feat: decouple notifications panel using widget registry mechanism

[awais-ansari]

Summary

Removes the tightly coupled upgrade/upsell ("notifications") panel from the Learning MFE core and replaces it with a pluggable widget registry system. The right sidebar now supports dynamically-registered external widgets, making it easy to add, remove, or replace sidebar panels without forking the MFE. Proposal

Motivation

The built-in upgrade panel (NotificationTray) caused several issues:

1. Misleading naming: "Notifications" implied platform-level notifications, conflicting with the separate notification tray in the header.
2. Non-Core: The upgrade panel is a non-core feature. It should not be bundled into the Open edX core.
3. Empty panel UX problem: In courses without a paid track, the panel rendered empty but remained visible.

Architecture: Pluggable Widget Registry

The right sidebar now operates on a widget registry (SIDEBARS) built at runtime from:

Built-in widgets: only DISCUSSIONS are included by default.
External widgets: installed via npm and registered via SIDEBAR_WIDGETS in env.config.jsx
Each widget provides:

{
  id: string,
  priority: number, 
  Sidebar: ReactComponent,   
  Trigger: ReactComponent, 
  isAvailable: (context) => boolean,
  enabled: boolean,
  Provider?: ReactComponent, 
}

Rename: notifications → upgrade

All internal references to the old "Notifications" panel are renamed for clarity:

1. WIDGETS.NOTIFICATIONS → WIDGETS.UPGRADE
2. NotificationTray → UpgradePanel
3. NotificationTrigger → UpgradeTrigger
4. NotificationIcon → UpgradeIcon
5. notificationStatus context → upgradeWidgetStatus
6. LocalStorage keys updated accordingly

Extracted Upgrade Widget Package

The upgrade panel is extracted from the sidebar core into upgrade widget. It is no longer bundled by default. Instances that need it register it via env.config.jsx.

Configuration

import { upgradeWidgetConfig } from './src/widgets/upgrade/src/index';

const config = {
  SIDEBAR_WIDGETS: [upgradeWidgetConfig],
};

export default config;

When the upgrade widget is promoted to its own npm package @edx/learning-upgrade-widget, operators will install it and update the import path. No other changes needed.

Two-Sidebar Collaboration

The architecture docs in ARCHITECTURE.md fully describe the shared currentSidebar state between the LEFT (Course Outline) and RIGHT (widget panels) sidebars, including:

• Priority cascade: DISCUSSIONS (10) → UPGRADE (20) → external widgets → COURSE_OUTLINE (fallback)
• Auto-open logic on initial load
• Unit shift behavior for each scenario
• State persistence via localStorage / sessionStorage

Removed

• src/courseware/course/new-sidebar - Entire unused new-sidebar directory
• src/courseware/course/sidebar/sidebars/notifications - Built-in notification widget
• NotificationTraySlot
• NotificationWidgetSlot
• NotificationsDiscussionsSidebarSlot - Replaced by RightSidebarSlot
• NotificationsDiscussionsTriggerSlot - Replaced by RightSidebarTriggerSlot

Testing

• 12 new test suites covering hooks, defaultWidgets, storage utils, SidebarContextProvider, SidebarTriggers, SidebarBase, UpgradePanel, UpgradeTrigger, UpgradeIcon, UpgradeWidgetContext, and upgrade utils
• All use cases are documented in USE_CASE_VERIFICATION.md

Migration Notes

• No breaking changes for instances that don't use the upgrade widget. Discussions and course outline work are identical.
• Instances using the upgrade panel: Add SIDEBAR_WIDGETS: [upgradeWidgetConfig] to env.config.jsx.
• Plugin slot consumers:
  - Replace NotificationTraySlot / NotificationsDiscussionsSidebarSlot with RightSidebarSlot. Replace
  - Replace NotificationsDiscussionsTriggerSlot with RightSidebarTriggerSlot.
• localStorage: Old notificationStatus.{courseId} keys are not migrated to new key format upgradeWidget.{courseId} starts fresh.

[codecov]

Codecov Report

❌ Patch coverage is 98.07074% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.27%. Comparing base (d77f39f) to head (8959969).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...eware/course/sequence/lock-paywall/LockPaywall.jsx	84.61%	2 Missing ⚠️
src/courseware/course/sidebar/SidebarContext.js	50.00%	1 Missing ⚠️
...urseware/course/sidebar/SidebarContextProvider.jsx	97.29%	1 Missing ⚠️
src/courseware/course/sidebar/utils/storage.js	96.55%	1 Missing ⚠️
src/widgets/upgrade/src/widgetConfig.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1885      +/-   ##
==========================================
+ Coverage   91.16%   91.27%   +0.11%     
==========================================
  Files         349      343       -6     
  Lines        5830     5766      -64     
  Branches     1389     1387       -2     
==========================================
- Hits         5315     5263      -52     
+ Misses        498      484      -14     
- Partials       17       19       +2     

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[awais-ansari]

@brian-smith-tcril Please review this PR.

[arbrandes]

First off: this is amazingly well documented. Congrats, and thank you! I'm probably going to start using this PR as a benchmark for how complicated frontend architectural decisions should be implemented.

Second: this is mostly an architecture review based on the ADR, ARCHITECTURE.md,and a glance at USE_CASE_VERIFICATION.md. I have not looked closely at the code, yet.

Lastly, I'm coming at this "from the future". Prior to the Willow cutoff in October of this year, frontend-app-learning will be converted to frontend-base, and this is one of the situations where the new slot architecture will help (or, at least, affect). Some of the inline comments are just FYIs related to that, and a couple are meant to help with the transition later. Either way, we should keep this in mind.

[arbrandes]

Thanks for addressing my previous concerns (rename to widgets/, drop separate package, etc.). I tested this and it works - at least for the Dicussions widget and the outline. Nice!

Looking at the code as it stands now (with some help from Claude), this is what I found:

---

1. Edge-case bug: Mismatch between what sidebar is "rendered" vs what is "open" for layout purposes

Sidebar.jsx:8 renders any widget in the SIDEBARS registry (all enabled widgets), and SidebarTriggers.jsx:23 renders triggers for all of them too. But useIsSidebarOpen() and upgradePanelVisible check availableSidebarIds, which only includes widgets whose isAvailable() returns true.

So if a widget's trigger doesn't self-hide (like UpgradeTrigger), a user can open a panel that's physically rendered but that layout code considers "closed". Example: Upgrade is registered but the course has no verified track - the trigger shows, clicking it opens the panel, but sequence navigation tabs don't shrink to accommodate it.

Fix: either filter SidebarTriggers by availableSidebarIds, or have useIsSidebarOpen() check SIDEBARS instead. The first is simpler.

---

2. Warning: The old notificationTrayVisible was dead code - this PR activates that layout logic

On master, LockPaywall destructures notificationTrayVisible from SidebarContext, but the old provider never sets it - it was always undefined. The layout variables that depended on it (shouldDisplayGatedContentOneColumn, etc.) were dead code.

The new code replaces it with upgradePanelVisible = availableSidebarIds.includes(currentSidebar), which CAN be true, activating layout adjustments that previously never triggered. The variable name is also misleading: it's true for any open sidebar widget (including Discussions), not specifically the upgrade panel.

I have not tested this: have you? (Is there even a way for us to test it?)

---

3. Nit: No-op state call in useUnitShiftBehavior.js

useUnitShiftBehavior.js:122-124:

} else if (currentWidget) {
  // Current RIGHT sidebar panel still available and no higher priority - keep it
  setCurrentSidebar(currentSidebar);  // no-op

setCurrentSidebar(currentSidebar) with the same value is a no-op (React bails out). The adjacent branches call setSidebarId too, making this one look like a missing call. Removing the line or adding a comment would clarify intent.

---

4. Nit: Dead guard in useSidebarSync.js

useSidebarSync.js:39:

if (shouldDisplayFullScreen || previousUnitIdRef.current === null) {
  return;
}

React runs effects in hook declaration order. Since useUnitShiftBehavior is called before useSidebarSync, the ref is always set to unitId before this check runs. The === null branch is unreachable.

---

5. Nit: misleading variable name in SequenceNavigation.jsx

shouldDisplayUpgradeTriggerInSequence is just a small-screen breakpoint check unrelated to the upgrade widget. Consider a generic name like isSmallScreen.

---

6. Codebase layout: course-outline doesn't belong in src/widgets/

src/widgets/course-outline/ is tightly coupled to the sidebar framework via WIDGETS.COURSE_OUTLINE constants, dedicated plugin slots, and special-case logic in all three sidebar hooks. It's not pluggable - removing the directory would break the core layout. Placing it in src/widgets/ alongside truly decoupled widgets like Upgrade implies a level of decoupling that doesn't exist.

(It's fine to leave Discussions in there, as it is a properly independent widget - just a default one.)

[arbrandes]

Alright, I think this is good enough to go. Thanks for bearing with me!

[pdpinch]

This change broke our build of the MFE. Since this involved changing the name/api for a pluginslot, it should have gone through the DEPR process and gotten some more communication.

In particular, what is the plan for addressing this in the Verawood release?

[arbrandes]

@pdpinch, you're right, we did not consider backward-compatibility at all, here. I'm going to bring this up with the Axim engineering team, today.

[arbrandes]

Revert PR: #1898.

[arbrandes]

@pdpinch, instead of reverting it, we added backward-compatibility:

#1899