feat(input): #24 Phase K.2 - auto-enter player mode at login + MMB mouse-look + DebugPanel free-fly + Tab to chat-input focus

Five changes:

1. PlayerModeAutoEntry — testable guard class that fires once after
   EnterWorld + WorldSession.State.InWorld + player entity present +
   PlayerController.State == InWorld. GameWindow arms the entry
   after EnterWorld; per-frame Tick checks all four guards and
   invokes the same fly-to-player transition the Tab handler runs.
   User-initiated fly toggle (DebugPanel button) Cancel()s pending
   entry. Skip in offline mode (no ACDREAM_LIVE) — Holtburg orbit
   stays default for testing.

2. MouseLookState + KeyBindings.RetailDefaults() binds MMB Hold to
   InputAction.CameraInstantMouseLook. GameWindow subscribes:
   - Press: hide cursor, capture position, _mouseLookActive = true.
   - Release: restore cursor, deactivate.
   - WantCaptureMouse=true while held → suspend (release cursor).
   - MouseMove while active: combined drive — chase camera yaw +
     character heading move together (retail's signature mouse-look
     behavior). Camera Y still pitches camera-only.

3. DebugPanel "Toggle Free-Fly Mode" button via DebugVM.ToggleFlyMode
   action delegate — replaces the F-key as the primary discovery
   path for free-fly. Gated on DevToolsEnabled.

4. ChatPanel.FocusInput() one-shot + IPanelRenderer.SetKeyboardFocusHere
   primitive. GameWindow's ToggleChatEntry (Tab) subscriber calls
   _chatPanel.FocusInput() so Tab moves focus to the chat input
   field. Replaces the K.1c TODO stub.

5. WantCaptureMouse gating reinforcement on surviving mouse handlers
   (no new code; verified intact from K.1b).

21 new tests (8 PlayerModeAutoEntry, 10 MouseLookState, 3 ChatPanel
focus). 1183 total green. 0 warnings, 0 errors.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.UI.Abstractions.Tests/Input/MmbMouseLookTests.cs

@@ -0,0 +1,166 @@
+using AcDream.UI.Abstractions.Input;
+
+namespace AcDream.UI.Abstractions.Tests.Input;
+
+/// <summary>
+/// Phase K.2 — MMB-hold instant mouse-look state machine. While
+/// active, mouse-X drives the character's heading (and the chase
+/// camera follows automatically because <c>ChaseCamera.Update</c>
+/// reads the player yaw). The state machine guards activation on
+/// ImGui's <c>WantCaptureMouse</c> so a panel-hovered MMB doesn't
+/// hijack the cursor.
+/// </summary>
+public sealed class MmbMouseLookTests
+{
+    private sealed class YawSink
+    {
+        public float Total;
+        public int   ApplyCount;
+        public void Apply(float d) { Total += d; ApplyCount++; }
+    }
+
+    [Fact]
+    public void Press_ActivatesAndCapturesCursorPosition()
+    {
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+
+        ml.Press(cursorX: 320f, cursorY: 240f, wantCaptureMouse: false);
+
+        Assert.True(ml.Active);
+        Assert.Equal(320f, ml.CapturedCursorX);
+        Assert.Equal(240f, ml.CapturedCursorY);
+    }
+
+    [Fact]
+    public void Release_DeactivatesWhenActive()
+    {
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+        ml.Press(0f, 0f, wantCaptureMouse: false);
+
+        ml.Release();
+
+        Assert.False(ml.Active);
+    }
+
+    [Fact]
+    public void Press_WhileImGuiCapturesMouse_DoesNotActivate()
+    {
+        // Defense in depth — the dispatcher already filters on
+        // WantCaptureMouse, but if a binding ever fires through the
+        // state machine itself must not turn on.
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+
+        ml.Press(0f, 0f, wantCaptureMouse: true);
+
+        Assert.False(ml.Active);
+    }
+
+    [Fact]
+    public void OnWantCaptureMouseChanged_TrueWhileActive_Deactivates()
+    {
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+        ml.Press(0f, 0f, wantCaptureMouse: false);
+        Assert.True(ml.Active);
+
+        // ImGui takes mouse focus mid-hold (e.g. tooltip pop-up over
+        // the cursor) → suspend mouse-look so the panel gets the
+        // cursor.
+        ml.OnWantCaptureMouseChanged(wantCaptureMouse: true);
+
+        Assert.False(ml.Active);
+    }
+
+    [Fact]
+    public void OnWantCaptureMouseChanged_FalseWhileInactive_NoOp()
+    {
+        // Going from "ImGui captures" to "ImGui doesn't capture" must
+        // NOT auto-reactivate — only an explicit Press does.
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+
+        ml.OnWantCaptureMouseChanged(wantCaptureMouse: false);
+
+        Assert.False(ml.Active);
+    }
+
+    [Fact]
+    public void ApplyDelta_WhileActive_DrivesYawSink()
+    {
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply) { SensitivityRadiansPerPixel = 0.01f };
+        ml.Press(0f, 0f, wantCaptureMouse: false);
+
+        ml.ApplyDelta(dx: 10f, extraSensitivity: 1.0f);
+
+        // Sign: dragging right (positive dx) yaws the character right
+        // — by the acdream Yaw convention that's negative yaw delta.
+        // Magnitude: 10 * 0.01 * 1.0 = 0.1 rad.
+        Assert.Equal(1, sink.ApplyCount);
+        Assert.Equal(-0.1f, sink.Total, 5);
+    }
+
+    [Fact]
+    public void ApplyDelta_WhileInactive_DoesNothing()
+    {
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+        // Never pressed.
+
+        ml.ApplyDelta(dx: 100f, extraSensitivity: 1.0f);
+
+        Assert.Equal(0, sink.ApplyCount);
+        Assert.Equal(0f, sink.Total);
+    }
+
+    [Fact]
+    public void ApplyDelta_AfterRelease_DoesNothing()
+    {
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+        ml.Press(0f, 0f, wantCaptureMouse: false);
+        ml.Release();
+
+        ml.ApplyDelta(dx: 50f, extraSensitivity: 1.0f);
+
+        Assert.Equal(0, sink.ApplyCount);
+    }
+
+    [Fact]
+    public void Press_WhileAlreadyActive_IsIdempotent()
+    {
+        // Repeated Press calls must not blow away the originally
+        // captured cursor position — the cursor-restore-on-release
+        // path needs the original anchor.
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply);
+        ml.Press(100f, 200f, wantCaptureMouse: false);
+
+        ml.Press(999f, 888f, wantCaptureMouse: false);
+
+        Assert.Equal(100f, ml.CapturedCursorX);
+        Assert.Equal(200f, ml.CapturedCursorY);
+    }
+
+    [Fact]
+    public void ApplyDelta_DriverDrivesCharacterAndCameraInOneSink()
+    {
+        // Combined drive: the test only exposes a single yaw mutator,
+        // and that's the design — the yaw mutator GameWindow passes
+        // updates _playerController.Yaw, and the chase camera reads
+        // the same yaw via ChaseCamera.Update(pos, playerYaw). So a
+        // single sink in this test models both behaviors.
+        var sink = new YawSink();
+        var ml = new MouseLookState(sink.Apply) { SensitivityRadiansPerPixel = 0.005f };
+        ml.Press(0f, 0f, wantCaptureMouse: false);
+
+        ml.ApplyDelta(dx:  4f, extraSensitivity: 0.5f);  // -0.01
+        ml.ApplyDelta(dx: -2f, extraSensitivity: 0.5f);  // +0.005
+
+        Assert.Equal(2, sink.ApplyCount);
+        Assert.Equal(-0.005f, sink.Total, 5);
+    }
+}