Remove unused FlashError pipeline (UI + global state + style/type surface) (#2928)

`FlashError` was legacy UI/state that was never wired into real runtime
flows (only self-referenced and window-exported for ad-hoc testing).
This PR removes that dead path end-to-end to reduce global surface area
and stale styling/types.

- **Scope: UI removal (`frontend/app/app.tsx`)**
- Deleted the `FlashError` component and its render site (`<FlashError
/>`).
- Removed now-unused imports tied to that component (`removeFlashError`,
`Fragment`, `useState`).

- **Scope: global store cleanup (`frontend/app/store/global.ts`,
`frontend/app/store/global-atoms.ts`)**
  - Removed `pushFlashError` / `removeFlashError`.
- Removed `flashErrors` atom from global atom initialization and
registry.
- Kept notification path intact (`pushNotification`,
`removeNotificationById`, etc.).

- **Scope: external/debug surface cleanup (`frontend/wave.ts`)**
- Removed `pushFlashError` from imports and from `window` export wiring.

- **Scope: type + style cleanup (`frontend/types/custom.d.ts`,
`frontend/app/app.scss`, `frontend/app/theme.scss`)**
  - Removed `GlobalAtomsType.flashErrors`.
  - Removed `FlashErrorType`.
- Removed `.flash-error-container` style block and related z-index token
`--zindex-flash-error-container`.

```ts
// before
(window as any).pushFlashError = pushFlashError;

// after
(window as any).pushNotification = pushNotification;
```

- **`<screenshot>`**
- User-provided screenshot URL (if suitable for PR timeline context):

https://github.com/user-attachments/assets/aacc2e61-a65c-4dbf-bfcc-f9f99a490f20

<!-- START COPILOT CODING AGENT TIPS -->
---

💬 We'd love your input! Share your thoughts on Copilot coding agent in
our [2 minute survey](https://gh.io/copilot-coding-agent-survey).

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: sawka <2722291+sawka@users.noreply.github.com>

Author: Copilot

frontend/app/app.scss

@@ -111,41 +111,3 @@ a {
         transition-delay: none !important;
     }
 }
-
-.flash-error-container {
-    position: absolute;
-    right: 10px;
-    bottom: 10px;
-    z-index: var(--zindex-flash-error-container);
-    display: flex;
-    flex-direction: column;
-    gap: 10px;
-
-    .flash-error {
-        background: var(--error-color);
-        color: var(--main-text-color);
-        border-radius: 4px;
-        padding: 10px;
-        display: flex;
-        flex-direction: column;
-        width: 280px;
-        border: 1px solid transparent;
-        max-height: 100px;
-        cursor: pointer;
-
-        .flash-error-scroll {
-            overflow-y: auto;
-            display: flex;
-            flex-direction: column;
-        }
-
-        &.hovered {
-            border: 1px solid var(--main-text-color);
-        }
-
-        .flash-error-title {
-            font-weight: bold;
-            margin-bottom: 5px;
-        }
-    }
-}

frontend/app/app.tsx

@@ -14,7 +14,6 @@ import {
     getTabIndicatorAtom,
     globalStore,
     isDev,
-    removeFlashError,
 } from "@/store/global";
 import { appHandleKeyDown, keyboardMouseDownHandler } from "@/store/keymodel";
 import { getElemAsStr } from "@/util/focusutil";
@@ -25,7 +24,7 @@ import clsx from "clsx";
 import debug from "debug";
 import { Provider, useAtomValue } from "jotai";
 import "overlayscrollbars/overlayscrollbars.css";
-import { Fragment, useEffect, useState } from "react";
+import { useEffect } from "react";
 import { DndProvider } from "react-dnd";
 import { HTML5Backend } from "react-dnd-html5-backend";
 import { AppBackground } from "./app-bg";
@@ -237,78 +236,6 @@ const TabIndicatorAutoClearing = () => {
     return null;
 };
 
-const FlashError = () => {
-    const flashErrors = useAtomValue(atoms.flashErrors);
-    const [hoveredId, setHoveredId] = useState<string>(null);
-    const [ticker, setTicker] = useState<number>(0);
-
-    useEffect(() => {
-        if (flashErrors.length == 0 || hoveredId != null) {
-            return;
-        }
-        const now = Date.now();
-        for (let ferr of flashErrors) {
-            if (ferr.expiration == null || ferr.expiration < now) {
-                removeFlashError(ferr.id);
-            }
-        }
-        setTimeout(() => setTicker(ticker + 1), 1000);
-    }, [flashErrors, ticker, hoveredId]);
-
-    if (flashErrors.length == 0) {
-        return null;
-    }
-
-    function copyError(id: string) {
-        const ferr = flashErrors.find((f) => f.id === id);
-        if (ferr == null) {
-            return;
-        }
-        let text = "";
-        if (ferr.title != null) {
-            text += ferr.title;
-        }
-        if (ferr.message != null) {
-            if (text.length > 0) {
-                text += "\n";
-            }
-            text += ferr.message;
-        }
-        navigator.clipboard.writeText(text);
-    }
-
-    function convertNewlinesToBreaks(text) {
-        return text.split("\n").map((part, index) => (
-            <Fragment key={index}>
-                {part}
-                <br />
-            </Fragment>
-        ));
-    }
-
-    return (
-        <div className="flash-error-container">
-            {flashErrors.map((err, idx) => (
-                <div
-                    key={idx}
-                    className={clsx("flash-error", { hovered: hoveredId === err.id })}
-                    onClick={() => copyError(err.id)}
-                    onMouseEnter={() => setHoveredId(err.id)}
-                    onMouseLeave={() => setHoveredId(null)}
-                    title="Click to Copy Error Message"
-                >
-                    <div className="flash-error-scroll">
-                        {err.title != null ? <div className="flash-error-title">{err.title}</div> : null}
-                        {err.message != null ? (
-                            <div className="flash-error-message">{convertNewlinesToBreaks(err.message)}</div>
-                        ) : null}
-                    </div>
-                </div>
-            ))}
-        </div>
-    );
-};
-
 const AppInner = () => {
     const prefersReducedMotion = useAtomValue(atoms.prefersReducedMotionAtom);
     const client = useAtomValue(ClientModel.getInstance().clientAtom);
@@ -340,7 +267,6 @@ const AppInner = () => {
             <DndProvider backend={HTML5Backend}>
                 <Workspace />
             </DndProvider>
-            <FlashError />
             {isDev() ? <NotificationBubbles></NotificationBubbles> : null}
         </div>
     );

frontend/app/store/global-atoms.ts

@@ -119,7 +119,6 @@ function initGlobalAtoms(initOpts: GlobalInitOptions) {
         const connStatuses = Array.from(connStatusMap.values()).map((atom) => get(atom));
         return connStatuses;
     });
-    const flashErrorsAtom = atom<FlashErrorType[]>([]);
     const notificationsAtom = atom<NotificationType[]>([]);
     const notificationPopoverModeAtom = atom<boolean>(false);
     const reinitVersion = atom(0);
@@ -144,7 +143,6 @@ function initGlobalAtoms(initOpts: GlobalInitOptions) {
         documentHasFocus: documentHasFocusAtom,
         modalOpen,
         allConnStatus: allConnStatusAtom,
-        flashErrors: flashErrorsAtom,
         notifications: notificationsAtom,
         notificationPopoverMode: notificationPopoverModeAtom,
         reinitVersion,

frontend/app/store/global.ts

@@ -736,16 +736,6 @@ function clearAllTabIndicators() {
     }
 }
 
-function pushFlashError(ferr: FlashErrorType) {
-    if (ferr.expiration == null) {
-        ferr.expiration = Date.now() + 5000;
-    }
-    ferr.id = crypto.randomUUID();
-    globalStore.set(atoms.flashErrors, (prev) => {
-        return [...prev, ferr];
-    });
-}
-
 function addOrUpdateNotification(notif: NotificationType) {
     globalStore.set(atoms.notifications, (prevNotifications) => {
         // Remove any existing notification with the same ID
@@ -769,12 +759,6 @@ function removeNotificationById(id: string) {
     });
 }
 
-function removeFlashError(id: string) {
-    globalStore.set(atoms.flashErrors, (prev) => {
-        return prev.filter((ferr) => ferr.id !== id);
-    });
-}
-
 function removeNotification(id: string) {
     globalStore.set(atoms.notifications, (prev) => {
         return prev.filter((notif) => notif.id !== id);
@@ -831,13 +815,11 @@ export {
     loadConnStatus,
     loadTabIndicators,
     openLink,
-    pushFlashError,
     pushNotification,
     readAtom,
     recordTEvent,
     refocusNode,
     registerBlockComponentModel,
-    removeFlashError,
     removeNotification,
     removeNotificationById,
     replaceBlock,

frontend/app/theme.scss

@@ -65,7 +65,6 @@
     --zindex-layout-ephemeral-node-backdrop: 8;
     --zindex-layout-ephemeral-node: 9;
     --zindex-block-mask-inner: 10;
-    --zindex-flash-error-container: 550;
     --zindex-app-background: -1;
 
     // z-indexes in xterm.css

frontend/types/custom.d.ts

@@ -25,7 +25,6 @@ declare global {
         updaterStatusAtom: jotai.PrimitiveAtom<UpdaterStatus>;
         modalOpen: jotai.PrimitiveAtom<boolean>;
         allConnStatus: jotai.Atom<ConnStatus[]>;
-        flashErrors: jotai.PrimitiveAtom<FlashErrorType[]>;
         notifications: jotai.PrimitiveAtom<NotificationType[]>;
         notificationPopoverMode: jotai.Atom<boolean>;
         reinitVersion: jotai.PrimitiveAtom<number>;
@@ -408,14 +407,6 @@ declare global {
         baseDir: string;
     };
 
-    type FlashErrorType = {
-        id: string;
-        icon: string;
-        title: string;
-        message: string;
-        expiration: number;
-    };
-
     export type NotificationActionType = {
         label: string;
         actionKey: string;

frontend/wave.ts

@@ -26,7 +26,6 @@ import {
     initGlobalWaveEventSubs,
     loadConnStatus,
     loadTabIndicators,
-    pushFlashError,
     pushNotification,
     removeNotificationById,
     subscribeToConnEvents,
@@ -50,7 +49,6 @@ let savedInitOpts: WaveInitOpts = null;
 (window as any).countersPrint = countersPrint;
 (window as any).countersClear = countersClear;
 (window as any).getLayoutModelForStaticTab = getLayoutModelForStaticTab;
-(window as any).pushFlashError = pushFlashError;
 (window as any).pushNotification = pushNotification;
 (window as any).removeNotificationById = removeNotificationById;
 (window as any).modalsModel = modalsModel;