LlamaCasty/MyMistakes.md

MyMistakes.md

Two jobs, distinguished by heading:

1. Per-task failure log — updated before every commit touching that task: current iteration + why the last one failed. On task complete, committed AND pushed → truncate to this stub. A new task does NOT seed this file until its first failure.
2. Recipes registry (DERIVED-SOLUTION RULE, see AGENTS.md 🔬) — the durable home for one-off derived solutions, recipes, and how-tos. The moment you work out a reusable solution, write it here in the same session. GREP THIS FILE FIRST when you hit a "I've done this before but have to figure it out again" wall. Recipe entries stay permanently (they are NOT truncated on task completion) — only the failure log truncates.

🔬 Recipes registry

Shrink / re-encode an image for the README (screenshots → small hero image)

Worked out 2026-08-29 (the recipe was NEVER recorded the first time it was done, so it had to be re-derived from scratch — that's the incident this entry exists to end).

Approach: a throwaway Windows-dotnet console app uses WPF's imaging stack (System.Windows.Media.Imaging) — same framework the app runs on, zero NuGet packages, high-quality downscale via TransformedBitmap. Screenshots compress far smaller as JPEG than PNG (PNG 1400px = ~1.2MB; JPEG q82 1400px = ~188KB).

Recipe (run via the Windows dotnet host from WSL):

1. Create imgresize.csproj targeting net8.0-windows with <UseWPF>true</UseWPF> (SDK controller). Put it in a Windows-visible temp path, e.g. C:\Users\gramp\AppData\Local\Temp\imgresize — NOT /tmp (Windows dotnet can't reach a Linux-only path reliably).
2. Program.cs: load BitmapImage (CacheOption=OnLoad → Freeze()), downscale with TransformedBitmap(src, new ScaleTransform(scale, scale)) to max width (1400 for the README hero), encode with JpegBitmapEncoder { QualityLevel = 82 }, save.
3. Run:

"/mnt/c/Program Files/dotnet/dotnet.exe" run -c Release --project .
   -- "C:\Users\gramp\Downloads\Screenshot 2026-08-29 075626.png"
      "C:\Users\gramp\Documents\Code\projects\ytLive\docs\ytLlive-preview.jpg" 1400

4. Point README.md at the .jpg (not .png).

Result: 3.2MB screenshot → 1400×794 → 188KB ytLlive-preview.jpg in docs/.

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Splitting a large file into partials — NEVER awk … > SRC while awking SRC

(2026-08-31, Commit D) Tried to split SocialsDialogViewModel.cs in one line: { awk '…' SRC; echo ""; awk '…2…' SRC; } > SRC. The first write truncated SRC to 1 line, so the second awk read the already-truncated file → the whole source was lost (1 line left). Recovered with git checkout -- SRC, then redid it, but the same bug could have meant making it up from scratch.

Rule: when a cut needs N blocks from one source into N files, never write a block back onto the source that the awks still read. Instead:

1. Read the source once at the start into temp files (mktemp -d, one file per block), with a $D variable you carry forward.
2. Verify block sizes (wc -l) and brace balance (python3 -c counting {/}) before touching any real file.
3. Then assemble each new file from cat D/block … — never truncating the source until every read is done.

git status can't save you here if you don't notice until the file is gone — git checkout -- <path> from the last commit is the recovery. Cheap insurance: restore-then-retry, do it atomically from temp files the first time.

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Verifying an ffmpeg decode contract from WSL (no real CLR needed)

(2026-08-31, TASK 21) When a change depends on ffmpeg producing output with an exact frame-size contract (rawvideo W×H×4 BGRA), you can prove the command + frame accounting here without any .NET process:

1. Fetch a static Linux ffmpeg into /tmp/opencode (no sudo needed): curl -sLO https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz && tar -xf …
2. Generate a tiny known clip: ffmpeg -f lavfi -i "testsrc2=duration=1:size=640x360:rate=30" -pix_fmt yuv420p clip.mp4
3. Decode with exactly the app's args: -f rawvideo -pix_fmt bgra -vf scale=640:360 -an
4. Assert total_bytes % (W*H*4) == 0 (python3) → exact integer frames, no pad.

Why not a dotnet-spawned ffmpeg here: the only CLR on this box (/home/gramps/bin/dotnet) is a Windows-bound shim — Process.Start resolves paths to \\wsl.localhost\Debian\… and throws "not a valid application for this OS" when handed a Linux ELF ffmpeg. So never plan to have dotnet exec a Linux ffmpeg here; verify the contract with shell/python instead, and leave the CLR→real-ffmpeg run to the native Windows suite.

WPF hit-test truth in tests: UIElement.InputHitTest, NOT VisualTreeHelper.HitTest

(2026-09-01, the RoundClip "known failure" post-mortem — a failure the map carried as "not a regression" for weeks without ever recording WHY.)

The trap: VisualTreeHelper.HitTest(window, pt) returned the window's WebViewHostPanel overlay (IsHitTestVisible="False", Opacity=0, ZERO children) for EVERY point in the window — so a "corner is grabbable" assertion could never pass, and it looked like a real interaction bug. The actual input pipeline (UIElement.InputHitTest, what Mouse routing uses) correctly returned the element's Grid at elem-center/corner-in/ corner-exact and fell through to CanvasGrid just past the corner. The product was fine; the TEST was probing an API that doesn't model input semantics.

Rule: any test asserting "where does a click land" uses window.InputHitTest(pt) + IsDescendantOf — never VisualTreeHelper.HitTest.

Diagnosis recipe (how the lie was caught in ~3 probe cycles, no guessing): add a TEMP probe [Fact] in the RealApp collection that hit-tests a spread of points (elem-center / corner-in / corner-exact / corner-out / bg-center) and Assert.Fails with a composed dump: per-point VTH hit + InputHitTest hit + ancestor chain (GetParent walk with #Name) + panel properties (IsHitTestVisible/Opacity/children/actual size) + TranslatePoint origins. Run the class alone, read the message, delete the probe.

Two sibling facts learned the same session (record-once):

1. A UserControl owns its own XAML namescope — after extracting a region out of a window, window.FindName("InnerPart") returns null; resolve the UserControl by its window-level name, then pane.FindName("InnerPart"). And window-scope STYLES are invisible to a UserControl's StaticResource at parse time — move such styles to Themes/Controls.xaml (the app-scope rule exists for this).
2. Per-class dotnet.exe vstest from WSL DOES execute the RealApp/MainWindow tests fine (they passed natively 2026-09-01) — only the FULL suite hangs (WASAPI startup). And the test process shares %APPDATA%\ytLlive\startup.log with the real app: lines like camera 'test-camera' failed are test noise, not DB state — to check pollution, query the DB directly (python3 sqlite3, SELECT DeviceId FROM Webcam), not the log.