Update README for Phase 7b and fix stale Phase 7 reference

Reconciliation sweep already shipped in 52583f2; document the new
playerTrackingEnabled/playerPositionIntervalTicks config options.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015tKdPZt78zbPUZMXWzKEKt

README.md

@@ -54,11 +54,25 @@ serverToken=<token from MCMapper-Backend's `bun run seed`>
 
 then restart. With those set, the mod connects to the backend, backfills already-loaded
 overworld chunks, and streams event-driven column deltas (block place/break) in batches every
-`deltaFlushIntervalTicks` (default 20 = 1s). No periodic reconciliation sweep yet (Phase 7),
+`deltaFlushIntervalTicks` (default 20 = 1s). A periodic reconciliation sweep (Phase 7) also
-and only the overworld — other dimensions and `forge-1_7_10`/`neoforge-26_1` land in later
+walks a bounded number of currently-loaded chunks per tick (`reconciliationChunksPerSweep`,
-phases. The WS client and JSON encoding are hand-rolled (no third-party dependency) — see
+default 4) and re-sends any that drifted from what the backend last acknowledged, to catch
+mutations event hooks miss (world-gen, other mods, `/fill`). Only the overworld is tracked —
+other dimensions and `forge-1_7_10`/`neoforge-26_1` land in later phases. The WS client and
+JSON encoding are hand-rolled (no third-party dependency) — see
 `common/src/main/java/.../ws/SimpleWebSocketClient.java` and `.../json/MiniJson.java` for why.
 
+### Player position tracking (Phase 7b)
+
+When `playerTrackingEnabled` (default `true`), the leaf sends a throttled roster of online
+overworld players (`{"type":"player_positions",...}`, see `DefaultBackendConnection`'s
+class-level wire-protocol doc comment) every `playerPositionIntervalTicks` (default 40 = 2s) —
+always the *full current roster*, not a diff, so a logged-out player simply stops appearing in
+the next send. This is a mod-local toggle only: whether the backend actually relays positions on
+to web viewers is a separate, independent per-server admin setting on the backend side (see
+MCMapper-Backend's README) — a server operator can track positions server-side without exposing
+them publicly, or vice versa.
+
 ## Attribution
 
 See `THIRD_PARTY_NOTICES.md`.