* fix(desktop): keep composer draft across compression tip rotation
Auto-compression swaps the live stored session id while the user may still
be typing. Scope the composer/queue key on the lineage root and migrate any
tip-keyed draft/queue entries onto that durable key when the tip rotates so
the in-progress prompt does not vanish when the response lands.
* test(desktop): cover draft survival across compression tip rotation
Add regression coverage for migrateSessionDraft, lineage-scoped composer
keys, and the rotation path that previously wiped an in-progress draft.
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