Sim: cross region boundaries; word mid-zone clears as region clears

Mirror runAutopilotWalk's multi-region auto-advance in the headless sim:
on a mid-zone stopComplete (active multi-region exp with a next region),
advanceToNextRegion and keep simulating instead of scoring a premature
"cleared". A transit error there is now recorded as halted, not cleared.

Also fix misleading run-complete wording: a non-boss region clear of a
multi-region zone now reads "Cleared {region}. The way to {next} opens
ahead." instead of "Cleared {zone}. Run complete." New midZoneRegionClear
helper shares finalizeExpeditionOnZoneClear's gating; the path is shared
with manual !region travel, so both autopilot and manual play get it.

(cherry picked from commit 5d2bba70849a0a3fdeac285cc55ea9b8fadea29c)

internal/plugin/dnd_expedition_extract.go

@@ -170,6 +170,29 @@ func (p *AdventurePlugin) finalizeExpeditionOnZoneClear(userID id.UserID, runID
 	return p.AwardCompletionMilestones(exp, false)
 }
 
+// midZoneRegionClear reports whether the just-completed run (runID) is the
+// active expedition's current run AND finishes a non-boss region of a
+// multi-region zone — i.e. a region clear that leaves the expedition active
+// with a next region to cross into. Returns the cleared region, the next
+// region, and true in that case; zero-values + false for a full zone clear,
+// a standalone run, or any read error. Used to word the run-complete message
+// (region-cleared vs zone-cleared) without re-deriving region state inline.
+func midZoneRegionClear(userID id.UserID, runID string) (cur, next ExpeditionRegion, ok bool) {
+	exp, err := getActiveExpedition(userID)
+	if err != nil || exp == nil || exp.RunID != runID || !IsMultiRegionZone(exp.ZoneID) {
+		return ExpeditionRegion{}, ExpeditionRegion{}, false
+	}
+	region, found := CurrentRegion(exp)
+	if !found || region.IsZoneBoss {
+		return ExpeditionRegion{}, ExpeditionRegion{}, false
+	}
+	nxt, found := nextRegion(exp.ZoneID, region.ID)
+	if !found {
+		return ExpeditionRegion{}, ExpeditionRegion{}, false
+	}
+	return region, nxt, true
+}
+
 // getResumableExpedition returns the most recent 'extracting' row for the
 // user, regardless of age (caller checks the 7-day window).
 func getResumableExpedition(userID id.UserID) (*Expedition, error) {