Make an FX reclaim step one whole track's chain: drop the resume cursor, yield only between tracks

src/core/view/fx_state.h

@@ -19,9 +19,13 @@ enum class FxWorkKind {
     Offline,  // reclaim: every live FX offline
 };
 
-// One track's whole FX move. Track-granular so a drain may stop between tracks,
-// and resumable WITHIN a track by FX identity: a slot cursor would silently skip
-// or repeat a plugin if the chain were edited between two ticks.
+// One track's whole FX move, and the ATOMIC unit of work: a drain may stop
+// between items, never inside one, so an item is either untouched or complete
+// and no partial state survives a tick boundary. Do not reintroduce a
+// within-track resume cursor — carrying one across ticks meant reconciling it
+// against a chain the user may have edited in between, and the case an FX with
+// no reported identity forced (a cursor that reads as "nothing done yet" and
+// re-walks the item forever) was a live non-termination hazard.
 struct FxTrackWork {
     std::string trackGuid;
     FxWorkKind  kind = FxWorkKind::Offline;
@@ -32,28 +36,8 @@ struct FxTrackWork {
     // read it, so resolveFxWork synthesises the targets from what it is handed.
     std::vector<FxOfflineOp> targets;
 
-    // Identity of the last FX this item's drain completed; empty means EITHER
-    // nothing has completed yet OR the completed FX itself carried no identity
-    // (REAPER reports no GUID for it, or it came from a Slot-keyed record) — see
-    // resumeAfterSlot below, which disambiguates the two. This is load-bearing
-    // for forward progress, not an optimisation: without the disambiguation, an
-    // unidentified FX would look like "none yet" and the drain would restart at
-    // the top of the list every tick, forever. Compare-before-write makes every
-    // write idempotent, so an identity that has since left the chain safely
-    // restarts the item rather than stranding it.
-    std::string resumeAfterFxGuid;
-
-    // Position of the last completed op, consulted only when resumeAfterFxGuid
-    // is empty, to tell "resumed past an unidentified FX at this slot" apart
-    // from "nothing done yet" (-1). Every FxOfflineOp carries its slot
-    // regardless of keying, so this is available for both Online and Offline
-    // work.
-    int resumeAfterSlot = -1;
-
     bool operator==(const FxTrackWork& o) const {
-        return trackGuid == o.trackGuid && kind == o.kind && targets == o.targets &&
-               resumeAfterFxGuid == o.resumeAfterFxGuid &&
-               resumeAfterSlot == o.resumeAfterSlot;
+        return trackGuid == o.trackGuid && kind == o.kind && targets == o.targets;
     }
 };
 
@@ -82,8 +66,8 @@ std::vector<FxOfflineOp> fxRestoreTargets(const ViewModeModel& model,
 
 // Resolves one work item against the chain as it stands, where `liveFxGuids[i]`
 // is the identity of the FX at slot `i` right now (empty when REAPER reported
-// none). Honors the resume point, then matches by identity: an identity that is
-// not live is DROPPED, never re-pointed at a slot.
+// none) — the item's WHOLE move, matched by identity: an identity that is not
+// live is DROPPED, never re-pointed at a slot.
 FxRestoreResolution resolveFxWork(const FxTrackWork& work,
                                   const std::vector<std::string>& liveFxGuids);