Public API map

This map is an orientation aid, not a substitute for rustdoc. It shows where public concepts live and which feature boundaries introduce optional dependencies.

`poise-core`

Candidate model

API	Role
`Candidate`	Borrowed policy view of identity, weight, load, status, eligibility
`Backend`	Concrete candidate with application data
`Status`	Ready, draining, or unavailable administrative state
`Weight`	Validated nonzero integer capacity ratio
`Selection`	Validated policy result wrapper around a slice index
`PickError`	Typed no-candidate and arithmetic failures

Policy contract

API	Role
`Policy<C, Context>`	Mutable selection operation
`PolicyExt::choose`	Convenience lookup returning a candidate borrow
`Random`, `WeightedRandom`	Stateless stochastic spread
`RoundRobin`, `SmoothWeightedRoundRobin`	Stateful cyclic spread
`LeastLoaded`, `PowerOfTwoChoices`	Load-aware choice
`Rendezvous`, `WeightedRendezvous`	Table-free affinity
`BoundedLoadRendezvous`	Affinity with prospective capacity spillover
`RingHash`, `Maglev`	Cached affinity structures
`PriorityWeightedRandom`	Priority, spillover, and panic
`LocalityWeightedRandom`	Priority plus locality health weighting

Feedback and load

API	Role
`Outcome`	Success, failure, overload, cancellation
`LoadMetric`	Comparable load measurement
`InFlight`, `InFlightGuard`	Atomic concurrency accounting
`PeakEwma`, `PeakEwmaGuard`	Latency-and-concurrency estimator
`LoadScore`	Ordered validated score representation

Probe observations

API	Role
`ProbePool`	Bounded, self-expiring pool of out-of-band replica observations
`ProbePoolConfig`, `ProbePoolConfigError`	Capacity, reuse, and age bounds
`ProbeReading`	One reported queue depth and observed latency
`ProbeEntry`	A retained observation and its remaining reuse budget
`ProbeDecision`	A selection against a candidate slice, and the observation behind it
`ProbeDecisionError`	Absent, rejected, and out-of-bounds decision outcomes

`poise-discovery`

API	Role
`Directory`	Single-writer transactional membership state
`Change`, `Effect`, `Applied`	Reconciliation input and report
`Revision`	Monotonically increasing snapshot version
`Discovered`, `Membership`	Candidate wrapper and lifecycle
`Snapshot<T>`	Immutable revisioned state
`snapshot_channel`	Single-publisher, multi-reader channel
`SnapshotPublisher`	Atomic publication boundary
`SnapshotReader`, `SnapshotStream`	Coalescing subscribers

`poise-health`

API	Role
`HealthSignal`, `HealthChecked`	Composable candidate eligibility
`PassiveHealth`, `CircuitPermit`	Epoch-safe passive circuit
`CircuitConfig`, `CircuitSnapshot`	Circuit configuration and observation
`ActiveHealth`, `ActiveProbe`	Executor-neutral scheduled health state
`ActiveHealthConfig`, `ActiveSnapshot`	Probe thresholds and observation
`OutcomeWindow`, `OutcomeStats`	Bounded recent result history
`PenaltyScore`	Load-compatible recent-failure penalty
`OutlierDetector`, `OutlierReport`	Pure group-relative analysis

`poise-tower`

API	Role
`Endpoint<C, S, L>`	Candidate, Tower service, and generation load tracker
`Balance`	Readiness-aware policy-driven Tower service
`BalanceError`	Selection, readiness, tracker, and service failures
`RequestContext`, `UseRequest`	Borrowed request projection for affinity
`LoadTracker`, `LoadGuard`	Dispatch-time reservation contract
`DiscoveryBalance`	Transactional snapshot-to-endpoint reconciler
`EndpointFactory`, `InFlightFactory`	Service-generation construction
`StreamingDiscoveryBalance`	Discovery-driven Tower service
`StreamingConfig`, `StreamEndPolicy`	Fairness and terminal behavior

Enable the discovery feature for reconciliation APIs.

`poise-tokio`

API	Role
`TokioProbe`	Async probe operation
`ActiveHealthRunner`	Timer and timeout adapter
`ProbeRunnerConfig`, `ProbeTimeoutPolicy`	Runtime-specific probe behavior
`next_snapshot`, `wait_for_revision`	Allocation-free async discovery waits

Features health and discovery are independently selectable.

`poise-observe`

API	Role
`Observer`, `NoopObserver`, `Fanout`	Portable event sink composition
`ObservedPolicy`	Selection decorator
`Attempt`	RAII attempt lifecycle
`Metrics`, `MetricsSnapshot`	Fixed-cardinality cumulative counters
`DecisionEvent`, `AttemptEvent`	Structured portable events
`TracingObserver`, `TracedPolicy`	Optional tracing integration
`TowerObserver`	Optional readiness-failure adapter

The tracing and tower features are off by default.

Documentation layers

This book explains contracts, composition, and operations.
Crate-level rustdoc is the authoritative signature and feature reference.
Source tests are executable examples of edge behavior.
Focused policy chapters define arithmetic and churn guarantees.
The live showcase reports verification provenance, not API documentation.

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