Assets/_Project/Scripts/Gameplay/PlayerGoldManager.cs

@@ -143,11 +143,17 @@ namespace TD.Gameplay
         /// <summary>
         /// Server-side entry point for awarding gold (wave clear, enemy kill).
         /// Direct call — not Rpc-wrapped — because awards always originate
-        /// from server-authoritative game events. Also increments
-        /// <see cref="GoldEarnedThisWave"/> so the HUD's per-wave counter reflects
-        /// it; spending does not decrement that counter (it tracks earnings, not balance).
+        /// from server-authoritative game events. When <paramref name="countAsEarned"/>
+        /// is true (the default) it also increments <see cref="GoldEarnedThisWave"/> so the
+        /// HUD's per-wave counter reflects it; spending does not decrement that counter (it
+        /// tracks earnings, not balance).
         /// </summary>
-        public void AwardGold(int amount)
+        /// <param name="countAsEarned">
+        /// Pass false for gold returned to the player that isn't income — e.g. a tower-sell
+        /// refund. The player's balance still rises, but the per-wave "earned" counter does not,
+        /// so refunds don't inflate round-income stats.
+        /// </param>
+        public void AwardGold(int amount, bool countAsEarned = true)
         {
             if (!IsServer)
             {
@@ -158,7 +164,7 @@ namespace TD.Gameplay
 
             if (amount <= 0) return;
             currentGold.Value += amount;
-            goldEarnedThisWave.Value += amount;
+            if (countAsEarned) goldEarnedThisWave.Value += amount;
         }
 
         /// <summary>

Assets/_Project/Scripts/Gameplay/TowerInstance.cs

@@ -105,6 +105,24 @@ namespace TD.Gameplay
                 readPerm: NetworkVariableReadPermission.Everyone,
                 writePerm: NetworkVariableWritePermission.Server);
 
+        // Total gold sunk into this tower: its placement cost plus any gold later spent
+        // upgrading it. Set on the server at spawn (= placement cost) and grown by the
+        // (future) upgrade system via ServerAddUpgradeInvestment. Replicated so the HUD's
+        // Sell button can preview the exact refund without a server round-trip.
+        private readonly NetworkVariable<int> goldInvested =
+            new NetworkVariable<int>(
+                0,
+                readPerm: NetworkVariableReadPermission.Everyone,
+                writePerm: NetworkVariableWritePermission.Server);
+
+        // Number of upgrades applied to this tower. 0 = never upgraded. Drives the Wall's
+        // "full refund only while un-upgraded" rule and will back tier display later.
+        private readonly NetworkVariable<int> upgradeCount =
+            new NetworkVariable<int>(
+                0,
+                readPerm: NetworkVariableReadPermission.Everyone,
+                writePerm: NetworkVariableWritePermission.Server);
+
         // ----- Local resolved state -------------------------------------------
 
         // Resolved on every client in OnNetworkSpawn from definitionTypeId via the catalog.
@@ -144,6 +162,12 @@ namespace TD.Gameplay
         /// <summary>The footprint anchor tile (SW corner, world-tile coords).</summary>
         public Vector2Int AnchorTile => anchorTile.Value;
 
+        /// <summary>Total gold sunk into this tower so far (placement + upgrades).</summary>
+        public int GoldInvested => goldInvested.Value;
+
+        /// <summary>How many upgrades have been applied to this tower (0 = never upgraded).</summary>
+        public int UpgradeCount => upgradeCount.Value;
+
         /// <summary>World-unit height the post-construction drop animation falls from.</summary>
         public float DropHeight => dropHeight;
 
@@ -254,6 +278,11 @@ namespace TD.Gameplay
                 anchorTile.Value = pendingAnchor;
                 ownerSlot.Value = pendingOwner;
 
+                // Seed invested gold with the placement cost — the same amount
+                // TowerPlacementManager deducted to build this tower. The upgrade system
+                // grows this later via ServerAddUpgradeInvestment.
+                goldInvested.Value = pendingDefinition != null ? pendingDefinition.GoldCost : 0;
+
                 // Clear the pending data — it's now committed to NetworkVariables.
                 hasPendingInit = false;
             }
@@ -345,6 +374,84 @@ namespace TD.Gameplay
         // Re-tint on every client (and the server) when the replicated paint color changes.
         private void HandlePaintColorChanged(PaintColor previous, PaintColor current) => ApplyTint();
 
+        // ----- Selling --------------------------------------------------------
+
+        // Server-only guard: a fast double-click could deliver two sell RPCs before the
+        // despawn propagates. Mirrors BuildSiteVisual.serverCancelled.
+        private bool serverSold;
+
+        /// <summary>
+        /// Gold returned if this tower is sold right now. Single source of truth for both
+        /// the server (which awards it) and the HUD (which labels the Sell button). By
+        /// default this is <see cref="TowerDefinition.SellRefundPercent"/> of everything
+        /// invested; a tower flagged <see cref="TowerDefinition.FullRefundIfUnupgraded"/>
+        /// (the Wall) returns the full amount while it has never been upgraded.
+        /// </summary>
+        public int ComputeSellRefund()
+        {
+            int invested = goldInvested.Value;
+            if (resolvedDefinition == null)
+                return Mathf.RoundToInt(invested * 0.75f);
+
+            if (resolvedDefinition.FullRefundIfUnupgraded && upgradeCount.Value == 0)
+                return invested;
+
+            return Mathf.RoundToInt(invested * resolvedDefinition.SellRefundPercent);
+        }
+
+        /// <summary>
+        /// Server-only: records gold spent upgrading this tower (so a later sell refunds a
+        /// share of it) and marks the tower upgraded — which forfeits any
+        /// full-refund-while-unupgraded rule. The upgrade system calls this when it lands.
+        /// </summary>
+        public void ServerAddUpgradeInvestment(int cost)
+        {
+            if (!IsServer) return;
+            if (cost > 0) goldInvested.Value += cost;
+            upgradeCount.Value += 1;
+        }
+
+        /// <summary>
+        /// Client → server request to sell this tower. Accepted only from the tower's owner
+        /// (same ownership rule as placement and paint). The server refunds gold, broadcasts
+        /// the sell VFX/SFX from a persistent object, then despawns the tower —
+        /// <see cref="OnNetworkDespawn"/> restores the footprint's grid state and clears
+        /// selection on every peer.
+        /// </summary>
+        [Rpc(SendTo.Server)]
+        public void RequestSellServerRpc(RpcParams rpcParams = default)
+        {
+            if (!IsServer) return;
+            if (serverSold) return; // idempotent guard against a double-click
+
+            ulong senderClientId = rpcParams.Receive.SenderClientId;
+            PlayerSlot senderSlot = PlayerMatchState.SlotForClient(senderClientId);
+            if (senderSlot == PlayerSlot.None || senderSlot != ownerSlot.Value)
+            {
+                Debug.Log($"[TowerInstance] Sell rejected: client {senderClientId} " +
+                          $"({senderSlot}) does not own tower owned by {ownerSlot.Value}.");
+                return;
+            }
+
+            serverSold = true;
+
+            int refund = ComputeSellRefund();
+            var goldManager = PlayerGoldManager.GetForClient(senderClientId);
+            if (goldManager != null && refund > 0)
+                // countAsEarned: false — a sell refund returns spent gold, it is not round
+                // income, so it must not inflate the per-wave "earned" counter.
+                goldManager.AwardGold(refund, countAsEarned: false);
+
+            // Broadcast VFX/SFX from the persistent placement manager, capturing the world
+            // position NOW — this NetworkObject despawns below, so it can't carry the RPC to
+            // remote peers itself (same reason WaveManager routes kill/leak popups).
+            var pm = TowerPlacementManager.Instance;
+            if (pm != null) pm.BroadcastSellEffect(transform.position);
+
+            if (NetworkObject != null && NetworkObject.IsSpawned)
+                NetworkObject.Despawn(destroy: true);
+        }
+
         // ----- IMinimapEntity -------------------------------------------------
         //
         // Towers are static, so WorldPosition is cheap (no movement to track). Color reflects

Assets/_Project/Scripts/Gameplay/TowerPlacementManager.cs

@@ -5,6 +5,7 @@ using UnityEngine;
 using TD.Core;
 using TD.Levels;
 using TD.Towers;
+using TD.VFX;
 
 namespace TD.Gameplay
 {
@@ -350,6 +351,26 @@ namespace TD.Gameplay
                       $"client {req.SenderClientId} ({placingSlot}) at anchor {req.Anchor}.");
         }
 
+        // ----- Sell effects (persistent broadcaster) ----------------------
+
+        /// <summary>
+        /// Server-only: tells every peer to play the tower-sold VFX/SFX at
+        /// <paramref name="worldPos"/>. Called by <see cref="TowerInstance"/> as it sells,
+        /// because the tower's own NetworkObject despawns the same frame — a persistent
+        /// object must carry the broadcast so it isn't dropped.
+        /// </summary>
+        public void BroadcastSellEffect(Vector3 worldPos)
+        {
+            if (!IsServer) return;
+            PlaySellEffectRpc(worldPos);
+        }
+
+        [Rpc(SendTo.Everyone)]
+        private void PlaySellEffectRpc(Vector3 worldPos)
+        {
+            SellEffectSpawner.Instance?.Play(worldPos);
+        }
+
         // ----- Server-side commit hooks called by Builder ------------------
 
         /// <summary>

Assets/_Project/Scripts/Towers/TowerDefinition.cs

@@ -47,6 +47,22 @@ namespace TD.Towers
                  "successful server-side placement validation.")]
         public int GoldCost;
 
+        // -------------------------------------------------------------------
+        // Selling
+        // -------------------------------------------------------------------
+
+        [Header("Selling")]
+        [Tooltip("Portion of the gold INVESTED in this tower (placement cost plus any gold " +
+                 "later spent upgrading it) that is refunded when it is sold, as a 0–1 factor. " +
+                 "Default 0.75 = 75%.")]
+        [Range(0f, 1f)]
+        public float SellRefundPercent = 0.75f;
+
+        [Tooltip("When true, this tower refunds 100% of its invested gold while it has never " +
+                 "been upgraded (upgradeCount == 0); once upgraded it falls back to " +
+                 "SellRefundPercent. Set on the Wall so a fresh wall can be re-mazed for free.")]
+        public bool FullRefundIfUnupgraded = false;
+
         // -------------------------------------------------------------------
         // Construction
         // -------------------------------------------------------------------

Assets/_Project/Scripts/UI/HUDController.cs

@@ -1178,19 +1178,30 @@ namespace TD.UI
             return btn;
         }
 
+        // Sell action for a completed tower. Refund is computed on the TowerInstance (single
+        // source of truth shared with the server) so the badge shows exactly what the player
+        // gets back. Hotkey is Key.None: the bottom-right slot's letter (B) is already the
+        // global buff-menu toggle — see CreateBuffMenuButton — so binding it here would fire
+        // both. The button stays click-only.
         private VisualElement CreateSellButton(TowerInstance tower, Key hotkey)
         {
-            int sellValue = tower.Definition != null
-                ? Mathf.RoundToInt(tower.Definition.GoldCost * 0.7f)
-                : 0;
+            // Only the tower's owner can sell it (the server enforces this too). A non-owner
+            // may have this tower view-selected — show the slot disabled with no refund badge
+            // so the action reads as unavailable rather than misleading.
+            bool ownedByLocal = tower != null
+                                && PlayerMatchState.Local != null
+                                && tower.Owner == PlayerMatchState.Local.Slot;
+
+            int sellValue = ownedByLocal ? tower.ComputeSellRefund() : 0;
             var btn = CreateActionButton(
                 costText: sellValue > 0 ? $"+{sellValue}g" : "",
-                hotkey: hotkey,
+                hotkey: Key.None,
                 onClick: () =>
                 {
-                    /* TODO: sell flow */
+                    if (tower != null)
+                        tower.RequestSellServerRpc();
                 });
-            btn.SetEnabled(false);
+            btn.SetEnabled(ownedByLocal);
             return btn;
         }
 
@@ -1437,7 +1448,11 @@ namespace TD.UI
                 ttStats.text = "(stats pending)";
             }
 
-            int sellValue = Mathf.RoundToInt(def.GoldCost * 0.7f);
+            // Sell preview for a freshly placed (un-upgraded) tower: mirrors
+            // TowerInstance.ComputeSellRefund for invested == GoldCost, upgradeCount == 0.
+            int sellValue = def.FullRefundIfUnupgraded
+                ? def.GoldCost
+                : Mathf.RoundToInt(def.GoldCost * def.SellRefundPercent);
             ttCost.text = $"Cost: {def.GoldCost}g  ·  Sell: {sellValue}g";
         }
 

Assets/_Project/Scripts/VFX/CoinBurstVfx.cs

@@ -0,0 +1,101 @@
+// Assets/_Project/Scripts/VFX/CoinBurstVfx.cs
+using UnityEngine;
+
+namespace TD.VFX
+{
+    /// <summary>
+    /// Self-contained, code-configured gold-coin burst used as the zero-art placeholder for the
+    /// tower-sell effect. Configures its own <see cref="ParticleSystem"/> for a short radial
+    /// spray of gold specks thrown up in random arcs under gravity, then destroys itself.
+    /// </summary>
+    /// <remarks>
+    /// Instantiated at runtime by <see cref="SellEffectSpawner"/> when no authored VFX prefab is
+    /// assigned. It can also be dropped on a prefab in the editor and tuned. Replace with an
+    /// authored particle / VFX-graph prefab (assigned on the spawner) when art is ready — nothing
+    /// else needs to change.
+    /// </remarks>
+    [RequireComponent(typeof(ParticleSystem))]
+    public class CoinBurstVfx : MonoBehaviour
+    {
+        [Tooltip("How many coin specks to throw.")]
+        [SerializeField] private int coinCount = 14;
+
+        [Tooltip("Longest a speck lives (seconds). The whole effect self-destructs shortly after.")]
+        [SerializeField] private float lifetime = 0.6f;
+
+        [Tooltip("Gold tint applied to the specks.")]
+        [SerializeField] private Color coinColor = new Color(1f, 0.84f, 0.2f, 1f);
+
+        private void Awake()
+        {
+            var ps = GetComponent<ParticleSystem>();
+            if (ps == null) ps = gameObject.AddComponent<ParticleSystem>();
+            Configure(ps);
+        }
+
+        private void Configure(ParticleSystem ps)
+        {
+            // Reconfiguring modules requires the system to be stopped first.
+            ps.Stop(true, ParticleSystemStopBehavior.StopEmittingAndClear);
+
+            var main = ps.main;
+            main.duration          = 0.1f;
+            main.loop              = false;
+            main.playOnAwake       = false;
+            main.startLifetime     = new ParticleSystem.MinMaxCurve(lifetime * 0.6f, lifetime);
+            main.startSpeed        = new ParticleSystem.MinMaxCurve(2.5f, 5f);
+            main.startSize         = new ParticleSystem.MinMaxCurve(0.07f, 0.16f);
+            main.startRotation     = new ParticleSystem.MinMaxCurve(0f, Mathf.PI * 2f);
+            main.startColor        = coinColor;
+            main.gravityModifier   = 2.5f; // arc up then fall back down quickly
+            main.simulationSpace   = ParticleSystemSimulationSpace.World;
+            main.maxParticles      = 64;
+            main.stopAction        = ParticleSystemStopAction.None;
+
+            var emission = ps.emission;
+            emission.enabled      = true;
+            emission.rateOverTime = 0f; // burst only, no continuous stream
+            emission.SetBursts(new[] { new ParticleSystem.Burst(0f, (short)coinCount) });
+
+            // Hemisphere pointing up → specks spray outward and upward in random directions.
+            var shape = ps.shape;
+            shape.enabled   = true;
+            shape.shapeType = ParticleSystemShapeType.Hemisphere;
+            shape.radius    = 0.12f;
+
+            // Fade the specks out over the back half of their life so they "decay quickly".
+            var col = ps.colorOverLifetime;
+            col.enabled = true;
+            var grad = new Gradient();
+            grad.SetKeys(
+                new[] { new GradientColorKey(coinColor, 0f), new GradientColorKey(coinColor, 1f) },
+                new[]
+                {
+                    new GradientAlphaKey(1f, 0f),
+                    new GradientAlphaKey(1f, 0.55f),
+                    new GradientAlphaKey(0f, 1f),
+                });
+            col.color = new ParticleSystem.MinMaxGradient(grad);
+
+            // Give the specks a visible, transparent-capable material even with no assigned art.
+            var renderer = GetComponent<ParticleSystemRenderer>();
+            if (renderer != null)
+            {
+                renderer.renderMode = ParticleSystemRenderMode.Billboard;
+                if (renderer.sharedMaterial == null)
+                {
+                    Shader shader = Shader.Find("Universal Render Pipeline/Particles/Unlit")
+                                    ?? Shader.Find("Sprites/Default")
+                                    ?? Shader.Find("Legacy Shaders/Particles/Alpha Blended Premultiply");
+                    if (shader != null)
+                        renderer.material = new Material(shader) { color = coinColor };
+                }
+            }
+
+            ps.Play();
+
+            // Tear down after the last speck has died (plus a small margin).
+            Destroy(gameObject, lifetime + 0.25f);
+        }
+    }
+}

Assets/_Project/Scripts/VFX/SellEffectSpawner.cs

@@ -0,0 +1,83 @@
+// Assets/_Project/Scripts/VFX/SellEffectSpawner.cs
+using UnityEngine;
+using TD.Audio;
+
+namespace TD.VFX
+{
+    /// <summary>
+    /// Scene singleton that plays the "tower sold" feedback — a burst of gold coins plus a
+    /// coin-rustle sound — at a world position. Mirrors <see cref="TD.UI.FloatingTextSpawner"/>:
+    /// visual-only, plain <c>MonoBehaviour</c>, invoked on every peer via a ClientRpc so all
+    /// players see and hear a sale locally.
+    /// </summary>
+    /// <remarks>
+    /// <b>Who calls this:</b> <see cref="TD.Gameplay.TowerPlacementManager.BroadcastSellEffect"/>
+    /// routes a ClientRpc here when a tower is sold.
+    ///
+    /// <b>Inspector setup:</b> drop this on a <c>SellEffectSpawner</c> GameObject in each Match
+    /// scene. The VFX prefab is OPTIONAL — leave it empty to use the built-in
+    /// <see cref="CoinBurstVfx"/> placeholder, or assign an authored particle/VFX-graph prefab.
+    /// Assign the coin-rustle clip on <see cref="sellSound"/>.
+    /// </remarks>
+    public class SellEffectSpawner : MonoBehaviour
+    {
+        // ----- Singleton --------------------------------------------------
+
+        public static SellEffectSpawner Instance { get; private set; }
+
+        // ----- Inspector --------------------------------------------------
+
+        [Tooltip("Optional authored VFX prefab spawned at the sale position. Leave empty to " +
+                 "fall back to the built-in code-generated CoinBurstVfx placeholder.")]
+        [SerializeField] private GameObject coinBurstPrefab;
+
+        [Tooltip("Coin-rustle sound played (2D, via AudioManager) when a tower is sold.")]
+        [SerializeField] private SoundConfig sellSound;
+
+        [Tooltip("Vertical offset above the sale position where the coin burst originates, so " +
+                 "it reads as coming from the tower body rather than the ground.")]
+        [SerializeField] private float verticalOffset = 0.75f;
+
+        // ----- Lifecycle --------------------------------------------------
+
+        private void Awake()
+        {
+            if (Instance != null && Instance != this)
+            {
+                Debug.LogWarning("[SellEffectSpawner] Duplicate instance detected. " +
+                                 "Only one should exist per scene.");
+                return;
+            }
+            Instance = this;
+        }
+
+        private void OnDestroy()
+        {
+            if (Instance == this) Instance = null;
+        }
+
+        // ----- Public API -------------------------------------------------
+
+        /// <summary>Plays the coin burst + rustle sound at <paramref name="worldPos"/>.</summary>
+        public void Play(Vector3 worldPos)
+        {
+            Vector3 spawnPos = worldPos + Vector3.up * verticalOffset;
+
+            if (coinBurstPrefab != null)
+            {
+                Instantiate(coinBurstPrefab, spawnPos, Quaternion.identity);
+            }
+            else
+            {
+                // Zero-art fallback: a self-configuring, self-destroying particle burst.
+                var go = new GameObject("CoinBurst");
+                go.transform.position = spawnPos;
+                go.AddComponent<CoinBurstVfx>();
+            }
+
+            if (sellSound.clip != null)
+                AudioManager.Instance?.Play(sellSound.clip, AudioCategory.UI,
+                                            sellSound.RandomPitch(), sellSound.volume);
+        }
+    }
+}