adventure: send Pete the run, room by room

The engine narrates every fight, trap and haul to one Matrix DM and then
discards the shape underneath it. This records that shape as it happens so
Pete can retell the run to somebody who wasn't in the room.

Beats ride the roster ticker (one extra request per two minutes, not one per
room) but on their own table, never pete_emit_queue: they are high-volume and
low-stakes, and a chatty run must not be able to spend the retry budget a
death dispatch depends on. Unlike the snapshots they ARE retried — a dropped
beat is a hole in a story, not a stale number the next tick corrects.

Recording is a leaf everywhere it is called. If a beat can't be written the
walk carries on exactly as it did before this existed.

Privacy is stricter here than on the board. The board omits an opted-out
player from a snapshot; a liveblog would be an account of where they are and
what is happening to them, so their beats never leave the box at all — and a
run whose owner can't be resolved is refused rather than published.

Claude-Session: https://claude.ai/code/session_012bxpQQJDjC1mTtLN3VVtBQ

internal/plugin/dnd_expedition_region_cmd.go

@@ -170,6 +170,13 @@ func (p *AdventurePlugin) advanceToNextRegion(userID id.UserID, exp *Expedition,
 	tc := resolveTransitWanderingCheck(exp, charClass, nil)
 	_ = processTransitWanderingCheck(exp, tc)
 
+	// The liveblog beat goes on the *outgoing* run, and it has to be filed before
+	// the run is retired — a region crossing is the last thing that happens in
+	// the region being left, and it is what explains why that run's log stops.
+	if outgoing, _ := getZoneRun(exp.RunID); outgoing != nil {
+		beatRegion(outgoing, cur.Name, next.Name)
+	}
+
 	// R2 — retire the outgoing region's DungeonRun before mutating
 	// CurrentRegion so retireRegionRun keys the right region.
 	if err := retireRegionRun(exp, cur.ID); err != nil {