feat: atomically create matchmaking proposals

server/store/proposal_sql.go

@@ -0,0 +1,49 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	"github.com/cosmic-clash/cosmic-clash/server/domain"
+)
+
+const ProposalInsertSQL = `INSERT INTO proposals
+    (proposal_id, playlist, state, expires_at, revision)
+VALUES ($1, $2, 'OPEN', $3, 0)`
+
+// CreateProposal atomically claims the queue tickets and creates the proposal.
+// Every statement runs inside the same SERIALIZABLE retry callback; callers
+// must never publish a proposal from a cache-only candidate list.
+func CreateProposal(ctx context.Context, db *sql.DB, proposal domain.Proposal, ticketIDs map[string]string, now time.Time) error {
+	if proposal.ProposalID == "" || len(proposal.Participants) == 0 {
+		return fmt.Errorf("invalid proposal transaction")
+	}
+	return RunSerializable(ctx, db, DefaultSerializableAttempts, func(ctx context.Context, tx *sql.Tx) error {
+		if _, err := tx.ExecContext(ctx, ProposalInsertSQL, proposal.ProposalID, proposal.Playlist, proposal.ExpiresAt); err != nil {
+			return err
+		}
+		for _, participant := range proposal.Participants {
+			ticketID := ticketIDs[participant.PlayerID]
+			if participant.PlayerID == "" || ticketID == "" {
+				return fmt.Errorf("missing proposal ticket mapping")
+			}
+			if _, err := tx.ExecContext(ctx, ProposalParticipantInsertSQL, proposal.ProposalID, participant.PlayerID, ticketID); err != nil {
+				return err
+			}
+			result, err := tx.ExecContext(ctx, QueueTicketProposeSQL, ticketID, now)
+			if err != nil {
+				return err
+			}
+			changed, err := result.RowsAffected()
+			if err != nil {
+				return err
+			}
+			if changed != 1 {
+				return fmt.Errorf("queue ticket claim lost")
+			}
+		}
+		return nil
+	})
+}

server/store/serializable_test.go

@@ -19,7 +19,7 @@ func TestRetryableRecognisesPostgresSerializationAndDeadlockErrors(t *testing.T)
 }
 
 func TestClaimSQLContainsDurableOwnershipFences(t *testing.T) {
-	for _, fragment := range []string{"FOR UPDATE SKIP LOCKED", "state = 'QUEUED'", "proposal_participants", "revision = revision + 1"} {
+	for _, fragment := range []string{"FOR UPDATE SKIP LOCKED", "state = 'QUEUED'", "proposal_participants", "revision = revision + 1", "INSERT INTO proposals"} {
 		if !containsAnySQL(fragment) {
 			t.Fatalf("claim boundary missing %q", fragment)
 		}
@@ -27,7 +27,7 @@ func TestClaimSQLContainsDurableOwnershipFences(t *testing.T) {
 }
 
 func containsAnySQL(fragment string) bool {
-	return index(CandidateClaimSQL, fragment) >= 0 || index(ProposalParticipantInsertSQL, fragment) >= 0 || index(QueueTicketProposeSQL, fragment) >= 0
+	return index(CandidateClaimSQL, fragment) >= 0 || index(ProposalParticipantInsertSQL, fragment) >= 0 || index(QueueTicketProposeSQL, fragment) >= 0 || index(ProposalInsertSQL, fragment) >= 0
 }
 
 func index(s, fragment string) int {