Added the system from trail

Runtime/DialogLineLibrary.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace Jovian.EncounterSystem {
+    /// <summary>One dialog line — an id/text pair in a <see cref="DialogLineLibrary"/>.</summary>
+    [Serializable]
+    public class DialogLine {
+        /// <summary>Stable key referenced by <see cref="DialogLineRef"/> (e.g. "common.farewell").</summary>
+        public string id;
+
+        /// <summary>The actual text shown to the player.</summary>
+        [TextArea(2, 6)]
+        public string text;
+    }
+
+    /// <summary>
+    /// Single-asset registry of reusable dialog lines. One library file holds many lines; dialog
+    /// options reference them by id via <see cref="DialogLineRef"/>. Split into multiple libraries
+    /// (e.g. CommonLines, TownDialogue) only when a single file becomes unwieldy.
+    /// </summary>
+    [CreateAssetMenu(fileName = "DialogLineLibrary", menuName = "Jovian/Encounter System/Dialog Line Library", order = 4)]
+    public class DialogLineLibrary : ScriptableObject {
+        /// <summary>All lines in the library.</summary>
+        public List<DialogLine> lines = new();
+
+        private Dictionary<string, string> cache;
+
+        /// <summary>Return the text for <paramref name="id"/>, or <c>null</c> if not found.</summary>
+        public string Resolve(string id) {
+            if(string.IsNullOrEmpty(id)) {
+                return null;
+            }
+
+            EnsureCache();
+            return cache.TryGetValue(id, out var text) ? text : null;
+        }
+
+        /// <summary>Force the next <see cref="Resolve"/> call to rebuild the id → text cache.
+        /// Called automatically from <c>OnValidate</c> after inspector edits.</summary>
+        public void InvalidateCache() {
+            cache = null;
+        }
+
+        private void EnsureCache() {
+            if(cache != null) {
+                return;
+            }
+
+            cache = new Dictionary<string, string>();
+            if(lines == null) {
+                return;
+            }
+
+            foreach(var line in lines) {
+                if(line != null && !string.IsNullOrEmpty(line.id)) {
+                    cache[line.id] = line.text;
+                }
+            }
+        }
+
+#if UNITY_EDITOR
+        private void OnValidate() {
+            InvalidateCache();
+        }
+#endif
+    }
+}