docs: restructure TASKS.md into a catalog — one file per task in TASKS/

TASKS.md is now the index (status table, open items, research pointer).
33 files: 32 task files + 1 research facts file. The full take-saga
narrative and all design decisions are preserved verbatim; the catalog
makes the queue readable without opening every task body. Schema and
AGENTS.md updated to reflect the new layout.

TASKS/task-17-web-source-rendering.md

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+# TASK 17 — Web source rendering (WebView2)
+
+> Catalog: [`TASKS.md`](../TASKS.md) — status and requirements live here.
+
+
+**Goal:** make the web source actually render URLs into the preview and stream output.
+
+### Status: ✅ Done — required for v1 (2026-08-28)
+
+1. ✅ Add `Microsoft.Web.WebView2` NuGet package
+2. ✅ Schema v10: `WebUri TEXT` column on `Source` table + migration in `LayoutStore.cs`
+3. ✅ Persist `Source.WebUri` on save/load (currently in-memory only — lost on restart)
+4. ✅ Hidden off-screen `WebView2` control per web source — navigates to `WebUri`, renders in-app
+5. ✅ Frame capture from WebView2 (`CoreWebView2.CapturePreviewAsync`) → `WriteableBitmap` (BGRA8)
+6. ✅ Wire into `FramePump` resolver — `Source { Type: WebSource }` → latest WebView2 frame
+7. ✅ Wire into `SceneCompositor` — render web source as an image element at its position/size
+8. ✅ Preview shows live web content (not just a blank rectangle)
+9. ☐ Handle navigation errors, invalid URIs, timeout gracefully
+
+**Rendering model (2026-08-28, canvas-size viewport + ALPHA-BBOX crop — DONE, creator-verified):**
+the page renders at the MASTER CANVAS size (1920×1080), stable, never tracked (no reflow/truncation;
+scrollbars suppressed via `overflow:hidden`). `FindContentBounds` scans the Bgra32 capture and crops
+to the bounding box of non-transparent pixels — the widget's true rendered extent, measured from the
+frame itself (NO DOM query, immune to layout timing; can never truncate content; full-canvas widgets
+fall through to the full frame = prior verified-good image). `Stretch="Fill"` maps the cropped frame
+flush under the selection box → box hugs the widget on all four sides. `QueryContentBoundsAsync` +
+the JS content-bounds script are DELETED. **RESULT: bounding verified PERFECT by the creator with
+two widgets.** Root-cause note on the earlier "remaining defect/gap": that was a WIDGET GLOW EFFECT
+(the widget's own CSS glow pushes out its perceived borders), not a code bug — the alpha-bbox was
+already hugging the glow halo. Lesson: test with a second, plain widget before changing code.
+⚠️ Lesson bank: never return `JSON.stringify` from `ExecuteScriptAsync` (double-encodes); never
+measure DOM stuff on NavigationCompleted (unsettled layout broke the image — `a5b9952`); avoid
+sizing the container to the crop (`ab29ec8` reverted — made it worse); a widget glow effect can
+fake a gap — verify with a plain widget first; measure rendered pixels instead.
+
+**Properties panel (2026-08-28):** web URI ✓/✕ icon buttons are `IsTabStop="False"` so Tab flows
+X→Y→W→H→URI; the ✕ button now clears the URI textbox (was reverting to the pre-accept snapshot).
+Slider style gained `IsMoveToPointEnabled="True"` — click-anywhere-on-bar jumps the thumb to the
+click (volume sliders keep their manual `SetSliderValueFromClick`, harmless duplication).
+
+### Design decisions
+
+- WebView2 is the only option for Windows — it's pre-installed on Windows 10 20H2+ and Windows 11
+- The web source is a standard element — positioned/sized/opacitied like any image source
+- Frame capture rate can be lower than video FPS (5-10 fps for web content is fine)
+- This enables Streamlabs/StreamElements overlays via web URLs
+