fix(D2-W2): correct manual-lane exemption, drop read-only item C_LANEPLAYS write

isOnManualLane predicate now correctly treats unnamed fixed-lane lanes as manual;
item-side C_LANEPLAYS loop removed (SDK read-only); explicit #include <set> in
view_mode_model.cpp; undo-block omission in detectNewContent documented as intentional.

tests/test_lane_keys.cpp

@@ -46,6 +46,29 @@ static void testManagedLaneKey() {
     CHECK(!managedLaneKey("guitar-double").has_value());
 }
 
+static void testIsOnManualLane() {
+    // Non-fixed-lane track: concept does not apply regardless of name.
+    CHECK(!isOnManualLane(false, ""));          // normal track, unnamed ⇒ not manual
+    CHECK(!isOnManualLane(false, "Comp 1"));    // normal track, user name ⇒ not manual
+    CHECK(!isOnManualLane(false, "reasampler:design"));  // normal track, managed name ⇒ not manual
+
+    // Fixed-lane track: managed lane (tool-prefixed) ⇒ NOT manual (tool drives it).
+    CHECK(!isOnManualLane(true, "reasampler:design"));
+    CHECK(!isOnManualLane(true, "reasampler:arrange"));
+    CHECK(!isOnManualLane(true, "reasampler:"));  // prefix-only: still managed
+
+    // Fixed-lane track: unnamed lane (empty P_LANENAME) ⇒ manual.
+    // REAPER starts fixed lanes unnamed; an item on an unnamed fixed lane is a user
+    // comp lane and must be exempt from auto-tag.
+    CHECK(isOnManualLane(true, ""));
+
+    // Fixed-lane track: user-named but non-managed ⇒ manual.
+    CHECK(isOnManualLane(true, "Comp 1"));
+    CHECK(isOnManualLane(true, "Lead vocal"));
+    CHECK(isOnManualLane(true, "reasample"));    // near-miss, no colon ⇒ manual
+    CHECK(isOnManualLane(true, "Reasampler:x")); // wrong case ⇒ manual
+}
+
 static void testRoundTrip() {
     // Minting then reading must agree: managedLaneKey(laneNameForMode(m)) recovers the
     // prefixed name for every mode id.
@@ -62,6 +85,7 @@ static void testRoundTrip() {
 int main() {
     testIsManagedLaneName();
     testManagedLaneKey();
+    testIsOnManualLane();
     testRoundTrip();
 
     if (g_fail == 0) std::printf("All tests passed.\n");