Realtime Sync for Opened Accounts: per-account `EventSource` lifecycle scoped to open tabs only

[saknarajapakshe]

Goal

Keep an account's inbox live-updating only while it has a tab open — not for every authenticated account in the background

Background

Today, each tab opens one EventSource to /api/v1/events while isAuthenticated && inboxName is true. The backend (realtime.Hub, server/internal/realtime/hub.go) keeps one ref-counted IMAP IDLE connection per watched mailbox per session, torn down when the last subscriber disconnects — no backend changes are needed, this is entirely a frontend subscription-lifecycle change.

Scope (revised — significantly smaller than originally spec'd, and now effectively closed)

Because #23's window.open named-target change means each account maps to exactly one tab for its entire life (no in-place switching between already-linked accounts anymore), ref-counting and cross-tab liveness tracking are no longer required for correctness: a tab's own mount/unmount already is that account's "opened"/"closed" signal, and DataContext's existing per-tab EventSource effect (opens while isAuthenticated && inboxName, closes on unmount) already satisfies "only accounts with a tab open stay live" as-is, with no changes needed.

The one remaining in-place transition (#29 — addAccount reassigning an already-active tab from one account to another) also turned out not to need any new hook API: #29's fix resets inboxName back to "" the instant the active account changes, which already forces the existing realtime effect to close the old account's EventSource and reopen a fresh one (reading the new session's token) once the new account's inbox name resolves. So there is no onAccountOpened/onAccountClosed callback to wire into — the mechanism is automatic.

• Wire into Implement switchAccount(): state reset, cache hydration, and background sync for the addAccount in-place switch #29's onAccountOpened/onAccountClosed hook points — not needed, see above. Implement switchAccount(): state reset, cache hydration, and background sync for the addAccount in-place switch #29 already lands this issue's entire functional requirement as a side effect of its own fix.
• Handle connection lifecycle: reconnect on drop, teardown on logout/session removal (coordinate with Account Lifecycle Management: remove account, sign out everywhere, and session expiry/re-auth #25 — when 5.1 removes an account or 5.2 invalidates its session, this issue's subscription for that account must also close). This piece is still open — confirm today's EventSource/isAuthenticated wiring already covers it, or file the small remaining piece separately.
• Scoped to each account's default/inbox mailbox only, matching what a single-account tab watches today — already true today, no change needed.
• Cut from scope: the cross-tab liveness heartbeat (localStorage/BroadcastChannel, crash/force-quit detection) originally planned here. It solved "does this account have a tab open somewhere" for ref-counting a shared subscription — a problem that no longer exists once an account maps to at most one tab. If a future need arises for showing a "currently open elsewhere" indicator in the switcher UI, that's a cosmetic addition, not a functional dependency, and can be scoped separately then.

Acceptance criteria

• Opening account A's tab starts a live subscription for A; accounts with no open tab receive no updates until opened (already true today via DataContext's existing per-tab effect).
• Closing an account's only tab tears down its subscription (already true today via unmount cleanup).
• The addAccount-driven in-place transition (Implement switchAccount(): state reset, cache hydration, and background sync for the addAccount in-place switch #29) correctly closes the old account's subscription and opens the new one's without a page reload (confirmed as an automatic side effect of Implement switchAccount(): state reset, cache hydration, and background sync for the addAccount in-place switch #29's inboxName reset).
• Removing an account or invalidating its session (Account Lifecycle Management: remove account, sign out everywhere, and session expiry/re-auth #25) also tears down its subscription — verify once Account Lifecycle Management: remove account, sign out everywhere, and session expiry/re-auth #25 lands.
• No backend changes required — confirmed existing Hub ref-counting behavior is sufficient as-is.

Files likely touched

None expected beyond what #29 already covers — revisit only if #25's removal/invalidation flow surfaces a gap.

Dependencies

Depends on #22 (switch-flow hook points — resolved without new API, see #29) and #23 (tab-open/close is driven by the switcher's window.open behavior).

Sub-issues

• 4.1 Opened-account tracking + EventSource lifecycle — resolved as a side effect of Implement switchAccount(): state reset, cache hydration, and background sync for the addAccount in-place switch #29, no separate implementation needed.