feat: implement Tier 2 channel modes (+b/+i/+s/+k/+l) (#92)

## Summary

Implements the second tier of IRC channel features as described in [#86](#86).

## Features

### 1. Ban System (+b)
- `channel_bans` table with mask, set_by, created_at
- Add/remove/list bans via MODE +b/-b
- Wildcard matching (`*!*@*.example.com`, `badnick!*@*`, etc.)
- Ban enforcement on both JOIN and PRIVMSG
- RPL_BANLIST (367) / RPL_ENDOFBANLIST (368) for ban listing

### 2. Invite-Only (+i)
- `is_invite_only` column on channels table
- INVITE command: operators can invite users
- `channel_invites` table tracks pending invites
- Invites consumed on successful JOIN
- ERR_INVITEONLYCHAN (473) for uninvited JOIN attempts

### 3. Secret (+s)
- `is_secret` column on channels table
- Secret channels hidden from LIST for non-members
- Secret channels hidden from WHOIS channel list for non-members

### 4. Channel Key (+k)
- `channel_key` column on channels table
- MODE +k sets key, MODE -k clears it
- Key required on JOIN (`JOIN #channel key`)
- ERR_BADCHANNELKEY (475) for wrong/missing key

### 5. User Limit (+l)
- `user_limit` column on channels table (0 = no limit)
- MODE +l sets limit, MODE -l removes it
- ERR_CHANNELISFULL (471) when limit reached

## ISUPPORT Changes
- CHANMODES updated to `b,k,Hl,imnst`
- RPL_MYINFO modes updated to `ikmnostl`

## Tests

### Database-level tests:
- Wildcard matching (10 patterns)
- Ban CRUD operations
- Session ban checking
- Invite-only flag toggle
- Invite CRUD + clearing
- Secret channel filtering (LIST and WHOIS)
- Channel key set/get/clear
- User limit set/get/clear

### Handler-level tests:
- Ban add/remove/list via MODE
- Ban blocks JOIN
- Ban blocks PRIVMSG
- Invite-only JOIN rejection + INVITE acceptance
- Secret channel hidden from LIST
- Channel key required on JOIN
- User limit enforcement
- Mode string includes new modes
- ISUPPORT updated CHANMODES
- Non-operators cannot set any Tier 2 modes

## Schema Changes
- Added `is_invite_only`, `is_secret`, `channel_key`, `user_limit` to `channels` table
- Added `channel_bans` table
- Added `channel_invites` table
- All changes in `001_initial.sql` (pre-1.0.0 repo)

closes #86

Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: #92
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/db/queries.go

@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strconv"
+	"strings"
 	"time"
 
 	"git.eeqj.de/sneak/neoirc/pkg/irc"
@@ -1835,3 +1836,534 @@ func (database *Database) PruneSpentHashcash(
 
 	return deleted, nil
 }
+
+// --- Tier 2: Ban system (+b) ---
+
+// BanInfo represents a channel ban entry.
+type BanInfo struct {
+	Mask      string
+	SetBy     string
+	CreatedAt time.Time
+}
+
+// AddChannelBan inserts a ban mask for a channel.
+func (database *Database) AddChannelBan(
+	ctx context.Context,
+	channelID int64,
+	mask, setBy string,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`INSERT OR IGNORE INTO channel_bans
+		 (channel_id, mask, set_by, created_at)
+		 VALUES (?, ?, ?, ?)`,
+		channelID, mask, setBy, time.Now())
+	if err != nil {
+		return fmt.Errorf("add channel ban: %w", err)
+	}
+
+	return nil
+}
+
+// RemoveChannelBan removes a ban mask from a channel.
+func (database *Database) RemoveChannelBan(
+	ctx context.Context,
+	channelID int64,
+	mask string,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`DELETE FROM channel_bans
+		 WHERE channel_id = ? AND mask = ?`,
+		channelID, mask)
+	if err != nil {
+		return fmt.Errorf("remove channel ban: %w", err)
+	}
+
+	return nil
+}
+
+// ListChannelBans returns all bans for a channel.
+//
+//nolint:dupl // different query+type vs filtered variant
+func (database *Database) ListChannelBans(
+	ctx context.Context,
+	channelID int64,
+) ([]BanInfo, error) {
+	rows, err := database.conn.QueryContext(ctx,
+		`SELECT mask, set_by, created_at
+		 FROM channel_bans
+		 WHERE channel_id = ?
+		 ORDER BY created_at ASC`,
+		channelID)
+	if err != nil {
+		return nil, fmt.Errorf("list channel bans: %w", err)
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	var bans []BanInfo
+
+	for rows.Next() {
+		var ban BanInfo
+
+		if scanErr := rows.Scan(
+			&ban.Mask, &ban.SetBy, &ban.CreatedAt,
+		); scanErr != nil {
+			return nil, fmt.Errorf(
+				"scan channel ban: %w", scanErr,
+			)
+		}
+
+		bans = append(bans, ban)
+	}
+
+	if rowErr := rows.Err(); rowErr != nil {
+		return nil, fmt.Errorf(
+			"iterate channel bans: %w", rowErr,
+		)
+	}
+
+	return bans, nil
+}
+
+// IsSessionBanned checks if a session's hostmask matches
+// any ban in the channel. Returns true if banned.
+func (database *Database) IsSessionBanned(
+	ctx context.Context,
+	channelID, sessionID int64,
+) (bool, error) {
+	// Get the session's hostmask parts.
+	var nick, username, hostname string
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT nick, username, hostname
+		 FROM sessions WHERE id = ?`,
+		sessionID,
+	).Scan(&nick, &username, &hostname)
+	if err != nil {
+		return false, fmt.Errorf(
+			"get session hostmask: %w", err,
+		)
+	}
+
+	hostmask := FormatHostmask(nick, username, hostname)
+
+	// Get all ban masks for the channel.
+	bans, banErr := database.ListChannelBans(ctx, channelID)
+	if banErr != nil {
+		return false, banErr
+	}
+
+	for _, ban := range bans {
+		if MatchBanMask(ban.Mask, hostmask) {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+// MatchBanMask checks if hostmask matches a ban pattern
+// using IRC-style wildcard matching (* and ?).
+func MatchBanMask(pattern, hostmask string) bool {
+	return wildcardMatch(
+		strings.ToLower(pattern),
+		strings.ToLower(hostmask),
+	)
+}
+
+// wildcardMatch implements simple glob-style matching
+// with * (any sequence) and ? (any single character).
+func wildcardMatch(pattern, str string) bool {
+	for len(pattern) > 0 {
+		switch pattern[0] {
+		case '*':
+			// Skip consecutive asterisks.
+			for len(pattern) > 0 && pattern[0] == '*' {
+				pattern = pattern[1:]
+			}
+
+			if len(pattern) == 0 {
+				return true
+			}
+
+			for i := 0; i <= len(str); i++ {
+				if wildcardMatch(pattern, str[i:]) {
+					return true
+				}
+			}
+
+			return false
+		case '?':
+			if len(str) == 0 {
+				return false
+			}
+
+			pattern = pattern[1:]
+			str = str[1:]
+		default:
+			if len(str) == 0 || pattern[0] != str[0] {
+				return false
+			}
+
+			pattern = pattern[1:]
+			str = str[1:]
+		}
+	}
+
+	return len(str) == 0
+}
+
+// --- Tier 2: Invite-only (+i) ---
+
+// IsChannelInviteOnly checks if a channel has +i mode.
+func (database *Database) IsChannelInviteOnly(
+	ctx context.Context,
+	channelID int64,
+) (bool, error) {
+	var isInviteOnly int
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT is_invite_only FROM channels
+		 WHERE id = ?`,
+		channelID,
+	).Scan(&isInviteOnly)
+	if err != nil {
+		return false, fmt.Errorf(
+			"check invite only: %w", err,
+		)
+	}
+
+	return isInviteOnly != 0, nil
+}
+
+// SetChannelInviteOnly sets or unsets +i mode.
+func (database *Database) SetChannelInviteOnly(
+	ctx context.Context,
+	channelID int64,
+	inviteOnly bool,
+) error {
+	val := 0
+	if inviteOnly {
+		val = 1
+	}
+
+	_, err := database.conn.ExecContext(ctx,
+		`UPDATE channels
+		 SET is_invite_only = ?, updated_at = ?
+		 WHERE id = ?`,
+		val, time.Now(), channelID)
+	if err != nil {
+		return fmt.Errorf(
+			"set invite only: %w", err,
+		)
+	}
+
+	return nil
+}
+
+// AddChannelInvite records that a session has been
+// invited to a channel.
+func (database *Database) AddChannelInvite(
+	ctx context.Context,
+	channelID, sessionID int64,
+	invitedBy string,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`INSERT OR IGNORE INTO channel_invites
+		 (channel_id, session_id, invited_by, created_at)
+		 VALUES (?, ?, ?, ?)`,
+		channelID, sessionID, invitedBy, time.Now())
+	if err != nil {
+		return fmt.Errorf("add channel invite: %w", err)
+	}
+
+	return nil
+}
+
+// HasChannelInvite checks if a session has been invited
+// to a channel.
+func (database *Database) HasChannelInvite(
+	ctx context.Context,
+	channelID, sessionID int64,
+) (bool, error) {
+	var count int
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT COUNT(*) FROM channel_invites
+		 WHERE channel_id = ? AND session_id = ?`,
+		channelID, sessionID,
+	).Scan(&count)
+	if err != nil {
+		return false, fmt.Errorf(
+			"check invite: %w", err,
+		)
+	}
+
+	return count > 0, nil
+}
+
+// ClearChannelInvite removes a session's invite to a
+// channel (called after successful JOIN).
+func (database *Database) ClearChannelInvite(
+	ctx context.Context,
+	channelID, sessionID int64,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`DELETE FROM channel_invites
+		 WHERE channel_id = ? AND session_id = ?`,
+		channelID, sessionID)
+	if err != nil {
+		return fmt.Errorf("clear invite: %w", err)
+	}
+
+	return nil
+}
+
+// --- Tier 2: Secret (+s) ---
+
+// IsChannelSecret checks if a channel has +s mode.
+func (database *Database) IsChannelSecret(
+	ctx context.Context,
+	channelID int64,
+) (bool, error) {
+	var isSecret int
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT is_secret FROM channels
+		 WHERE id = ?`,
+		channelID,
+	).Scan(&isSecret)
+	if err != nil {
+		return false, fmt.Errorf(
+			"check secret: %w", err,
+		)
+	}
+
+	return isSecret != 0, nil
+}
+
+// SetChannelSecret sets or unsets +s mode.
+func (database *Database) SetChannelSecret(
+	ctx context.Context,
+	channelID int64,
+	secret bool,
+) error {
+	val := 0
+	if secret {
+		val = 1
+	}
+
+	_, err := database.conn.ExecContext(ctx,
+		`UPDATE channels
+		 SET is_secret = ?, updated_at = ?
+		 WHERE id = ?`,
+		val, time.Now(), channelID)
+	if err != nil {
+		return fmt.Errorf("set secret: %w", err)
+	}
+
+	return nil
+}
+
+// ListAllChannelsWithCountsFiltered returns all channels
+// with member counts, excluding secret channels that
+// the given session is not a member of.
+//
+//nolint:dupl // different query+type vs ListChannelBans
+func (database *Database) ListAllChannelsWithCountsFiltered(
+	ctx context.Context,
+	sessionID int64,
+) ([]ChannelInfoFull, error) {
+	rows, err := database.conn.QueryContext(ctx,
+		`SELECT c.name, COUNT(cm.id) AS member_count,
+		        c.topic
+		 FROM channels c
+		 LEFT JOIN channel_members cm
+		   ON cm.channel_id = c.id
+		 WHERE c.is_secret = 0
+		    OR c.id IN (
+		       SELECT channel_id FROM channel_members
+		       WHERE session_id = ?
+		    )
+		 GROUP BY c.id
+		 ORDER BY c.name ASC`,
+		sessionID)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"list channels filtered: %w", err,
+		)
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	var channels []ChannelInfoFull
+
+	for rows.Next() {
+		var chanInfo ChannelInfoFull
+
+		if scanErr := rows.Scan(
+			&chanInfo.Name,
+			&chanInfo.MemberCount,
+			&chanInfo.Topic,
+		); scanErr != nil {
+			return nil, fmt.Errorf(
+				"scan channel: %w", scanErr,
+			)
+		}
+
+		channels = append(channels, chanInfo)
+	}
+
+	if rowErr := rows.Err(); rowErr != nil {
+		return nil, fmt.Errorf(
+			"iterate channels: %w", rowErr,
+		)
+	}
+
+	return channels, nil
+}
+
+// GetSessionChannelsFiltered returns channels a session
+// belongs to, optionally excluding secret channels for
+// WHOIS (when the querier is not in the same channel).
+// If querierID == targetID, returns all channels.
+func (database *Database) GetSessionChannelsFiltered(
+	ctx context.Context,
+	targetSID, querierSID int64,
+) ([]ChannelInfo, error) {
+	// If querying yourself, return all channels.
+	if targetSID == querierSID {
+		return database.GetSessionChannels(ctx, targetSID)
+	}
+
+	rows, err := database.conn.QueryContext(ctx,
+		`SELECT c.id, c.name, c.topic
+		 FROM channels c
+		 JOIN channel_members cm
+		   ON cm.channel_id = c.id
+		 WHERE cm.session_id = ?
+		   AND (c.is_secret = 0
+		        OR c.id IN (
+		           SELECT channel_id FROM channel_members
+		           WHERE session_id = ?
+		        ))
+		 ORDER BY c.name ASC`,
+		targetSID, querierSID)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"get session channels filtered: %w", err,
+		)
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	var channels []ChannelInfo
+
+	for rows.Next() {
+		var chanInfo ChannelInfo
+
+		if scanErr := rows.Scan(
+			&chanInfo.ID,
+			&chanInfo.Name,
+			&chanInfo.Topic,
+		); scanErr != nil {
+			return nil, fmt.Errorf(
+				"scan channel: %w", scanErr,
+			)
+		}
+
+		channels = append(channels, chanInfo)
+	}
+
+	if rowErr := rows.Err(); rowErr != nil {
+		return nil, fmt.Errorf(
+			"iterate channels: %w", rowErr,
+		)
+	}
+
+	return channels, nil
+}
+
+// --- Tier 2: Channel Key (+k) ---
+
+// GetChannelKey returns the key for a channel (empty
+// string means no key set).
+func (database *Database) GetChannelKey(
+	ctx context.Context,
+	channelID int64,
+) (string, error) {
+	var key string
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT channel_key FROM channels
+		 WHERE id = ?`,
+		channelID,
+	).Scan(&key)
+	if err != nil {
+		return "", fmt.Errorf("get channel key: %w", err)
+	}
+
+	return key, nil
+}
+
+// SetChannelKey sets or clears the key for a channel.
+func (database *Database) SetChannelKey(
+	ctx context.Context,
+	channelID int64,
+	key string,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`UPDATE channels
+		 SET channel_key = ?, updated_at = ?
+		 WHERE id = ?`,
+		key, time.Now(), channelID)
+	if err != nil {
+		return fmt.Errorf("set channel key: %w", err)
+	}
+
+	return nil
+}
+
+// --- Tier 2: User Limit (+l) ---
+
+// GetChannelUserLimit returns the user limit for a
+// channel (0 means no limit).
+func (database *Database) GetChannelUserLimit(
+	ctx context.Context,
+	channelID int64,
+) (int, error) {
+	var limit int
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT user_limit FROM channels
+		 WHERE id = ?`,
+		channelID,
+	).Scan(&limit)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"get channel user limit: %w", err,
+		)
+	}
+
+	return limit, nil
+}
+
+// SetChannelUserLimit sets the user limit for a channel.
+func (database *Database) SetChannelUserLimit(
+	ctx context.Context,
+	channelID int64,
+	limit int,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`UPDATE channels
+		 SET user_limit = ?, updated_at = ?
+		 WHERE id = ?`,
+		limit, time.Now(), channelID)
+	if err != nil {
+		return fmt.Errorf(
+			"set channel user limit: %w", err,
+		)
+	}
+
+	return nil
+}

internal/db/queries_test.go

@@ -1017,3 +1017,474 @@ func TestGetOperCount(t *testing.T) {
 		t.Fatalf("expected 1 oper, got %d", count)
 	}
 }
+
+// --- Tier 2 Tests ---
+
+func TestWildcardMatch(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		pattern string
+		input   string
+		match   bool
+	}{
+		{"*!*@*", "nick!user@host", true},
+		{"*!*@*.example.com", "nick!user@foo.example.com", true},
+		{"*!*@*.example.com", "nick!user@other.net", false},
+		{"badnick!*@*", "badnick!user@host", true},
+		{"badnick!*@*", "goodnick!user@host", false},
+		{"nick!user@host", "nick!user@host", true},
+		{"nick!user@host", "nick!user@other", false},
+		{"*", "anything", true},
+		{"?ick!*@*", "nick!user@host", true},
+		{"?ick!*@*", "nn!user@host", false},
+		// Case-insensitive.
+		{"Nick!*@*", "nick!user@host", true},
+	}
+
+	for _, tc := range tests {
+		result := db.MatchBanMask(tc.pattern, tc.input)
+		if result != tc.match {
+			t.Errorf(
+				"MatchBanMask(%q, %q) = %v, want %v",
+				tc.pattern, tc.input, result, tc.match,
+			)
+		}
+	}
+}
+
+func TestChannelBanCRUD(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	chID, err := database.GetOrCreateChannel(ctx, "#test")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// No bans initially.
+	bans, err := database.ListChannelBans(ctx, chID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(bans) != 0 {
+		t.Fatalf("expected 0 bans, got %d", len(bans))
+	}
+
+	// Add a ban.
+	err = database.AddChannelBan(
+		ctx, chID, "*!*@evil.com", "op",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bans, err = database.ListChannelBans(ctx, chID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(bans) != 1 {
+		t.Fatalf("expected 1 ban, got %d", len(bans))
+	}
+
+	if bans[0].Mask != "*!*@evil.com" {
+		t.Fatalf("wrong mask: %s", bans[0].Mask)
+	}
+
+	// Duplicate add is ignored (OR IGNORE).
+	err = database.AddChannelBan(
+		ctx, chID, "*!*@evil.com", "op2",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bans, _ = database.ListChannelBans(ctx, chID)
+	if len(bans) != 1 {
+		t.Fatalf("expected 1 ban after dup, got %d", len(bans))
+	}
+
+	// Remove ban.
+	err = database.RemoveChannelBan(
+		ctx, chID, "*!*@evil.com",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bans, _ = database.ListChannelBans(ctx, chID)
+	if len(bans) != 0 {
+		t.Fatalf("expected 0 bans after remove, got %d", len(bans))
+	}
+}
+
+func TestIsSessionBanned(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	sid, _, _, err := database.CreateSession(
+		ctx, "victim", "victim", "evil.com", "",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chID, err := database.GetOrCreateChannel(ctx, "#bantest")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Not banned initially.
+	banned, err := database.IsSessionBanned(ctx, chID, sid)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if banned {
+		t.Fatal("should not be banned initially")
+	}
+
+	// Add ban matching the hostmask.
+	err = database.AddChannelBan(
+		ctx, chID, "*!*@evil.com", "op",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	banned, err = database.IsSessionBanned(ctx, chID, sid)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !banned {
+		t.Fatal("should be banned")
+	}
+}
+
+func TestChannelInviteOnly(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	chID, err := database.GetOrCreateChannel(ctx, "#invite")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Default: not invite-only.
+	isIO, err := database.IsChannelInviteOnly(ctx, chID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if isIO {
+		t.Fatal("should not be invite-only by default")
+	}
+
+	// Set invite-only.
+	err = database.SetChannelInviteOnly(ctx, chID, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	isIO, _ = database.IsChannelInviteOnly(ctx, chID)
+	if !isIO {
+		t.Fatal("should be invite-only")
+	}
+
+	// Unset.
+	err = database.SetChannelInviteOnly(ctx, chID, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	isIO, _ = database.IsChannelInviteOnly(ctx, chID)
+	if isIO {
+		t.Fatal("should not be invite-only")
+	}
+}
+
+func TestChannelInviteCRUD(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	sid, _, _, err := database.CreateSession(
+		ctx, "invited", "", "", "",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chID, err := database.GetOrCreateChannel(ctx, "#inv")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// No invite initially.
+	has, err := database.HasChannelInvite(ctx, chID, sid)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if has {
+		t.Fatal("should not have invite")
+	}
+
+	// Add invite.
+	err = database.AddChannelInvite(ctx, chID, sid, "op")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	has, _ = database.HasChannelInvite(ctx, chID, sid)
+	if !has {
+		t.Fatal("should have invite")
+	}
+
+	// Clear invite.
+	err = database.ClearChannelInvite(ctx, chID, sid)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	has, _ = database.HasChannelInvite(ctx, chID, sid)
+	if has {
+		t.Fatal("invite should be cleared")
+	}
+}
+
+func TestChannelSecret(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	chID, err := database.GetOrCreateChannel(ctx, "#secret")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Default: not secret.
+	isSec, err := database.IsChannelSecret(ctx, chID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if isSec {
+		t.Fatal("should not be secret by default")
+	}
+
+	err = database.SetChannelSecret(ctx, chID, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	isSec, _ = database.IsChannelSecret(ctx, chID)
+	if !isSec {
+		t.Fatal("should be secret")
+	}
+}
+
+// createTestSession is a helper to create a session and
+// return only the session ID.
+func createTestSession(
+	t *testing.T,
+	database *db.Database,
+	nick string,
+) int64 {
+	t.Helper()
+
+	sid, _, _, err := database.CreateSession(
+		t.Context(), nick, "", "", "",
+	)
+	if err != nil {
+		t.Fatalf("create session %s: %v", nick, err)
+	}
+
+	return sid
+}
+
+func TestSecretChannelFiltering(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	// Create two sessions.
+	sid1 := createTestSession(t, database, "member")
+	sid2 := createTestSession(t, database, "outsider")
+
+	// Create a secret channel.
+	chID, _ := database.GetOrCreateChannel(ctx, "#secret")
+	_ = database.SetChannelSecret(ctx, chID, true)
+	_ = database.JoinChannel(ctx, chID, sid1)
+
+	// Create a non-secret channel.
+	chID2, _ := database.GetOrCreateChannel(ctx, "#public")
+	_ = database.JoinChannel(ctx, chID2, sid1)
+
+	// Member should see both.
+	list, err := database.ListAllChannelsWithCountsFiltered(
+		ctx, sid1,
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(list) != 2 {
+		t.Fatalf("member should see 2 channels, got %d", len(list))
+	}
+
+	// Outsider should only see public.
+	list, _ = database.ListAllChannelsWithCountsFiltered(
+		ctx, sid2,
+	)
+	if len(list) != 1 {
+		t.Fatalf("outsider should see 1 channel, got %d", len(list))
+	}
+
+	if list[0].Name != "#public" {
+		t.Fatalf("outsider should see #public, got %s", list[0].Name)
+	}
+}
+
+func TestWhoisChannelFiltering(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	sid1 := createTestSession(t, database, "target")
+	sid2 := createTestSession(t, database, "querier")
+
+	// Create secret channel, target joins it.
+	chID, _ := database.GetOrCreateChannel(ctx, "#hidden")
+	_ = database.SetChannelSecret(ctx, chID, true)
+	_ = database.JoinChannel(ctx, chID, sid1)
+
+	// Querier (non-member) should not see the channel.
+	channels, err := database.GetSessionChannelsFiltered(
+		ctx, sid1, sid2,
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(channels) != 0 {
+		t.Fatalf(
+			"querier should see 0 channels, got %d",
+			len(channels),
+		)
+	}
+
+	// Target querying self should see it.
+	channels, _ = database.GetSessionChannelsFiltered(
+		ctx, sid1, sid1,
+	)
+	if len(channels) != 1 {
+		t.Fatalf(
+			"self-query should see 1 channel, got %d",
+			len(channels),
+		)
+	}
+}
+
+//nolint:dupl // structurally similar to TestChannelUserLimit
+func TestChannelKey(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	chID, err := database.GetOrCreateChannel(ctx, "#keyed")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Default: no key.
+	key, err := database.GetChannelKey(ctx, chID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if key != "" {
+		t.Fatalf("expected empty key, got %q", key)
+	}
+
+	// Set key.
+	err = database.SetChannelKey(ctx, chID, "secret123")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	key, _ = database.GetChannelKey(ctx, chID)
+	if key != "secret123" {
+		t.Fatalf("expected secret123, got %q", key)
+	}
+
+	// Clear key.
+	err = database.SetChannelKey(ctx, chID, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	key, _ = database.GetChannelKey(ctx, chID)
+	if key != "" {
+		t.Fatalf("expected empty key, got %q", key)
+	}
+}
+
+//nolint:dupl // structurally similar to TestChannelKey
+func TestChannelUserLimit(t *testing.T) {
+	t.Parallel()
+
+	database := setupTestDB(t)
+	ctx := t.Context()
+
+	chID, err := database.GetOrCreateChannel(ctx, "#limited")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Default: no limit.
+	limit, err := database.GetChannelUserLimit(ctx, chID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if limit != 0 {
+		t.Fatalf("expected 0 limit, got %d", limit)
+	}
+
+	// Set limit.
+	err = database.SetChannelUserLimit(ctx, chID, 50)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	limit, _ = database.GetChannelUserLimit(ctx, chID)
+	if limit != 50 {
+		t.Fatalf("expected 50, got %d", limit)
+	}
+
+	// Clear limit.
+	err = database.SetChannelUserLimit(ctx, chID, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	limit, _ = database.GetChannelUserLimit(ctx, chID)
+	if limit != 0 {
+		t.Fatalf("expected 0, got %d", limit)
+	}
+}

internal/db/schema/001_initial.sql

@@ -42,10 +42,36 @@ CREATE TABLE IF NOT EXISTS channels (
     hashcash_bits INTEGER NOT NULL DEFAULT 0,
     is_moderated INTEGER NOT NULL DEFAULT 0,
     is_topic_locked INTEGER NOT NULL DEFAULT 1,
+    is_invite_only INTEGER NOT NULL DEFAULT 0,
+    is_secret INTEGER NOT NULL DEFAULT 0,
+    channel_key TEXT NOT NULL DEFAULT '',
+    user_limit INTEGER NOT NULL DEFAULT 0,
     created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
+-- Channel bans
+CREATE TABLE IF NOT EXISTS channel_bans (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    channel_id INTEGER NOT NULL REFERENCES channels(id) ON DELETE CASCADE,
+    mask TEXT NOT NULL,
+    set_by TEXT NOT NULL,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    UNIQUE(channel_id, mask)
+);
+CREATE INDEX IF NOT EXISTS idx_channel_bans_channel ON channel_bans(channel_id);
+
+-- Channel invites (in-memory would be simpler but DB survives restarts)
+CREATE TABLE IF NOT EXISTS channel_invites (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    channel_id INTEGER NOT NULL REFERENCES channels(id) ON DELETE CASCADE,
+    session_id INTEGER NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
+    invited_by TEXT NOT NULL DEFAULT '',
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    UNIQUE(channel_id, session_id)
+);
+CREATE INDEX IF NOT EXISTS idx_channel_invites_channel ON channel_invites(channel_id);
+
 -- Channel members
 CREATE TABLE IF NOT EXISTS channel_members (
     id INTEGER PRIMARY KEY AUTOINCREMENT,