Health survives a door, and experience needs you to be there

Arriving anywhere set health to maximum, so a run cost nothing: walk in,
take what you could, walk out, walk back in whole. Current health now
lives on the character record for the same reason the inventory does --
SimWorld builds a blank player on every instance change, so anything that
must survive a door has to be written down -- and it is banked at every
transfer, every disconnect, and on every item transaction, since a potion
moves an item and hit points in one action.

The hub is where that damage is paid off, at 10% of maximum per second:
about ten seconds from nothing, fast enough not to be a chore and slow
enough to be a decision before walking back in. The dungeon rate is
unchanged, so waiting one out is still not a plan. Regeneration is a
property of the world now rather than a constant.

adopt() no longer touches current health. It is called mid-session by
on_choose_upgrade, and reading health from the record there would snap a
player back to whatever was last written to disk; recompute_max_hp still
clamps downwards so Glass Cannon takes the hit points above the new
ceiling with it. ServerRuntime._adopt_character stays the one place a
record becomes a live player.

Experience is still undivided, but now only among players within
XP_AWARD_RADIUS of the kill -- ten percent past what a player can see, so
anyone who watched it die is inside and someone parked in the entrance
room is not. The death events carry a position for this, and deliberately
do not put it on the wire: encode_events still writes the id alone.

diag_progression covers the whole chain end to end -- wounded in a
dungeon, escaped to the hub with the wound intact, healing there, and
walking back in still hurt -- because a unit test cannot transfer a peer.
Both halves were mutation-tested against it; the unit suite alone missed
the arrival heal entirely.

The Proving Grounds is recorded in the roadmap as a debugging tool that
does not ship: it pays full experience for a boss with 8% health.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -142,6 +142,15 @@ couple of minutes instead of a quarter of an hour, and because it is a portal
 rather than a launch flag you can compare it to a real run without restarting
 the server.
 
+**It is a debugging tool and does not ship.** It pays exactly the same
+experience a real run does — `Progression.xp_for_boss` ignores its argument and
+`xp_for_enemy` keys on the enemy id, which the difficulty multipliers do not
+touch — while its boss has 8% of its health and its trash drops ten times as
+often. That makes it strictly the best place to level and to farm, which is
+correct for a harness and would be ruinous in a release. Remove it from
+`Dungeons.ORDER` (and its `P` marker from the lobby stamp) before shipping, or
+give `DungeonDef` an `xp_mult` alongside the three multipliers it already has.
+
 Adding a dungeon is one entry in `Dungeons.ORDER` plus one more `P` marker in
 the lobby stamp — the Nth marker, in reading order, opens the Nth entry, so the
 two have to stay in the same order.