v1.18.0-Tavush

Metadata takes any ordered or bool value, activations run on a worker pool, every container
iterates the same way, and a long list of hook, livelock, pipe and retry fixes.

BREAKING

All() is the one iterator on every container, and it is an iter.Seq. signal.Group,
port.Group, port.Collection, component.Collection, cycle.Group and
ActivationResultCollection all have All() iter.Seq[T]: insertion order on the groups, name order
on the keyed collections. It replaces ForEach, ForEachIf, Each, AllOrdered, the
slice-returning All() on the groups and the map-returning All() on the keyed types.
signal.Group.AllPayloads() becomes Payloads() iter.Seq[any], and cycle.Group gains
ByNumber(n), since with a history limit a cycle's position is not its number.

// before
err := p.Signals().ForEach(func(s *signal.Signal) error { use(s); return nil })
for _, s := range p.Signals().All() { use(s) }
payloads := p.Signals().AllPayloads()

// after
for s := range p.Signals().All() { use(s) } // break, continue and return err work as usual
signals := slices.Collect(p.Signals().All())  // when a slice is needed
for payload := range p.Signals().Payloads() { use(payload) }

One vocabulary across groups, collections and activation results.

• Keyed collections (port.Collection, component.Collection): Any() → First(),
  AnyMatch(p) → Any(p), FindAny(p) → Find(p). ActivationResultCollection.FindAny → Find.
• ActivationResult: ActivationError() → Err(), ActivationErrors() → Errors();
  component.IsWaitingForInput(r) and WantsToKeepInputs(r) become the methods r.IsWaiting()
  and r.KeepsInputs(). ActivationErrorWithComponentName is removed.
• Component.ValidateBeforeAddingToMesh → Validate; PluginRegistered → HasPlugin on both
  FMesh and Component.

// before
if result.ActivationError() != nil { ... }
first := fm.Components().Any()

// after
if result.Err() != nil { ... }
first := fm.Components().First()

Activation results are built whole. NewActivationResult(name, code, errs...) replaces
NewActivationResult(name) plus SetActivated, SetActivationCode and AddActivationError;
Activated() is derived from the code. ActivationResultCollection.Remove and Clear and
cycle.Group.RemoveOldest are removed.

Collection methods with no caller are gone. Map, MapIf and Without on port.Group,
cycle.Group, port.Collection and component.Collection (their elements are live pointers, so
loop in place; Filter stays); component.Collection.Clear; port.Collection.PutSignalsOnEach,
PipeEachTo and Flush; signal.Group.Reduce, Contains and ContainsPayloadFunc
(ContainsPayload stays); the component.ResultMapper type. The port.Group constructors are
unexported.

WithErrorHandlingStrategy rejects an unknown strategy at New, with
ErrUnsupportedErrorHandlingStrategy, instead of failing a cycle after it has already run.

Added

• meta.Value widens from string | float64 to cmp.Ordered | ~bool: a metadata entry can be
  int, bool, any sized int, uint or float, or a named type built on one of them, such as
  type Celsius float64. The read rule is unchanged: an entry reads back only as the type it was
  written with, so Set("n", 3) is read with Value[int], not Value[float64].
• fmesh.WithMaxConcurrency(n) and fmesh.WithUnlimitedConcurrency(). The ready components of a
  cycle share at most n goroutines (default GOMAXPROCS) instead of starting one each, which was
  27 % of CPU in the throughput benchmark.

Changed

• A run allocates about half as much (root benchmarks, geomean vs v1.17.0: allocs/op −51 %,
  B/op −49 %, time/op −36 %). Building a mesh is linear in the number of components (100k
  components in 0.8 s, not 73 s). Run history is released after Run, and history eviction is O(1).
• Observer hooks run every registered hook and join the errors: AfterRun, AfterCycle,
  AfterActivation, OnComponentAdded, OnSignalsDelivered and OnClear. AfterCycle runs
  however the cycle ends, and an AfterRun error is joined to the run's. Before hooks,
  OnCreation, OnSignalsAdded and the pipe hooks stay fail-fast.
• AfterRun hooks receive the context Run was called with, not the run context that a time
  limit has already expired.
• AddComponents validates the whole batch before adopting any component; a rejected batch
  leaves every component where it was.
• Errors from OnClear and OnCreation hooks name the component and port.
• ActivationResultCollection is walked in component-name order, and never runs user code under
  its lock.

Fixed

• Livelock detection counts a stall from its first stalled cycle, so WithLivelockThreshold(n)
  no longer fires one cycle late, and a waiter that drops its inputs is no longer reported as a
  livelock.
• A component whose BeforeActivation hook failed has its inputs cleared, so they no longer pile
  up under IgnoreAll.
• A pipe whose OnOutboundPipe or OnInboundPipe hook fails is removed again, so a retried
  PipeTo no longer delivers every signal twice.
• WithRetry: an output port that was empty before the activation is no longer refilled with an
  empty group between attempts; a WithRetryIf backoff checks the context after waiting; a panic
  on a later attempt keeps the errors of the attempts before it.
• Adding ports or components is all-or-nothing, also for a duplicate within one call; adding them
  one by one is no longer quadratic.
• Doc comments, the wiki and the agent docs were checked against the code and corrected.