diff --git a/web/src/hooks/useAnchoredFloating.ts b/web/src/hooks/useAnchoredFloating.ts
new file mode 100644
index 000000000..96413ca16
--- /dev/null
+++ b/web/src/hooks/useAnchoredFloating.ts
@@ -0,0 +1,95 @@
+// useAnchoredFloating — robust popover positioning via @floating-ui/dom. Anchors
+// a portaled floating element to a reference (a real DOM element OR a virtual
+// element for a text caret) and keeps it glued through scroll, resize, and layout
+// shifts via autoUpdate. Handles flip (open up when there's no room below) and
+// shift (stay on-screen). This replaces the hand-rolled `position: fixed` coords
+// that detached on scroll and could land at the top-left before the anchor was
+// measured.
+
+import * as React from "react";
+import {
+    computePosition,
+    autoUpdate,
+    offset,
+    flip,
+    shift,
+    size,
+    type Placement,
+    type ReferenceElement,
+} from "@floating-ui/dom";
+
+export interface AnchoredFloatingOptions {
+    placement?: Placement;
+    gap?: number;
+    /** Constrain the floating element to the available viewport height. */
+    maxHeight?: boolean;
+    /** Match the reference element's width (for full-width menus). */
+    sameWidth?: boolean;
+    padding?: number;
+}
+
+export function useAnchoredFloating(open: boolean, opts: AnchoredFloatingOptions = {}) {
+    const { placement = "bottom-start", gap = 6, maxHeight = false, sameWidth = false, padding = 8 } = opts;
+    const [reference, setReference] = React.useState<ReferenceElement | null>(null);
+    const [floating, setFloating] = React.useState<HTMLElement | null>(null);
+    // Hidden until the first position is computed, so it never flashes at 0,0.
+    // Uses `visibility` (not opacity) so a framer-motion entrance can own opacity
+    // without fighting this style.
+    const [style, setStyle] = React.useState<React.CSSProperties>({
+        position: "fixed",
+        top: 0,
+        left: 0,
+        visibility: "hidden",
+    });
+
+    React.useLayoutEffect(() => {
+        if (!open || !reference || !floating) return;
+        const update = () => {
+            computePosition(reference, floating, {
+                strategy: "fixed",
+                placement,
+                middleware: [
+                    offset(gap),
+                    flip({ padding }),
+                    shift({ padding }),
+                    size({
+                        padding,
+                        apply({ availableHeight, rects, elements }) {
+                            const s: Record<string, string> = {};
+                            if (maxHeight) s.maxHeight = `${Math.max(140, Math.floor(availableHeight))}px`;
+                            if (sameWidth) s.width = `${Math.round(rects.reference.width)}px`;
+                            Object.assign(elements.floating.style, s);
+                        },
+                    }),
+                ],
+            }).then(({ x, y }) => {
+                setStyle({
+                    position: "fixed",
+                    top: 0,
+                    left: 0,
+                    transform: `translate3d(${Math.round(x)}px, ${Math.round(y)}px, 0)`,
+                    visibility: "visible",
+                });
+            });
+        };
+        const cleanup = autoUpdate(reference, floating, update);
+        return cleanup;
+    }, [open, reference, floating, placement, gap, maxHeight, sameWidth, padding]);
+
+    return { setReference, setFloating, floatingStyle: style };
+}
+
+// caretReference builds a floating-ui virtual element for a text caret: it
+// reports the caret's viewport rect and points autoUpdate at the editor DOM (its
+// contextElement) so scrolling that container re-anchors the popover.
+export function caretReference(getRect: () => DOMRect | null, contextElement: Element | null): ReferenceElement {
+    return {
+        contextElement: contextElement ?? undefined,
+        getBoundingClientRect: () => {
+            const r = getRect();
+            if (r) return r;
+            // Off-screen fallback keeps computePosition happy until the next tick.
+            return new DOMRect(-9999, -9999, 0, 0);
+        },
+    };
+}