fix: keep conversation composer in the viewport under layout push

Long unbreakable tokens (OAuth URLs) grew the AppFrame center column past the viewport because the layout-push rule used the grid default min-height:auto. Cap --dsh-sidebar-height the same way setBottomHeight does (viewport minus PANEL_MIN) and let the column shrink and wrap.

src/client/layout-push.ts

@@ -0,0 +1,32 @@
+/**
+ * Size written to `--dsh-sidebar-width` / `--dsh-sidebar-height`.
+ * The conversation column (output + composer) must keep at least
+ * {@link PANEL_MIN} of the viewport after the bottom panel claims height.
+ */
+import { BOTTOM_MIN, PANEL_MIN } from './state.ts'
+
+export interface LayoutPushInput {
+  narrow: boolean
+  panelOpen: boolean
+  bottomOpen: boolean
+  width: number
+  bottomHeight: number
+  viewportWidth: number
+  viewportHeight: number
+}
+
+export interface LayoutPushSize {
+  width: number
+  height: number
+}
+
+/** Compute the live layout-push size. Narrow drawers float and push 0. */
+export function layoutPushSize(input: LayoutPushInput): LayoutPushSize {
+  if (input.narrow) return { width: 0, height: 0 }
+  const maxWidth = Math.max(PANEL_MIN, input.viewportWidth)
+  const maxHeight = Math.max(BOTTOM_MIN, input.viewportHeight - PANEL_MIN)
+  return {
+    width: input.panelOpen ? Math.min(Math.max(0, input.width), maxWidth) : 0,
+    height: input.bottomOpen ? Math.min(Math.max(0, input.bottomHeight), maxHeight) : 0,
+  }
+}