fix: don't auto-open right sidebar by default (#1923)

* fix: don't auto-open right sidebar by default

The navigation (course outline) sidebar should be the default; PR #1713
removed the alwaysOpenAuxiliarySidebar waffle flag guard but kept the
auto-open branches in place, effectively hardcoding the flag to true.

- useInitialSidebar defaults to COURSE_OUTLINE when nothing is stored,
  and honors a stored RIGHT panel preference even before async widget
  data has loaded (avoids a transient flicker that downstream effects
  would otherwise write back to storage).
- Add a session-scoped "sidebar closed by user" flag in sessionStorage,
  parallel to the existing outline-collapsed flag. toggleSidebar sets it
  when the resulting state is null, clears it on open.
- useResponsiveBehavior and useUnitShiftBehavior respect the flag so a
  user-closed state survives unit navigation and full-page remounts
  within the same tab session.

Refs: https://github.com/openedx/wg-build-test-release/issues/574

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* refactor: drop OUTLINE_SIDEBAR_HIDDEN in favor of SIDEBAR_CLOSED_BY_USER

The OUTLINE_SIDEBAR_HIDDEN sessionStorage flag was set only by the
course-outline collapse trigger, which already calls toggleSidebar(null) →
setSidebarClosedByUser(true). Every reader of isOutlineSidebarCollapsed
runs inside a path where closed-by-user is already false (either explicit
top-level checks or transitive via useInitialSidebar's null return), so
outline-hidden=true was never observably distinct from closed-by-user=true.

- Remove the constant, the two storage helpers, and all call sites in
  useInitialSidebar / useUnitShiftBehavior / useResponsiveBehavior /
  useSidebarSync / course-outline/hooks.js.
- useSidebarSync swaps the flag in-place rather than adding a top-level
  early-return, so the corrective setCurrentSidebar(null) branches still
  fire if currentSidebar is somehow stale while closed-by-user is true.
- useInitialSidebar: also refine the stored-RIGHT-panel block so that when
  widget data has loaded and the stored preference is no longer in the
  registry, we fall back to firstAvailable instead of returning a stored
  ID nothing can render.
- Clarify the isInitiallySidebarOpen JSDoc to spell out the viewport/URL
  precondition.
- Update ARCHITECTURE.md and the course-outline README to reference the
  unified flag.

Refs: https://github.com/openedx/wg-build-test-release/issues/574

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix: keep current sidebar open across unit navigation

useUnitShiftBehavior was actively switching state on unit nav in ways that
contradict the spec in wg-build-test-release#574:

- CASE 1 (COURSE_OUTLINE open + RIGHT panel available) was switching to the
  RIGHT panel, which conflicts with expected behavior #2 ("nav stays open
  on advance"). The behavior looked correct in the browser only because
  useSidebarSync immediately reverted the switch via stale-memo cancellation —
  two unnecessary state updates and storage writes per unit nav. Drop the
  switching branch; CASE 1 now just marks the ref and returns.
- CASE 3 (RIGHT panels available + currentSidebar=null) was auto-opening the
  first RIGHT panel on a wide viewport, conflicting with expected behavior #3
  ("nothing open → advance → still nothing"). The closed-by-user gate above
  catches the realistic null path, so this branch was state-drift recovery.
  Recover to COURSE_OUTLINE (the wide-viewport default per the prior commits)
  instead of opening a RIGHT panel.

Refs: https://github.com/openedx/wg-build-test-release/issues/574

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* test: align sidebar tests with the new behavior

Tracks the source changes across the previous commits on this branch:

- storage.test.js: drop the removed outline-collapsed describes; keep the
  parallel isSidebarClosedByUser / setSidebarClosedByUser coverage.
- useInitialSidebar.test.js: drop isOutlineSidebarCollapsed mock, restructure
  with a "when isInitiallySidebarOpen is true and the sidebar has not been
  closed by the user" wrapper around the storage-state describes. Add the
  anti-flicker case (stored RIGHT panel before widget data has loaded).
- useUnitShiftBehavior.test.js: drop the isOutlineSidebarCollapsed mock, swap
  in isSidebarClosedByUser, add the closed-by-user no-op, restructure the
  CASE-block describes under a single precondition wrapper, and update CASE 1
  and CASE 3 assertions to match the new "keep current sidebar open" /
  "recover to COURSE_OUTLINE" behavior.
- useResponsiveBehavior.test.js, useSidebarSync.test.js: rename in-place from
  the outline-collapsed flag to closed-by-user; add closed-by-user no-op
  coverage.
- SidebarContextProvider.test.jsx: drop the outline-collapsed mocks, add
  setSidebarClosedByUser assertions to the UC7* toggleSidebar tests; simplify
  UC7a to just assert the initial sidebar is non-null on desktop.
- Course.test.jsx: replace the two pre-fix tests (which asserted the buggy
  auto-open of discussions) with a `describe('sidebar behavior')` block
  covering: default outline, closed-by-user persistence, stored-discussions /
  stored-outline on render, and the four click-to-toggle transitions (close
  outline, open outline closing discussions, open discussions closing outline,
  close discussions).
- SidebarUnit.test.jsx: drop the two stale sessionStorage assertions; the
  toggleSidebar call assertions above each one carry the meaningful coverage.
- test-utils.jsx: have setupDiscussionSidebar also return its testStore so
  tests can reuse it (avoids a second initializeTestStore that resets the
  discussion topics axios mock).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix: open COURSE_OUTLINE on resize-to-wide instead of a RIGHT panel

useResponsiveBehavior auto-opened the first available RIGHT panel when the
viewport reached the wide breakpoint with no sidebar open, falling back to
COURSE_OUTLINE only when no RIGHT panels were available. That contradicts
the wide-viewport default in this PR (#1 in wg-build-test-release#574:
"nav opens by default") — and is the same kind of bug as the previous
unit-shift CASE 3 else-if.

Always open COURSE_OUTLINE in that branch. getFirstAvailablePanel is no
longer needed in this hook; drop the prop from SidebarContextProvider too.

Refs: https://github.com/openedx/wg-build-test-release/issues/574

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* test: useResponsiveBehavior opens COURSE_OUTLINE on resize-to-wide

Track the source change: drop the getFirstAvailablePanel param from
buildParams, replace the two "opens X" tests (first-available vs
COURSE_OUTLINE-fallback) with a single "opens COURSE_OUTLINE on desktop
when no sidebar is open" assertion. The fallback-with-no-RIGHT-panels case
collapses into the same code path under the simplified source.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>