fix: insert onto selected track(s) at edit cursor, not a new track

Wire both insert actions to CurrentTrack (InsertMedia base 0). Per selected
track: SetOnlyTrackSelected, reset cursor to snapshot, InsertMedia; then restore
original selection + cursor. No-op when no track selected. Corrected stale
extraflags / new-track / preservePitch comments.

tests/test_insert_plan.cpp

@@ -25,11 +25,11 @@ constexpr int MATCH_HALF  = 16;
 constexpr int MATCH_DBL   = 32;
 constexpr int NO_PITCH    = 64;
 
-static void testDefaultIsNewTrackNativeLength() {
-    // Defaults: new track (base 1), no conform, pitch preserved.
+static void testDefaultIsCurrentTrackNativeLength() {
+    // Defaults: current track (base 0), no conform, pitch preserved.
     InsertOptions opts;
     const int mode = computeInsertMode(opts);
-    CHECK(mode == 1);                       // base 1 only, no other bits
+    CHECK(mode == 0);                       // base 0 only, no other bits
     CHECK((mode & STRETCH_FIT) == 0);       // never stretch-to-time-sel
     CHECK((mode & MATCH_1X) == 0);          // no tempo bits at native length
     CHECK((mode & MATCH_HALF) == 0);
@@ -47,11 +47,11 @@ static void testCurrentTrackBaseIsZero() {
 }
 
 static void testConform1xSetsOnlyMatchBit() {
-    InsertOptions opts;                      // new track base 1
+    InsertOptions opts;                      // current track base 0 (default)
     opts.conform = TempoConform::Ratio1x;
     const int mode = computeInsertMode(opts);
     CHECK((mode & MATCH_1X) == MATCH_1X);    // the 1x match bit is set
-    CHECK((mode & 3) == 1);                  // base target unchanged
+    CHECK((mode & 3) == 0);                  // base target: current track (0)
     CHECK((mode & STRETCH_FIT) == 0);        // still never the stretch bit
     CHECK((mode & (MATCH_HALF | MATCH_DBL)) == 0);  // no other ratio bits
     CHECK((mode & NO_PITCH) == 0);           // pitch preserved by default
@@ -87,7 +87,20 @@ static void testPreservePitchGatesTheNoPitchBit() {
     noConformNoPitch.conform = TempoConform::None;
     noConformNoPitch.preservePitch = false;
     CHECK((computeInsertMode(noConformNoPitch) & NO_PITCH) == 0);
-    CHECK(computeInsertMode(noConformNoPitch) == 1);  // just base 1, nothing else
+    CHECK(computeInsertMode(noConformNoPitch) == 0);  // base 0 (current track), nothing else
+}
+
+static void testDefaultActionIsCurrentTrackBase0() {
+    // The default InsertOptions must compute base 0 (current track) so that both
+    // insert actions (default + conform) target the user's selected track(s), not
+    // a new track. This is the wired M6 insert-target change.
+    InsertOptions defaultOpts;
+    CHECK(defaultOpts.target == InsertTarget::CurrentTrack);
+    CHECK((computeInsertMode(defaultOpts) & 3) == 0);  // base 0
+
+    InsertOptions conformOpts;
+    conformOpts.conform = TempoConform::Ratio1x;
+    CHECK((computeInsertMode(conformOpts) & 3) == 0);  // conform variant also base 0
 }
 
 static void testStretchBitNeverSetAcrossAllOptions() {
@@ -107,11 +120,12 @@ static void testStretchBitNeverSetAcrossAllOptions() {
 }
 
 int main() {
-    testDefaultIsNewTrackNativeLength();
+    testDefaultIsCurrentTrackNativeLength();
     testCurrentTrackBaseIsZero();
     testConform1xSetsOnlyMatchBit();
     testConformHalfAndDoubleRatios();
     testPreservePitchGatesTheNoPitchBit();
+    testDefaultActionIsCurrentTrackBase0();
     testStretchBitNeverSetAcrossAllOptions();
 
     if (g_fail == 0) std::printf("insert_plan: all tests passed\n");