Prototype voluntary seat handover with durable private retries

Let a current owner issue, cancel or replace a private 24-hour one-time offer.
Recipients accept the same faction and saved game while old browser sessions,
recovery keys and entry receipts lose authority. Preserve exact claim retries
across refresh, restart and later offers, with private tab-scoped continuation.

Fence every claim mutation to its winning transaction. Add durable receipts
and additive backfill for already-issued offers without changing game JSON or
existing seat authority. Block competing navigation during unresolved owner
operations; remove invalidated owner kits on confirmed recovery.

Record the pending CHOAM Nexus after-victory secrecy/window decision without
inventing the unresolved gameplay or opening mode/publication gates.

Validation: types/lint and 4,364 offline tests passed; production build passed;
43 HTTP tests passed. Added 19 offline and 3 HTTP regressions. Independent
privacy/persistence review passed, including deterministic CAS interleavings,
rollback, legacy migration and exact receipt restoration. Browser room 2EMYG4CY
retained private setup choices after handover/refresh and continued into Storm;
follow-up recovery removed its invalid offer with cards/forces/spice unchanged.
All 218 opening rooms preserved (291 after QA and both broad runs). The opening
456 seat, 49 recovery-key, 56 recovery-receipt and 106 entry-receipt rows were
also verified unchanged. Server reused; no restart or recurring automation.

Final private report: ~/.local/share/dune/checkpoints/20260913-seat-handover/
verification-final/report.json. Source fingerprint:
8949cdf58eb8bc8bd33f2657c6b21352b3ee5e17e2a556c684a89073015632f4.
Check/build/HTTP duration: 140565/6689/24835 ms. The earlier broad run passed;
a final recovery-UI review fix required the second source-bound run.
Goal aggregate counter 64,301,976 -> 65,031,751 before Git (729,775) for this
bounded capability and its concurrency/recovery review; full goal remains active.

docs/CURRENT_STATUS.md

@@ -57,13 +57,15 @@ restoration after necessary restarts. No recurring automation is installed.
 | Six-faction Advanced | Genuine offline setup across 456 configurations; four-profile full-game simulations and JSON continuations. | Base gaps plus provisional special-Karama outcomes, remaining timing audits and authentic multiplayer/browser acceptance. Public starts remain disabled. |
 | Twelve factions and optional modules | Many bounded faction, card, Homeworld and Nexus slices have controls, bots and recovery evidence; Discovery includes free entry, Cistern, carried flight and bounded Jacurutu, Testing Station and Shrine effects. | Every unfinished effect and interaction, occupation entitlement, Orgiz, mixed physical dial allocation and contested Discovery benefits and complete combined games. Inventory or fixture coverage does not enable a module. |
 | AI difficulty | Four profiles consume private legal views; recorded Basic and Advanced studies complete. | Demonstrate a consistent Medium → Hard → Brutal strength ordering, improve strategic gaps, and repeat targeted studies after relevant policy/rule changes. |
-| Multiplayer | Versioned writes, saved seats, owner recovery kits, uncertain-request retry and voluntary own-seat AI control. | Intentional transfer, unprepared abandoned-seat recovery, unattended continuation and remaining network-failure acceptance. Preserve privacy and existing games. |
+| Multiplayer | Versioned writes, saved seats, owner recovery kits, uncertain-request retry, voluntary own-seat AI control and a [voluntary seat handover prototype](SEAT_HANDOVER.md). | Broader handover/disconnection acceptance, unprepared abandoned-seat recovery, unattended continuation and remaining network-failure acceptance. Preserve privacy and existing games. |
 | Player experience | Internal component inspectors and many desktop/phone feature journeys verified. | Complete end-to-end games, accessible controls, responsive layout, clear rules/errors and recovery across all supported combinations. |
 
 The [base/Advanced audit](BASE_ADVANCED_READINESS_20260907.md) includes historical missing-feature rows. Its follow-ups supersede the Fremen cancellation and BG setup findings; [genuine setup](ADVANCED_SETUP_TEST_SEAM.md) and the [Advanced study](AI_ADVANCED_SETUP_CALIBRATION_20260907.md) supersede the old Basic-then-flip testing concern. They do not settle the remaining rules.
 
 Likewise, the [Truthtrance readiness audit](TRUTHTRANCE_NONBATTLE_READINESS_20260907.md) predates [spice facts](TRUTHTRANCE_SPICE_FACTS.md), [card-count facts](TRUTHTRANCE_CARD_COUNT.md) and [Basic shipment promises](TRUTHTRANCE_SHIPMENT_PROMISES.md). Current `TruthFact` already includes these facts; do not rebuild them. Typed preparation and BG conversion now support the active reserve-shipment scope in base Advanced without Guild or optional modules. Broader facts, earlier-phase promises, remaining Advanced/expansion commitment scope and freeform interpretation remain incomplete.
 
+The voluntary [seat handover prototype](SEAT_HANDOVER.md) connects private one-time offers, recipient controls, exact saved retry proof and active-token custody fencing. It preserves existing game state and revokes previous owner recovery authority. Full disconnected-seat acceptance remains open. CHOAM Nexus after-victory inspection awaits the [private-window decision](NEXUS_CHOAM_SECRET_ALLY.md#after-victory-inspection-audit); development continues independently.
+
 ## Next milestone: rapid functional coverage
 
 The first connected batch is the [Ixians & Tleilaxu prototype](IX_PROTOTYPE.md):