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echo-suppressor-phase4-live-sites.md

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Echo-suppressor live call-site inventory — refreshed for Phase 4 §4.2

Status: the Phase-0 audit begin-suppress-audit.csv is STALE. Its 24 rows cite legacy Reconciler.Mount.cs / Reconciler.Update.cs line numbers that no longer exist — §4.5 deleted the legacy dispatch-switch arms and §4.2 (part A, commit 8a67e34a) deleted the ~28 orphaned legacy value-control handler bodies they left behind. The categories in the CSV (eliminable-tight-diff / coercion / float-precision / items-coercion / user-state-races) still describe the semantic classes, but the locations are wrong. Use this file as the current source of truth for the §4.2 "eliminate ChangeEchoSuppressor" surface.

This inventory was produced while scoping §4.2 part B and is the prerequisite the spec author asked to refresh before the elimination is attempted (see the §4.2 handoff note in 047-extensible-control-model-phase4-implementation.md).

How the mechanism works today (counter token, causal)

  • ReactorBinding.WriteSuppressed(ctrl, mutate) / WriteSuppressed<T> (PUBLIC API, src/Reactor/Core/ReactorBinding.cs:29-46) bumps ReactorState.EchoSuppressCount then runs mutate.
  • Each control's change-event trampoline calls ChangeEchoSuppressor.ShouldSuppress as its first line; that consumes exactly one pending token (decrement) and returns early, so the synthesized echo from the programmatic write never reaches the user callback. This is a causal token — it suppresses the next event caused by the write, regardless of value.
  • Separately, EchoSuppressScopeDepth (ReactorState, bumped around ApplySetters, Reconciler.cs:2263/2270) suppresses any echo while a user-authored .Set(c => c.IsOn = true) lambda runs — the engine cannot predict which value-bearing DPs the lambda writes, so there is no expected value here.
  • Storage is on the attached ReactorState DP (not a CWT) to survive dual-RCW wrappers (issues #86 / #114).

Why full elimination is a dedicated effort, not an autopilot pass

The spec proposes replacing the counter with per-control "expected Y ± tolerance, suppress one echo" metadata. Independent review (rubber-duck, this session) confirmed this is causally weaker and must not be rushed:

  1. A value-predicate token cannot prove the matching event was caused by the write. A real user event that lands on the same value/tolerance before the pending metadata clears would be swallowed → silent missed callback / state corruption. (Even Slider/NumberBox bounds are user-reachable values.)
  2. EchoSuppressScopeDepth / ApplySetters has no value to compare — a scoped suppression primitive must survive regardless.
  3. ReactorBinding.WriteSuppressed(UIElement, Action) is public and carries no value / readback / property-identity / tolerance — external authors (e.g. the MarqueeControl external proof) rely on the current shape.
  4. Existing fixtures (EchoSuppressionFixtures, Spec047EchoStranding) cover the no-echo and stranded-token classes but not the new "real event coincides with expected value" regression class. New regression coverage is required before any rewrite.

Recommendation: refresh-audit (this file) + new regression fixtures + spec review first; then migrate per-class with the counter retained until every class has a proven replacement. Do not delete the suppressor / EchoSuppressCount / EchoSuppressScopeDepth until all classes below are covered.

Live call sites (post-§4.2A; verified by ripgrep)

Class A — general controlled value (causal counter required)

Trampoline ShouldSuppress gate + WriteSuppressed programmatic write. Value collision possible (user can reproduce the engine-written value), so NOT safe to drop to value-compare.

Site File:line
ControlledPropEntry trampoline / Update V1Protocol/Descriptor/PropEntry.cs:205, 253
HandCodedControlledPropEntry Update V1Protocol/Descriptor/PropEntry.cs:388
AutoSuggestBoxDescriptor …/Descriptors/AutoSuggestBoxDescriptor.cs:63
ComboBoxDescriptor …/Descriptors/ComboBoxDescriptor.cs:44
ExpanderDescriptor …/Descriptors/ExpanderDescriptor.cs:60, 68
FlipViewDescriptor …/Descriptors/FlipViewDescriptor.cs:34
GridViewDescriptor …/Descriptors/GridViewDescriptor.cs:20
ListBoxDescriptor …/Descriptors/ListBoxDescriptor.cs:37
NumberBoxDescriptor (ValueChanged) …/Descriptors/NumberBoxDescriptor.cs:51
PasswordBoxDescriptor …/Descriptors/PasswordBoxDescriptor.cs:35
PivotDescriptor …/Descriptors/PivotDescriptor.cs:32
PipsPagerDescriptor …/Descriptors/PipsPagerDescriptor.cs:31
RadioButtonsDescriptor …/Descriptors/RadioButtonsDescriptor.cs:44
RichEditBoxDescriptor (gate + bare-mount BeginSuppress) …/Descriptors/RichEditBoxDescriptor.cs:51, 91
SelectorBarDescriptor …/Descriptors/SelectorBarDescriptor.cs:36
TabViewDescriptor …/Descriptors/TabViewDescriptor.cs:48
TemplatedFlipViewDescriptor …/Descriptors/TemplatedFlipViewDescriptor.cs:53
TextBoxDescriptor …/Descriptors/TextBoxDescriptor.cs:60
SliderHandler V1Protocol/Handlers/SliderHandler.cs:47, 95
TextBoxHandler V1Protocol/Handlers/TextBoxHandler.cs:94, 119, 126
ToggleSwitchHandler V1Protocol/Handlers/ToggleSwitchHandler.cs:40, 66
CheckBox legacy body (Path-B via CheckBoxHandler) Reconciler.Mount.cs:452,460,468; Reconciler.Update.cs:627,635,643,653

Class B — coercion (Slider/NumberBox Min/Max)

CoercingOneWayPropEntry.Update wraps the write in WriteSuppressed when the new Min/Max coerces the live Value. Bounds are user-reachable → also not collision-immune.

Site File:line
CoercingOneWayPropEntry V1Protocol/Descriptor/PropEntry.cs:502
SliderHandler Min/Max V1Protocol/Handlers/SliderHandler.cs:83, 90
NumberBoxDescriptor Min/Max (.CoercingOneWay) …/Descriptors/NumberBoxDescriptor.cs:71-78

Class C — float precision (NumberBox immediate mode)

Already tolerance-based via AreNumberBoxValuesEquivalent (1e-12 relative), but feeds the Class-A NumberBox callback path.

Site File:line
HandleNumberBoxImmediateTextChanged Reconciler.Mount.cs:427 (BeginSuppress), :423-425 (AreNumberBoxValuesEquivalent)

Class D — collection batch (CalendarView)

Per-mutation IObservableVector echoes suppressed across a clear+add / diff batch. A counter/scope is the natural fit; value-compare does not model "suppress N events".

Site File:line
CollectionDiffControlledPropEntry V1Protocol/Descriptor/PropEntry.cs:818
CalendarViewDescriptor trampoline …/Descriptors/CalendarViewDescriptor.cs:63
SyncSelectedDates shim Reconciler.Update.cs:2551, 2561

Class E — setter scope (no expected value)

Site File:line
EchoSuppressScopeDepth + ApplySetters Reconciler.cs:606, 2263, 2270; consumed in ChangeEchoSuppressor.cs:64

KD-1 drain + public API + source

Site File:line
OnCustomEvent ShouldSuppress drain V1Protocol/ReactorBindingT.cs:178
ReactorBinding<T>.WriteSuppressed (instance) V1Protocol/ReactorBindingT.cs:192
ReactorBinding.WriteSuppressed / <T> (PUBLIC) ReactorBinding.cs:29, 41 → BeginSuppress 33, 45
ChangeEchoSuppressor (the class to delete) ChangeEchoSuppressor.cs:37-73
ReactorState.EchoSuppressCount (the −4-byte field) + resets Reconciler.cs:602, 763, 788, 1097