fix(multiplayer): bind signed workload tokens to allocation_id only

The just-landed signed workload token embedded (allocation_id, match_id,
server_id) as claims. That doesn't actually work for its intended delivery
channel: the token is meant to be requested as a GameServerAllocation
annotation in the SAME request that asks Agones to pick a server, so at mint
time the allocator knows allocation_id (it generates it) but not yet which
server_id Agones will return -- server_id only exists in Agones's response,
after the annotation request has already been sent. Embedding it was simply
not possible for the real caller this was built for; only the (allocator ->
signed_token) unit tests and hand-constructed integration tests happened to
supply it directly, masking the gap.

Fixes it by having the token bind only allocation_id (the one identifier
actually known at mint time) plus expiry. match_id/server_id are resolved at
verify time from the durable allocations table via the new
store.AllocationBindingByAllocationID, keyed by allocation_id -- which the
allocator already records immediately after Agones responds. This is
strictly stronger, not just a workaround: a caller can no longer claim any
match/server pairing at all, even one that happens to be internally
consistent -- the binding returned is entirely durable-record-derived.

Verified: server/workload's unit tests updated for the new two-field claim
shape; server/api's Postgres integration suite gains
TestWorkloadVerifierFromSignedTokenNeverTrustsCallerSuppliedBinding (two
distinct real allocations each resolve to their own, and only their own,
match/server pairing) replacing the now-inapplicable mismatched-triple test.
Full `go build ./... && go vet ./... && gofmt -l . && go test ./... -race`
and `go test -tags integration ./... -race` both clean; the api integration
suite re-run 3x clean against a live postgres:17-alpine container.

server/api/workload_verifier_integration_test.go

@@ -48,8 +48,8 @@ func openIntegrationPostgres(t *testing.T) *sql.DB {
 }
 
 // seedRealAllocation claims a real ready server and allocation row, exactly
-// the durable state a signed workload token must later be cross-checked
-// against (see store.AllocationBindingStillValid).
+// the durable state a signed workload token's allocation_id must resolve
+// against (see store.AllocationBindingByAllocationID).
 func seedRealAllocation(t *testing.T, db *sql.DB, allocationID, matchID string, now time.Time) domain.Allocation {
 	t.Helper()
 	ctx := context.Background()
@@ -65,11 +65,13 @@ func seedRealAllocation(t *testing.T, db *sql.DB, allocationID, matchID string,
 }
 
 // TestWorkloadVerifierFromSignedTokenAcceptsARealAllocation proves the full
-// wired path: a token issued by workload.IssueSignedWorkloadToken for a real
-// allocation row verifies successfully through
-// WorkloadVerifierFromSignedToken and returns a binding matching what
-// serverMutation actually checks (ServerID, MatchID). This is the "wired,
-// working" counterpart to cmd/control-plane's
+// wired path: a token issued by workload.IssueSignedWorkloadToken naming only
+// a real allocation_id verifies successfully through
+// WorkloadVerifierFromSignedToken and returns a binding whose match_id/
+// server_id came from the durable allocation record (the token itself never
+// carries them -- see signed_token.go), matching what serverMutation
+// actually checks (ServerID, MatchID). This is the "wired, working"
+// counterpart to cmd/control-plane's
 // TestServerRoutesRequireWorkloadVerifyToBeWired, which pins the
 // unconfigured-503 case.
 func TestWorkloadVerifierFromSignedTokenAcceptsARealAllocation(t *testing.T) {
@@ -78,7 +80,7 @@ func TestWorkloadVerifierFromSignedTokenAcceptsARealAllocation(t *testing.T) {
 	allocation := seedRealAllocation(t, db, "alloc-verify-1", "match-verify-1", now)
 
 	secret := []byte("integration-test-secret")
-	token, err := workload.IssueSignedWorkloadToken(secret, allocation.AllocationID, allocation.MatchID, allocation.ServerID, now, time.Minute)
+	token, err := workload.IssueSignedWorkloadToken(secret, allocation.AllocationID, now, time.Minute)
 	if err != nil {
 		t.Fatalf("issue token: %v", err)
 	}
@@ -97,14 +99,14 @@ func TestWorkloadVerifierFromSignedTokenAcceptsARealAllocation(t *testing.T) {
 }
 
 // TestWorkloadVerifierFromSignedTokenRejectsAnUnknownAllocation proves the
-// durable cross-check actually runs: a validly-signed, unexpired token whose
-// allocation was never recorded (e.g. superseded, or simply fabricated) must
-// still be rejected. Signature and expiry checks alone are not enough.
+// durable lookup actually runs: a validly-signed, unexpired token whose
+// allocation was never recorded (e.g. simply fabricated) must still be
+// rejected. Signature and expiry checks alone are not enough.
 func TestWorkloadVerifierFromSignedTokenRejectsAnUnknownAllocation(t *testing.T) {
 	db := openIntegrationPostgres(t)
 	now := time.Now().UTC()
 	secret := []byte("integration-test-secret")
-	token, err := workload.IssueSignedWorkloadToken(secret, "alloc-never-recorded", "match-never-recorded", "server-never-recorded", now, time.Minute)
+	token, err := workload.IssueSignedWorkloadToken(secret, "alloc-never-recorded", now, time.Minute)
 	if err != nil {
 		t.Fatalf("issue token: %v", err)
 	}
@@ -114,22 +116,44 @@ func TestWorkloadVerifierFromSignedTokenRejectsAnUnknownAllocation(t *testing.T)
 	}
 }
 
-// TestWorkloadVerifierFromSignedTokenRejectsAMismatchedTriple proves the
-// cross-check binds all three identifiers together, not each independently:
-// a real allocation's own allocation_id combined with someone else's
-// match/server must still fail.
-func TestWorkloadVerifierFromSignedTokenRejectsAMismatchedTriple(t *testing.T) {
+// TestWorkloadVerifierFromSignedTokenNeverTrustsCallerSuppliedBinding proves
+// the binding returned is entirely derived from the durable allocation row,
+// never from anything embedded in or inferable from the token: two distinct
+// allocations produce tokens that resolve to their own, and only their own,
+// match/server pairing.
+func TestWorkloadVerifierFromSignedTokenNeverTrustsCallerSuppliedBinding(t *testing.T) {
 	db := openIntegrationPostgres(t)
 	now := time.Now().UTC()
-	allocation := seedRealAllocation(t, db, "alloc-verify-2", "match-verify-2", now)
+	first := seedRealAllocation(t, db, "alloc-verify-2a", "match-verify-2a", now)
+	second := seedRealAllocation(t, db, "alloc-verify-2b", "match-verify-2b", now)
 	secret := []byte("integration-test-secret")
-	token, err := workload.IssueSignedWorkloadToken(secret, allocation.AllocationID, "a-different-match", allocation.ServerID, now, time.Minute)
-	if err != nil {
-		t.Fatalf("issue token: %v", err)
-	}
 	verify := WorkloadVerifierFromSignedToken(secret, db)
-	if _, err := verify(token, now.Add(time.Second)); err == nil {
-		t.Fatal("expected rejection for a real allocation id paired with the wrong match id")
+
+	firstToken, err := workload.IssueSignedWorkloadToken(secret, first.AllocationID, now, time.Minute)
+	if err != nil {
+		t.Fatalf("issue first token: %v", err)
+	}
+	firstBinding, err := verify(firstToken, now.Add(time.Second))
+	if err != nil {
+		t.Fatalf("verify first: %v", err)
+	}
+	if firstBinding.MatchID != first.MatchID || firstBinding.ServerID != first.ServerID {
+		t.Fatalf("first binding %+v resolved to the wrong allocation", firstBinding)
+	}
+
+	secondToken, err := workload.IssueSignedWorkloadToken(secret, second.AllocationID, now, time.Minute)
+	if err != nil {
+		t.Fatalf("issue second token: %v", err)
+	}
+	secondBinding, err := verify(secondToken, now.Add(time.Second))
+	if err != nil {
+		t.Fatalf("verify second: %v", err)
+	}
+	if secondBinding.MatchID != second.MatchID || secondBinding.ServerID != second.ServerID {
+		t.Fatalf("second binding %+v resolved to the wrong allocation", secondBinding)
+	}
+	if secondBinding.MatchID == firstBinding.MatchID || secondBinding.ServerID == firstBinding.ServerID {
+		t.Fatalf("distinct allocations resolved to the same binding: %+v vs %+v", firstBinding, secondBinding)
 	}
 }
 
@@ -148,7 +172,7 @@ func TestWorkloadVerifierFromSignedTokenClosesTheDefaultUnwiredGap(t *testing.T)
 	now := time.Now().UTC()
 	allocation := seedRealAllocation(t, db, "alloc-verify-3", "match-verify-3", now)
 	secret := []byte("integration-test-secret")
-	token, err := workload.IssueSignedWorkloadToken(secret, allocation.AllocationID, allocation.MatchID, allocation.ServerID, now, time.Minute)
+	token, err := workload.IssueSignedWorkloadToken(secret, allocation.AllocationID, now, time.Minute)
 	if err != nil {
 		t.Fatalf("issue token: %v", err)
 	}