fix: resolve 43 lint findings blocking CI

- server.go: drop unused (*Server).serve int return (unparam) and
  remove the dead exitCode field so cleanShutdown no longer writes
  to a field nothing reads.
- service.go: rename range var ch -> modeChar in parseUserModeString
  and the isKnownUserModeChar parameter (varnamelen).
- service_test.go: rename tc -> testCase (varnamelen); lift the
  inline struct and caseState to package-level named types
  (applyUserModeCase, applyUserModeCaseState) with every field
  set explicitly (exhaustruct); split the 167-line case table into
  four categorised helpers (funlen); extract the per-case runner
  and outcome/state verifiers into helpers so TestApplyUserMode
  drops below gocognit 30 and flattens the wantErr nestif block.

No changes to .golangci.yml, Makefile, Dockerfile, or CI config.
No //nolint was used to silence any of these findings.

docker build --no-cache . passes clean: 0 lint issues, all tests
pass with -race, binary compiles.

internal/server/server.go

@@ -45,7 +45,6 @@ type Params struct {
 // It manages routing, middleware, and lifecycle.
 type Server struct {
 	startupTime   time.Time
-	exitCode      int
 	sentryEnabled bool
 	log           *slog.Logger
 	ctx           context.Context //nolint:containedctx // signal handling pattern
@@ -143,7 +142,7 @@ func (srv *Server) enableSentry() {
 	srv.sentryEnabled = true
 }
 
-func (srv *Server) serve() int {
+func (srv *Server) serve() {
 	srv.ctx, srv.cancelFunc = context.WithCancel(
 		context.Background(),
 	)
@@ -168,8 +167,6 @@ func (srv *Server) serve() int {
 	<-srv.ctx.Done()
 
 	srv.cleanShutdown()
-
-	return srv.exitCode
 }
 
 func (srv *Server) cleanupForExit() {
@@ -177,8 +174,6 @@ func (srv *Server) cleanupForExit() {
 }
 
 func (srv *Server) cleanShutdown() {
-	srv.exitCode = 0
-
 	ctxShutdown, shutdownCancel := context.WithTimeout(
 		context.Background(), shutdownTimeout,
 	)

internal/service/service.go

@@ -880,23 +880,23 @@ func parseUserModeString(
 	ops := make([]userModeOp, 0, len(modeStr)-1)
 	adding := true
 
-	for _, ch := range modeStr {
-		switch ch {
+	for _, modeChar := range modeStr {
+		switch modeChar {
 		case '+':
 			adding = true
 		case '-':
 			adding = false
 		default:
-			if !isKnownUserModeChar(ch) {
+			if !isKnownUserModeChar(modeChar) {
 				return nil, unknownFlag
 			}
 
-			if ch == 'o' && adding {
+			if modeChar == 'o' && adding {
 				return nil, unknownFlag
 			}
 
 			ops = append(ops, userModeOp{
-				char: ch, adding: adding,
+				char: modeChar, adding: adding,
 			})
 		}
 	}
@@ -910,8 +910,8 @@ func parseUserModeString(
 
 // isKnownUserModeChar reports whether the character is a
 // recognized user mode letter.
-func isKnownUserModeChar(ch rune) bool {
-	switch ch {
+func isKnownUserModeChar(modeChar rune) bool {
+	switch modeChar {
 	case 'w', 'o':
 		return true
 	default:

internal/service/service_test.go

@@ -393,6 +393,248 @@ func TestQueryUserMode(t *testing.T) {
 	}
 }
 
+// applyUserModeCaseState is the subset of session user-mode
+// state the rigorous TestApplyUserMode suite asserts on. It
+// mirrors the columns (oper, wallops) that the parser is
+// permitted to mutate.
+type applyUserModeCaseState struct {
+	oper    bool
+	wallops bool
+}
+
+// applyUserModeCase describes one rigor-suite case for
+// Service.ApplyUserMode: the pre-call DB state, the mode
+// string input, and the expected post-call observable state
+// (mode string on success, IRC error code on rejection, and
+// persisted session state either way).
+type applyUserModeCase struct {
+	name         string
+	initialState applyUserModeCaseState
+	modeStr      string
+	wantModes    string
+	wantErr      bool
+	wantErrCode  irc.IRCMessageType
+	wantState    applyUserModeCaseState
+}
+
+// applyUserModeCases returns every case listed in sneak's
+// review of PR #96 plus a few adjacent ones. Split across
+// helpers by category so each stays under funlen.
+func applyUserModeCases() []applyUserModeCase {
+	cases := applyUserModeHappyPathCases()
+	cases = append(cases, applyUserModeSignTransitionCases()...)
+	cases = append(cases, applyUserModeMalformedCases()...)
+	cases = append(cases, applyUserModeUnknownLetterCases()...)
+
+	return cases
+}
+
+// applyUserModeHappyPathCases covers valid single-char and
+// multi-char-without-sign-transition mode operations.
+func applyUserModeHappyPathCases() []applyUserModeCase {
+	return []applyUserModeCase{
+		{
+			name:         "+w from empty",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+w",
+			wantModes:    "+w",
+			wantErr:      false,
+			wantErrCode:  0,
+			wantState:    applyUserModeCaseState{oper: false, wallops: true},
+		},
+		{
+			name:         "-w from +w",
+			initialState: applyUserModeCaseState{oper: false, wallops: true},
+			modeStr:      "-w",
+			wantModes:    "+",
+			wantErr:      false,
+			wantErrCode:  0,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "-o from +o",
+			initialState: applyUserModeCaseState{oper: true, wallops: false},
+			modeStr:      "-o",
+			wantModes:    "+",
+			wantErr:      false,
+			wantErrCode:  0,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "-wo from +ow",
+			initialState: applyUserModeCaseState{oper: true, wallops: true},
+			modeStr:      "-wo",
+			wantModes:    "+",
+			wantErr:      false,
+			wantErrCode:  0,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+	}
+}
+
+// applyUserModeSignTransitionCases covers multi-char mode
+// strings where '+' and '-' flip partway through. +o is
+// never legal via MODE, so strings containing it must be
+// rejected atomically.
+func applyUserModeSignTransitionCases() []applyUserModeCase {
+	return []applyUserModeCase{
+		{
+			name:         "+w-o from +o",
+			initialState: applyUserModeCaseState{oper: true, wallops: false},
+			modeStr:      "+w-o",
+			wantModes:    "+w",
+			wantErr:      false,
+			wantErrCode:  0,
+			wantState:    applyUserModeCaseState{oper: false, wallops: true},
+		},
+		{
+			// +o is rejected before any op applies; wallops
+			// stays set.
+			name:         "-w+o always rejects +o",
+			initialState: applyUserModeCaseState{oper: true, wallops: true},
+			modeStr:      "-w+o",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: true, wallops: true},
+		},
+		{
+			// Wallops must NOT be cleared; oper must NOT be
+			// cleared. Rejection is fully atomic.
+			name:         "+o-w+w rejects because of +o",
+			initialState: applyUserModeCaseState{oper: true, wallops: true},
+			modeStr:      "+o-w+w",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: true, wallops: true},
+		},
+	}
+}
+
+// applyUserModeMalformedCases covers inputs that lack a
+// leading '+' or '-' and inputs that consist of bare signs
+// without mode letters. All must be rejected with no side
+// effects.
+func applyUserModeMalformedCases() []applyUserModeCase {
+	return []applyUserModeCase{
+		{
+			name:         "w no prefix rejects",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "w",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			// Prove wallops is NOT cleared — the whole point
+			// of sneak's review.
+			name: "xw no prefix rejects (would have been" +
+				" silently -w before)",
+			initialState: applyUserModeCaseState{oper: false, wallops: true},
+			modeStr:      "xw",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: true},
+		},
+		{
+			name:         "empty string rejects",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "bare + rejects",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "bare - rejects",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "-",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "+-+ rejects (no mode letters)",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+-+",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+	}
+}
+
+// applyUserModeUnknownLetterCases covers well-formed prefix
+// strings that contain unknown mode letters. Rejection must
+// be atomic: any valid letters before the invalid one must
+// not persist.
+func applyUserModeUnknownLetterCases() []applyUserModeCase {
+	return []applyUserModeCase{
+		{
+			name:         "-x+y rejects unknown -x",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "-x+y",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "+y-x rejects unknown +y",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+y-x",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name:         "+z unknown mode rejects",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+z",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			// Wallops must NOT be set.
+			name: "+wz rejects whole thing; +w side effect" +
+				" must NOT persist",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+wz",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+		{
+			name: "+wo rejects whole thing; +w side effect" +
+				" must NOT persist",
+			initialState: applyUserModeCaseState{oper: false, wallops: false},
+			modeStr:      "+wo",
+			wantModes:    "",
+			wantErr:      true,
+			wantErrCode:  irc.ErrUmodeUnknownFlag,
+			wantState:    applyUserModeCaseState{oper: false, wallops: false},
+		},
+	}
+}
+
 // TestApplyUserMode is the rigorous table-driven suite for
 // the shared user-mode parser. It covers every case listed
 // in sneak's review of PR #96 plus a few adjacent ones.
@@ -400,253 +642,159 @@ func TestQueryUserMode(t *testing.T) {
 // persisted session state, to prove that rejected input
 // leaves no side effects.
 func TestApplyUserMode(t *testing.T) {
-	type caseState struct {
-		oper    bool
-		wallops bool
+	for _, testCase := range applyUserModeCases() {
+		t.Run(testCase.name, func(t *testing.T) {
+			runApplyUserModeCase(t, testCase)
+		})
 	}
+}
 
-	// Each case starts from initialState, calls
-	// ApplyUserMode(modeStr), and verifies either the
-	// returned mode string (wantModes) or an IRCError with
-	// wantErrCode. After the call, the DB must match
-	// wantState — proving that rejected input made no
-	// change.
-	cases := []struct {
-		name         string
-		initialState caseState
-		modeStr      string
-		wantModes    string
-		wantErr      bool
-		wantErrCode  irc.IRCMessageType
-		wantState    caseState
-	}{
-		// Happy path: single-char operations.
-		{
-			name:      "+w from empty",
-			modeStr:   "+w",
-			wantModes: "+w",
-			wantState: caseState{wallops: true},
-		},
-		{
-			name:         "-w from +w",
-			initialState: caseState{wallops: true},
-			modeStr:      "-w",
-			wantModes:    "+",
-			wantState:    caseState{},
-		},
-		{
-			name:         "-o from +o",
-			initialState: caseState{oper: true},
-			modeStr:      "-o",
-			wantModes:    "+",
-			wantState:    caseState{},
-		},
-		// Multi-char without sign transitions.
-		{
-			name:         "-wo from +ow",
-			initialState: caseState{oper: true, wallops: true},
-			modeStr:      "-wo",
-			wantModes:    "+",
-			wantState:    caseState{},
-		},
-		// Multi-char with sign transitions.
-		{
-			name:         "+w-o from +o",
-			initialState: caseState{oper: true},
-			modeStr:      "+w-o",
-			wantModes:    "+w",
-			wantState:    caseState{wallops: true},
-		},
-		{
-			name:         "-w+o always rejects +o",
-			initialState: caseState{wallops: true, oper: true},
-			modeStr:      "-w+o",
-			wantErr:      true,
-			wantErrCode:  irc.ErrUmodeUnknownFlag,
-			// +o is rejected before any op applies; wallops
-			// stays set.
-			wantState: caseState{wallops: true, oper: true},
-		},
-		{
-			name:         "+o-w+w rejects because of +o",
-			initialState: caseState{wallops: true, oper: true},
-			modeStr:      "+o-w+w",
-			wantErr:      true,
-			wantErrCode:  irc.ErrUmodeUnknownFlag,
-			// Wallops must NOT be cleared; oper must NOT be
-			// cleared. Rejection is fully atomic.
-			wantState: caseState{wallops: true, oper: true},
-		},
-		{
-			name:        "-x+y rejects unknown -x",
-			modeStr:     "-x+y",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		{
-			name:        "+y-x rejects unknown +y",
-			modeStr:     "+y-x",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		// Malformed prefix — must not silently treat as '-'.
-		{
-			name:        "w no prefix rejects",
-			modeStr:     "w",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		{
-			name: "xw no prefix rejects (would have been" +
-				" silently -w before)",
-			initialState: caseState{wallops: true},
-			modeStr:      "xw",
-			wantErr:      true,
-			wantErrCode:  irc.ErrUmodeUnknownFlag,
-			// Prove wallops is NOT cleared — the whole point
-			// of sneak's review.
-			wantState: caseState{wallops: true},
-		},
-		{
-			name:        "empty string rejects",
-			modeStr:     "",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		// Bare signs with no mode letters reject.
-		{
-			name:        "bare + rejects",
-			modeStr:     "+",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		{
-			name:        "bare - rejects",
-			modeStr:     "-",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		{
-			name:        "+-+ rejects (no mode letters)",
-			modeStr:     "+-+",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		// Unknown mode letters reject whole string.
-		{
-			name:        "+z unknown mode rejects",
-			modeStr:     "+z",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-		{
-			name: "+wz rejects whole thing; +w side effect" +
-				" must NOT persist",
-			modeStr:     "+wz",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			// Wallops must NOT be set.
-			wantState: caseState{},
-		},
-		{
-			name: "+wo rejects whole thing; +w side effect" +
-				" must NOT persist",
-			modeStr:     "+wo",
-			wantErr:     true,
-			wantErrCode: irc.ErrUmodeUnknownFlag,
-			wantState:   caseState{},
-		},
-	}
+// runApplyUserModeCase executes one applyUserModeCase: seed
+// the session state, invoke ApplyUserMode, and verify both
+// the returned value and the post-call persisted state.
+func runApplyUserModeCase(
+	t *testing.T, testCase applyUserModeCase,
+) {
+	t.Helper()
 
-	for _, tc := range cases {
-		t.Run(tc.name, func(t *testing.T) {
 	env := newTestEnv(t)
 	ctx := t.Context()
 	sid := createSession(ctx, t, env.db, "alice")
 
-			if tc.initialState.oper {
-				if err := env.db.SetSessionOper(
+	seedApplyUserModeState(ctx, t, env.db, sid, testCase.initialState)
+
+	result, err := env.svc.ApplyUserMode(
+		ctx, sid, testCase.modeStr,
+	)
+
+	verifyApplyUserModeOutcome(t, testCase, result, err)
+	verifyApplyUserModeState(ctx, t, env.db, sid, testCase.wantState)
+}
+
+// seedApplyUserModeState installs the pre-call session
+// state described by initialState.
+func seedApplyUserModeState(
+	ctx context.Context,
+	t *testing.T,
+	database *db.Database,
+	sid int64,
+	initialState applyUserModeCaseState,
+) {
+	t.Helper()
+
+	if initialState.oper {
+		if err := database.SetSessionOper(
 			ctx, sid, true,
 		); err != nil {
 			t.Fatalf("init oper: %v", err)
 		}
 	}
 
-			if tc.initialState.wallops {
-				if err := env.db.SetSessionWallops(
+	if initialState.wallops {
+		if err := database.SetSessionWallops(
 			ctx, sid, true,
 		); err != nil {
 			t.Fatalf("init wallops: %v", err)
 		}
 	}
+}
 
-			result, err := env.svc.ApplyUserMode(
-				ctx, sid, tc.modeStr,
-			)
+// verifyApplyUserModeOutcome asserts the direct return
+// value of ApplyUserMode. It dispatches to the error- or
+// success-specific verifier based on wantErr.
+func verifyApplyUserModeOutcome(
+	t *testing.T,
+	testCase applyUserModeCase,
+	result string,
+	err error,
+) {
+	t.Helper()
+
+	if testCase.wantErr {
+		verifyApplyUserModeError(t, testCase, err)
+
+		return
+	}
+
+	verifyApplyUserModeSuccess(t, testCase, result, err)
+}
+
+// verifyApplyUserModeError checks that err is a
+// *service.IRCError whose code matches wantErrCode.
+func verifyApplyUserModeError(
+	t *testing.T, testCase applyUserModeCase, err error,
+) {
+	t.Helper()
 
-			if tc.wantErr {
 	var ircErr *service.IRCError
 	if !errors.As(err, &ircErr) {
-					t.Fatalf(
-						"expected IRCError, got %v", err,
-					)
+		t.Fatalf("expected IRCError, got %v", err)
 	}
 
-				if ircErr.Code != tc.wantErrCode {
+	if ircErr.Code != testCase.wantErrCode {
 		t.Errorf(
 			"code: want %d got %d",
-						tc.wantErrCode, ircErr.Code,
+			testCase.wantErrCode, ircErr.Code,
 		)
 	}
-			} else {
+}
+
+// verifyApplyUserModeSuccess checks that err is nil and the
+// returned mode string matches wantModes.
+func verifyApplyUserModeSuccess(
+	t *testing.T,
+	testCase applyUserModeCase,
+	result string,
+	err error,
+) {
+	t.Helper()
+
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
 
-				if result != tc.wantModes {
+	if result != testCase.wantModes {
 		t.Errorf(
 			"modes: want %q got %q",
-						tc.wantModes, result,
+			testCase.wantModes, result,
 		)
 	}
-			}
+}
 
-			// Whether or not the call errored, the persisted
-			// state must match wantState — this is the
-			// atomicity guarantee sneak demanded.
-			gotOper, err := env.db.IsSessionOper(ctx, sid)
+// verifyApplyUserModeState asserts the post-call persisted
+// session state. This is the atomicity guarantee sneak
+// demanded: whether the call succeeded or was rejected, the
+// DB must match wantState exactly.
+func verifyApplyUserModeState(
+	ctx context.Context,
+	t *testing.T,
+	database *db.Database,
+	sid int64,
+	wantState applyUserModeCaseState,
+) {
+	t.Helper()
+
+	gotOper, err := database.IsSessionOper(ctx, sid)
 	if err != nil {
 		t.Fatalf("read oper: %v", err)
 	}
 
-			gotWallops, err := env.db.IsSessionWallops(
-				ctx, sid,
-			)
+	gotWallops, err := database.IsSessionWallops(ctx, sid)
 	if err != nil {
 		t.Fatalf("read wallops: %v", err)
 	}
 
-			if gotOper != tc.wantState.oper {
+	if gotOper != wantState.oper {
 		t.Errorf(
 			"oper: want %v got %v",
-					tc.wantState.oper, gotOper,
+			wantState.oper, gotOper,
 		)
 	}
 
-			if gotWallops != tc.wantState.wallops {
+	if gotWallops != wantState.wallops {
 		t.Errorf(
 			"wallops: want %v got %v",
-					tc.wantState.wallops, gotWallops,
+			wantState.wallops, gotWallops,
 		)
 	}
-		})
-	}
 }