Keep the extension's tick out of REAPER's own project load, and re-earn the park holds across one load

src/app/main.cpp

@@ -183,6 +183,17 @@ static void OnTimer()
     // the idle fast-path is a SINGLE POINTER TEST — drive only when a capture is live.
     if (capture::g_rtCapture) capture::DriveRealtimeCapture(g_session);
 
+    // A project load or save is IN FLIGHT, so this tick is running inside its own message
+    // pump — a restore brings plugins online and a plugin load pumps. Everything below
+    // would then act on a half-restored project: poll() reads the pre-load <EXTSTATE> that
+    // OnBeginLoadProjectState defers past precisely because it is wrong, and the reclaim
+    // tick writes FX into a project REAPER is still rewriting. The extension's other
+    // re-entrancy guards cover OUR pumps; this one covers REAPER's. Consumes nothing, so
+    // the first tick after the load runs as if this one had never been due. Self-lowering
+    // (reaper_plugin_functions.h:1584-1587), and placed after the realtime drive so that
+    // fast path keeps its single-pointer-test shape. See src/shell/view/CLAUDE.md.
+    if (GetCurrentProjectInLoadSave()) return;
+
     // poll()'s undo/redo-reload and project-switch Load branches call
     // loadFromProject, replacing g_session.view() wholesale — deferred here while
     // an applyMode is on the stack (reachable if a pumped message loop re-enters

src/shell/view/CLAUDE.md

@@ -108,9 +108,12 @@ decide membership or mode rules.
   ONE undo block: `applyMode` opens it on a REAL SWITCH ONLY (`fx_reclaim`'s
   `UndoSpan`) and RETURNS WITH IT OPEN, for the reclaimer to close once the drain has
   converged. This does not move an FX write back onto the switch — the writes still
-  run on the timer, off the 1897ms path. Whether a block held from an ACTION into a
-  later timer callback holds is `[verify — DAW]`; if it does not, the switch and its
-  parking land as two points, which is the intended degradation.
+  run on the timer, off the 1897ms path. **DAW-CONFIRMED, no longer inferred:** a block
+  opened in the `applyMode` ACTION and closed several timer callbacks later by the drain
+  holds — switch, then an undisturbed parking drained to completion, then one Ctrl-Z gave
+  exactly ONE undo entry and returned to the previous mode. (The two-point degradation
+  this once hedged against never materialised; the degradations that DO occur are the
+  transport deferral and `mintManagedLanes`' early close, both named below.)
 - **No path may return past a terminating condition with the span open.** A leaked
   block swallows every edit the user makes afterwards, indefinitely, so every
   terminating path routes through ONE idempotent close (`fxReclaimEndUndoSpan`): the
@@ -225,7 +228,30 @@ decide membership or mode rules.
   OFFLINE work once a track has read continuously parked for `kParkHoldMs`
   (3000ms). A flip inside that window flips the flags twice but the debounce
   never matures, so the reclaimer finds every chain already where the record
-  wants it and writes nothing.
+  wants it and writes nothing. **Undoing a switch mid-park is that same flip**, so a
+  state load DROPS the holds where an invalidation keeps them (`FxReclaimQueue::abandon`,
+  and again at the end of `run` for an abandon that arrived through a write's own pump,
+  which found the clock moved into the drain's local). Keeping them fired the post-load
+  re-park on the FIRST tick after the load, with zero debounce, in the wake of REAPER's
+  own restore; re-earning them is what makes the undo cost nothing and keeps the writes
+  clear of the load.
+- **NOTHING THE EXTENSION DOES PER TICK RUNS WHILE REAPER IS IN A PROJECT LOAD OR SAVE.**
+  `BeginLoadProjectState` fires before REAPER restores anything, and the restore itself
+  brings plugins online — a plugin load pumps the message loop, which is how a timer tick
+  lands INSIDE the load. `main.cpp`'s `OnTimer` therefore returns immediately while
+  `GetCurrentProjectInLoadSave()` names a project
+  (`reaper_plugin_functions.h:1584-1587`), self-lowering, with no latch to leak. Without
+  it, that tick's `poll()` reads the half-restored `<EXTSTATE>` — the very pre-load value
+  the hook defers past because it is wrong — the reapply plans against it, and the reclaim
+  tick writes FX into a project REAPER is still rewriting; each such round is its own
+  settle-and-close, so a re-convergence that owes ONE point costs one per round. That last
+  step is reachable by inspection, not measured: the DAW report it answers is one undo
+  entry per FX after a Ctrl-Z mid-drain, and whether this is the whole of that cause is
+  `[verify — DAW]`. The extension's other re-entrancy guards (`modeApplyInProgress`,
+  `fxReclaimDrainInProgress`) cover OUR pumps only; this is the one that covers REAPER's.
+  It consumes nothing — reload request, load signal, wakeup, derived queue and pin all
+  stand. The realtime-capture drive deliberately sits AHEAD of it, keeping its
+  single-pointer-test idle path and its behaviour across a load unchanged.
 - **Show-both semantics:** a per-track "pin visible across modes" flag re-enables
   processing whenever shown. A show-both leaf appears in every mode's visible set
   and is never parked — its driven flags stay at snapshot/restored values, FX

src/shell/view/fx_reclaim.h

@@ -386,8 +386,18 @@ public:
         abandoned_ = true;
         discard();
         pending_ = false;
-        // The pin STAYS — it is what the next tick's retarget tests the debounce clock
-        // against, and that clock outlives this exactly as it outlives an invalidation.
+        // The HOLDS GO, where an invalidation keeps them — the one place the two differ on
+        // the clock, and for the same reason they differ on the wakeup. A hold records "this
+        // track has read continuously parked since T", an observation about the project this
+        // load is replacing; after the load the chains may sit anywhere (an undo of a park
+        // restores them online) and no such continuity is in evidence. Keeping it fired the
+        // post-load re-park on the FIRST tick after the load, with zero debounce, right in
+        // the wake of REAPER's restore. Undoing a switch mid-park is precisely the A->B->A
+        // flip kParkHoldMs exists to make free: re-earning the hold is what makes it free
+        // again, and what keeps the re-convergence's writes clear of the load.
+        clock_.forget();
+        // The pin STAYS — beginTick compares it to decide a retarget, and losing it there
+        // would read as "no project" rather than "same project, nothing derived yet".
     }
 
     // Read by the shell's host on every step; false again from the next run(), because the
@@ -477,6 +487,11 @@ public:
         // The hold is keyed on the track and outlives any re-derivation, so it comes
         // back whether or not the drain's own work survives.
         clock_.swap(clock);
+        // ...but not across a state load. An abandon reaching us through a write's own
+        // message pump found the clock already moved out into the drain's local, so its
+        // forget cleared an empty member; redo it now the holds are back. `abandoned_` is
+        // cleared at this call's entry, so it can only mean an abandon landed inside it.
+        if (abandoned_) clock_.forget();
 
         // Assembled field by field rather than positionally: the aggregate is read by
         // the undo span's close decision now, and a silently mis-slotted bool there
@@ -686,8 +701,9 @@ void fxReclaimLabelUndoSpan(const char* label, int mask);
 void fxReclaimEndUndoSpan();
 
 // EVERY project-state load, undo-driven or not — Ctrl-Z, Ctrl-Shift-Z, a project open, a
-// File > Revert, a new project. Ends the span, stops any drain on the stack, and leaves the
-// loop ASLEEP until something that re-read the model wakes it (FxReclaimQueue::abandon).
+// File > Revert, a new project. Ends the span, stops any drain on the stack, drops the
+// debounce holds, and leaves the loop ASLEEP until something that re-read the model wakes
+// it — FxReclaimQueue::abandon owns all four and the reasoning behind each.
 //
 // Called from the projectconfig BeginLoadProjectState hook, which fires BEFORE REAPER
 // restores anything: that is the ONLY point at which the block can still close over the

tests/test_fx_reclaim.cpp

@@ -1272,14 +1272,75 @@ static void testAStateLoadStopsTheDrainWhereItStandsRatherThanFinishingTheTrack(
     CHECK(q.stale());
     CHECK(!q.pending());
 
-    // ...and the stop belonged to that tick alone. The reloaded project's own drain writes.
+    // ...and the stop belonged to that tick alone. The reloaded project's own drain writes —
+    // but not before its holds are earned again: the abandon dropped them (it reached the
+    // clock through the drain's own local, see FxReclaimQueue::run), so the re-park starts
+    // its 3s from the first post-load tick rather than inheriting the pre-load observation.
     host.abandonAfterWrite = -1;
     q.adopt(derive(vm, {"{T1}", "{T2}"}));
+    CHECK(q.run(host).writes == 0);  // first post-load tick: the holds start here
+    CHECK(!host.offlineAt("{T1}", 1));
+    host.clock += kParkHoldMs;
     CHECK(q.run(host).writes == 2);  // {T1}'s remaining slot, and {T2}'s whole chain
     CHECK(host.offlineAt("{T1}", 1));
     CHECK(host.offlineAt("{T2}", 0));
 }
 
+static void testTheWholePostLoadReconvergenceIsOneSpanHoweverFarTheParkingGot() {
+    // The acceptance property behind a Ctrl-Z landing anywhere in the drain: whatever
+    // fraction of the parking had completed, everything the reloaded project owes rides
+    // ONE span and costs ONE point. Two things carry it — the abandon dropping the holds,
+    // so nothing writes on the tick that re-derives (the load's own wake), and the lazy
+    // open being the drain's, so the many ticks that follow share one block.
+    ViewModeModel vm = parkedDesignLeaves({{"{T1}", {"{FX-A}", "{FX-B}"}},
+                                           {"{T2}", {"{FX-C}"}},
+                                           {"{T3}", {"{FX-D}"}}});
+    FakeHost host;
+    host.chains["{T1}"] = onlineChain({"{FX-A}", "{FX-B}"});
+    host.chains["{T2}"] = onlineChain({"{FX-C}"});
+    host.chains["{T3}"] = onlineChain({"{FX-D}"});
+    host.stepCostMs = 40.0;  // over the offline budget: one track per tick, many ticks
+
+    UndoSpan span;  // the switch's, still open when the undo arrives
+    CHECK(span.begin(kProjA, "ReaSampler: activate Design view", 9));
+    host.span = &span;
+
+    FxReclaimQueue q = queueOf(vm, {"{T1}", "{T2}", "{T3}"});
+    q.run(host);
+    host.clock += kParkHoldMs;
+    host.reentrant         = &q;
+    host.abandonAfterWrite = 1;  // Ctrl-Z one write in — the parking is part-done
+    q.run(host);
+    CHECK(!span.open());  // the terminator closed the switch's point over pre-load state
+    host.reentrant         = nullptr;
+    host.abandonAfterWrite = -1;
+
+    // The reloaded model's reapply raises the wakeup and the queue re-derives.
+    q.invalidate();
+    q.adopt(derive(vm, {"{T1}", "{T2}", "{T3}"}));
+
+    int closes = 0;
+    auto tick = [&]() {
+        const ReclaimRunResult r = q.run(host);
+        if (spanEndsAfter(r) && span.end()) ++closes;
+        return r;
+    };
+
+    CHECK(!tick().settled);   // the holds start here, so this tick writes nothing at all
+    CHECK(host.spanOpens == 0);
+    CHECK(!span.open());
+    CHECK(closes == 0);
+
+    host.clock += kParkHoldMs;
+    int ticks = 0;
+    while (!tick().settled && ++ticks < 20) {}
+    CHECK(ticks >= 2);             // it really did take several ticks to converge...
+    CHECK(host.spanOpens == 1);    // ...under ONE span, opened by the drain's first write
+    CHECK(closes == 1);            // ...closed exactly once, on the tick that settled
+    CHECK(!span.open());
+    CHECK(host.offlineAt("{T1}", 1) && host.offlineAt("{T2}", 0) && host.offlineAt("{T3}", 0));
+}
+
 static void testARevertBetweenTicksLeavesTheLoopAsleepOnAStaleModel() {
     // File > Revert is the load that re-reads NOTHING: it keeps the same ReaProject, so the
     // session's identity poll answers NoOp, no reload follows and therefore no reapply
@@ -1576,6 +1637,7 @@ int main() {
     testADrainNoSwitchOpenedMintsOnePointOfItsOwn();
 
     testAStateLoadStopsTheDrainWhereItStandsRatherThanFinishingTheTrack();
+    testTheWholePostLoadReconvergenceIsOneSpanHoweverFarTheParkingGot();
     testARevertBetweenTicksLeavesTheLoopAsleepOnAStaleModel();
 
     testTheDirectionReadsOnlineWhileTheParksOwnOfflineWorkWaitsOutItsHold();