fix(workspaces): mobile (tall) grid can't scroll — root height collapse + touch capture

Two blockers for scrolling the tall grid on a phone:

1. HomeTileGrid's root was `flex-1` inside a BLOCK parent (the workspace
   region), so flex-1 did nothing and the root sized to its content; the
   scroller's `h-full` collapsed to auto and overflow-y-auto never engaged —
   extra tiles were clipped by the shell's `overflow-hidden` with no way to
   scroll. The root is now `h-full`, so the scroller gets a definite height
   and tall mode scrolls (wide mode was unaffected: horizontal overflow
   scrolls regardless of container height).

2. `setPointerCapture` was called for TOUCH pointers at pointerdown, which
   can suppress native panning in WebKit. Touch now skips explicit capture:
   the browser's implicit capture already retargets the press, and after the
   long-press lift the moved events bubble up to the grid container where the
   handlers live — scroll gestures keep working and touch drags are intact.

Verification: svelte-check 0 errors/0 warnings; vitest 1694/1694; build ok.
Needs a human on a real phone: swipe the tall grid when tiles overflow —
it must scroll; long-press-and-drag a tile must still reorder.

2 files changed, 14 insertions, 2 deletions

diff --git a/backend-handoff.md b/backend-handoff.md
index 735d2cd..c15db17 100644
--- a/backend-handoff.md
+++ b/backend-handoff.md
@@ -286,6 +286,13 @@ changes, NO contract changes — the wire types and every endpoint consumed are
   elements to the GRID CONTAINER, which `setPointerCapture`s the pointer and never gets
   re-parented/`pointer-events: none`/unmounted — so move/up stream to it over empty cells and off
   the canvas, and capture can never be lost to a DOM move again.
+- **Mobile (tall) scroll fix**: the grid's root was `flex-1` inside a BLOCK parent (the workspace
+  region), so it sized to its content and the scroller's `h-full` collapsed → `overflow-y-auto`
+  never engaged and the shell's `overflow-hidden` clipped the extra tiles. The root is now `h-full`,
+  giving the scroller a definite height so tall mode scrolls. Also: touch pointers are no longer
+  `setPointerCapture`d at pointerdown (an early touch capture can suppress native panning in
+  WebKit; touch already gets implicit capture and post-lift moves bubble to the container), keeping
+  touch scrolling reliable while drags still work.
 - **Drag append bound** (`dragAppendLimit` in `logic/tile-layout.ts`; `cellAt` in
   `HomeTileGrid.svelte`): the drop target is clamped to at most 3 columns (wide) / rows (tall)
   past the committed content edge (span-aware, measured on the COMMITTED layout so it can't
diff --git a/src/features/workspaces/ui/HomeTileGrid.svelte b/src/features/workspaces/ui/HomeTileGrid.svelte
index d259aea..489c783 100644
--- a/src/features/workspaces/ui/HomeTileGrid.svelte
+++ b/src/features/workspaces/ui/HomeTileGrid.svelte
@@ -160,7 +160,12 @@
     if (!tileEl || insideInteractive(e.target)) return;
     const id = tileEl.getAttribute("data-tile-id");
     if (id === null) return;
-    gridEl?.setPointerCapture?.(e.pointerId);
+    // Capture mouse/pen so fast drags keep streaming to this container. TOUCH
+    // is purposely NOT captured here: an early touch capture can suppress
+    // native scrolling (WebKit), and touch already gets the browser's implicit
+    // capture — after the long-press lift the moved events bubble up to this
+    // container anyway.
+    if (e.pointerType !== "touch") gridEl?.setPointerCapture?.(e.pointerId);
     // Where within the tile the pointer grabbed — the follow transform keeps
     // THIS point under the pointer (not the tile's top-left origin).
     const rect = tileEl.getBoundingClientRect();
@@ -453,7 +458,7 @@
 
 <svelte:window onkeydowncapture={windowKeydown} />
 
-<div class="relative min-h-0 flex-1">
+<div class="relative h-full">
   <div
     bind:this={scrollerEl}
     class="h-full overscroll-contain"