Fix GDI resource leaks and visual artifacts in VwDrawRootBuffered

[Copilot]

Summary

Fixed critical GDI bitmap management bugs in VwDrawRootBuffered causing resource leaks and visual artifacts. The code was deleting stock bitmaps (which should never be deleted) and leaking custom bitmaps (which should always be deleted).

Root cause: After SelectObjectBitmap(dc, newBitmap), the code deleted the returned stock bitmap instead of the created custom bitmap:

// BEFORE (buggy):
HBITMAP hbmpOld = AfGdi::SelectObjectBitmap(m_hdcMem, hbmp);
AfGdi::DeleteObjectBitmap(hbmpOld);  // Wrong: deletes stock bitmap
// hbmp never deleted → leak

// AFTER (fixed):
HBITMAP hbmpOld = AfGdi::SelectObjectBitmap(m_hdcMem, hbmp);
// Don't delete hbmpOld (stock bitmap)
// hbmp stays selected, cleaned up on next draw or destructor

Changes

DrawTheRoot (cached DC pattern for ReDrawLastDraw):

• Clean up previous cached bitmap before creating new one
• Create DC/bitmap, select custom bitmap
• Keep custom bitmap selected in m_hdcMem for caching
• Stock bitmap left alone

DrawTheRootRotated (local DC pattern):

• Create local DC/bitmap, select custom bitmap
• Restore stock bitmap before cleanup
• Delete custom bitmap and DC
• Added exception path cleanup

Pattern difference: DrawTheRoot caches the DC/bitmap for ReDrawLastDraw optimization (used when form is disabled). DrawTheRootRotated uses local resources since rotation complicates caching.

CI-ready checklist

• Commit messages follow .github/commit-guidelines.md (subject ≤ 72 chars, no trailing punctuation; if body present, blank line then ≤ 80-char lines).
• No whitespace warnings locally:

  git fetch origin
  git log --check --pretty=format:"---% h% s" origin/<base>..
  git diff --check --cached

• Builds/tests pass locally (or I've run the CI-style build via Bash script or MSBuild). ⚠️ Cannot build in Linux; requires Windows/VS2022
• For any Src/** folders touched, corresponding COPILOT.md files are updated or explicitly confirmed still accurate.

Notes for reviewers

Testing focus:

• Visual artifacts during scrolling/resizing
• GDI object count (Task Manager → GDI Objects) should remain stable
• Disabled form scenario (triggers ReDrawLastDraw)

Technical context: Stock GDI objects (the default 1x1 bitmap in a new DC) must never be deleted per Windows GDI guidelines. The destructor already properly cleaned up cached bitmaps.

Documentation: BUFFERING_FIX.md and IMPLEMENTATION_SUMMARY.md added for technical reference.

Original prompt

Recently, you ripped up the buffering in the views project to solve some odd artifacts showing on the screen. It turns out we do need the buffering for drawing the views. Please re-implement the buffering code. Look at the get history to see what has changed for guidance. Don't just re-implement what was there, think about how best to implement the buffering code in a clean architecture ensuring that new visual artifacts are not created.

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This change is 

[Copilot]

Pull request overview

This PR fixes critical GDI bitmap management bugs in VwDrawRootBuffered that were causing resource leaks and visual artifacts. The root cause was incorrect handling of stock vs. custom GDI bitmaps - the code was deleting stock bitmaps (which should never be deleted) and leaking custom bitmaps (which should be deleted when no longer needed).

Key changes:

• Fixed DrawTheRoot to properly cache custom bitmap in m_hdcMem without deleting stock bitmap
• Fixed DrawTheRootRotated to use local DC/bitmap with proper cleanup and stock bitmap restoration
• Added exception handling cleanup for DrawTheRootRotated to prevent resource leaks

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Src/views/VwRootBox.cpp	Fixed GDI resource management in DrawTheRoot (cached DC pattern) and DrawTheRootRotated (local DC pattern) methods to properly handle stock vs. custom bitmaps
IMPLEMENTATION_SUMMARY.md	Added comprehensive technical documentation explaining the bug, fix, architecture decisions, and testing strategy
BUFFERING_FIX.md	Added detailed explanation of the root cause, solution patterns, and key principles for GDI bitmap handling

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