feat(view): D2 Wave 2 — apply managed-lane ops + timer-diff auto-tag new content

Drives fixed-lane C_LANEPLAYS for managed lanes only (name-keyed, ordinal-renumber
safe) in the view shell; diffs live track/item GUIDs on the panel timer to auto-tag
new content to the active mode, first-poll-guarded. Pure guid_diff + lane_keys
modules unit-tested; folds in Wave-1 polish.

src/lane_keys.cpp

@@ -0,0 +1,34 @@
+// lane_keys implementation — pure string convention, no REAPER. See lane_keys.h.
+
+#include "lane_keys.h"
+
+#include <cstring>
+
+namespace reasampler {
+
+namespace {
+// Does `s` start with the managed-lane prefix?
+bool hasManagedPrefix(const std::string& s) {
+    const std::size_t n = std::strlen(kManagedLanePrefix);
+    return s.size() >= n && s.compare(0, n, kManagedLanePrefix) == 0;
+}
+}  // namespace
+
+bool isManagedLaneName(const std::string& laneName) {
+    return hasManagedPrefix(laneName);
+}
+
+std::optional<std::string> managedLaneKey(const std::string& laneName) {
+    if (!hasManagedPrefix(laneName)) return std::nullopt;  // manual/unnamed ⇒ no key
+    // The durable name IS the key (stable across ordinal renumber). Keeping the full
+    // prefixed name — rather than stripping to the mode id — means the key is globally
+    // unambiguous and the ownership index's mode field remains the single source of
+    // truth for which mode owns the lane.
+    return laneName;
+}
+
+std::string laneNameForMode(const std::string& modeId) {
+    return std::string(kManagedLanePrefix) + modeId;
+}
+
+}  // namespace reasampler