feat(capture): bindable capture family — master/tracks/items/razor (M7)

Four wet capture actions route to OfflineRenderBackend (snapshot/restore
RENDER_*, 32-bit float), produce a Sample, add to the bank, persist. Pure
render_settings maps source mode to RENDER_SETTINGS and parses P_RAZOREDITS
(tested). No arrange insertion. True dry deferred to M10.

src/capture.cpp

@@ -4,10 +4,19 @@
 // reaper_plugin_functions.h WITHOUT REAPERAPI_IMPLEMENT — main.cpp is the one TU
 // that defines the API pointers; here they are extern (CLAUDE.md §contract).
 //
-// Scope (M3): ONE source mode — the time-selection master mix. Drives the
-// RENDER_* project settings via GetSetProjectInfo / _String, snapshots and
-// restores every setting it changes (non-destructive), triggers a render, then
-// populates a Sample. It NEVER inserts into the arrange (load-bearing principle).
+// Scope (M7): the full offline source family — master mix / time selection,
+// selected tracks, selected items, razor area — all wet-only with optional tail.
+// Drives the RENDER_* project settings via GetSetProjectInfo / _String
+// (the source-selection bits come from render_settings.cpp, the pure mapping),
+// snapshots and restores every setting it changes (non-destructive), triggers a
+// render, then populates a Sample. It NEVER inserts into the arrange
+// (load-bearing principle) — RENDER_ADDTOPROJ&1 is cleared on every path.
+//
+// The backend is SOURCE-AGNOSTIC: it does NOT read the DAW selection. The action
+// layer (main.cpp) resolves each source mode to a concrete time range (+ track
+// GUIDs for track captures) and hands it in via the CaptureRequest. This keeps
+// the render-driving here and the selection-reading testable/visible up in the
+// actions layer.
 //
 // RENDER PROGRESS WINDOW (Item 2 finding — not suppressible via stock API):
 // Triggering kActionRenderUsingMostRecentSettings (42230) causes REAPER to show
@@ -30,6 +39,7 @@
 #include <vector>
 
 #include "capture_paths.h"
+#include "render_settings.h"
 
 #define REAPERAPI_MINIMAL
 #define REAPERAPI_WANT_EnumProjects
@@ -61,11 +71,6 @@ constexpr int kActionRenderUsingMostRecentSettings = 42230;
 // ourselves for exact, unrounded bounds). Verified: SDK header line ~3042.
 constexpr double kBoundsCustom = 0.0;
 
-// RENDER_SETTINGS master-mix bit pattern. Per the SDK header (line ~3041):
-// (&(1|2))==0 => master mix, &8=use render matrix. We want plain master mix:
-// no stems (bits 1|2 clear), no render matrix. Value 0 = master mix, no matrix.
-constexpr double kRenderSettingsMasterMix = 0.0;
-
 // RENDER_TAILFLAG bit &1 = apply tail for custom time bounds. We clear it for
 // the spike (exact bounds, no added silence — precision invariant).
 constexpr double kTailFlagNone = 0.0;
@@ -226,13 +231,16 @@ std::string makeUniqueTag() {
 CaptureResult OfflineRenderBackend::capture(const CaptureRequest& request) {
     CaptureResult result;
 
-    // M3 implements only the master-mix / time-selection case. Both mean "render
-    // the master mix over the requested bounds".
-    if (request.sourceMode != SourceMode::MasterMix &&
-        request.sourceMode != SourceMode::TimeSelection) {
+    // Resolve the RENDER_SETTINGS source/processing bits for this mode + wet/dry
+    // (pure mapping, unit-tested in render_settings). An unsupported mode (only
+    // SourceMode::Realtime — that is the M8 realtime backend) is refused here so
+    // the offline path never silently renders the wrong thing.
+    const RenderSettingsChoice choice =
+        renderSettingsFor(request.sourceMode, request.wetDry);
+    if (!choice.supported) {
         result.status  = CaptureStatus::UnsupportedMode;
-        result.message = "OfflineRenderBackend (M3) supports only master-mix / "
-                         "time-selection capture.";
+        result.message = "OfflineRenderBackend does not render this source mode "
+                         "(realtime capture is the M8 backend).";
         return result;
     }
 
@@ -350,8 +358,11 @@ CaptureResult OfflineRenderBackend::capture(const CaptureRequest& request) {
         GetSetProjectInfo(proj, "RENDER_TAILMS", 0.0, true);
     }
 
-    // Master mix, no stems, no render matrix.
-    GetSetProjectInfo(proj, "RENDER_SETTINGS", kRenderSettingsMasterMix, true);
+    // Source-selection bits for this mode, from the pure render_settings mapping
+    // (verified against SDK header ~3041). All M7 actions are wet-only:
+    // master mix = 0; tracks = &128; items = &32|single-file; razor = &4096|single-file.
+    GetSetProjectInfo(proj, "RENDER_SETTINGS",
+                      static_cast<double>(choice.settings), true);
 
     // Resolve the effective sample rate. When the request carries 0 ("follow
     // project"), read PROJECT_SRATE explicitly so RENDER_SRATE is set to the
@@ -448,6 +459,10 @@ CaptureResult OfflineRenderBackend::capture(const CaptureRequest& request) {
     // Seconds are the authoritative source for the render. Do NOT add DAW-
     // unverifiable PPQ resolution here — it requires a live REAPER to validate.
     s.wetDry        = request.wetDry;
+    // Track GUIDs for track-scoped captures (empty for master/items/razor). The
+    // caller resolved the selection to canonical GUID strings; we record them so a
+    // "re-capture from source" (M10) knows which tracks the sample came from.
+    s.trackGuids    = request.trackGuids;
     s.channelCount  = request.channelCount;
     // Store the resolved sample rate only when it is known (> 0). If the project
     // never pinned a rate (PROJECT_SRATE read 0), we did not force RENDER_SRATE
@@ -465,7 +480,7 @@ CaptureResult OfflineRenderBackend::capture(const CaptureRequest& request) {
 
     result.status  = CaptureStatus::Ok;
     result.sample  = s;
-    result.message = "Captured master mix [" +
+    result.message = "Captured [" +
                      std::to_string(request.startSeconds) + "s, " +
                      std::to_string(request.endSeconds) + "s] -> " +
                      paths.relativePath;