fix(desktop): honor lineage when gating background queue drain

[zapabob]

Summary

• Treat compression lineage root and tip as the same conversation when deciding whether a background queue may auto-drain.
• Skip drain when the selected or busy stored id shares lineage with the queue key, not only on exact string equality.

Why

Composer/queue keys prefer the durable lineage root (resolveComposerSessionKey), while `` / selected session may hold the live compression tip. Strict equality then mis-classified a busy or selected chat as idle/offscreen, allowing double drain or drain during an active tip turn — a session-bleed / wrong-transcript class bug.

Complements merged #66001 (originating-session drain) and lineage work around #43483. Deliberately does not duplicate open #66240 (restored-queue manual send).

Test plan

• use-background-queue-drain.test.tsx lineage busy + tip-selected cases
• Manual: compress a session with a queued follow-up; confirm background drain waits for the tip turn

[teknium1]

Thanks for the focused regression fix. Current main still uses strict equality for the selected and busy gates in apps/desktop/src/app/session/hooks/use-background-queue-drain.ts:161-165, while resolveComposerSessionKey deliberately scopes queues to the lineage root in apps/desktop/src/store/session.ts:203-213. The proposed lineage predicate addresses that mismatch, and the added busy-tip and selected-tip tests cover both affected gates.

No substantive correctness issue found in this focused change. This is an automated hermes-sweeper review.

[zapabob]

Current official main already implements this exact fix in c9de69c: the background drainer uses idsShareLineage for both selected and busy gates, and the official commit includes the busy-tip and selected-tip regression tests from this PR. A rebase produces only an implementation-overlap conflict, so there is no remaining delta to carry. Closing as implemented on main without rewriting the contributor branch.