feat: atomically create matchmaking proposals

multiplayer-next.md

@@ -88,7 +88,10 @@ product policy are in [`docs/MATCHMAKING.md`](docs/MATCHMAKING.md).
   and ranked identity/arena metadata before creating proposal state; durable
   queue precedence and allocation integration remain.
 - [ ] **IN PROGRESS:** Fence proposals/participants in a PostgreSQL serializable transaction;
-  prove loss of an acknowledged Redis write cannot split players.
+  prove loss of an acknowledged Redis write cannot split players. The Go store
+  adapter now performs proposal insertion, participant insertion, and every
+  queue-ticket promotion in one rollback-safe SERIALIZABLE callback; live DB/
+  Redis failover testing remains.
 - [ ] Casual: target 3v3 humans, after 60 s allow >=2 humans (one/team) plus
   bots, kickoff-only human backfill and no backfill loss/decline penalty.
 - [ ] **IN PROGRESS:** Ranked: exactly six humans, solo-only, no bots/backfill,

multiplayer-todo.md

@@ -1195,7 +1195,7 @@ the local/CI/community transport, not a silent production fallback.
 | 8.15 `[D:7.8,8.3]` | **IN PROGRESS.** Pure Go probe validation treats Steam location as opaque, requires nonce/freshness/region and server-computed RTT, and implements discrepancy quarantine/release; authenticated HTTP now accepts only opaque location/nonce input through a server-owned probe provider | `server/domain/probes.go`, adversarial fixtures and `server/api/service.go` cover stale/wrong/forged evidence, the 25 ms/30% threshold, three-sample quarantine, five-clean release, authenticated provider arguments and rejection of client RTT fields; Steam coordinator and regional probe adapters remain |
 | 8.16 `[D:8.14,8.15]` | **IN PROGRESS.** Pure Go candidate/team selection implements the <=100 ms ceiling, pairwise widening tolerance, anchor inclusion, deterministic set/region scoring and balanced team partitioning; queue-backed formation now consumes the server-owned projection and fences duplicate player identities | `server/domain/matcher.go`, `teams.go` and adversarial fixtures cover no-common-region, tolerance boundaries, lexical ties, mean-rating balance, malformed candidates, duplicate identities and queue-backed oldest-anchor formation; full population fixtures and durable matcher claim integration remain |
 | 8.17 `[D:8.14,8.16]` | **IN PROGRESS.** Pure Go proposal policy sends a 10-second response window to every selected human, requires unanimous acceptance, applies exact decline/timeout cooldowns and ranked escalation; authenticated API exposes revisioned accept/decline mutations; formed matches now pass through a playlist-aware proposal boundary | `server/domain/proposal.go`, `formation.go` and `server/api/service.go` plus adversarial fixtures cover partial/unanimous response, expiry, replay/conflict, stale API revision, casual lineup preparation and ranked metadata validation; queue precedence and allocation integration remain |
-| 8.18 `[D:8.5,8.14,8.17]` | **IN PROGRESS.** Go store layer defines PostgreSQL SERIALIZABLE whole-transaction retries and queue candidate/proposal claim SQL using `FOR UPDATE SKIP LOCKED` plus durable uniqueness/revision fences | `server/store/serializable.go` and tests cover retry classification and claim-boundary invariants; live PostgreSQL adapter/row decoding, Redis candidate index/repair, worker-failure and concurrent two-matcher integration tests remain |
+| 8.18 `[D:8.5,8.14,8.17]` | **IN PROGRESS.** Go store layer defines PostgreSQL SERIALIZABLE whole-transaction retries and queue candidate/proposal claim SQL using `FOR UPDATE SKIP LOCKED` plus durable uniqueness/revision fences; proposal creation now inserts proposal/participants and promotes every ticket in one rollback-safe transaction | `server/store/serializable.go`, `proposal_sql.go` and tests cover retry classification, claim-boundary invariants, zero-row claim aborts and atomic statement ordering; live PostgreSQL adapter/row decoding, Redis candidate index/repair, worker-failure and concurrent two-matcher integration tests remain |
 | 8.19 `[D:8.18]` | **IN PROGRESS.** Pure Go casual lineup requires 2–6 humans with at least one per team, fills missing slots with explicit bots, permits kickoff-only bot-slot backfill and assigns no backfill penalty/rating update; proposal preparation now derives the lineup from formed teams | `server/domain/casual.go`, `formation.go` cover both-team minimum, bot shape, live-play rejection, zero-penalty backfill and casual proposal composition; queue candidate selection, opt-in 10 s backfill proposals, reconnect/leave penalties and live integration remain |
 | 8.20 `[D:8.18]` | **IN PROGRESS.** Pure Go ranked admission requires six unique verified solo humans, rejects bots/backfill/parties, and allows only random-enabled non-elevated arenas; proposal preparation requires matching metadata for every formed player | `server/domain/ranked.go`, `formation.go` cover count, identity, party, bot/backfill, arena eligibility and formed-player metadata rejection; `ArenaRegistry` integration, allocation wiring and innocent-ticket restoration remain |
 | 8.21 `[D:8.5,8.20]` | **IN PROGRESS.** Pure Go rating core implements canonical Glicko-2, daily inactivity, ranked 1/3 and casual 1/N human-opponent weights, deterministic opponent ordering, and authoritative draw/overtime/abandon scoring | `server/domain/rating.go` has canonical/inactivity/weight/invalid-input plus draw/OT/abandon fixtures; PostgreSQL snapshot locking, rating transaction integration, seasons and concurrent result transaction tests remain |

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 {