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Outgoing kind-20000 geohash messages mine a NIP-13 nonce tag (8 leading zero bits, ~256 hashes, typically <1 ms) off the main actor before signing. Mining is hard-capped at 2 s and cancellable (newer send or channel switch): on cap/cancel the committed target steps down so the message still ships promptly with an honest commitment - sending is never blocked and nothing is dropped. The hot loop serializes the canonical event once and rewrites only the fixed-width nonce bytes. Inbound kind-20000 events are scored per NIP-13 commitment semantics (committed target counts; the ID must actually meet it, extra work earns nothing) and never hard-rejected: validated PoW >= 8 bits skips the per-sender rate-limit bucket while the per-content flood bucket still applies, so old non-mining clients keep working under today's strict limits while bulk spam gets expensive. Presence heartbeats (kind 20001), kind-1 notes, and DMs are unchanged; no UI beyond a pow= field in an existing sampled debug log. Reimplemented from scratch rather than cherry-picking the stale feature/pow-geohash-mining-ui branch (unbounded loop, hard receive filtering, mining UI, XCTest, force unwraps). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>