Add bot-driven room app UI via im.paarrot.ui state.

Bots can publish a declarative panel UI that takes over a room; user
actions are sent as im.paarrot.ui.action timeline events.

docs/README.md

@@ -62,6 +62,7 @@ New feature? Copy [`handoff/TEMPLATE.md`](./handoff/TEMPLATE.md) into `handoff/f
 | Sub-rooms | [sub-rooms](./handoff/features/sub-rooms/HANDOFF.md) |
 | Lobby (space card view) | [lobby-forums](./handoff/features/lobby-forums/HANDOFF.md) |
 | Forum spaces (post feed UI) | [forum](./handoff/features/forum/HANDOFF.md) |
+| Room App UI (bot-driven) | [room-app-ui](./handoff/features/room-app-ui/HANDOFF.md) |
 
 ### Settings & customization
 

docs/handoff/features/room-app-ui/HANDOFF.md

@@ -0,0 +1,93 @@
+# Room App UI — handoff
+
+## Summary
+
+Bots can publish a declarative UI into Matrix room state (`im.paarrot.ui`). Paarrot takes over the room view with that UI. User interactions are sent as timeline events (`im.paarrot.ui.action`), not chat messages. The bot updates state to re-render panels.
+
+## User-facing behavior
+
+- When a room has a valid `im.paarrot.ui` state event, opening the room shows the app UI instead of the chat timeline (forum rooms still win over app UI).
+- **Show chat** returns to the normal timeline without clearing bot state; a banner offers **Show app** to go back.
+- Action events are hidden from the chat timeline (same as confetti relay events).
+- Room settings → Permissions includes **Set Room App UI** and **Send Room App Actions**.
+
+## Architecture
+
+```
+Bot → state im.paarrot.ui
+  → Room.tsx detects via useStateEvent
+    → RoomAppView → RoomAppSchema (declarative nodes)
+      → user clicks → mx.sendEvent(im.paarrot.ui.action)
+        → Bot updates im.paarrot.ui → live re-render
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/types/matrix/room.ts` | `StateEvent.PaarrotUi`, `MessageEvent.PaarrotUiAction`, node types |
+| `cinny/src/app/utils/room.ts` | `getPaarrotUiContent`, `hasRoomAppUi` |
+| `cinny/src/app/features/room/Room.tsx` | Takeover branch + Show chat / Show app |
+| `cinny/src/app/features/room-app/` | `RoomAppView`, schema renderer, CSS sanitize/scope |
+| `cinny/src/app/features/room/RoomTimeline.tsx` | Hides `im.paarrot.ui.action` |
+| `cinny/src/app/features/room-settings/permissions/usePermissionItems.ts` | Permission labels |
+
+## Data model
+
+| Event | Kind | Content |
+|-------|------|---------|
+| `im.paarrot.ui` | state (`""`) | `{ version, title?, css?, root }` |
+| `im.paarrot.ui.action` | timeline | `{ action, component_id, value?, values?, ui_event_id? }` |
+
+See [samples/](./samples/) for pasteable Developer Tools payloads.
+
+MVP node types: `panel`, `row`, `text`, `button`, `input`, `select`, `image`, `spacer`.
+
+## Dependencies
+
+- folds UI primitives
+- matrix-js-sdk `sendEvent` / state sync
+- No bot-supplied JavaScript; CSS is sanitized and scoped under `[data-room-app]`
+
+## Integration points
+
+- Same room takeover pattern as forums (`Room.tsx` branch)
+- Developer Tools can send state/events for demos without a bot process
+
+## Testing
+
+### Manual
+
+1. In Developer Tools → Send State Event, type `im.paarrot.ui`, paste `samples/trivia-ui-state.json`.
+2. Open the room — app UI should replace the timeline.
+3. Click an answer — an `im.paarrot.ui.action` event is sent (hidden in timeline; visible in raw/dev tools).
+4. Click **Show chat**, then **Show app**.
+5. Clear state content / redact state to restore normal chat.
+
+### Automated
+
+- None yet
+
+## Known issues & gotchas
+
+- CSS scoping is best-effort, not a full CSS parser
+- Images allow `mxc://`, `https://`, and `http://` only
+- Forum rooms take priority over app UI
+- `sendEvent(..., as any)` cast mirrors other custom event types
+
+## Future work
+
+- `form` / `tabs` / `markdown` / `progress` nodes
+- Bot SDK helpers
+- Stronger CSS sandbox (Shadow DOM)
+- Encrypt custom action payloads helpers if needed
+
+## Related docs
+
+- [samples/trivia-ui-state.json](./samples/trivia-ui-state.json)
+- [samples/ui-action-event.json](./samples/ui-action-event.json)
+
+## Add your extra things here
+
+- Power level: bots need PL ≥ `state_default` (usually 50) or an explicit level for `im.paarrot.ui`
+- Action events use normal message event power levels unless overridden for `im.paarrot.ui.action`

docs/handoff/features/room-app-ui/samples/poll-ui-state.json

@@ -0,0 +1,34 @@
+{
+  "version": 1,
+  "title": "Poll Booth",
+  "root": {
+    "type": "panel",
+    "id": "poll",
+    "children": [
+      {
+        "type": "text",
+        "id": "prompt",
+        "text": "Where should we go for lunch?"
+      },
+      {
+        "type": "select",
+        "id": "choice",
+        "name": "choice",
+        "label": "Your vote",
+        "options": [
+          { "label": "Ramen", "value": "ramen" },
+          { "label": "Pizza", "value": "pizza" },
+          { "label": "Salad", "value": "salad" }
+        ],
+        "value": "ramen"
+      },
+      {
+        "type": "button",
+        "id": "vote",
+        "label": "Submit vote",
+        "action": "vote",
+        "variant": "Primary"
+      }
+    ]
+  }
+}

docs/handoff/features/room-app-ui/samples/trivia-ui-state.json

@@ -0,0 +1,88 @@
+{
+  "version": 1,
+  "title": "Trivia Night",
+  "css": ".score { font-weight: 700; } .hint { opacity: 0.75; }",
+  "root": {
+    "type": "panel",
+    "id": "main",
+    "children": [
+      {
+        "type": "text",
+        "id": "q",
+        "text": "Capital of France?"
+      },
+      {
+        "type": "text",
+        "id": "hint",
+        "className": "hint",
+        "text": "Pick one answer below."
+      },
+      {
+        "type": "spacer",
+        "id": "sp1",
+        "size": 16
+      },
+      {
+        "type": "row",
+        "id": "answers",
+        "children": [
+          {
+            "type": "button",
+            "id": "a",
+            "label": "Paris",
+            "action": "answer",
+            "value": "paris",
+            "variant": "Primary"
+          },
+          {
+            "type": "button",
+            "id": "b",
+            "label": "Lyon",
+            "action": "answer",
+            "value": "lyon",
+            "variant": "Secondary"
+          },
+          {
+            "type": "button",
+            "id": "c",
+            "label": "Marseille",
+            "action": "answer",
+            "value": "marseille",
+            "variant": "Secondary"
+          }
+        ]
+      },
+      {
+        "type": "spacer",
+        "id": "sp2",
+        "size": 24
+      },
+      {
+        "type": "text",
+        "id": "score_label",
+        "className": "score",
+        "text": "Score: 0"
+      },
+      {
+        "type": "input",
+        "id": "nick",
+        "name": "nickname",
+        "label": "Display name on the board",
+        "placeholder": "Optional nickname"
+      },
+      {
+        "type": "row",
+        "id": "submit_row",
+        "children": [
+          {
+            "type": "button",
+            "id": "join",
+            "label": "Join board",
+            "action": "join",
+            "variant": "Success"
+          }
+        ]
+      }
+    ]
+  }
+}

docs/handoff/features/room-app-ui/samples/ui-action-event.json

@@ -0,0 +1,9 @@
+{
+  "action": "answer",
+  "component_id": "a",
+  "value": "paris",
+  "values": {
+    "nickname": "Ada"
+  },
+  "ui_event_id": "$REPLACE_WITH_CURRENT_im.paarrot.ui_EVENT_ID"
+}

src/app/features/room-app/RoomAppSchema.tsx

@@ -0,0 +1,205 @@
+import React, { useCallback, useMemo, useState } from 'react';
+import { Box, Button, Input, Text, config } from 'folds';
+import { MatrixClient } from 'matrix-js-sdk';
+import {
+  PaarrotUiActionContent,
+  PaarrotUiButtonNode,
+  PaarrotUiContent,
+  PaarrotUiNode,
+} from '../../../types/matrix/room';
+import { mxcUrlToHttp } from '../../utils/matrix';
+import { isAllowedRoomAppImageSrc, scopeRoomAppCss } from './sanitizeRoomAppCss';
+import * as css from './RoomAppView.css';
+
+const SCOPE = '[data-room-app]';
+
+type RoomAppSchemaProps = {
+  mx: MatrixClient;
+  content: PaarrotUiContent;
+  uiEventId?: string;
+  useAuthentication: boolean;
+  onAction: (payload: PaarrotUiActionContent) => void | Promise<void>;
+};
+
+function fieldName(node: { id: string; name?: string }): string {
+  return node.name || node.id;
+}
+
+function spacerSize(size?: number): 'sm' | 'md' | 'lg' {
+  if (typeof size === 'number' && size <= 8) return 'sm';
+  if (typeof size === 'number' && size >= 24) return 'lg';
+  return 'md';
+}
+
+export function RoomAppSchema({
+  mx,
+  content,
+  uiEventId,
+  useAuthentication,
+  onAction,
+}: RoomAppSchemaProps) {
+  const [values, setValues] = useState<Record<string, string>>({});
+  const [sending, setSending] = useState(false);
+
+  const scopedCss = useMemo(
+    () => (content.css ? scopeRoomAppCss(content.css, SCOPE) : ''),
+    [content.css]
+  );
+
+  const setField = useCallback((name: string, value: string) => {
+    setValues((prev) => ({ ...prev, [name]: value }));
+  }, []);
+
+  const handleButton = useCallback(
+    async (node: PaarrotUiButtonNode) => {
+      if (node.disabled || sending) return;
+      setSending(true);
+      try {
+        await onAction({
+          action: node.action,
+          component_id: node.id,
+          value: node.value,
+          values: { ...values },
+          ui_event_id: uiEventId,
+        });
+      } finally {
+        setSending(false);
+      }
+    },
+    [onAction, sending, uiEventId, values]
+  );
+
+  const renderNode = (node: PaarrotUiNode): React.ReactNode => {
+    switch (node.type) {
+      case 'panel':
+        return (
+          <div key={node.id} className={css.Panel} data-room-app-node={node.id}>
+            {node.children?.map((child) => renderNode(child))}
+          </div>
+        );
+      case 'row':
+        return (
+          <div key={node.id} className={css.Row} data-room-app-node={node.id}>
+            {node.children?.map((child) => renderNode(child))}
+          </div>
+        );
+      case 'text':
+        return (
+          <Text
+            key={node.id}
+            as="p"
+            size="T400"
+            className={node.className}
+            data-room-app-node={node.id}
+          >
+            {node.text ?? ''}
+          </Text>
+        );
+      case 'button': {
+        const variant = node.variant ?? 'Primary';
+        return (
+          <Button
+            key={node.id}
+            type="button"
+            size="400"
+            variant={variant}
+            radii="300"
+            disabled={node.disabled || sending}
+            onClick={() => handleButton(node)}
+            data-room-app-node={node.id}
+          >
+            <Text size="B400">{node.label}</Text>
+          </Button>
+        );
+      }
+      case 'input': {
+        const name = fieldName(node);
+        const current = values[name] ?? node.value ?? '';
+        return (
+          <div key={node.id} className={css.Field} data-room-app-node={node.id}>
+            {node.label && (
+              <Text as="label" size="L400" htmlFor={`room-app-${node.id}`}>
+                {node.label}
+              </Text>
+            )}
+            <Input
+              id={`room-app-${node.id}`}
+              name={name}
+              variant="Background"
+              radii="300"
+              type={node.inputType ?? 'text'}
+              placeholder={node.placeholder}
+              value={current}
+              onChange={(evt) => setField(name, evt.currentTarget.value)}
+            />
+          </div>
+        );
+      }
+      case 'select': {
+        const name = fieldName(node);
+        const current = values[name] ?? node.value ?? '';
+        return (
+          <div key={node.id} className={css.Field} data-room-app-node={node.id}>
+            {node.label && (
+              <Text as="label" size="L400" htmlFor={`room-app-${node.id}`}>
+                {node.label}
+              </Text>
+            )}
+            <Box as="span" grow="Yes" style={{ position: 'relative' }}>
+              <select
+                id={`room-app-${node.id}`}
+                name={name}
+                value={current}
+                onChange={(evt) => setField(name, evt.currentTarget.value)}
+                style={{
+                  width: '100%',
+                  padding: `${config.space.S200} ${config.space.S300}`,
+                  borderRadius: config.radii.R300,
+                  border: '1px solid var(--bq-border, CurrentColor)',
+                  background: 'transparent',
+                  color: 'inherit',
+                  font: 'inherit',
+                }}
+              >
+                {(node.options ?? []).map((opt) => (
+                  <option key={opt.value} value={opt.value}>
+                    {opt.label}
+                  </option>
+                ))}
+              </select>
+            </Box>
+          </div>
+        );
+      }
+      case 'image': {
+        if (!isAllowedRoomAppImageSrc(node.src)) return null;
+        const httpSrc = node.src.startsWith('mxc://')
+          ? mxcUrlToHttp(mx, node.src, useAuthentication) ?? undefined
+          : node.src;
+        if (!httpSrc) return null;
+        return (
+          <img
+            key={node.id}
+            className={css.Image}
+            src={httpSrc}
+            alt={node.alt ?? ''}
+            width={node.width}
+            height={node.height}
+            data-room-app-node={node.id}
+          />
+        );
+      }
+      case 'spacer':
+        return <div key={node.id} className={css.Spacer({ size: spacerSize(node.size) })} />;
+      default:
+        return null;
+    }
+  };
+
+  return (
+    <div data-room-app="">
+      {scopedCss ? <style>{scopedCss}</style> : null}
+      {renderNode(content.root)}
+    </div>
+  );
+}

src/app/features/room-app/RoomAppView.css.ts

@@ -0,0 +1,74 @@
+import { style } from '@vanilla-extract/css';
+import { recipe } from '@vanilla-extract/recipes';
+import { DefaultReset, config, toRem } from 'folds';
+
+export const Root = style([
+  DefaultReset,
+  {
+    display: 'flex',
+    flexDirection: 'column',
+    flexGrow: 1,
+    minHeight: 0,
+    minWidth: 0,
+  },
+]);
+
+export const Header = style({
+  paddingLeft: config.space.S200,
+  paddingRight: config.space.S200,
+});
+
+export const Body = style([
+  DefaultReset,
+  {
+    flexGrow: 1,
+    minHeight: 0,
+    overflow: 'auto',
+    padding: config.space.S400,
+  },
+]);
+
+export const Panel = style({
+  display: 'flex',
+  flexDirection: 'column',
+  gap: config.space.S300,
+  width: '100%',
+});
+
+export const Row = style({
+  display: 'flex',
+  flexDirection: 'row',
+  flexWrap: 'wrap',
+  gap: config.space.S200,
+  alignItems: 'center',
+});
+
+export const Field = style({
+  display: 'flex',
+  flexDirection: 'column',
+  gap: config.space.S100,
+  minWidth: toRem(160),
+  flexGrow: 1,
+});
+
+export const Image = style({
+  maxWidth: '100%',
+  height: 'auto',
+  borderRadius: config.radii.R300,
+});
+
+export const Spacer = recipe({
+  base: {
+    flexShrink: 0,
+  },
+  variants: {
+    size: {
+      sm: { height: config.space.S200 },
+      md: { height: config.space.S400 },
+      lg: { height: config.space.S600 },
+    },
+  },
+  defaultVariants: {
+    size: 'md',
+  },
+});

src/app/features/room-app/RoomAppView.tsx

@@ -0,0 +1,67 @@
+import React, { useCallback } from 'react';
+import { Box, Button, Header, Text, config } from 'folds';
+import { Room } from 'matrix-js-sdk';
+import { Page } from '../../components/page';
+import { useMatrixClient } from '../../hooks/useMatrixClient';
+import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
+import { useStateEvent } from '../../hooks/useStateEvent';
+import { useRoomName } from '../../hooks/useRoomMeta';
+import {
+  MessageEvent,
+  PaarrotUiActionContent,
+  StateEvent,
+} from '../../../types/matrix/room';
+import { parsePaarrotUiContent } from '../../utils/room';
+import { RoomAppSchema } from './RoomAppSchema';
+import * as css from './RoomAppView.css';
+
+type RoomAppViewProps = {
+  room: Room;
+  onShowChat: () => void;
+};
+
+export function RoomAppView({ room, onShowChat }: RoomAppViewProps) {
+  const mx = useMatrixClient();
+  const useAuthentication = useMediaAuthentication();
+  const roomName = useRoomName(room);
+  const uiEvent = useStateEvent(room, StateEvent.PaarrotUi);
+  const content = parsePaarrotUiContent(uiEvent?.getContent());
+  const title = content?.title || roomName || 'Room App';
+
+  const handleAction = useCallback(
+    async (payload: PaarrotUiActionContent) => {
+      await mx.sendEvent(room.roomId, MessageEvent.PaarrotUiAction as any, payload);
+    },
+    [mx, room.roomId]
+  );
+
+  return (
+    <Page>
+      <Header className={css.Header} size="600">
+        <Box grow="Yes" alignItems="Center" gap="200">
+          <Box grow="Yes" alignItems="Center" gap="200" minWidth="0">
+            <Text size="H6" truncate>
+              {title}
+            </Text>
+          </Box>
+          <Button size="300" variant="Secondary" radii="300" onClick={onShowChat}>
+            <Text size="B300">Show chat</Text>
+          </Button>
+        </Box>
+      </Header>
+      <Box className={css.Body} grow="Yes" direction="Column" style={{ gap: config.space.S400 }}>
+        {content ? (
+          <RoomAppSchema
+            mx={mx}
+            content={content}
+            uiEventId={uiEvent?.getId()}
+            useAuthentication={useAuthentication}
+            onAction={handleAction}
+          />
+        ) : (
+          <Text size="T400">This room’s app UI is missing or invalid.</Text>
+        )}
+      </Box>
+    </Page>
+  );
+}

src/app/features/room-app/index.ts

@@ -0,0 +1,7 @@
+export { RoomAppView } from './RoomAppView';
+export { RoomAppSchema } from './RoomAppSchema';
+export {
+  sanitizeRoomAppCss,
+  scopeRoomAppCss,
+  isAllowedRoomAppImageSrc,
+} from './sanitizeRoomAppCss';

src/app/features/room-app/sanitizeRoomAppCss.ts

@@ -0,0 +1,91 @@
+/**
+ * Strip dangerous CSS constructs from bot-supplied stylesheets.
+ * Not a full CSS parser — best-effort for MVP scoped injection.
+ */
+export function sanitizeRoomAppCss(css: string): string {
+  let out = css;
+  out = out.replace(/@import\b[^;{]*;?/gi, '');
+  out = out.replace(/url\s*\(\s*['"]?\s*javascript:[^)]*\)/gi, 'url(about:blank)');
+  out = out.replace(/expression\s*\([^)]*\)/gi, 'initial');
+  out = out.replace(/-moz-binding\s*:[^;]+;?/gi, '');
+  out = out.replace(/behavior\s*:[^;]+;?/gi, '');
+  out = out.replace(/@charset\b[^;]*;?/gi, '');
+  return out;
+}
+
+/**
+ * Prefix plain selectors with a scope so bot CSS cannot escape the room app root.
+ * At-rules (@media, @supports, @keyframes) are kept with nested rules re-scoped where possible.
+ */
+export function scopeRoomAppCss(css: string, scopeSelector: string): string {
+  const sanitized = sanitizeRoomAppCss(css).trim();
+  if (!sanitized) return '';
+
+  const scopeRule = (selectors: string, body: string): string => {
+    const scoped = selectors
+      .split(',')
+      .map((s) => {
+        const sel = s.trim();
+        if (!sel) return '';
+        if (sel.startsWith(scopeSelector)) return sel;
+        return `${scopeSelector} ${sel}`;
+      })
+      .filter(Boolean)
+      .join(', ');
+    return `${scoped}{${body}}`;
+  };
+
+  const rewriteBlock = (block: string): string => {
+    const trimmed = block.trim();
+    if (!trimmed) return '';
+
+    if (trimmed.startsWith('@')) {
+      const open = trimmed.indexOf('{');
+      if (open === -1) return `${trimmed};`;
+      const header = trimmed.slice(0, open).trim();
+      const inner = trimmed.slice(open + 1);
+      // @keyframes / @font-face: keep as-is (namespaced risk is low for MVP)
+      if (/^@(keyframes|font-face)\b/i.test(header)) {
+        return `${header}{${inner}}`;
+      }
+      // @media / @supports: re-scope nested rules
+      const nested = rewriteCssChunk(inner);
+      return `${header}{${nested}}`;
+    }
+
+    const open = trimmed.indexOf('{');
+    if (open === -1) return '';
+    const selectors = trimmed.slice(0, open);
+    const body = trimmed.slice(open + 1);
+    return scopeRule(selectors, body);
+  };
+
+  const rewriteCssChunk = (chunk: string): string => {
+    const parts: string[] = [];
+    let depth = 0;
+    let start = 0;
+    for (let i = 0; i < chunk.length; i += 1) {
+      const ch = chunk[i];
+      if (ch === '{') depth += 1;
+      else if (ch === '}') {
+        depth -= 1;
+        if (depth === 0) {
+          parts.push(rewriteBlock(chunk.slice(start, i)));
+          start = i + 1;
+        }
+      }
+    }
+    return parts.filter(Boolean).join('\n');
+  };
+
+  return rewriteCssChunk(sanitized);
+}
+
+export function isAllowedRoomAppImageSrc(src: string): boolean {
+  const trimmed = src.trim();
+  return (
+    trimmed.startsWith('mxc://') ||
+    trimmed.startsWith('https://') ||
+    trimmed.startsWith('http://')
+  );
+}

src/app/features/room-settings/permissions/usePermissionItems.ts

@@ -204,6 +204,19 @@ export const usePermissionGroups = (): PermissionGroup[] => {
           },
           name: 'Modify Widgets',
         },
+        {
+          location: {
+            state: true,
+            key: StateEvent.PaarrotUi,
+          },
+          name: 'Set Room App UI',
+        },
+        {
+          location: {
+            key: MessageEvent.PaarrotUiAction,
+          },
+          name: 'Send Room App Actions',
+        },
       ],
     };
 

src/app/features/room/Room.tsx

@@ -1,5 +1,5 @@
-import React, { useCallback, useEffect } from 'react';
-import { Box, Line } from 'folds';
+import React, { useCallback, useEffect, useMemo, useState } from 'react';
+import { Box, Button, Line, Text, config } from 'folds';
 import { decodeRouteParam } from '../../pages/pathUtils';
 import { useParams } from 'react-router-dom';
 import { isKeyHotkey } from 'is-hotkey';
@@ -18,8 +18,11 @@ import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useRoomMembers } from '../../hooks/useRoomMembers';
 import { activeRoomIdAtom } from '../../state/activeRoom';
 import { isMediaDrawerAtom } from '../../state/mediaDrawer';
-import { isForum } from '../../utils/room';
+import { isForum, parsePaarrotUiContent } from '../../utils/room';
 import { ForumRoomView } from './ForumRoomView';
+import { useStateEvent } from '../../hooks/useStateEvent';
+import { StateEvent } from '../../../types/matrix/room';
+import { RoomAppView } from '../room-app';
 
 export function Room() {
   const { eventId: rawEventId } = useParams();
@@ -41,6 +44,16 @@ export function Room() {
   const showRightDrawer =
     !skinny && (isPeopleDrawer || isMediaDrawer);
 
+  const uiEvent = useStateEvent(room, StateEvent.PaarrotUi);
+  const hasAppUi = useMemo(() => !!parsePaarrotUiContent(uiEvent?.getContent()), [uiEvent]);
+  const [preferChat, setPreferChat] = useState(false);
+
+  useEffect(() => {
+    setPreferChat(false);
+  }, [room.roomId]);
+
+  const showAppView = !forumRoom && hasAppUi && !preferChat;
+
   // Update titlebar with current room ID
   useEffect(() => {
     setActiveRoomId(room.roomId);
@@ -63,10 +76,38 @@ export function Room() {
     <PowerLevelsContextProvider value={powerLevels}>
       <Box grow="Yes">
         {!showMediaSolo &&
-          (forumRoom ? (
+          (showAppView ? (
+            <RoomAppView room={room} onShowChat={() => setPreferChat(true)} />
+          ) : forumRoom ? (
             <ForumRoomView room={room} eventId={eventId} />
           ) : (
+            <Box grow="Yes" direction="Column" style={{ minWidth: 0, minHeight: 0 }}>
+              {hasAppUi && preferChat && (
+                <Box
+                  shrink="No"
+                  alignItems="Center"
+                  justifyContent="SpaceBetween"
+                  gap="200"
+                  style={{
+                    padding: `${config.space.S200} ${config.space.S300}`,
+                    borderBottom: '1px solid var(--bq-surface-border, CurrentColor)',
+                  }}
+                >
+                  <Text size="T300">Room app available</Text>
+                  <Button
+                    size="300"
+                    variant="Primary"
+                    radii="300"
+                    onClick={() => setPreferChat(false)}
+                  >
+                    <Text size="B300">Show app</Text>
+                  </Button>
+                </Box>
+              )}
+              <Box grow="Yes" direction="Column" style={{ minWidth: 0, minHeight: 0 }}>
                 <RoomView room={room} eventId={eventId} />
+              </Box>
+            </Box>
           ))}
         {showMediaSolo && <MediaDrawer room={room} solo />}
         {!showMediaSolo && showRightDrawer && (

src/app/features/room/RoomTimeline.tsx

@@ -2011,6 +2011,7 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
         return 'CALL_EVENT_PENDING' as unknown as React.ReactNode;
       },
       [MessageEvent.RelayEmojiConfetti]: () => null,
+      [MessageEvent.PaarrotUiAction]: () => null,
     },
     (mEventId, mEvent, item) => {
       if (!showHiddenEvents) return null;

src/app/utils/room.ts

@@ -24,6 +24,7 @@ import {
   Membership,
   MessageEvent,
   NotificationType,
+  PaarrotUiContent,
   RoomToParents,
   RoomType,
   StateEvent,
@@ -125,6 +126,33 @@ export const getPaarrotRoomKind = (room: Room | null): string | undefined => {
   return typeof kind === 'string' ? kind : undefined;
 };
 
+/**
+ * Valid bot-driven room UI state (im.paarrot.ui with version + root node).
+ */
+export const parsePaarrotUiContent = (raw: unknown): PaarrotUiContent | undefined => {
+  if (!raw || typeof raw !== 'object') return undefined;
+  const content = raw as PaarrotUiContent;
+  if (
+    typeof content.version !== 'number' ||
+    !content.root ||
+    typeof content.root !== 'object' ||
+    typeof content.root.type !== 'string' ||
+    typeof content.root.id !== 'string'
+  ) {
+    return undefined;
+  }
+  return content;
+};
+
+export const getPaarrotUiContent = (room: Room | null): PaarrotUiContent | undefined => {
+  if (!room) return undefined;
+  const event = room.currentState?.getStateEvents(StateEvent.PaarrotUi, '');
+  if (!event) return undefined;
+  return parsePaarrotUiContent(event.getContent());
+};
+
+export const hasRoomAppUi = (room: Room | null): boolean => getPaarrotUiContent(room) !== undefined;
+
 /**
  * m.forum space root (forum board lobby), not a plain m.space or a lone m.forum topic channel.
  * Matrix sets create type m.forum on forum spaces but SDK isSpaceRoom() is often still false;

src/types/matrix/room.ts

@@ -48,6 +48,9 @@ export enum StateEvent {
   /** Paarrot room classification marker for custom room behaviors */
   PaarrotRoomKind = 'im.paarrot.room.kind',
 
+  /** Bot-driven declarative room UI (takes over room view) */
+  PaarrotUi = 'im.paarrot.ui',
+
   /** Matrix RTC call membership (MSC3401) */
   CallMember = 'org.matrix.msc3401.call.member',
 }
@@ -61,8 +64,114 @@ export enum MessageEvent {
 
   /** Relay emoji confetti burst tied to a target message */
   RelayEmojiConfetti = 'app.relay.emoji_confetti',
+
+  /** User interaction with bot-driven room UI (im.paarrot.ui) */
+  PaarrotUiAction = 'im.paarrot.ui.action',
 }
 
+/** Declarative UI node types for im.paarrot.ui */
+export type PaarrotUiNodeType =
+  | 'panel'
+  | 'row'
+  | 'text'
+  | 'button'
+  | 'input'
+  | 'select'
+  | 'image'
+  | 'spacer';
+
+export type PaarrotUiNodeBase = {
+  type: PaarrotUiNodeType;
+  id: string;
+};
+
+export type PaarrotUiPanelNode = PaarrotUiNodeBase & {
+  type: 'panel';
+  children?: PaarrotUiNode[];
+};
+
+export type PaarrotUiRowNode = PaarrotUiNodeBase & {
+  type: 'row';
+  children?: PaarrotUiNode[];
+};
+
+export type PaarrotUiTextNode = PaarrotUiNodeBase & {
+  type: 'text';
+  text?: string;
+  className?: string;
+};
+
+export type PaarrotUiButtonNode = PaarrotUiNodeBase & {
+  type: 'button';
+  label: string;
+  action: string;
+  value?: string | number | boolean;
+  disabled?: boolean;
+  variant?: 'Primary' | 'Secondary' | 'Success' | 'Warning' | 'Critical';
+};
+
+export type PaarrotUiInputNode = PaarrotUiNodeBase & {
+  type: 'input';
+  name?: string;
+  label?: string;
+  placeholder?: string;
+  value?: string;
+  inputType?: 'text' | 'number' | 'password';
+};
+
+export type PaarrotUiSelectOption = {
+  label: string;
+  value: string;
+};
+
+export type PaarrotUiSelectNode = PaarrotUiNodeBase & {
+  type: 'select';
+  name?: string;
+  label?: string;
+  options?: PaarrotUiSelectOption[];
+  value?: string;
+};
+
+export type PaarrotUiImageNode = PaarrotUiNodeBase & {
+  type: 'image';
+  src: string;
+  alt?: string;
+  width?: number;
+  height?: number;
+};
+
+export type PaarrotUiSpacerNode = PaarrotUiNodeBase & {
+  type: 'spacer';
+  size?: number;
+};
+
+export type PaarrotUiNode =
+  | PaarrotUiPanelNode
+  | PaarrotUiRowNode
+  | PaarrotUiTextNode
+  | PaarrotUiButtonNode
+  | PaarrotUiInputNode
+  | PaarrotUiSelectNode
+  | PaarrotUiImageNode
+  | PaarrotUiSpacerNode;
+
+/** Content of state event im.paarrot.ui */
+export type PaarrotUiContent = {
+  version: number;
+  title?: string;
+  css?: string;
+  root: PaarrotUiNode;
+};
+
+/** Content of timeline event im.paarrot.ui.action */
+export type PaarrotUiActionContent = {
+  action: string;
+  component_id: string;
+  value?: string | number | boolean;
+  values?: Record<string, string>;
+  ui_event_id?: string;
+};
+
 export enum RoomType {
   Space = 'm.space',
   Forum = 'm.forum',