Adv 2.0 L4f-prep: DisplayName migration scaffold (schema + dual-write + helper)

Adds player_meta.display_name with idempotent backfill, dual-writes from
createAdvCharacter (in-tx) and saveAdvCharacter (post-commit), and a
loadDisplayName helper with AdvCharacter fallback. Readers are not flipped
yet — soak begins now; per-call-site swap follows in a later session.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/adventure.go

@@ -194,6 +194,11 @@ func (p *AdventurePlugin) Init() error {
 	if err := backfillPlayerMetaArena(); err != nil {
 		slog.Error("player_meta: arena backfill failed", "err", err)
 	}
+	// Adv 2.0 Phase L4f-prep — one-shot DisplayName backfill into
+	// player_meta. Idempotent (only fills empty display_name rows).
+	if err := backfillPlayerMetaDisplayName(); err != nil {
+		slog.Error("player_meta: display_name backfill failed", "err", err)
+	}
 	// Phase L3 — cancel any open/active legacy coop dungeon runs and
 	// refund member contributions + unsettled bets. Idempotent.
 	closeAndRefundLegacyCoopRuns(p.euro)

internal/plugin/adventure_character.go

@@ -2,6 +2,7 @@ package plugin
 
 import (
 	"database/sql"
+	"log/slog"
 	"time"
 
 	"gogobee/internal/db"
@@ -557,6 +558,16 @@ func createAdvCharacter(userID id.UserID, displayName string) error {
 		return err
 	}
 
+	// Adv 2.0 Phase L4f-prep — dual-write display_name into player_meta.
+	// Inside the same tx so the two rows are created atomically.
+	if _, err = tx.Exec(
+		`INSERT INTO player_meta (user_id, display_name) VALUES (?, ?)
+		 ON CONFLICT(user_id) DO UPDATE SET display_name = excluded.display_name`,
+		string(userID), displayName,
+	); err != nil {
+		return err
+	}
+
 	// Create tier-0 equipment in all slots
 	for _, slot := range allSlots {
 		def := equipmentTiers[slot][0]
@@ -697,7 +708,14 @@ func saveAdvCharacter(char *AdventureCharacter) error {
 		boolToInt(char.TreasuresLocked),
 		string(char.UserID),
 	)
-	return err
+	if err != nil {
+		return err
+	}
+	// Adv 2.0 Phase L4f-prep — dual-write display_name into player_meta.
+	if dnErr := upsertPlayerMetaDisplayName(char.UserID, char.DisplayName); dnErr != nil {
+		slog.Error("player_meta: display_name dual-write failed", "user", char.UserID, "err", dnErr)
+	}
+	return nil
 }
 
 func boolToInt(b bool) int {

internal/plugin/player_meta.go

@@ -21,6 +21,7 @@ type PlayerMeta struct {
 	ArenaWins     int
 	ArenaLosses   int
 	InvasionScore int
+	DisplayName   string
 }
 
 // loadPlayerMeta reads the player_meta row for a user. Returns a
@@ -30,9 +31,9 @@ type PlayerMeta struct {
 func loadPlayerMeta(userID id.UserID) (*PlayerMeta, error) {
 	m := &PlayerMeta{UserID: userID}
 	err := db.Get().QueryRow(
-		`SELECT arena_wins, arena_losses, invasion_score FROM player_meta WHERE user_id = ?`,
+		`SELECT arena_wins, arena_losses, invasion_score, display_name FROM player_meta WHERE user_id = ?`,
 		string(userID),
-	).Scan(&m.ArenaWins, &m.ArenaLosses, &m.InvasionScore)
+	).Scan(&m.ArenaWins, &m.ArenaLosses, &m.InvasionScore, &m.DisplayName)
 	if err == sql.ErrNoRows {
 		return m, nil
 	}
@@ -77,3 +78,80 @@ func backfillPlayerMetaArena() error {
 	slog.Info("player_meta: arena counters backfilled", "rows", n)
 	return nil
 }
+
+// upsertPlayerMetaDisplayName writes display_name for a user, leaving other
+// columns untouched. Used by the dual-write path during the L4f-prep
+// DisplayName migration: every place that mutates AdvCharacter.DisplayName
+// also calls this so player_meta.display_name stays in sync until soak
+// completes and readers flip over (gogobee_legacy_migration.md §7).
+func upsertPlayerMetaDisplayName(userID id.UserID, displayName string) error {
+	_, err := db.Get().Exec(
+		`INSERT INTO player_meta (user_id, display_name) VALUES (?, ?)
+		 ON CONFLICT(user_id) DO UPDATE SET display_name = excluded.display_name`,
+		string(userID), displayName,
+	)
+	return err
+}
+
+// loadDisplayName returns the player's display name from player_meta when
+// present, falling back to adventure_characters.display_name during the
+// L4f-prep soak window. Empty string if the user has no row in either
+// table. Callers should prefer this helper over reading char.DisplayName
+// directly so the eventual reader flip is a no-op at the call site.
+func loadDisplayName(userID id.UserID) (string, error) {
+	var name string
+	err := db.Get().QueryRow(
+		`SELECT display_name FROM player_meta WHERE user_id = ?`,
+		string(userID),
+	).Scan(&name)
+	if err == nil && name != "" {
+		return name, nil
+	}
+	if err != nil && err != sql.ErrNoRows {
+		return "", err
+	}
+	// Fallback during soak.
+	err = db.Get().QueryRow(
+		`SELECT display_name FROM adventure_characters WHERE user_id = ?`,
+		string(userID),
+	).Scan(&name)
+	if err == sql.ErrNoRows {
+		return "", nil
+	}
+	return name, err
+}
+
+// backfillPlayerMetaDisplayName copies adventure_characters.display_name
+// into player_meta.display_name for any row whose display_name is still
+// the empty default. Idempotent: safe to re-run; only updates rows that
+// haven't been populated yet (either by backfill or the dual-write path).
+func backfillPlayerMetaDisplayName() error {
+	// Ensure a player_meta row exists for every adventure_characters user
+	// (arena backfill already does this, but display_name backfill must
+	// not assume order — re-run cheaply via INSERT OR IGNORE).
+	if _, err := db.Get().Exec(`
+		INSERT OR IGNORE INTO player_meta (user_id)
+		SELECT user_id FROM adventure_characters
+	`); err != nil {
+		return err
+	}
+	res, err := db.Get().Exec(`
+		UPDATE player_meta
+		SET display_name = (
+			SELECT display_name FROM adventure_characters
+			WHERE adventure_characters.user_id = player_meta.user_id
+		)
+		WHERE display_name = ''
+		  AND EXISTS (
+			SELECT 1 FROM adventure_characters
+			WHERE adventure_characters.user_id = player_meta.user_id
+			  AND adventure_characters.display_name <> ''
+		  )
+	`)
+	if err != nil {
+		return err
+	}
+	n, _ := res.RowsAffected()
+	slog.Info("player_meta: display_name backfilled", "rows", n)
+	return nil
+}

internal/plugin/player_meta_test.go

@@ -106,3 +106,99 @@ func TestUpsertPlayerMetaArena_RoundTrip(t *testing.T) {
 		t.Errorf("missing user not zero: %+v", mZ)
 	}
 }
+
+// Phase L4f-prep — DisplayName migration. Backfill is idempotent and only
+// touches empty rows; dual-write through createAdvCharacter / saveAdvCharacter
+// stays consistent across re-runs; loadDisplayName falls back to AdvCharacter
+// when player_meta hasn't been populated yet.
+
+func TestPlayerMetaDisplayNameBackfill_Idempotent(t *testing.T) {
+	setupAuditTestDB(t)
+
+	uid := id.UserID("@meta-dn-bf:example")
+	if err := createAdvCharacter(uid, "DisplayedName"); err != nil {
+		t.Fatalf("createAdvCharacter: %v", err)
+	}
+	// Reset player_meta to empty display_name so the backfill has work.
+	if _, err := db.Get().Exec(
+		`UPDATE player_meta SET display_name = '' WHERE user_id = ?`,
+		string(uid),
+	); err != nil {
+		t.Fatalf("clear: %v", err)
+	}
+
+	if err := backfillPlayerMetaDisplayName(); err != nil {
+		t.Fatalf("backfill 1: %v", err)
+	}
+	got, err := loadDisplayName(uid)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	if got != "DisplayedName" {
+		t.Errorf("after backfill: got %q want %q", got, "DisplayedName")
+	}
+
+	// Layer a dual-write rename. Backfill re-run must NOT clobber it back
+	// (it only touches rows with empty display_name).
+	if err := upsertPlayerMetaDisplayName(uid, "Renamed"); err != nil {
+		t.Fatalf("dual-write: %v", err)
+	}
+	if err := backfillPlayerMetaDisplayName(); err != nil {
+		t.Fatalf("backfill 2: %v", err)
+	}
+	got2, _ := loadDisplayName(uid)
+	if got2 != "Renamed" {
+		t.Errorf("backfill clobbered dual-write: got %q want %q", got2, "Renamed")
+	}
+}
+
+func TestLoadDisplayName_FallsBackToAdvCharacter(t *testing.T) {
+	setupAuditTestDB(t)
+
+	uid := id.UserID("@meta-dn-fb:example")
+	if err := createAdvCharacter(uid, "FromAdvChar"); err != nil {
+		t.Fatalf("createAdvCharacter: %v", err)
+	}
+	// Simulate a row that exists in adventure_characters but whose
+	// player_meta display_name hasn't been populated yet (pre-backfill,
+	// pre-dual-write soak case).
+	if _, err := db.Get().Exec(
+		`UPDATE player_meta SET display_name = '' WHERE user_id = ?`,
+		string(uid),
+	); err != nil {
+		t.Fatalf("clear: %v", err)
+	}
+
+	got, err := loadDisplayName(uid)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	if got != "FromAdvChar" {
+		t.Errorf("fallback: got %q want %q", got, "FromAdvChar")
+	}
+
+	// Unknown user → empty string, no error.
+	got2, err := loadDisplayName(id.UserID("@meta-dn-nobody:example"))
+	if err != nil {
+		t.Fatalf("load missing: %v", err)
+	}
+	if got2 != "" {
+		t.Errorf("missing user: got %q want empty", got2)
+	}
+}
+
+func TestCreateAdvCharacter_DualWritesDisplayName(t *testing.T) {
+	setupAuditTestDB(t)
+
+	uid := id.UserID("@meta-dn-create:example")
+	if err := createAdvCharacter(uid, "FreshName"); err != nil {
+		t.Fatalf("createAdvCharacter: %v", err)
+	}
+	got, err := loadDisplayName(uid)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	if got != "FreshName" {
+		t.Errorf("create dual-write: got %q want %q", got, "FreshName")
+	}
+}