fix(server): resolve golangci-lint contextcheck, errcheck, gocritic findings

contextcheck: add ctx context.Context as first param to ListVisibleChannels,
BlockUser, CreateDM, CreateInvite, UpdateProfile, SendMessage; pass r.Context()
from HTTP handlers and ctx from WS handler; replace context.Background() in
telemetry spans with the propagated ctx.

errcheck: suppress justified Close() errors — defer func(){ _ = rows.Close() }()
in sqlite_events.go (idiomatic; rows.Err() checked), _ = resp.Body.Close() in
host_http.go (body fully consumed), _ = f.Close() in host_ui.go (read-only fd).

gocritic/rangeValCopy: rewrite for _, ch := range all (line 60) to indexed loop
in ChannelService.ListVisibleChannels to avoid 144-byte per-iteration copy.

Server/api/channel_handler.go

@@ -76,7 +76,7 @@ func handleListChannels(svc *service.Services) http.HandlerFunc {
 			return
 		}
 
-		channels, err := svc.Channels.ListVisibleChannels(user.ID)
+		channels, err := svc.Channels.ListVisibleChannels(r.Context(), user.ID)
 		if err != nil {
 			slog.Error("handleListChannels", "err", err)
 			writeJSON(w, http.StatusInternalServerError, errorResponse{

Server/api/dm_handler.go

@@ -73,7 +73,7 @@ func handleCreateDM(svc *service.Services) http.HandlerFunc {
 			return
 		}
 
-		result, err := svc.DMs.CreateDM(user.ID, req.RecipientID)
+		result, err := svc.DMs.CreateDM(r.Context(), user.ID, req.RecipientID)
 		if err != nil {
 			writeServiceError(w, err)
 			return
@@ -169,7 +169,7 @@ func handleBlockUser(svc *service.Services) http.HandlerFunc {
 			return
 		}
 
-		if err := svc.Blocks.BlockUser(user.ID, targetID); err != nil {
+		if err := svc.Blocks.BlockUser(r.Context(), user.ID, targetID); err != nil {
 			writeServiceError(w, err)
 			return
 		}

Server/api/invite_handler.go

@@ -73,7 +73,7 @@ func handleCreateInvite(svc *service.Services) http.HandlerFunc {
 			return
 		}
 
-		inv, err := svc.Invites.CreateInvite(user.ID, req.MaxUses, req.ExpiresInHours)
+		inv, err := svc.Invites.CreateInvite(r.Context(), user.ID, req.MaxUses, req.ExpiresInHours)
 		if err != nil {
 			writeServiceError(w, err)
 			return

Server/api/profile_handler.go

@@ -133,7 +133,7 @@ func handleUpdateProfile(svc *service.Services, broadcaster ProfileBroadcaster)
 			req.Avatar = &trimmed
 		}
 
-		updated, err := svc.Users.UpdateProfile(user.ID, req.Username, req.Avatar)
+		updated, err := svc.Users.UpdateProfile(r.Context(), user.ID, req.Username, req.Avatar)
 		if err != nil {
 			writeServiceError(w, err)
 			return

Server/plugin/host_http.go

@@ -120,7 +120,7 @@ func (r *Registry) HTTPDo(ctx context.Context, inst *Instance, req HTTPRequest)
 	if err != nil {
 		return nil, fmt.Errorf("plugin http: do: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	// Cap body size so a hostile/large response cannot OOM the host. We
 	// LimitReader to maxResponseBytes+1 so we can detect truncation.
 	limited := io.LimitReader(resp.Body, maxResponseBytes+1)

Server/plugin/host_ui.go

@@ -98,7 +98,7 @@ func (r *Registry) AssetHandler(inst *Instance) http.Handler {
 			http.NotFound(w, req)
 			return
 		}
-		defer f.Close()
+		defer func() { _ = f.Close() }()
 		http.ServeContent(w, req, rel, info.ModTime(), f)
 	})
 }

Server/service/block.go

@@ -22,8 +22,8 @@ func NewBlockService(st store.Store) *BlockService {
 
 // BlockUser blocks a target user. Validates the target exists and
 // prevents self-blocking.
-func (s *BlockService) BlockUser(blockerID, targetID int64) error {
-	ctx, span := telemetry.GlobalTracer("service/block").Start(context.Background(), "BlockService.BlockUser",
+func (s *BlockService) BlockUser(ctx context.Context, blockerID, targetID int64) error {
+	ctx, span := telemetry.GlobalTracer("service/block").Start(ctx, "BlockService.BlockUser",
 		telemetry.Int64("blocker_id", blockerID),
 		telemetry.Int64("target_id", targetID),
 	)

Server/service/channel.go

@@ -29,9 +29,9 @@ func NewChannelService(st store.Store, perms *PermissionService) *ChannelService
 
 // ListVisibleChannels returns channels the user has ReadMessages permission for.
 // DM channels are excluded (they are accessed via DMService).
-func (s *ChannelService) ListVisibleChannels(userID int64) ([]db.Channel, error) {
+func (s *ChannelService) ListVisibleChannels(ctx context.Context, userID int64) ([]db.Channel, error) {
 	// Phase B Step 8 — span the public service entrypoint.
-	ctx, span := telemetry.GlobalTracer("service/channel").Start(context.Background(),
+	ctx, span := telemetry.GlobalTracer("service/channel").Start(ctx,
 		"ChannelService.ListVisibleChannels",
 		telemetry.Int64("user_id", userID),
 	)
@@ -57,9 +57,9 @@ func (s *ChannelService) ListVisibleChannels(userID int64) ([]db.Channel, error)
 	if isAdmin {
 		// Admin sees all non-DM channels.
 		var visible []db.Channel
-		for _, ch := range all {
-			if ch.Type != "dm" {
-				visible = append(visible, ch)
+		for i := range all {
+			if all[i].Type != "dm" {
+				visible = append(visible, all[i])
 			}
 		}
 		return visible, nil

Server/service/dm.go

@@ -30,8 +30,8 @@ type CreateDMResult struct {
 
 // CreateDM creates or retrieves a DM channel between two users.
 // Validates that neither user has blocked the other.
-func (s *DMService) CreateDM(userID, recipientID int64) (*CreateDMResult, error) {
-	ctx, span := telemetry.GlobalTracer("service/dm").Start(context.Background(), "DMService.CreateDM",
+func (s *DMService) CreateDM(ctx context.Context, userID, recipientID int64) (*CreateDMResult, error) {
+	ctx, span := telemetry.GlobalTracer("service/dm").Start(ctx, "DMService.CreateDM",
 		telemetry.Int64("user_id", userID),
 		telemetry.Int64("recipient_id", recipientID),
 	)

Server/service/invite.go

@@ -27,8 +27,8 @@ const maxInviteExpiryHoursVal = 720
 func MaxInviteExpiryHours() int { return maxInviteExpiryHoursVal }
 
 // CreateInvite creates a new invite code with optional max uses and expiry.
-func (s *InviteService) CreateInvite(createdBy int64, maxUses int, expiresInHours int) (*db.Invite, error) {
-	ctx, span := telemetry.GlobalTracer("service/invite").Start(context.Background(), "InviteService.CreateInvite",
+func (s *InviteService) CreateInvite(ctx context.Context, createdBy int64, maxUses int, expiresInHours int) (*db.Invite, error) {
+	ctx, span := telemetry.GlobalTracer("service/invite").Start(ctx, "InviteService.CreateInvite",
 		telemetry.Int64("created_by", createdBy),
 	)
 	start := time.Now()

Server/service/message.go

@@ -116,10 +116,10 @@ func NewMessageService(st store.Store, perms *PermissionService, limiter *auth.R
 
 // SendMessage validates, persists, and prepares broadcast data for a new message.
 // Callers are responsible for emitting the appropriate events.
-func (s *MessageService) SendMessage(p SendMessageParams) (*SendMessageResult, error) {
+func (s *MessageService) SendMessage(ctx context.Context, p SendMessageParams) (*SendMessageResult, error) {
 	// Phase B Step 8 — wrap the public service entrypoint in a tracing span
 	// and a duration histogram. Both are no-ops in the default build.
-	ctx, span := telemetry.GlobalTracer("service/message").Start(context.Background(), "MessageService.SendMessage",
+	ctx, span := telemetry.GlobalTracer("service/message").Start(ctx, "MessageService.SendMessage",
 		telemetry.Int64("user_id", p.UserID),
 		telemetry.Int64("channel_id", p.ChannelID),
 	)

Server/service/message_test.go

@@ -1,6 +1,7 @@
 package service
 
 import (
+	"context"
 	"errors"
 	"strings"
 	"testing"
@@ -34,7 +35,7 @@ func newTestMessageService() (*MessageService, *store.MemStore) {
 func TestSendMessage_Valid(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -58,7 +59,7 @@ func TestSendMessage_Valid(t *testing.T) {
 func TestSendMessage_EmptyContent(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	_, err := svc.SendMessage(SendMessageParams{
+	_, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -79,7 +80,7 @@ func TestSendMessage_ExceedsMaxLength(t *testing.T) {
 	// maxMessageLen is 4000 runes; create content that exceeds it.
 	longContent := strings.Repeat("a", 4001)
 
-	_, err := svc.SendMessage(SendMessageParams{
+	_, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -97,7 +98,7 @@ func TestSendMessage_ExceedsMaxLength(t *testing.T) {
 func TestSendMessage_ChannelNotFound(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	_, err := svc.SendMessage(SendMessageParams{
+	_, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 999,
 		UserID:    1,
 		Username:  "alice",
@@ -114,7 +115,7 @@ func TestSendMessage_ChannelNotFound(t *testing.T) {
 func TestSendMessage_InvalidChannelID(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	_, err := svc.SendMessage(SendMessageParams{
+	_, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 0,
 		UserID:    1,
 		Username:  "alice",
@@ -145,7 +146,7 @@ func TestSendMessage_NoPermission(t *testing.T) {
 	permSvc := NewPermissionService(ms, checker)
 	svc := NewMessageService(ms, permSvc, nil)
 
-	_, err := svc.SendMessage(SendMessageParams{
+	_, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -163,7 +164,7 @@ func TestEditMessage_OwnerCanEdit(t *testing.T) {
 	svc, _ := newTestMessageService()
 
 	// Send a message first.
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -192,7 +193,7 @@ func TestEditMessage_NonOwnerFails(t *testing.T) {
 	ms.SeedUser(&db.User{ID: 2, Username: "bob"})
 
 	// User 1 sends a message.
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -215,7 +216,7 @@ func TestEditMessage_NonOwnerFails(t *testing.T) {
 func TestEditMessage_EmptyContentFails(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -237,7 +238,7 @@ func TestEditMessage_EmptyContentFails(t *testing.T) {
 func TestDeleteMessage_OwnerCanDelete(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -265,7 +266,7 @@ func TestDeleteMessage_NonOwnerWithoutModFails(t *testing.T) {
 	ms.SeedUser(&db.User{ID: 2, Username: "bob"})
 
 	// User 1 sends.
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -312,7 +313,7 @@ func TestDeleteMessage_ModCanDeleteOthersMessage(t *testing.T) {
 	svc := NewMessageService(ms, permSvc, nil)
 
 	// User 1 sends a message.
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",
@@ -347,7 +348,7 @@ func TestDeleteMessage_InvalidMessageID(t *testing.T) {
 func TestSendMessage_HTMLSanitized(t *testing.T) {
 	svc, _ := newTestMessageService()
 
-	result, err := svc.SendMessage(SendMessageParams{
+	result, err := svc.SendMessage(context.Background(), SendMessageParams{
 		ChannelID: 10,
 		UserID:    1,
 		Username:  "alice",

Server/service/user.go

@@ -24,8 +24,8 @@ func NewUserService(st store.Store) *UserService {
 
 // UpdateProfile updates a user's username and/or avatar.
 // Returns the updated user for response building.
-func (s *UserService) UpdateProfile(userID int64, username string, avatar *string) (*db.User, error) {
-	ctx, span := telemetry.GlobalTracer("service/user").Start(context.Background(), "UserService.UpdateProfile",
+func (s *UserService) UpdateProfile(ctx context.Context, userID int64, username string, avatar *string) (*db.User, error) {
+	ctx, span := telemetry.GlobalTracer("service/user").Start(ctx, "UserService.UpdateProfile",
 		telemetry.Int64("user_id", userID),
 	)
 	start := time.Now()

Server/store/sqlite_events.go

@@ -40,7 +40,7 @@ func (s *SQLiteStore) GetEventsSince(ctx context.Context, afterSeq int64, limit
 	if err != nil {
 		return nil, fmt.Errorf("GetEventsSince: %w", err)
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 	return scanEventRows(rows)
 }
 
@@ -61,7 +61,7 @@ func (s *SQLiteStore) GetEventsSinceForChannels(ctx context.Context, afterSeq in
 		if err != nil {
 			return nil, fmt.Errorf("GetEventsSinceForChannels (global only): %w", err)
 		}
-		defer rows.Close()
+		defer func() { _ = rows.Close() }()
 		return scanEventRows(rows)
 	}
 
@@ -87,7 +87,7 @@ func (s *SQLiteStore) GetEventsSinceForChannels(ctx context.Context, afterSeq in
 	if err != nil {
 		return nil, fmt.Errorf("GetEventsSinceForChannels: %w", err)
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 	return scanEventRows(rows)
 }
 
@@ -180,7 +180,7 @@ func (s *SQLiteStore) ListPlugins(ctx context.Context) ([]db.PluginRow, error) {
 	if err != nil {
 		return nil, fmt.Errorf("ListPlugins: %w", err)
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 	var out []db.PluginRow
 	for rows.Next() {
 		var p db.PluginRow
@@ -233,7 +233,7 @@ func (s *SQLiteStore) PluginKVScan(ctx context.Context, pluginID int64, prefix s
 	if err != nil {
 		return nil, fmt.Errorf("PluginKVScan: %w", err)
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 	out := make(map[string][]byte)
 	for rows.Next() {
 		var k string

Server/ws/handlers_chat.go

@@ -15,11 +15,11 @@ func registerChatHandlers(r *HandlerRegistry, deps ChatDeps) {
 }
 
 // handleChatSendV2 processes a chat_send command via the MessageService.
-func handleChatSendV2(_ context.Context, cmd Command, info ClientInfo, deps any) Result {
+func handleChatSendV2(ctx context.Context, cmd Command, info ClientInfo, deps any) Result {
 	d := deps.(ChatDeps)
 	sendCmd := cmd.(ChatSendCmd)
 
-	result, err := d.MessageSvc.SendMessage(service.SendMessageParams{
+	result, err := d.MessageSvc.SendMessage(ctx, service.SendMessageParams{
 		ChannelID:     sendCmd.ChannelID(),
 		UserID:        info.UserID,
 		Username:      info.Username,