More const qualifications. The source of a paste is const.

src/LabelTrack.cpp

@@ -2471,7 +2471,7 @@ bool LabelTrack::Copy(double t0, double t1, Track ** dest)
 }
 
 
-bool LabelTrack::PasteOver(double t, Track * src)
+bool LabelTrack::PasteOver(double t, const Track * src)
 {
    if (src->GetKind() != Track::Label)
       return false;
@@ -2497,7 +2497,7 @@ bool LabelTrack::PasteOver(double t, Track * src)
    return true;
 }
 
-bool LabelTrack::Paste(double t, Track *src)
+bool LabelTrack::Paste(double t, const Track *src)
 {
    if (src->GetKind() != Track::Label)
       return false;

src/LabelTrack.h

@@ -159,7 +159,7 @@ class AUDACITY_DLL_API LabelTrack final : public Track
    // one in Track.
    bool Copy (double t0, double t1, Track ** dest) override;// const;
    bool Clear(double t0, double t1) override;
-   bool Paste(double t, Track * src) override;
+   bool Paste(double t, const Track * src) override;
    bool Repeat(double t0, double t1, int n);
 
    bool Silence(double t0, double t1) override;
@@ -220,7 +220,7 @@ class AUDACITY_DLL_API LabelTrack final : public Track
    void MayMoveLabel( int iLabel, int iEdge, double fNewTime);
 
    // This pastes labels without shifting existing ones
-   bool PasteOver(double t, Track *src);
+   bool PasteOver(double t, const Track *src);
 
    // PRL:  These functions were not used because they were not overrides!  Was that right?
    //bool SplitCut(double b, double e, Track **dest) /* not override */;

src/NoteTrack.cpp

@@ -520,7 +520,7 @@ bool NoteTrack::Clear(double t0, double t1)
    return true;
 }
 
-bool NoteTrack::Paste(double t, Track *src)
+bool NoteTrack::Paste(double t, const Track *src)
 {
    // Paste inserts src at time t. If src has a positive offset,
    // the offset is treated as silence which is also inserted. If

src/NoteTrack.h

@@ -93,7 +93,7 @@ class AUDACITY_DLL_API NoteTrack final : public Track {
    bool Copy (double t0, double t1, Track **dest) override;
    bool Trim (double t0, double t1) /* not override */;
    bool Clear(double t0, double t1) override;
-   bool Paste(double t, Track *src) override;
+   bool Paste(double t, const Track *src) override;
    bool Shift(double t) /* not override */;
 
 #ifdef EXPERIMENTAL_MIDI_OUT

src/Track.h

@@ -183,7 +183,7 @@ class AUDACITY_DLL_API Track /* not final */ : public XMLTagHandler
    virtual bool Cut  (double WXUNUSED(t0), double WXUNUSED(t1), Track ** WXUNUSED(dest)) {return false;}
    virtual bool Copy (double WXUNUSED(t0), double WXUNUSED(t1), Track ** WXUNUSED(dest)) {return false;}
    virtual bool Clear(double WXUNUSED(t0), double WXUNUSED(t1)) {return false;}
-   virtual bool Paste(double WXUNUSED(t), Track * WXUNUSED(src)) {return false;}
+   virtual bool Paste(double WXUNUSED(t), const Track * WXUNUSED(src)) {return false;}
 
    // This can be used to adjust a sync-lock selected track when the selection
    // is replaced by one of a different length.

src/WaveTrack.cpp

@@ -1181,7 +1181,7 @@ bool WaveTrack::SyncLockAdjust(double oldT1, double newT1)
    return true;
 }
 
-bool WaveTrack::Paste(double t0, Track *src)
+bool WaveTrack::Paste(double t0, const Track *src)
 {
    bool editClipCanMove = true;
    gPrefs->Read(wxT("/GUI/EditClipCanMove"), &editClipCanMove);

src/WaveTrack.h

@@ -156,7 +156,7 @@ class AUDACITY_DLL_API WaveTrack final : public Track {
    bool Cut(double t0, double t1, Track **dest) override;
    bool Copy(double t0, double t1, Track **dest) override;
    bool Clear(double t0, double t1) override;
-   bool Paste(double t0, Track *src) override;
+   bool Paste(double t0, const Track *src) override;
    bool ClearAndPaste(double t0, double t1,
                               Track *src,
                               bool preserve = true,