feat(multiplayer): run leased allocator worker

server/allocator/worker.go

@@ -0,0 +1,60 @@
+package allocator
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"time"
+
+	"github.com/cosmic-clash/cosmic-clash/server/domain"
+)
+
+// MatchClaimSource is the durable allocator work queue. Implementations must
+// lease a match before returning it and fence binding by allocation ID.
+type MatchClaimSource interface {
+	ClaimAllocatingMatch(context.Context, time.Time) (domain.AllocationRequest, bool, error)
+	BindAllocatedMatch(context.Context, domain.Allocation) error
+}
+
+// Worker consumes one leased match at a time. Provider failures deliberately
+// retain the lease: an HTTP/provider failure can be ambiguous after an external
+// allocation, so releasing it could allocate two GameServers for one match.
+type Worker struct {
+	Claims  MatchClaimSource
+	Service Service
+	Now     func() time.Time
+}
+
+// RunOnce returns whether it found a claimed match. It never exposes an
+// endpoint itself; Service first records the provider allocation durably and
+// BindAllocatedMatch then attaches that already-recorded allocation to the
+// fenced match claim.
+func (w Worker) RunOnce(ctx context.Context) (bool, error) {
+	if w.Claims == nil || w.Now == nil {
+		return false, errNotConfigured
+	}
+	request, found, err := w.Claims.ClaimAllocatingMatch(ctx, w.Now())
+	if err != nil || !found {
+		return found, err
+	}
+	result, err := w.Service.Allocate(ctx, request, AllocationLabels(request))
+	if err != nil {
+		return true, fmt.Errorf("allocate claimed match %s: %w", request.MatchID, err)
+	}
+	if err := w.Claims.BindAllocatedMatch(ctx, result.Allocation); err != nil {
+		return true, fmt.Errorf("bind allocated match %s: %w", request.MatchID, err)
+	}
+	return true, nil
+}
+
+// AllocationLabels are the compatibility selectors shared with the Fleet
+// template. They are derived only from the durable match plan, never client
+// input or mutable worker configuration.
+func AllocationLabels(request domain.AllocationRequest) map[string]string {
+	return map[string]string{
+		"cosmic-clash.io/region":    request.Region,
+		"cosmic-clash.io/build":     request.Build,
+		"cosmic-clash.io/protocol":  strconv.Itoa(request.Protocol),
+		"cosmic-clash.io/transport": request.Transport,
+	}
+}