feat(files): a press anywhere on a file's row plays it

A table row (and its narrow card) can carry its object's default action:
a click or tap on the row runs it, a press on a control inside the row,
the click that ends a text selection and a drag do not.

frontend/src/components/ui/rowOpen.ts

@@ -0,0 +1,60 @@
+import type { MouseEvent, PointerEvent } from "react";
+import { endsTextSelection, movedPastSlop } from "../../lib/textSelection";
+
+// A table row (or its narrow card twin) as the click and tap surface of its object's default action,
+// the way a card is: a press anywhere on the row opens it, not only on the title inside it.
+//
+// What the row does NOT claim:
+//  - a press on a control inside it (its quick icons, its "…", a link, a field): that is the control's;
+//  - a click that ends a text selection, or a press that travelled (a drag across the row's padding):
+//    DESIGN.md "Text stays selectable" — no play or open fires;
+//  - an event from a portal (a popover a cell opened): React bubbles it through the row, the DOM does
+//    not, so only a target the row really contains counts.
+// The long-press menu's trailing click is swallowed by its own trigger (`useContextMenu`), before it
+// reaches the row.
+
+// What counts as a control of its own. `[tabindex]` covers a focusable cell (a hover card's trigger);
+// the row's own roving tab stop is the row itself, which the containment check below leaves out.
+const CONTROL =
+  'a, button, input, select, textarea, label, summary, [role="button"], [role="menuitem"], [role="checkbox"], [role="switch"], [contenteditable="true"], [tabindex]';
+
+// Where each row's press began, for the drag slop. Per element: the table row and its card twin are
+// two elements, and a press on one must not be measured against the other.
+const pressedAt = new WeakMap<Element, { x: number; y: number }>();
+
+type Handlers = {
+  onPointerDown?: (e: PointerEvent<HTMLElement>) => void;
+  onClick?: (e: MouseEvent<HTMLElement>) => void;
+};
+
+/** The row's props with its default action added on top of the caller's own (a context menu's
+ *  trigger props, which keep their handlers). `open` null: the row has no default action. */
+export function withRowOpen(
+  props: Record<string, unknown> | undefined,
+  open: (() => void) | null,
+): Record<string, unknown> {
+  const base = props ?? {};
+  if (!open) return base;
+  const { onPointerDown, onClick } = base as Handlers;
+  return {
+    ...base,
+    onPointerDown: (e: PointerEvent<HTMLElement>) => {
+      pressedAt.set(e.currentTarget, { x: e.clientX, y: e.clientY });
+      onPointerDown?.(e);
+    },
+    onClick: (e: MouseEvent<HTMLElement>) => {
+      onClick?.(e);
+      if (e.defaultPrevented || !claims(e)) return;
+      open();
+    },
+  };
+}
+
+function claims(e: MouseEvent<HTMLElement>): boolean {
+  const row = e.currentTarget;
+  const target = e.target;
+  if (!(target instanceof Element) || !row.contains(target)) return false;
+  const control = target.closest(CONTROL);
+  if (control && control !== row && row.contains(control)) return false;
+  return !endsTextSelection(e) && !movedPastSlop(pressedAt.get(row) ?? null, e);
+}