E2E: Fix space-home panel hide on channel open (@wip cluster C)

[mjkatgithub]

Planning

• Milestone: Phase 3
• Priority: P0
• Size: S
• Estimate: 1 SP
• Epic: Re-enable @wip chat E2E scenarios quarantined for green CI lane #134

Goal

Fix space-home panel visibility so opening a channel hides
[data-space-home-panel] as expected by quarantined E2E scenarios.

Scope

• Select space from rail shows overview and opens channel from list
• Leave seeded space channel from sidebar (panel shown after leave)
• Remove @wip / @space_home tags when green

Branch

bug/e2e-wip-space-home

Acceptance criteria

• Both cluster C scenarios pass without @wip.
• No regression on green space-home / rail scenarios.

Test checklist

E2E

• @space_home and related leave scenarios in chat.feature

Notes

Real root cause: the two cluster C scenarios shared one seeded space
channel. Leave seeded space channel removed alice from the invite-only
channel, so @space_home's re-join failed with 403 and the panel never
hid (the earlier watcher theory was wrong). Fix: a dedicated seeded
space-home channel isolates @space_home (alice stays a member, so the
select path runs). Committed visibleRooms subtree filter, lobby-room
retention in the watcher, and the panel-scoped E2E click are retained.
Verified: full non-@wip E2E green (32/32) on a clean Synapse seed.
Docs: N/A — E2E seed/step infrastructure only.

Emoji shortcode E2E (Composer emoji picker) is unrelated — still open.