocol. The rehydration mechanism is identical in each case; only the procedure by which the fallback acquires the durable lineage differs. In the single-log embodiment, the fallback reads the log directly. In the federated embodiment, the fallback queries the relevant partitions by lineage prefix and assembles the durable graph from the responses. In the replicated embodiment, the fallback reads from any quorum of replicas and verifies the responses against the consensus head.

The replay engine may be embodied as a single-threaded interpreter that walks the lineage in topological order, as a multi-threaded engine that exploits the partial order's parallelism, or as a streaming engine that begins emitting reconstructed envelopes as soon as their predecessors are available. The choice among embodiments does not affect the cryptographic binding of the rehydrated state, because each replayed node is verified by hash regardless of the order in which the engine encounters it.

The rehydration event may be embodied as a single graph node summarizing the entire replay, as a sequence of nodes each summarizing a segment of the replay, or as a per-node attestation that the fallback verified the corresponding original node. Implementers select among these embodiments based on the granularity of audit they require; the platform admits any embodiment whose events satisfy the admissibility predicate for rehydration events.

Embodiments differ in how they handle non-deterministic transformations. A pure-functional embodiment forbids non-deterministic transformations entirely, so that replay is always exact. A controlled-non-determinism embodiment permits transformations to consult an authorized randomness source whose outputs are themselves committed as graph nodes, so that replay is exact provided the randomness nodes are present. A relaxed embodiment permits transformations to produce semantically equivalent but bit-divergent outputs, accepting a divergence event when the fallback's bits differ from the primary's; this embodiment is suitable only for deployments in which semantic equivalence can be verified by a separate predicate.

Composition with Other Platform Primitives

Fallback rehydration composes with the execution graph manager because the durable lineage from which rehydration draws is the same graph the manager produces. There is no separate recovery log; the graph itself is the recovery substrate. This composition eliminates the consistency problems that arise in conventional systems where the execution log and the recovery log are distinct artifacts that may diverge under fault.

Rehydration composes with the trust-zone subsystem because each replayed node is checked against the zone state that obtained at the time of the original commit, not against the current zone state. A node that was admissible in its original zone remains replayable even if the zone has since been reconfigured; conversely, a fallback instance that does not itself satisfy the zone requirements of the rehydration event cannot proceed, because the rehydration event's admissibility predicate consults the fallback's current zone.

Rehydration composes with the policy-bound field subsystem because each replayed mutation is checked against the policy version recorded at the time of the original mutation. The platform thereby guarantees that replay does not retroactively apply a current policy to a historical mutation, which would otherwise produce a state that the original execution could not have produced.

Rehydration composes with the cryptographic commit subsystem because the recovery anchor is identified by hash and the rehydration event itself is anchored as part of the graph head. An external observer presented with the graph head before and after rehydration can verify that the rehydration was performed against the declared anchor and produced the declared continuation, without re-executing any of the replayed work.

Prior Art and Distinction

Conventional checkpoint-restart systems, including those used in high-performance computing and in container orchestration, capture process memory and resume execution from the captured image. Fallback rehydration differs in that it does not capture memory; it captures a structured lineage of admissibility-checked transformations, and recovery proceeds by replay rather than by image restoration. The distinction matters because a memory image is opaque to admissibility and audit, whereas a replayed lineage is transparent: every transformation that contributed to the rehydrated state is individually inspectable.

Database write-ahead logs allow recovery by replay of committed transactions. Fallback rehydration borrows the replay-by-log idea but differs in that the units replayed are agent-level transformations, not database operations, and the admissibility predicate is consulted at replay time, not only at original commit. A transformation that was admissible originally but whose admissibility cannot be verified at replay (for example, because its policy is unresolvable) halts the replay rather than proceeding silently.

Event-sourcing architectures store domain events in an append-only log and reconstruct application state by replay. Fallback rehydration generalizes this pattern by treating not only domain events but also delegations, zone transitions, and policy authorizations as replayable events, and by binding each event cryptographically to its lineage so that an attacker cannot forge an event or rearrange the order of events without detection.

Disclosure Scope

This disclosure describes and claims a method and apparatus for recovering an agent execution from primary-instance failure by rehydrating fallback state from a durable lineage of admissibility-checked transformations, wherein the rehydration is cryptographically bound by hash to the original lineage, wherein the rehydration is conditioned on a fault declaration emitted by a liveness oracle, wherein replay of the lineage is deterministic and verified node-by-node against the durable record, and wherein the fallback instance is required to commit a rehydration event into the durable graph before originating new work. The disclosure further claims embodiments in which the durable lineage is single-log, federated, or quorum-replicated; in which the replay engine is single-threaded, parallel, or streaming; and in which non-determinism is forbidden, controlled, or semantically reconciled. The scope of the disclosure is defined by the claims of US 19/230,933 and is not limited by any specific embodiment, oracle protocol, checkpoint policy, or fallback-election scheme described herein.