Fix five Wave-1 pure-layer FX/park review findings: resume-point stall, stale doc comments, implicit mode read, keying reset

src/core/view/fx_state.h

@@ -32,14 +32,28 @@ 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 ⇒ none yet. An
-    // optimisation only: every write is compare-before-write, so an identity that
-    // has since left the chain safely restarts the item rather than stranding it.
+    // 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;
+               resumeAfterFxGuid == o.resumeAfterFxGuid &&
+               resumeAfterSlot == o.resumeAfterSlot;
     }
 };
 
@@ -51,7 +65,13 @@ struct FxTrackWork {
 // opportunistic reclaim that may be deferred indefinitely without losing
 // anything. Within a kind, GUID order — deterministic, so a drain's position in
 // the list survives a re-derivation.
+//
+// `targetMode` is explicit, mirroring planToggle, rather than read from
+// `model.activeModeId()`: applyMode sets the active mode LAST, after its park
+// and restore loops, so a caller reading it from inside or before that block
+// would classify every track against the OUTGOING mode instead.
 std::vector<FxTrackWork> desiredFxState(const ViewModeModel& model,
+                                        const std::string& targetMode,
                                         const std::set<std::string>& liveTrackGuids);
 
 // One track's Online targets from its park record's FX half; empty when the