diff --git a/src/App.css b/src/App.css
index 56e145f3..9b502bcf 100644
--- a/src/App.css
+++ b/src/App.css
@@ -4277,21 +4277,14 @@ body.has-player .chat-fab {
   max-height: 92vh;
 }
 
-/* The composer's popovers (mention list, emoji picker) anchor to the input,
-   which sits at the very bottom of the modal. The modal body must not clip them
-   — let them escape the body entirely so they're never cropped. The message
-   list keeps its own scroll, so nothing else relies on the body clipping. */
+/* The chat sizes itself to the modal and the message list carries its own
+   scroll, so the body never has anything to scroll — dropping its clip keeps a
+   rounding overflow from raising a second, empty scrollbar beside the messages.
+   (The composer's popovers no longer need this: they are portaled to <body>.) */
 .modal-card:has(.chat) .modal-body {
   overflow: visible;
 }
 
-/* Open the mention list upward, into the roomy message area above the input. */
-.chat-composer .mention-dropdown {
-  top: auto;
-  bottom: 100%;
-  margin: 0 0 4px;
-}
-
 /* Very narrow viewports: stack the input and Send button. */
 @media (max-width: 400px) {
   .chat-composer {
@@ -5806,20 +5799,22 @@ body.has-player .chat-fab {
   font-weight: 600;
 }
 
+/* Portaled to <body> and positioned from JS (see useAnchoredFloat), for the
+   same reason as the emoji picker below: the editor sits inside cards, modal
+   bodies and scrollers whose overflow would clip an absolutely positioned
+   popup. Above the modal backdrop (1000), below tooltips (9999). */
 .mention-dropdown {
-  position: absolute;
-  top: 100%;
-  left: 0;
-  right: 0;
-  z-index: 200;
+  position: fixed;
+  z-index: 1100;
+  max-width: calc(100vw - 16px);
   list-style: none;
-  margin: 2px 0 0;
+  margin: 0;
   padding: 4px 0;
   background: var(--color-surface);
   border: 1px solid var(--color-border);
   border-radius: 8px;
   box-shadow: 0 4px 16px rgba(0, 0, 0, 0.18);
-  max-height: 220px;
+  max-height: var(--float-max-h, 220px);
   overflow-y: auto;
 }
 .mention-dropdown-item {
@@ -5840,12 +5835,14 @@ body.has-player .chat-fab {
 }
 
 /* ── Emoji picker (frimousse) ── */
+/* Portaled to <body> and positioned from JS (see useAnchoredFloat): anchored
+   with `position: fixed` so cards, modal bodies and scrollers can't clip it.
+   Above the modal backdrop (1000), below tooltips (9999). */
 .emoji-picker-float {
-  position: absolute;
-  bottom: calc(100% + 4px);
-  left: 0;
-  z-index: 201;
+  position: fixed;
+  z-index: 1100;
   width: 320px;
+  max-width: calc(100vw - 16px);
   background: var(--color-surface);
   border: 1px solid var(--color-border);
   border-radius: 8px;
@@ -5892,7 +5889,7 @@ body.has-player .chat-fab {
 }
 /* frimousse uses bare attributes (no data- prefix) */
 .emoji-picker-float [frimousse-viewport] {
-  max-height: 220px;
+  max-height: var(--float-max-h, 220px);
   /* frimousse already sets overflow-y: auto inline */
 }
 .emoji-picker-float [frimousse-category-header] {
diff --git a/src/components/MentionDropdown.tsx b/src/components/MentionDropdown.tsx
index 5515c7fb..1fc54d42 100644
--- a/src/components/MentionDropdown.tsx
+++ b/src/components/MentionDropdown.tsx
@@ -1,3 +1,4 @@
+import type { CSSProperties } from "react";
 import { Avatar } from "./Avatar.tsx";
 import type { UserResult } from "../hooks/useMentionAutocomplete.ts";
 
@@ -5,14 +6,16 @@ interface MentionDropdownProps {
   results: UserResult[];
   selectedIndex: number;
   onSelect: (username: string) => void;
+  /** Fixed-position placement from `useAnchoredFloat`; see TextEditor. */
+  style?: CSSProperties;
 }
 
 export function MentionDropdown(
-  { results, selectedIndex, onSelect }: MentionDropdownProps,
+  { results, selectedIndex, onSelect, style }: MentionDropdownProps,
 ) {
   if (results.length === 0) return null;
   return (
-    <ul className="mention-dropdown">
+    <ul className="mention-dropdown" style={style}>
       {results.map((user, i) => (
         <li
           key={user.id}
diff --git a/src/components/TextEditor.tsx b/src/components/TextEditor.tsx
index 1b545475..dd954ffe 100644
--- a/src/components/TextEditor.tsx
+++ b/src/components/TextEditor.tsx
@@ -6,6 +6,7 @@ import {
   useRef,
   useState,
 } from "react";
+import { createPortal } from "react-dom";
 import { EmojiPicker, type Locale as EmojiLocale } from "frimousse";
 import { Trans } from "@lingui/react/macro";
 import { useLingui } from "@lingui/react";
@@ -13,6 +14,7 @@ import { charCountClass } from "../utils/charCount.ts";
 import { MentionDropdown } from "./MentionDropdown.tsx";
 import { useMentionAutocomplete } from "../hooks/useMentionAutocomplete.ts";
 import { useEmojiTrigger } from "../hooks/useEmojiTrigger.ts";
+import { useAnchoredFloat } from "../hooks/useAnchoredFloat.ts";
 import { useAuth } from "../hooks/useAuth.ts";
 import { API_URL } from "../config/api.ts";
 
@@ -91,6 +93,23 @@ export const TextEditor = forwardRef<TextEditorHandle, TextEditorProps>(
       }
     }, [emojiOpen]);
 
+    // Both popups are portaled to <body> and anchored to the textarea: the
+    // editor sits inside cards, modal bodies and scrollers that clip anything
+    // absolutely positioned out of their box.
+    const emojiStyle = useAnchoredFloat(textareaRef, emojiOpen, {
+      width: 320,
+      chromeHeight: 40, // search row + borders
+      minContentHeight: 120,
+      maxContentHeight: 220,
+    });
+
+    const mentionStyle = useAnchoredFloat(textareaRef, mentionOpen, {
+      width: "anchor", // it used to be stretched edge to edge by left/right: 0
+      chromeHeight: 10, // list padding + borders
+      minContentHeight: 90,
+      maxContentHeight: 220,
+    });
+
     useEffect(() => {
       if (!autoResize) return;
       const el = textareaRef.current;
@@ -219,16 +238,19 @@ export const TextEditor = forwardRef<TextEditorHandle, TextEditorProps>(
             {value.length} / {maxLength}
           </span>
         )}
-        {mentionOpen && (
+        {mentionOpen && createPortal(
           <MentionDropdown
             results={mentionResults}
             selectedIndex={mentionSelectedIndex}
             onSelect={handleMentionSelect}
-          />
+            style={mentionStyle ?? { visibility: "hidden" }}
+          />,
+          document.body,
         )}
-        {emojiOpen && (
+        {emojiOpen && createPortal(
           <div
             className="emoji-picker-float"
+            style={emojiStyle ?? { visibility: "hidden" }}
             onKeyDownCapture={(e) => {
               if (e.key === "Escape") {
                 e.preventDefault();
@@ -294,7 +316,8 @@ export const TextEditor = forwardRef<TextEditorHandle, TextEditorProps>(
                 <EmojiPicker.List />
               </EmojiPicker.Viewport>
             </EmojiPicker.Root>
-          </div>
+          </div>,
+          document.body,
         )}
       </div>
     );
diff --git a/src/hooks/useAnchoredFloat.ts b/src/hooks/useAnchoredFloat.ts
new file mode 100644
index 00000000..59733472
--- /dev/null
+++ b/src/hooks/useAnchoredFloat.ts
@@ -0,0 +1,109 @@
+import {
+  type CSSProperties,
+  type RefObject,
+  useLayoutEffect,
+  useState,
+} from "react";
+
+/** Space between the anchor and the panel. */
+const GAP = 4;
+/** Space kept clear of the viewport edges. */
+const MARGIN = 8;
+
+interface AnchoredFloatOptions {
+  /**
+   * Preferred width in px, or "anchor" to match the anchor element's own width.
+   * Shrunk when the viewport is narrower either way.
+   */
+  width: number | "anchor";
+  /** Height of the panel's non-scrolling chrome (search row, borders…). */
+  chromeHeight: number;
+  minContentHeight: number;
+  maxContentHeight: number;
+}
+
+/**
+ * Positions a floating panel against an anchor element with `position: fixed`,
+ * so no ancestor's `overflow: hidden` / `overflow: auto` can clip it — cards,
+ * modal bodies and scrollers all cut off an absolutely positioned popup.
+ *
+ * Flips to whichever side of the anchor has the most room, clamps horizontally
+ * to the viewport, and publishes the room left for the scrolling part as the
+ * `--float-max-h` custom property.
+ *
+ * Returns `null` while closed; the first value lands in a layout effect, so the
+ * panel is never painted at the wrong spot.
+ */
+export function useAnchoredFloat(
+  anchorRef: RefObject<HTMLElement | null>,
+  open: boolean,
+  { width, chromeHeight, minContentHeight, maxContentHeight }:
+    AnchoredFloatOptions,
+): CSSProperties | null {
+  const [style, setStyle] = useState<CSSProperties | null>(null);
+
+  useLayoutEffect(() => {
+    if (!open) return;
+    const anchor = anchorRef.current;
+    if (!anchor) return;
+
+    const place = () => {
+      const r = anchor.getBoundingClientRect();
+      const vw = globalThis.innerWidth;
+      const vh = globalThis.innerHeight;
+
+      // Clamp the anchor's edges into the viewport first: an auto-growing
+      // textarea can be taller than the screen, and an off-screen edge would
+      // otherwise put the panel out of reach.
+      const anchorTop = Math.min(Math.max(r.top, MARGIN), vh - MARGIN);
+      const anchorBottom = Math.min(Math.max(r.bottom, MARGIN), vh - MARGIN);
+      const roomAbove = anchorTop - GAP - MARGIN;
+      const roomBelow = vh - anchorBottom - GAP - MARGIN;
+      const placeAbove = roomAbove >= roomBelow;
+
+      const w = Math.min(width === "anchor" ? r.width : width, vw - MARGIN * 2);
+      const content = Math.max(
+        minContentHeight,
+        Math.min(maxContentHeight, (placeAbove ? roomAbove : roomBelow) -
+          chromeHeight),
+      );
+
+      // Anchoring by `bottom` when above means the panel's own height never
+      // enters the computation, so it can't jump as the list loads.
+      const next: CSSProperties & Record<string, string | number> = {
+        position: "fixed",
+        width: w,
+        left: Math.min(
+          Math.max(MARGIN, r.left),
+          Math.max(MARGIN, vw - w - MARGIN),
+        ),
+        "--float-max-h": `${content}px`,
+      };
+      if (placeAbove) {
+        next.bottom = vh - anchorTop + GAP;
+        next.top = "auto";
+      } else {
+        next.top = anchorBottom + GAP;
+        next.bottom = "auto";
+      }
+      setStyle(next);
+    };
+
+    place();
+    // `true` catches scrolling in any ancestor scroller, not just the window.
+    globalThis.addEventListener("scroll", place, true);
+    globalThis.addEventListener("resize", place);
+    // The anchor itself moves when an auto-resizing textarea grows.
+    const observer = new ResizeObserver(place);
+    observer.observe(anchor);
+    return () => {
+      globalThis.removeEventListener("scroll", place, true);
+      globalThis.removeEventListener("resize", place);
+      observer.disconnect();
+    };
+  }, [open, anchorRef, width, chromeHeight, minContentHeight, maxContentHeight]);
+
+  // Gated on `open` rather than cleared on close: the stale value is never
+  // painted, since the layout effect re-places the panel before the next paint.
+  return open ? style : null;
+}