Ψ-W1-T2: disjoint per-mode solo surfaces and a playback-gated mode switch

Solo is cached, cleared and replayed per mode on a real switch only; the switch is refused visibly while the transport runs. The footer segment now routes through the activate actions, so a panel switch finally persists.

src/shell/view/CLAUDE.md

@@ -11,11 +11,21 @@ decide membership or mode rules.
 
 ## Invariants
 
-- **Never touches master or `B_MUTE`/`I_SOLO`.** The tool owns only visibility,
-  `B_MAINSEND`, `I_FXEN`, and per-FX offline, on every managed leaf, tagged or
-  untagged. User mute/solo survives every toggle untouched; the master track's
-  visibility flags are never driven (the SDK forbids `B_SHOWINTCP`/`B_SHOWINMIXER`
-  on master).
+- **Never touches master or `B_MUTE`; never LOSES solo.** The tool owns visibility,
+  `B_MAINSEND`, `I_FXEN`, per-FX offline, and — on a real mode switch only —
+  `I_SOLO`, on every managed leaf, tagged or untagged. `B_MUTE` is untouched
+  absolutely. The master track is untouched absolutely: it is outside `GetTrack`'s
+  index space, so it never enters the enumeration any of these writes iterate, and
+  its visibility flags are never driven (the SDK forbids
+  `B_SHOWINTCP`/`B_SHOWINMIXER` on master).
+- **Solo surfaces are disjoint per mode, cached not destroyed.** A real switch
+  (target != active) reads every live track's raw `I_SOLO`, banks the non-zero
+  values against the OUTGOING mode, clears them, and replays the incoming mode's
+  banked values verbatim — solo-in-place and safe-solo variants included, never
+  collapsed to a boolean. This is the same snapshot sense of non-destructive that
+  park/restore already gives visibility and FX state: the user's solo is never
+  lost, only parked with the mode it belongs to. A REAPPLY (target == active —
+  tag/untag/show-both, project load) touches solo not at all.
 - **Parking a track** (inactive-mode leaf) drives `B_SHOWINTCP=0`, `B_SHOWINMIXER=0`
   (hide both panels), `B_MAINSEND=0` (out of mix), `I_FXEN=0` (FX bypassed), and
   `TrackFX_SetOffline(track, fx, true)` for each FX (reclaim CPU) — full CPU-park,
@@ -72,7 +82,8 @@ applies the resulting lane state to live tracks.
 
 ## Modules
 
-- `view` — Design View shell: snapshots flag values before parking, drives hide + CPU-park on inactive-mode leaves (`B_SHOWINTCP`/`B_SHOWINMIXER`/`B_MAINSEND`/`I_FXEN` + per-FX offline), restores from snapshot. **Never touches master or `B_MUTE`/`I_SOLO`.**
+- `view` — Design View shell: snapshots flag values before parking, drives hide + CPU-park on inactive-mode leaves (`B_SHOWINTCP`/`B_SHOWINMIXER`/`B_MAINSEND`/`I_FXEN` + per-FX offline), restores from snapshot. Owns the one discriminator (`target != active`) that separates a real switch from a reapply, and with it both the playback gate (`transportBlocksModeSwitch`) and the solo cache/clear/restore seams. **Never touches master or `B_MUTE`.**
+- `view_solo` — the `I_SOLO` read/write pair behind the per-mode solo surface. Holds no policy: what to cache, clear, or replay is `core/view/solo_cache`.
 
 ## Gotchas
 

src/shell/view/view.cpp

@@ -15,11 +15,14 @@
 
 #include "shell/capture/item_read.h"
 #include "core/view/lane_keys.h"
+#include "core/view/solo_cache.h"
 #include "shell/capture/track_guid.h"
+#include "shell/view/view_solo.h"
 #include "core/view/view_tree.h"
 
 #define REAPERAPI_MINIMAL
 #define REAPERAPI_WANT_CountTracks
+#define REAPERAPI_WANT_GetPlayStateEx
 #define REAPERAPI_WANT_GetTrack
 #define REAPERAPI_WANT_GetMediaTrackInfo_Value
 #define REAPERAPI_WANT_SetMediaTrackInfo_Value
@@ -53,6 +56,19 @@ namespace {
 // I_FREEMODE value for fixed lanes. SDK: 0=normal, 1=free item positioning, 2=fixed lanes.
 constexpr int kFreeModeFixedLanes = 2;
 
+// GetPlayStateEx bitmask. SDK: &1 playing, &2 paused, &4 recording — paused is
+// deliberately excluded, nothing is moving there.
+constexpr int kTransportMoving = 1 | 4;
+
+// GUIDs the plan parks in the mode being entered — the set a solo restore skips.
+std::set<std::string> parkedGuidsOf(const TogglePlan& plan) {
+    std::set<std::string> parked;
+    for (const TrackPlan& tp : plan.park) {
+        if (!tp.flags.empty()) parked.insert(tp.flags.front().guid);
+    }
+    return parked;
+}
+
 // C_LANESCOLLAPSED=2: render a tool-split track like a normal single-lane
 // track showing only the playing lane (SDK: 1=collapsed, 2=hidden-lanes-exist
 // but displays as non-fixed-lane).
@@ -377,11 +393,27 @@ bool applyMintPlan(ViewModeModel& model, const LaneMintPlan& plan,
 
 } // namespace
 
+bool transportBlocksModeSwitch(ReaProject* proj) {
+    if (!GetPlayStateEx) return false;  // fail-open: never gate on a missing API pointer
+    return (GetPlayStateEx(proj) & kTransportMoving) != 0;
+}
+
 bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject* proj) {
     if (!model.modes().contains(targetModeId)) {
         return false;  // reject before touching the project — no partial apply
     }
 
+    // The discriminator behind both halves of the contract in view.h. A gate placed
+    // unconditionally here would break tagging and the project-load reapply during
+    // playback; a solo round on every reapply would flicker the user's solo on every
+    // membership edit.
+    const std::string outgoingModeId = model.activeModeId();
+    const bool realSwitch = targetModeId != outgoingModeId;
+
+    if (realSwitch && transportBlocksModeSwitch(proj)) {
+        return false;  // same fail-closed shape as the mode-exists guard above
+    }
+
     std::vector<std::pair<std::string, MediaTrack*>> handleByGuid;
     std::vector<TrackFolderEntry> entries = readFolderEntries(proj, handleByGuid);
     FolderTree tree = buildFolderTree(entries);
@@ -394,10 +426,26 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
     for (const auto& kv : handleByGuid) liveGuids.insert(kv.first);
     model.reconcile(liveGuids);
 
+    // Read before any write, and while activeModeId() still names the mode being left.
+    const std::map<std::string, int> outgoingSolo =
+        realSwitch ? view::soloedTracks(readTrackSolos(handleByGuid))
+                   : std::map<std::string, int>{};
+
     TogglePlan plan = model.planToggle(tree, targetModeId);
 
     Undo_BeginBlock2(proj);
 
+    // DISJOIN THE SOLO SURFACES. Both this clear and the replay after setActiveMode
+    // ride the existing undo block — one mode toggle stays one Ctrl-Z.
+    if (realSwitch) {
+        model.soloCache().store(outgoingModeId, outgoingSolo);
+        std::vector<view::SoloOp> clearOps;
+        clearOps.reserve(outgoingSolo.size());
+        for (const auto& entry : outgoingSolo)
+            clearOps.push_back(view::SoloOp{entry.first, 0});
+        applySoloOps(handleByGuid, clearOps);
+    }
+
     // PARK: snapshot before mutating, store into the model, then apply.
     for (const TrackPlan& tp : plan.park) {
         if (tp.flags.empty()) continue;  // every op in a TrackPlan targets one track
@@ -454,6 +502,15 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
 
     model.setActiveMode(targetModeId);
 
+    // Replay + consume, before the single relayout below picks the change up.
+    if (realSwitch) {
+        if (const std::map<std::string, int>* cached = model.soloCache().query(targetModeId)) {
+            applySoloOps(handleByGuid,
+                         view::planSoloRestore(*cached, liveGuids, parkedGuidsOf(plan)));
+            model.soloCache().clear(targetModeId);
+        }
+    }
+
     // Force REAPER to rebuild the TCP/MCP now rather than on the next user
     // interaction: TrackList_AdjustWindows(false) does the full relayout owed
     // when tracks appear/disappear; UpdateArrange() repaints.

src/shell/view/view.h

@@ -14,10 +14,19 @@ class ReaProject;
 
 namespace reasampler {
 
-// Snapshots each about-to-park track's flags into `model`, runs planToggle,
-// applies park/restore writes plus parent visibility flags, then sets the
-// active mode. Wrapped in one Undo block. Returns false (no mutation) if
-// `targetModeId` isn't registered. `proj` == nullptr means the current project.
+// True while `proj`'s transport is playing or recording — the condition under which
+// applyMode refuses a real mode switch. Exposed so the panel can paint the footer's
+// [Arrange|Design] segments disabled BEFORE the click rather than only refusing on
+// it. `proj` == nullptr means the current project.
+bool transportBlocksModeSwitch(ReaProject* proj);
+
+// Snapshots each about-to-park track's flags into `model`, caches/clears the
+// outgoing mode's solo state and replays the incoming mode's, runs planToggle,
+// applies park/restore writes plus parent visibility flags, then sets the active
+// mode. Wrapped in one Undo block. Returns false (no mutation) if `targetModeId`
+// isn't registered, or if this is a real switch (target != active) while the
+// transport is running. A reapply (target == active) is never gated and never
+// touches solo. `proj` == nullptr means the current project.
 bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject* proj);
 
 // Splits any track visible in more than one mode while carrying its own media

src/shell/view/view_solo.cpp

@@ -0,0 +1,47 @@
+// See view_solo.h. Compiled into the reaper_reasampler module; includes
+// reaper_plugin_functions.h without REAPERAPI_IMPLEMENT (main.cpp owns that).
+
+#include "shell/view/view_solo.h"
+
+#include <map>
+
+#define REAPERAPI_MINIMAL
+#define REAPERAPI_WANT_GetMediaTrackInfo_Value
+#define REAPERAPI_WANT_SetMediaTrackInfo_Value
+#include "reaper_plugin_functions.h"
+
+namespace reasampler {
+
+namespace {
+// SDK: int, 0=not soloed, 1=soloed, 2=soloed in place, 5=safe soloed,
+// 6=safe soloed in place. Documented under SetMediaTrackInfo_Value with no
+// read-only marker (unlike B_RECMON_IN_EFFECT in the same list), so it is settable.
+constexpr const char* kSoloParm = "I_SOLO";
+}  // namespace
+
+std::vector<view::TrackSolo> readTrackSolos(const TrackHandles& handles) {
+    std::vector<view::TrackSolo> live;
+    live.reserve(handles.size());
+    for (const auto& [guid, tr] : handles) {
+        if (!tr) continue;
+        live.push_back(view::TrackSolo{
+            guid, static_cast<int>(GetMediaTrackInfo_Value(tr, kSoloParm))});
+    }
+    return live;
+}
+
+void applySoloOps(const TrackHandles& handles, const std::vector<view::SoloOp>& ops) {
+    if (ops.empty()) return;  // the common case: nothing soloed, no project write
+
+    std::map<std::string, int> byGuid;
+    for (const view::SoloOp& op : ops) byGuid[op.guid] = op.value;
+
+    for (const auto& [guid, tr] : handles) {
+        if (!tr) continue;
+        auto it = byGuid.find(guid);
+        if (it == byGuid.end()) continue;
+        SetMediaTrackInfo_Value(tr, kSoloParm, static_cast<double>(it->second));
+    }
+}
+
+} // namespace reasampler

src/shell/view/view_solo.h

@@ -0,0 +1,28 @@
+#pragma once
+// The REAPER read/write half of the per-mode solo surface. Every decision about what
+// to cache, clear, or replay is core/view/solo_cache; this pair only moves I_SOLO
+// between the live tracks and that pure plan.
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "core/view/solo_cache.h"
+
+// Forward-declared to keep this header SDK-free; the .cpp includes the real SDK header.
+class MediaTrack;
+
+namespace reasampler {
+
+// The (GUID, handle) enumeration applyMode builds from GetTrack. GetTrack's index
+// space excludes the master track, so no solo read or write reachable through this
+// type can ever land on master.
+using TrackHandles = std::vector<std::pair<std::string, MediaTrack*>>;
+
+std::vector<view::TrackSolo> readTrackSolos(const TrackHandles& handles);
+
+// Applies each op to its live handle in ONE pass over `handles`; an op naming a GUID
+// absent from the enumeration is skipped (stale/deleted track).
+void applySoloOps(const TrackHandles& handles, const std::vector<view::SoloOp>& ops);
+
+} // namespace reasampler