Player blocking

Behavior

A player can block another player. Blocking is bidirectional in storage but asymmetric in effect:

The blocker maintains a list of blocked ids (returned in me as blocked).
The blocked player does not see the blocker's open (standing) challenges when using the auth standing_challenges query.

Blocking does not affect:

Direct (named) challenges
Accepted games or game chat
Automated tournaments or organizer events
The public standing_challenges query (unauthenticated clients see all open challenges)

Two records are written per block:

pk: PLAYER#<blockingPlayerId>   sk: BLOCKED#<blockedPlayerId>
pk: PLAYER#<blockedPlayerId>    sk: BLOCKEDBY#<blockingPlayerId>

Both are deleted on unblock.

Query	Purpose	`pars`
`block_player`	Create block records	`playerId`
`unblock_player`	Delete block records	`playerId`
`me`	Returns `blocked: string[]` of blocked player ids	—
`standing_challenges` (auth)	Filters challenges where `challenger.id` is in the requester's `BLOCKEDBY` set	`metaGame`

Self-blocking is rejected.

Block lists are queried with begins_with on sk (BLOCKED# / BLOCKEDBY#).
Open-challenge filtering runs in standingChallenges() when userId is provided (auth path only).