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+# Auto-Hide Caption Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Show the calculator window's title bar and close button only while the window is active; when it loses activation it stays on top as a chromeless display, with the number display never moving on screen.
+
+**Architecture:** `CCalculatorWindow` handles `WM_ACTIVATE` and toggles `WS_CAPTION | WS_SYSMENU` via a new `ApplyFrameStyle(bool)` helper that keeps the client rectangle fixed in screen coordinates (caption grows upward / retracts). Window position is persisted in canonical form (client origin) so the saved point no longer depends on the caption state.
+
+**Tech Stack:** C++17, ATL `CWindowImpl`, raw Win32 (`SetWindowLongPtr`, `AdjustWindowRectEx`, `SetWindowPos`), VS 2022 `v143`, Windows SDK 10.0.26100.0.
+
+**Spec:** `docs/superpowers/specs/2026-07-15-auto-hide-caption-design.md`
+
+## Global Constraints
+
+- Build the **`.vcxproj` directly**, never the `.sln` (the solution references a setup project not in this repo): `msbuild TaskbarCalculator.vcxproj /p:Configuration=Debug /p:Platform=x64`.
+- Commands assume an **x64 Native Tools Command Prompt for VS 2022** (`msbuild` and `cl` on PATH).
+- Match existing style: TCHAR/`_T()`, ATL `CString`, raw Win32; `CalculatorWindow.cpp` uses the `stdafx.h` PCH.
+- Only `CalculatorWindow.h` / `CalculatorWindow.cpp` may change. Engine (`calc`), `Settings` storage format, `App.cpp`, tray, packaging: untouched.
+- **Testing note:** this feature is pure UI; the repo's unit-test harness covers only the `calc` engine. Each task's test cycle is therefore: (a) build succeeds, (b) engine regression `tests\build-and-run.cmd` still reports **16/16 passed**, (c) a targeted manual check listed in the task. There is no failing-test-first step because no UI test harness exists and building one is out of scope (YAGNI).
+
+---
+
+### Task 1: Frame toggle on activation (`ApplyFrameStyle` + `WM_ACTIVATE`)
+
+**Files:**
+- Modify: `CalculatorWindow.h` (message map ~line 34-45, private section ~line 52-61, members ~line 76-85)
+- Modify: `CalculatorWindow.cpp` (new handler + helper, after `OnExitSizeMove` ~line 362)
+
+**Interfaces:**
+- Consumes: existing `CWindowImpl` plumbing; window is created in `CreateStandalone` with `WS_POPUP | WS_CAPTION | WS_SYSMENU`, ex-style `WS_EX_TOPMOST | WS_EX_TOOLWINDOW`.
+- Produces: `void CCalculatorWindow::ApplyFrameStyle(bool visible)` (private), `bool m_captionVisible` (private, starts `true`), `LRESULT OnActivate(UINT, WPARAM, LPARAM, BOOL&)`. Task 2 does not call these but relies on the invariant they establish: the client origin is the style-independent (canonical) position.
+
+- [ ] **Step 1: Declare handler, helper, and state in `CalculatorWindow.h`**
+
+In the message map, after `MESSAGE_HANDLER(WM_EXITSIZEMOVE, OnExitSizeMove)` add:
+
+```cpp
+    MESSAGE_HANDLER(WM_ACTIVATE, OnActivate)
+```
+
+In the private handler-prototype block, after the `OnExitSizeMove` declaration add:
+
+```cpp
+    LRESULT OnActivate(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled);
+```
+
+In the private section holding `m_fHasFocus` / `m_shown`, add the helper declaration and the state member:
+
+```cpp
+    void ApplyFrameStyle(bool visible);
+    bool m_captionVisible = true;   // window is created with WS_CAPTION | WS_SYSMENU
+```
+
+- [ ] **Step 2: Implement `OnActivate` and `ApplyFrameStyle` in `CalculatorWindow.cpp`**
+
+Insert after `OnExitSizeMove` (line ~362), before `Paint`:
+
+```cpp
+LRESULT CCalculatorWindow::OnActivate(UINT, WPARAM wParam, LPARAM, BOOL& bHandled)
+{
+    // Caption + close button only while the window is active.
+    ApplyFrameStyle(LOWORD(wParam) != WA_INACTIVE);
+    bHandled = FALSE;   // let default activation processing run too
+    return 0;
+}
+
+void CCalculatorWindow::ApplyFrameStyle(bool visible)
+{
+    if (visible == m_captionVisible)
+        return;
+    m_captionVisible = visible;
+
+    // The client rect must not move on screen: capture it before the style change.
+    RECT rc; GetClientRect(&rc);
+    ::MapWindowPoints(m_hWnd, NULL, (LPPOINT)&rc, 2);
+
+    LONG_PTR style = GetWindowLongPtr(GWL_STYLE);
+    if (visible)
+        style |= (WS_CAPTION | WS_SYSMENU);
+    else
+        style &= ~(WS_CAPTION | WS_SYSMENU);
+    SetWindowLongPtr(GWL_STYLE, style);
+
+    RECT r = rc;
+    AdjustWindowRectEx(&r, (DWORD)style, FALSE,
+        (DWORD)GetWindowLongPtr(GWL_EXSTYLE));
+
+    // Guard: never push the top edge above the work area.
+    RECT work; SystemParametersInfo(SPI_GETWORKAREA, 0, &work, 0);
+    if (r.top < work.top)
+        ::OffsetRect(&r, 0, work.top - r.top);
+
+    SetWindowPos(NULL, r.left, r.top, r.right - r.left, r.bottom - r.top,
+        SWP_FRAMECHANGED | SWP_NOZORDER | SWP_NOACTIVATE);
+}
+```
+
+Notes for the implementer:
+- `GetWindowLongPtr`/`SetWindowLongPtr`/`GetClientRect`/`SetWindowPos` are `CWindow` members operating on `m_hWnd`; the `::`-prefixed calls are deliberate raw Win32.
+- The early-return makes the toggle idempotent and prevents any recursion via nested `WM_ACTIVATE`.
+- `AdjustWindowRectEx` with `WS_EX_TOOLWINDOW` accounts for the small tool-window caption height automatically.
+
+- [ ] **Step 3: Build**
+
+Run: `msbuild TaskbarCalculator.vcxproj /p:Configuration=Debug /p:Platform=x64`
+Expected: `Build succeeded.` with `0 Error(s)`.
+
+- [ ] **Step 4: Engine regression**
+
+Run: `tests\build-and-run.cmd`
+Expected: `16/16 passed`.
+
+- [ ] **Step 5: Targeted manual check**
+
+Launch `x64\Debug\TaskbarCalculator.exe`, left-click the tray icon:
+- Window appears **with** caption + X (it is foreground).
+- Click any other window: caption and X disappear; the number display does not move.
+- Click the calculator body: caption and X reappear; display does not move.
+- Click X: window hides to tray (existing behavior).
+Exit via tray menu → Exit when done.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add CalculatorWindow.h CalculatorWindow.cpp
+git commit -m "feat: show caption and close button only while calculator window is active"
+```
+
+---
+
+### Task 2: Canonical (client-origin) position persistence
+
+**Files:**
+- Modify: `CalculatorWindow.cpp` — `OnExitSizeMove` (~line 357-362) and `PlaceInitial` (~line 159-178)
+
+**Interfaces:**
+- Consumes: `Settings::SaveWindowPos(POINT)` / `Settings::LoadWindowPos(POINT&)` (unchanged, `Settings.h`); the canonical-position invariant from Task 1.
+- Produces: no new symbols — changes the *meaning* of the persisted point from "window origin" to "client origin". Registry value names/types unchanged.
+
+- [ ] **Step 1: Save the client origin in `OnExitSizeMove`**
+
+Replace the body:
+
+```cpp
+LRESULT CCalculatorWindow::OnExitSizeMove(UINT, WPARAM, LPARAM, BOOL&)
+{
+    // Persist the canonical position (client origin), independent of caption state.
+    RECT rc; GetClientRect(&rc);
+    ::MapWindowPoints(m_hWnd, NULL, (LPPOINT)&rc, 2);
+    Settings::SaveWindowPos(POINT{ rc.left, rc.top });
+    return 0;
+}
+```
+
+- [ ] **Step 2: Restore by converting the canonical point to a window origin in `PlaceInitial`**
+
+Replace only the `LoadWindowPos` branch (the first-run bottom-right anchor stays as is):
+
+```cpp
+    POINT pt;
+    if (Settings::LoadWindowPos(pt)) {
+        // Saved point is canonical (client origin). Convert to the window
+        // origin for the style currently in effect.
+        RECT r = { pt.x, pt.y, pt.x + 1, pt.y + 1 };
+        AdjustWindowRectEx(&r,
+            (DWORD)GetWindowLongPtr(GWL_STYLE), FALSE,
+            (DWORD)GetWindowLongPtr(GWL_EXSTYLE));
+        SetWindowPos(NULL, r.left, r.top, 0, 0, SWP_NOSIZE | SWP_NOZORDER);
+        return;
+    }
+```
+
+Note: positions saved by older builds were window origins; they are reinterpreted as client origins exactly once (the window appears one caption height lower), then the position is stable forever after the first drag.
+
+- [ ] **Step 3: Build**
+
+Run: `msbuild TaskbarCalculator.vcxproj /p:Configuration=Debug /p:Platform=x64`
+Expected: `Build succeeded.` with `0 Error(s)`.
+
+- [ ] **Step 4: Engine regression**
+
+Run: `tests\build-and-run.cmd`
+Expected: `16/16 passed`.
+
+- [ ] **Step 5: Targeted manual check**
+
+Launch `x64\Debug\TaskbarCalculator.exe`, show the window, drag it somewhere distinctive (note where the *display* sits), exit via tray menu, relaunch, show the window:
+- The display is exactly where it was left — no vertical drift.
+- Repeat once more (exit while the window is inactive/chromeless): still no drift.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add CalculatorWindow.cpp
+git commit -m "fix: persist window position as client origin so caption toggle causes no drift"
+```
+
+---
+
+### Task 3: Full manual verification + docs
+
+**Files:**
+- Modify: `docs/superpowers/VERIFICATION.md` (append a section)
+
+**Interfaces:**
+- Consumes: the finished behavior from Tasks 1-2.
+- Produces: recorded verification evidence; no code.
+
+- [ ] **Step 1: Run the full checklist from the spec**
+
+Launch `x64\Debug\TaskbarCalculator.exe` and verify each item:
+1. Show from tray → window appears with caption + X.
+2. Click another app → caption disappears; display does not move.
+3. Click the calculator → caption reappears; display does not move.
+4. X → hides to tray.
+5. Drag by caption and drag by body both work; position persists after restart.
+6. Type `12+34` Enter → `46` (engine still wired through the edit control).
+7. Open tray menu / About: calculator loses the caption while they are open (accepted side effect, spec §Accepted side effects).
+
+- [ ] **Step 2: Record results in `docs/superpowers/VERIFICATION.md`**
+
+Append:
+
+```markdown
+## Auto-hide caption (2026-07-15)
+
+- ✅ Caption + X visible only while the window is active; chromeless when inactive.
+- ✅ Display never moves when the frame toggles (client rect pinned).
+- ✅ Position persists across restarts with no vertical drift (canonical client origin).
+- ✅ X hides to tray; drag by caption and by body both work.
+- ✅ Engine regression: 16/16 (`tests\build-and-run.cmd`).
+```
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add docs/superpowers/VERIFICATION.md
+git commit -m "docs: verification results for auto-hide caption"
+```