feat(desktop): 目标上方浮动情境提示

新增 FloatingPrompt 纯布局模块（含 measureWidth 与 PixelText 等宽规则）：短提示锚定在唯一目标头顶上方，水平居中并钳制在视口内，避开左下 HUD 带（height-160）与右上状态条带（宽度 248）；沿用现有 CJK 图集字体路径，不新造字形；对话/需求面板与菜单打开时不显示（复用 worldInputAllowed 判定与渲染门）。回归测试覆盖 1280x720/1920x1080 五个极限锚点、宽度测量、面板开启时提示为空且禁用世界输入。

1 files changed, 40 insertions, 0 deletions

diff --git a/src/LivingVillage.Desktop.Tests/PrototypeTests.fs b/src/LivingVillage.Desktop.Tests/PrototypeTests.fs
index af34802..7e4ce5f 100644
--- a/src/LivingVillage.Desktop.Tests/PrototypeTests.fs
+++ b/src/LivingVillage.Desktop.Tests/PrototypeTests.fs
@@ -630,6 +630,46 @@ type PrototypeTests () =
         CollectionAssert.AreEqual(snapshot, tieWorld.Npcs)
 
     [<TestMethod>]
+    member _.FloatingPromptStaysInViewportAndClearOfHudBands () =
+        for (width, height) in [ (1280, 720); (1920, 1080) ] do
+            let anchors : (float32 * float32) list =
+                [ (100.0f, 100.0f)      // near top-left
+                  (float32 width / 2.0f, float32 height / 2.0f)
+                  (float32 width - 60.0f, 120.0f)   // near top-right strip
+                  (200.0f, float32 height - 200.0f) // above bottom-left HUD band
+                  (float32 width - 100.0f, float32 height - 120.0f) ]
+            for (anchorX, anchorY) in anchors do
+                for text in [ "E 交谈"; "E 进屋"; "E 出屋" ] do
+                    let rect = FloatingPrompt.layout width height anchorX anchorY 0.0f 0.0f 2 text
+                    let textWidth = FloatingPrompt.measureWidth text 2
+                    Assert.AreEqual<int>(textWidth, rect.Width)
+                    Assert.IsTrue(rect.Width > 0, "prompt must not be truncated to zero width")
+                    Assert.IsTrue(rect.X >= 0 && rect.X + rect.Width <= width, sprintf "x overflow %A %A" (anchorX, anchorY) rect)
+                    Assert.IsTrue(rect.Y >= 0 && rect.Y + rect.Height <= height, sprintf "y overflow %A %A" (anchorX, anchorY) rect)
+                    // Never cover the bottom-left HUD band (camera 0: band starts at height - 160).
+                    Assert.IsTrue(rect.Y + rect.Height <= height - FloatingPrompt.hudBottomBandHeight + 8, sprintf "bottom HUD overlap %A %A" (anchorX, anchorY) rect)
+                    // Never cover the top-right status strip.
+                    if rect.X + rect.Width >= width - FloatingPrompt.hudTopRightWidth then
+                        Assert.IsTrue(rect.Y >= FloatingPrompt.hudTopRightHeight, sprintf "top-right HUD overlap %A %A" (anchorX, anchorY) rect)
+
+    [<TestMethod>]
+    member _.FloatingPromptMeasureMatchesPixelTextAdvances () =
+        // E(12) space(8) 交(16) 谈(16) at scale 2.
+        Assert.AreEqual<int>(52, FloatingPrompt.measureWidth "E 交谈" 2)
+        Assert.AreEqual<int>(20, FloatingPrompt.measureWidth "E " 2)
+
+    [<TestMethod>]
+    member _.FloatingPromptHiddenWhilePanelsOrMenusAreOpen () =
+        let world = Sim.initialWorldN 42UL 2
+        let dialogueView = { M5Interaction.initial with Panel = DialoguePanel }
+        let cleared = M5Interaction.refreshPrompt world dialogueView
+        Assert.AreEqual<string option>(None, cleared.Prompt)
+        Assert.IsFalse(M5Interaction.worldInputAllowed dialogueView)
+
+        let needsView = { M5Interaction.initial with Panel = NeedsPanel }
+        Assert.AreEqual<string option>(None, M5Interaction.refreshPrompt world needsView |> fun value -> value.Prompt)
+
+    [<TestMethod>]
     member _.WorldPanelDoesNotRenderA永久KeyList () =
         let world = Sim.initialWorldN 42UL 0
         let lines = M5Interaction.panelLines world M5Interaction.initial