NA loss recovery: compile one detected-loss reload-and-resume sequence

[arniber21]

What to build

Compile one detected atom-loss event into an explicit reservoir reload, replacement initialization, remapping, and verified resume sequence on a zoned neutral-atom target.

Issue #310 models analytic loss probability but deliberately excludes observed loss and replacement. This tracer bullet should introduce the minimum execution semantics necessary to react to a known loss without pretending to solve general online remapping: one workload reaches a detection point, receives a deterministic loss result, replaces the affected ancilla/data role according to a reviewed policy, and continues or fails safely.

Design review is required for atom identity versus logical role, branch semantics, and which losses are recoverable in the first slice.

Acceptance criteria

• The target model can declare atom reservoirs/reload zones, capacities, preparation time, and allowed transfer paths.
• quantum.na/execution semantics represent atom-presence or loss-detection results, replacement initialization, role remapping, and resume/fail decisions explicitly.
• One checked-in workload compiles a deterministic detected-loss branch through reload and continuation.
• Scheduling respects readout/detection latency, reservoir capacity, zone constraints, movement legality, initialization, and classical dependencies.
• The verifier rejects reuse of a lost atom, uninitialized replacement atoms, duplicate role ownership, illegal reservoir movement, and resume before remapping completes.
• Reports distinguish analytic expected loss from observed/injected loss events and account for reload atoms, moves, transfers, latency, retries, and peak capacity.
• Tests cover successful ancilla replacement, empty reservoir, unrecoverable data loss, repeated loss beyond policy, and deterministic no-loss execution.
• The execution package/reference interpreter can exercise both no-loss and injected-loss branches.
• Documentation states that this is compiler recovery scheduling, not a physical loss-detector or QEC threshold claim.

Out of scope

• General optimal online remapping under arbitrary simultaneous losses.
• Physical loss-detection pulse/camera implementation.
• Statistical Monte Carlo validation of the analytic model.

Blocked by

• NA/zoned: require readout-zone residency for measurement, reset, and reuse #482 — readout-zone scheduling
• quantum.na: carry measurement results, conditionals, and frame updates end to end #483 — classical feed-forward semantics
• quantum.na: specify a versioned controller execution and calibration-symbol contract #491 — controller execution contract

Related

• NA (exceed): atom-loss and heating-aware movement cost (Atomique Eqs. (1)–(2)) #310 — analytic atom-loss/heating model
• NA scheduler: model mid-circuit measurement, reset, and qubit reuse as first-class resources #282 — reset/reuse resources
• Epic: QEC-aware neutral-atom compilation path #245 — QEC-aware NA compilation