feat(observer): add observer mode and disconnect recovery

docs/GAME_CORE.md

@@ -1,9 +1,8 @@
 # Authoritative game core
 
-Milestones 006 and 007 provide the portable movement engine, gameplay object
-systems, terminal results, and view projector. The ESP remains the only owner
-of mutable game state. Reconnect behavior and browser controls remain out of
-scope until their later milestones.
+Milestones 006, 007, and 009 provide the portable movement engine, gameplay
+object systems, terminal results, view projector, and disconnect recovery. The
+ESP remains the only owner of mutable game state.
 
 ## Command processing
 
@@ -87,3 +86,20 @@ compass hint, and own-exit status. An opponent's carried key is included only
 while that opponent is currently visible. Observer snapshots contain both
 inventories and effect counters, both exit states and authoritative exit
 timestamps, every remaining ground object, and the public match result.
+
+## Disconnect recovery
+
+Both players start connected. Disconnecting either player during `active` or
+`finish_pending` stores that exact phase, clears queued commands, enters
+`paused`, and assigns the disconnected player a monotonic deadline 60,000 ms
+after detection. Commands processed during the pause are rejected before any
+position, inventory, effect counter, or result can change.
+If the disconnect occurs during `finish_pending`, the remaining 200 ms result
+window is preserved and continues only after both players reconnect.
+
+Restoring the reserved player session before the deadline reconnects the same
+player record. The stored phase resumes only when both player records are
+connected, so a second disconnected player cannot be bypassed. Reaching a
+disconnected player's deadline ends the match with the authoritative `draw`
+result and clears queued commands. Observer connection state never enters this
+state machine.