Reject unversioned party documents

internal/stage/semantic_contracts_initial.go

@@ -108,7 +108,7 @@ func buildPrepareSemanticConfig(env *Env) (prepareSemanticConfig, error) {
 	}
 	partyMode := cfg.Party.Mode
 	if partyMode == "" {
-		partyMode = config.PartyModeLegacy
+		return prepareSemanticConfig{}, fmt.Errorf("prepare semantic configuration requires a resolved canonical party")
 	}
 	payload := prepareSemanticConfig{
 		CampaignID:      strings.TrimSpace(cfg.Session.Campaign),

internal/stage/semantic_contracts_initial_test.go

@@ -26,9 +26,6 @@ func TestPrepareSemanticConfigSensitivity(t *testing.T) {
 		{name: "stable input owner", mutate: func(env *Env) {
 			env.Config.StableInputs.PartyFile.Source = "campaign_config"
 		}},
-		{name: "party mode", mutate: func(env *Env) {
-			env.Config.Party.Mode = config.PartyModeCanonical
-		}},
 	})
 
 	assertSemanticFingerprintUnchanged(t, prepareStage{}, initialSemanticEnv(), []struct {
@@ -129,6 +126,7 @@ func initialSemanticEnv() *Env {
 		StableInputs: config.ResolvedStableInputs{
 			PartyFile: config.ResolvedInputFile{Path: "/campaign/party.yml", ConfigPath: "/campaign/campaign.yml", Source: "session_config"},
 		},
+		Party: config.ResolvedParty{Mode: config.PartyModeCanonical},
 	}}
 }