feat: form matches from queue projections

multiplayer-next.md

@@ -79,6 +79,9 @@ product policy are in [`docs/MATCHMAKING.md`](docs/MATCHMAKING.md).
   region/team tie-break rules. Authenticated probe transport now routes opaque
   location/nonce data through a server-owned evidence provider and refuses
   client RTT values; Steam/coordinator adapters remain.
+- [ ] **IN PROGRESS:** Form deterministic candidate sets and balanced teams from
+  the server-owned queue projection. Queue-backed oldest-anchor formation and
+  duplicate-player fencing now exist; durable matcher claims remain.
 - [ ] **IN PROGRESS:** Send 10 s proposals to every selected human: ranked six, relaxed casual
   two to six with disclosed bots; enforce exact cooldown and queue-precedence
   behavior.

multiplayer-todo.md

@@ -1193,7 +1193,7 @@ the local/CI/community transport, not a silent production fallback.
 |---|---|---|
 | 8.14 `[D:8.4,8.5,8.8]` | **IN PROGRESS.** Pure Go queue domain enforces one active ticket per verified player under concurrent mutation, 10 s heartbeat/30 s expiry, retry-safe create/heartbeat/cancel, owner-only recovery reads and deterministic candidate projection; store layer adds a rebuildable candidate-cache boundary and authenticated HTTP queue adapter | `server/domain/queue.go`, `server/store/candidates.go` and `server/api/service.go` cover ownership/expiry/idempotency, concurrent create fencing, expired recovery as a terminal error, server-owned candidate resolution, bounded/strict JSON input and cache loss/atomic rebuild; PostgreSQL row adapter, real Redis index/TTLs and restart/failover integration remain |
 | 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 | `server/domain/matcher.go`, `teams.go` and adversarial fixtures cover no-common-region, tolerance boundaries, lexical ties, mean-rating balance and input-order independence; queue-backed candidate loading and full population fixtures 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 now exposes revisioned accept/decline mutations | `server/domain/proposal.go` and `server/api/service.go` plus adversarial fixtures cover partial/unanimous response, expiry, replay/conflict, stale API revision and ranked six-player/cooldown rules; casual 6→2 composition, 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 |
 | 8.19 `[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 | `server/domain/casual.go` covers both-team minimum, bot shape, live-play rejection and zero-penalty backfill; queue candidate selection, opt-in 10 s backfill proposals, reconnect/leave penalties and live integration remain |

server/domain/matcher.go

@@ -2,6 +2,7 @@ package domain
 
 import (
 	"fmt"
+	"math"
 	"sort"
 	"time"
 )
@@ -33,6 +34,33 @@ type Selection struct {
 	TotalWaitSeconds float64
 }
 
+type MatchFormation struct {
+	Selection Selection
+	Teams     Teams
+}
+
+// FormFromQueue is the queue-backed matcher boundary. Queue.Candidates owns
+// expiry and ordering; this method chooses the oldest projected candidate as
+// the anchor, then forms and partitions one deterministic match.
+func FormFromQueue(queue *Queue, size int, now time.Time) (MatchFormation, error) {
+	if queue == nil {
+		return MatchFormation{}, fmt.Errorf("queue is required")
+	}
+	candidates := queue.Candidates(now)
+	if len(candidates) == 0 {
+		return MatchFormation{}, fmt.Errorf("queue is empty")
+	}
+	selection, err := SelectCandidates(candidates[0], candidates[1:], size, now)
+	if err != nil {
+		return MatchFormation{}, err
+	}
+	teams, err := PartitionTeams(selection.Players)
+	if err != nil {
+		return MatchFormation{}, err
+	}
+	return MatchFormation{Selection: selection, Teams: teams}, nil
+}
+
 func RatingTolerance(waitSeconds float64) float64 {
 	if waitSeconds < 0 {
 		waitSeconds = 0
@@ -50,9 +78,11 @@ func SelectCandidates(anchor Candidate, candidates []Candidate, size int, now ti
 	}
 	pool := make([]Candidate, 0, len(candidates)+1)
 	seen := map[string]bool{}
+	seenPlayers := map[string]bool{}
 	add := func(candidate Candidate) {
-		if candidate.TicketID != "" && !seen[candidate.TicketID] {
+		if validCandidate(candidate) && !seen[candidate.TicketID] && !seenPlayers[candidate.PlayerID] {
 			seen[candidate.TicketID] = true
+			seenPlayers[candidate.PlayerID] = true
 			pool = append(pool, candidate)
 		}
 	}
@@ -97,6 +127,18 @@ func SelectCandidates(anchor Candidate, candidates []Candidate, size int, now ti
 	return best, nil
 }
 
+func validCandidate(candidate Candidate) bool {
+	if candidate.TicketID == "" || candidate.PlayerID == "" || candidate.EnqueuedAt.IsZero() || math.IsNaN(candidate.Rating) || math.IsInf(candidate.Rating, 0) {
+		return false
+	}
+	for region, rtt := range candidate.PredictedRTT {
+		if region != "EU" && region != "NA" || math.IsNaN(rtt) || math.IsInf(rtt, 0) || rtt < 0 {
+			return false
+		}
+	}
+	return len(candidate.PredictedRTT) > 0
+}
+
 func compatibleSet(players []Candidate, now time.Time) bool {
 	regions := commonRegions(players)
 	if len(regions) == 0 {

server/domain/matcher_test.go

@@ -66,3 +66,38 @@ func TestSelectCandidatesRejectsNoCommonRegion(t *testing.T) {
 		t.Fatal("selected players without a common <=100ms region")
 	}
 }
+
+func TestFormFromQueueUsesServerProjectionAndBalancesTeams(t *testing.T) {
+	now := time.Unix(100000, 0)
+	queue := NewQueue()
+	for _, id := range []string{"c", "a", "b", "d"} {
+		candidate := candidate(id, 1500, time.Second, 40, 45, now)
+		if _, err := queue.Create(candidate.PlayerID, candidate.TicketID, "create-key-"+id+"-123456", candidate, now.Add(-time.Duration(len(id))*time.Millisecond)); err != nil {
+			t.Fatal(err)
+		}
+	}
+	formation, err := FormFromQueue(queue, 4, now)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if formation.Selection.Players[0].TicketID != "a" || formation.Selection.Region != "EU" || len(formation.Teams.Team0) != 2 || len(formation.Teams.Team1) != 2 {
+		t.Fatalf("formation = %+v", formation)
+	}
+	seen := map[string]bool{}
+	for _, player := range append(formation.Teams.Team0, formation.Teams.Team1...) {
+		if seen[player.PlayerID] {
+			t.Fatalf("duplicate player in teams: %s", player.PlayerID)
+		}
+		seen[player.PlayerID] = true
+	}
+}
+
+func TestSelectCandidatesRejectsMalformedCandidateInsteadOfTrustingIt(t *testing.T) {
+	now := time.Unix(100000, 0)
+	anchor := candidate("a", 1500, 0, 40, 40, now)
+	malformed := candidate("b", 1500, 0, 40, 40, now)
+	malformed.PlayerID = anchor.PlayerID
+	if _, err := SelectCandidates(anchor, []Candidate{malformed}, 2, now); err == nil {
+		t.Fatal("duplicate player candidate accepted")
+	}
+}