refactor: dedupe ui lowercase helpers

2026-04-12 09:41:11 +00:00 · 2026-04-07 20:20:33 +01:00
parent abf81ff1ed
commit f665da8dbc
43 changed files with 226 additions and 135 deletions
--- a/ui/src/ui/app-chat.ts
+++ b/ui/src/ui/app-chat.ts
@@ -10,6 +10,7 @@ import { loadSessions } from "./controllers/sessions.ts";
 import type { GatewayBrowserClient, GatewayHelloOk } from "./gateway.ts";
 import { normalizeBasePath } from "./navigation.ts";
 import { parseAgentSessionKey } from "./session-key.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import type { ChatModelOverride, ModelCatalogEntry } from "./types.ts";
 import type { SessionsListResult } from "./types.ts";
 import type { ChatAttachment, ChatQueueItem } from "./ui-types.ts";
@@ -51,7 +52,7 @@ export function isChatStopCommand(text: string) {
  if (!trimmed) {
    return false;
  }
-  const normalized = trimmed.toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(trimmed);
  if (normalized === "/stop") {
    return true;
  }
@@ -69,7 +70,7 @@ function isChatResetCommand(text: string) {
  if (!trimmed) {
    return false;
  }
-  const normalized = trimmed.toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(trimmed);
  if (normalized === "/new" || normalized === "/reset") {
    return true;
  }
--- a/ui/src/ui/app-render.helpers.ts
+++ b/ui/src/ui/app-render.helpers.ts
@@ -16,6 +16,7 @@ import { loadSessions } from "./controllers/sessions.ts";
 import { icons } from "./icons.ts";
 import { iconForTab, pathForTab, titleForTab, type Tab } from "./navigation.ts";
 import { parseAgentSessionKey } from "./session-key.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import type { ThemeMode } from "./theme.ts";
 import {
  listThinkingLevelLabels,
@@ -607,7 +608,7 @@ function buildThinkingOptions(
    if (!trimmed) {
      return;
    }
-    const key = trimmed.toLowerCase();
+    const key = normalizeLowercaseStringOrEmpty(trimmed);
    if (seen.has(key)) {
      return;
    }
@@ -624,7 +625,7 @@ function buildThinkingOptions(
  };

  for (const label of listThinkingLevelLabels(provider)) {
-    const normalized = normalizeThinkLevel(label) ?? label.trim().toLowerCase();
+    const normalized = normalizeThinkLevel(label) ?? normalizeLowercaseStringOrEmpty(label);
    addOption(normalized);
  }
  if (currentOverride) {
@@ -807,7 +808,7 @@ function capitalize(s: string): string {
 * fallback display name.  Exported for testing.
 */
 export function parseSessionKey(key: string): SessionKeyInfo {
-  const normalized = key.toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(key);

  // ── Main session ─────────────────────────────────
  if (key === "main" || key === "agent:main:main") {
@@ -878,7 +879,7 @@ export function resolveSessionDisplayName(
 }

 export function isCronSessionKey(key: string): boolean {
-  const normalized = key.trim().toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(key);
  if (!normalized) {
    return false;
  }
@@ -946,7 +947,7 @@ export function resolveSessionOptionGroups(
    const parsed = parseAgentSessionKey(key);
    const group = parsed
      ? ensureGroup(
-          `agent:${parsed.agentId.toLowerCase()}`,
+          `agent:${normalizeLowercaseStringOrEmpty(parsed.agentId)}`,
          resolveAgentGroupLabel(state, parsed.agentId),
        )
      : ensureGroup("other", "Other Sessions");
@@ -1060,9 +1061,9 @@ function countHiddenCronSessions(sessionKey: string, sessions: SessionsListResul
 }

 function resolveAgentGroupLabel(state: AppViewState, agentIdRaw: string): string {
-  const normalized = agentIdRaw.trim().toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(agentIdRaw);
  const agent = (state.agentsList?.agents ?? []).find(
-    (entry) => entry.id.trim().toLowerCase() === normalized,
+    (entry) => normalizeLowercaseStringOrEmpty(entry.id) === normalized,
  );
  const name = agent?.identity?.name?.trim() || agent?.name?.trim() || "";
  return name && name !== agentIdRaw ? `${name} (${agentIdRaw})` : agentIdRaw;
--- a/ui/src/ui/app-render.ts
+++ b/ui/src/ui/app-render.ts
@@ -101,14 +101,15 @@ import {
  updateSkillEnabled,
 } from "./controllers/skills.ts";
 import { buildExternalLinkRel, EXTERNAL_LINK_TARGET } from "./external-link.ts";
-import "./components/dashboard-header.ts";
 import { icons } from "./icons.ts";
+import "./components/dashboard-header.ts";
 import { normalizeBasePath, TAB_GROUPS, subtitleForTab, titleForTab } from "./navigation.ts";
 import {
  buildAgentMainSessionKey,
  parseAgentSessionKey,
  resolveAgentIdFromSessionKey,
 } from "./session-key.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import { agentLogoUrl } from "./views/agents-utils.ts";
 import {
  resolveAgentConfig,
@@ -218,7 +219,7 @@ function uniquePreserveOrder(values: string[]): string[] {
    if (!normalized) {
      continue;
    }
-    const key = normalized.toLowerCase();
+    const key = normalizeLowercaseStringOrEmpty(normalized);
    if (seen.has(key)) {
      continue;
    }
--- a/ui/src/ui/app-tool-stream.ts
+++ b/ui/src/ui/app-tool-stream.ts
@@ -1,4 +1,5 @@
 import { formatUnknownText, truncateText } from "./format.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";

 const TOOL_STREAM_LIMIT = 50;
 const TOOL_STREAM_THROTTLE_MS = 80;
@@ -53,7 +54,11 @@ function resolveModelLabel(provider: unknown, model: unknown): string | null {
  const providerValue = toTrimmedString(provider);
  if (providerValue) {
    const prefix = `${providerValue}/`;
-    if (modelValue.toLowerCase().startsWith(prefix.toLowerCase())) {
+    if (
+      normalizeLowercaseStringOrEmpty(modelValue).startsWith(
+        normalizeLowercaseStringOrEmpty(prefix),
+      )
+    ) {
      const trimmedModel = modelValue.slice(prefix.length).trim();
      if (trimmedModel) {
        return `${providerValue}/${trimmedModel}`;
--- a/ui/src/ui/app.ts
+++ b/ui/src/ui/app.ts
@@ -72,6 +72,7 @@ import type { GatewayBrowserClient, GatewayHelloOk } from "./gateway.ts";
 import type { Tab } from "./navigation.ts";
 import { resolveAgentIdFromSessionKey } from "./session-key.ts";
 import { loadSettings, type UiSettings } from "./storage.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import { VALID_THEME_NAMES, type ResolvedTheme, type ThemeMode, type ThemeName } from "./theme.ts";
 import type {
  AgentsListResult,
@@ -118,7 +119,7 @@ function resolveOnboardingMode(): boolean {
  if (!raw) {
    return false;
  }
-  const normalized = raw.trim().toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(raw);
  return normalized === "1" || normalized === "true" || normalized === "yes" || normalized === "on";
 }

--- a/ui/src/ui/chat-event-reload.ts
+++ b/ui/src/ui/chat-event-reload.ts
@@ -1,4 +1,5 @@
 import type { ChatEventPayload } from "./controllers/chat.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";

 export function shouldReloadHistoryForFinalEvent(payload?: ChatEventPayload): boolean {
  if (!payload || payload.state !== "final") {
@@ -8,7 +9,7 @@ export function shouldReloadHistoryForFinalEvent(payload?: ChatEventPayload): bo
    return true;
  }
  const message = payload.message as Record<string, unknown>;
-  const role = typeof message.role === "string" ? message.role.toLowerCase() : "";
+  const role = normalizeLowercaseStringOrEmpty(message.role);
  if (role && role !== "assistant") {
    return true;
  }
--- a/ui/src/ui/chat-model-ref.ts
+++ b/ui/src/ui/chat-model-ref.ts
@@ -1,3 +1,4 @@
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import type { ModelCatalogEntry } from "./types.ts";

 export type ChatModelOverride =
@@ -68,8 +69,9 @@ export function resolveChatModelOverride(
  }

  let matchedValue = "";
+  const normalizedTrimmed = normalizeLowercaseStringOrEmpty(trimmed);
  for (const entry of catalog) {
-    if (entry.id.trim().toLowerCase() !== trimmed.toLowerCase()) {
+    if (normalizeLowercaseStringOrEmpty(entry.id) !== normalizedTrimmed) {
      continue;
    }
    const candidate = buildQualifiedChatModelValue(entry.id, entry.provider);
@@ -77,7 +79,9 @@ export function resolveChatModelOverride(
      matchedValue = candidate;
      continue;
    }
-    if (matchedValue.toLowerCase() !== candidate.toLowerCase()) {
+    if (
+      normalizeLowercaseStringOrEmpty(matchedValue) !== normalizeLowercaseStringOrEmpty(candidate)
+    ) {
      return { value: trimmed, source: "raw", reason: "ambiguous" };
    }
  }
--- a/ui/src/ui/chat-model-select-state.ts
+++ b/ui/src/ui/chat-model-select-state.ts
@@ -5,6 +5,7 @@ import {
  normalizeChatModelOverrideValue,
  resolvePreferredServerChatModelValue,
 } from "./chat-model-ref.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import type { ModelCatalogEntry } from "./types.ts";

 type ChatModelSelectStateInput = Pick<
@@ -66,7 +67,7 @@ function buildChatModelOptions(
    if (!trimmed) {
      return;
    }
-    const key = trimmed.toLowerCase();
+    const key = normalizeLowercaseStringOrEmpty(trimmed);
    if (seen.has(key)) {
      return;
    }
--- a/ui/src/ui/chat/grouped-render.ts
+++ b/ui/src/ui/chat/grouped-render.ts
@@ -5,6 +5,7 @@ import type { AssistantIdentity } from "../assistant-identity.ts";
 import { icons } from "../icons.ts";
 import { toSanitizedMarkdownHtml } from "../markdown.ts";
 import { openExternalUrlSafe } from "../open-external-url.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import { detectTextDirection } from "../text-direction.ts";
 import type { MessageGroup, ToolCard } from "../types/chat-types.ts";
 import { agentLogoUrl } from "../views/agents-utils.ts";
@@ -726,10 +727,11 @@ function renderGroupedMessage(
  const m = message as Record<string, unknown>;
  const role = typeof m.role === "string" ? m.role : "unknown";
  const normalizedRole = normalizeRoleForGrouping(role);
+  const normalizedRawRole = normalizeLowercaseStringOrEmpty(role);
  const isToolResult =
    isToolResultMessage(message) ||
-    role.toLowerCase() === "toolresult" ||
-    role.toLowerCase() === "tool_result" ||
+    normalizedRawRole === "toolresult" ||
+    normalizedRawRole === "tool_result" ||
    typeof m.toolCallId === "string" ||
    typeof m.tool_call_id === "string";

@@ -752,7 +754,12 @@ function renderGroupedMessage(
  // Detect pure-JSON messages and render as collapsible block
  const jsonResult = markdown && !opts.isStreaming ? detectJson(markdown) : null;

-  const bubbleClasses = ["chat-bubble", opts.isStreaming ? "streaming" : "", "fade-in", canCopyMarkdown ? "has-copy" : ""]
+  const bubbleClasses = [
+    "chat-bubble",
+    opts.isStreaming ? "streaming" : "",
+    "fade-in",
+    canCopyMarkdown ? "has-copy" : "",
+  ]
    .filter(Boolean)
    .join(" ");

--- a/ui/src/ui/chat/message-extract.ts
+++ b/ui/src/ui/chat/message-extract.ts
@@ -2,12 +2,13 @@ import { stripInboundMetadata } from "../../../../src/auto-reply/reply/strip-inb
 import { stripEnvelope } from "../../../../src/shared/chat-envelope.js";
 import { extractAssistantVisibleText as extractSharedAssistantVisibleText } from "../../../../src/shared/chat-message-content.js";
 import { stripThinkingTags } from "../format.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";

 const textCache = new WeakMap<object, string | null>();
 const thinkingCache = new WeakMap<object, string | null>();

 function processMessageText(text: string, role: string): string {
-  const shouldStripInboundMetadata = role.toLowerCase() === "user";
+  const shouldStripInboundMetadata = normalizeLowercaseStringOrEmpty(role) === "user";
  if (role === "assistant") {
    return stripThinkingTags(text);
  }
--- a/ui/src/ui/chat/message-normalizer.ts
+++ b/ui/src/ui/chat/message-normalizer.ts
@@ -8,6 +8,7 @@ import {
  isToolResultContentType,
  resolveToolBlockArgs,
 } from "../../../../src/chat/tool-content.js";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { NormalizedMessage, MessageContentItem } from "../types/chat-types.ts";

 /**
@@ -74,7 +75,7 @@ export function normalizeMessage(message: unknown): NormalizedMessage {
 * Normalize role for grouping purposes.
 */
 export function normalizeRoleForGrouping(role: string): string {
-  const lower = role.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(role);
  // Preserve original casing when it's already a core role.
  if (role === "user" || role === "User") {
    return role;
@@ -102,6 +103,6 @@ export function normalizeRoleForGrouping(role: string): string {
 */
 export function isToolResultMessage(message: unknown): boolean {
  const m = message as Record<string, unknown>;
-  const role = typeof m.role === "string" ? m.role.toLowerCase() : "";
+  const role = normalizeLowercaseStringOrEmpty(m.role);
  return role === "toolresult" || role === "tool_result";
 }
--- a/ui/src/ui/chat/search-match.ts
+++ b/ui/src/ui/chat/search-match.ts
@@ -1,10 +1,11 @@
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import { extractTextCached } from "./message-extract.ts";

 export function messageMatchesSearchQuery(message: unknown, query: string): boolean {
-  const normalizedQuery = query.trim().toLowerCase();
+  const normalizedQuery = normalizeLowercaseStringOrEmpty(query);
  if (!normalizedQuery) {
    return true;
  }
-  const text = (extractTextCached(message) ?? "").toLowerCase();
+  const text = normalizeLowercaseStringOrEmpty(extractTextCached(message));
  return text.includes(normalizedQuery);
 }
--- a/ui/src/ui/chat/slash-command-executor.ts
+++ b/ui/src/ui/chat/slash-command-executor.ts
@@ -11,6 +11,10 @@ import {
  isSubagentSessionKey,
  parseAgentSessionKey,
 } from "../session-key.ts";
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "../string-coerce.ts";
 import {
  formatThinkingLevels,
  normalizeThinkLevel,
@@ -60,7 +64,7 @@ function normalizeVerboseLevel(raw?: string | null): "off" | "on" | "full" | und
  if (!raw) {
    return undefined;
  }
-  const key = raw.toLowerCase();
+  const key = normalizeLowercaseStringOrEmpty(raw);
  if (["off", "false", "no", "0"].includes(key)) {
    return "off";
  }
@@ -313,7 +317,7 @@ async function executeFast(
  sessionKey: string,
  args: string,
 ): Promise<SlashCommandResult> {
-  const rawMode = args.trim().toLowerCase();
+  const rawMode = normalizeLowercaseStringOrEmpty(args);

  if (!rawMode || rawMode === "status") {
    try {
@@ -406,6 +410,7 @@ async function executeKill(
  args: string,
 ): Promise<SlashCommandResult> {
  const target = args.trim();
+  const normalizedTarget = normalizeLowercaseStringOrEmpty(target);
  if (!target) {
    return { content: "Usage: `/kill <id|all>`" };
  }
@@ -415,7 +420,7 @@ async function executeKill(
    if (matched.length === 0) {
      return {
        content:
-          target.toLowerCase() === "all"
+          normalizedTarget === "all"
            ? "No active sub-agent sessions found."
            : `No matching sub-agent sessions found for \`${target}\`.`,
      };
@@ -435,7 +440,7 @@ async function executeKill(
      if (rejected.length === 0) {
        return {
          content:
-            target.toLowerCase() === "all"
+            normalizedTarget === "all"
              ? "No active sub-agent runs to abort."
              : `No active runs matched \`${target}\`.`,
        };
@@ -443,7 +448,7 @@ async function executeKill(
      throw rejected[0]?.reason ?? new Error("abort failed");
    }

-    if (target.toLowerCase() === "all") {
+    if (normalizedTarget === "all") {
      return {
        content:
          successCount === matched.length
@@ -468,13 +473,13 @@ function resolveKillTargets(
  currentSessionKey: string,
  target: string,
 ): string[] {
-  const normalizedTarget = target.trim().toLowerCase();
+  const normalizedTarget = normalizeLowercaseStringOrEmpty(target);
  if (!normalizedTarget) {
    return [];
  }

  const keys = new Set<string>();
-  const normalizedCurrentSessionKey = currentSessionKey.trim().toLowerCase();
+  const normalizedCurrentSessionKey = normalizeLowercaseStringOrEmpty(currentSessionKey);
  const currentParsed = parseAgentSessionKey(normalizedCurrentSessionKey);
  const currentAgentId =
    currentParsed?.agentId ??
@@ -485,7 +490,7 @@ function resolveKillTargets(
    if (!key || !isSubagentSessionKey(key)) {
      continue;
    }
-    const normalizedKey = key.toLowerCase();
+    const normalizedKey = normalizeLowercaseStringOrEmpty(key);
    const parsed = parseAgentSessionKey(normalizedKey);
    const belongsToCurrentSession = isWithinCurrentSessionSubtree(
      normalizedKey,
@@ -550,8 +555,7 @@ function buildSessionIndex(sessions: GatewaySessionRow[]): Map<string, GatewaySe
 }

 function normalizeSessionKey(key?: string | null): string | undefined {
-  const normalized = key?.trim().toLowerCase();
-  return normalized || undefined;
+  return normalizeOptionalLowercaseString(key);
 }

 function resolveEquivalentSessionKeys(
@@ -658,11 +662,11 @@ function resolveSteerSubagent(
  currentSessionKey: string,
  target: string,
 ): string[] {
-  const normalizedTarget = target.trim().toLowerCase();
+  const normalizedTarget = normalizeLowercaseStringOrEmpty(target);
  if (!normalizedTarget) {
    return [];
  }
-  const normalizedCurrentSessionKey = currentSessionKey.trim().toLowerCase();
+  const normalizedCurrentSessionKey = normalizeLowercaseStringOrEmpty(currentSessionKey);
  const currentParsed = parseAgentSessionKey(normalizedCurrentSessionKey);
  const currentAgentId =
    currentParsed?.agentId ??
@@ -675,7 +679,7 @@ function resolveSteerSubagent(
    if (!key || !isSubagentSessionKey(key)) {
      continue;
    }
-    const normalizedKey = key.toLowerCase();
+    const normalizedKey = normalizeLowercaseStringOrEmpty(key);
    const parsed = parseAgentSessionKey(normalizedKey);
    const belongsToCurrentSession = isWithinCurrentSessionSubtree(
      normalizedKey,
@@ -692,7 +696,7 @@ function resolveSteerSubagent(
      normalizedKey === normalizedTarget ||
      normalizedKey.endsWith(`:subagent:${normalizedTarget}`) ||
      normalizedKey === `subagent:${normalizedTarget}` ||
-      (session.label ?? "").toLowerCase() === normalizedTarget;
+      normalizeLowercaseStringOrEmpty(session.label) === normalizedTarget;
    if (isMatch) {
      keys.add(key);
    }
@@ -728,7 +732,7 @@ async function resolveSteerTarget(
    const rest = trimmed.slice(spaceIdx + 1).trim();
    // Skip "all" — resolveKillTargets treats it as a wildcard, but steer/redirect
    // target a single session, so "all good now" should not match subagents.
-    if (rest && maybeTarget.toLowerCase() !== "all") {
+    if (rest && normalizeLowercaseStringOrEmpty(maybeTarget) !== "all") {
      const sessions =
        context.sessionsResult ?? (await client.request<SessionsListResult>("sessions.list", {}));
      const matched = resolveSteerSubagent(sessions?.sessions ?? [], sessionKey, maybeTarget);
--- a/ui/src/ui/chat/slash-commands.ts
+++ b/ui/src/ui/chat/slash-commands.ts
@@ -4,6 +4,7 @@ import type {
  CommandArgChoice,
 } from "../../../../src/auto-reply/commands-registry.types.js";
 import type { IconName } from "../icons.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";

 export type SlashCommandCategory = "session" | "model" | "agents" | "tools";

@@ -216,13 +217,13 @@ export const CATEGORY_LABELS: Record<SlashCommandCategory, string> = {
 };

 export function getSlashCommandCompletions(filter: string): SlashCommandDef[] {
-  const lower = filter.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(filter);
  const commands = lower
    ? SLASH_COMMANDS.filter(
        (cmd) =>
          cmd.name.startsWith(lower) ||
-          cmd.aliases?.some((alias) => alias.toLowerCase().startsWith(lower)) ||
-          cmd.description.toLowerCase().includes(lower),
+          cmd.aliases?.some((alias) => normalizeLowercaseStringOrEmpty(alias).startsWith(lower)) ||
+          normalizeLowercaseStringOrEmpty(cmd.description).includes(lower),
      )
    : SLASH_COMMANDS;
  return commands.toSorted((a, b) => {
@@ -266,11 +267,11 @@ export function parseSlashCommand(text: string): ParsedSlashCommand | null {
    return null;
  }

-  const normalizedName = name.toLowerCase();
+  const normalizedName = normalizeLowercaseStringOrEmpty(name);
  const command = SLASH_COMMANDS.find(
    (cmd) =>
      cmd.name === normalizedName ||
-      cmd.aliases?.some((alias) => alias.toLowerCase() === normalizedName),
+      cmd.aliases?.some((alias) => normalizeLowercaseStringOrEmpty(alias) === normalizedName),
  );
  if (!command) {
    return null;
--- a/ui/src/ui/connect-error.ts
+++ b/ui/src/ui/connect-error.ts
@@ -1,5 +1,6 @@
 import { ConnectErrorDetailCodes } from "../../../src/gateway/protocol/connect-error-details.js";
 import { resolveGatewayErrorDetailCode } from "./gateway.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";

 type ErrorWithMessageAndDetails = {
  message?: unknown;
@@ -39,7 +40,7 @@ function formatErrorFromMessageAndDetails(error: ErrorWithMessageAndDetails): st
      break;
  }

-  const normalized = message.trim().toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(message);
  if (
    normalized === "fetch failed" ||
    normalized === "failed to fetch" ||
--- a/ui/src/ui/controllers/chat.ts
+++ b/ui/src/ui/controllers/chat.ts
@@ -2,6 +2,7 @@ import { resetToolStream } from "../app-tool-stream.ts";
 import { extractText } from "../chat/message-extract.ts";
 import { formatConnectError } from "../connect-error.ts";
 import type { GatewayBrowserClient } from "../gateway.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { ChatAttachment } from "../ui-types.ts";
 import { generateUUID } from "../uuid.ts";
 import {
@@ -20,7 +21,7 @@ function isAssistantSilentReply(message: unknown): boolean {
    return false;
  }
  const entry = message as Record<string, unknown>;
-  const role = typeof entry.role === "string" ? entry.role.toLowerCase() : "";
+  const role = normalizeLowercaseStringOrEmpty(entry.role);
  if (role !== "assistant") {
    return false;
  }
@@ -128,7 +129,7 @@ function normalizeAssistantMessage(
  const candidate = message as Record<string, unknown>;
  const roleValue = candidate.role;
  if (typeof roleValue === "string") {
-    const role = options.roleCaseSensitive ? roleValue : roleValue.toLowerCase();
+    const role = options.roleCaseSensitive ? roleValue : normalizeLowercaseStringOrEmpty(roleValue);
    if (role !== "assistant") {
      return null;
    }
--- a/ui/src/ui/controllers/cron.ts
+++ b/ui/src/ui/controllers/cron.ts
@@ -2,6 +2,7 @@ import { t } from "../../i18n/index.ts";
 import { DEFAULT_CRON_FORM } from "../app-defaults.ts";
 import { toNumber } from "../format.ts";
 import type { GatewayBrowserClient } from "../gateway.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type {
  CronJob,
  CronDeliveryStatus,
@@ -900,13 +901,13 @@ export function startCronEdit(state: CronState, job: CronJob) {
 function buildCloneName(name: string, existingNames: Set<string>) {
  const base = name.trim() || "Job";
  const first = `${base} copy`;
-  if (!existingNames.has(first.toLowerCase())) {
+  if (!existingNames.has(normalizeLowercaseStringOrEmpty(first))) {
    return first;
  }
  let index = 2;
  while (index < 1000) {
    const next = `${base} copy ${index}`;
-    if (!existingNames.has(next.toLowerCase())) {
+    if (!existingNames.has(normalizeLowercaseStringOrEmpty(next))) {
      return next;
    }
    index += 1;
@@ -917,7 +918,9 @@ function buildCloneName(name: string, existingNames: Set<string>) {
 export function startCronClone(state: CronState, job: CronJob) {
  clearCronEditState(state);
  state.cronRunsJobId = job.id;
-  const existingNames = new Set(state.cronJobs.map((entry) => entry.name.trim().toLowerCase()));
+  const existingNames = new Set(
+    state.cronJobs.map((entry) => normalizeLowercaseStringOrEmpty(entry.name)),
+  );
  const cloned = jobToForm(job, state.cronForm);
  cloned.name = buildCloneName(job.name, existingNames);
  state.cronForm = cloned;
--- a/ui/src/ui/controllers/dreaming.ts
+++ b/ui/src/ui/controllers/dreaming.ts
@@ -1,4 +1,5 @@
 import type { GatewayBrowserClient } from "../gateway.ts";
+import { normalizeOptionalLowercaseString } from "../string-coerce.ts";
 import type { ConfigSnapshot } from "../types.ts";

 export type DreamingPhaseId = "light" | "deep" | "rem";
@@ -118,7 +119,7 @@ function normalizeFiniteScore(value: unknown, fallback = 0): number {
 }

 function normalizeStorageMode(value: unknown): DreamingStatus["storageMode"] {
-  const normalized = normalizeTrimmedString(value)?.toLowerCase();
+  const normalized = normalizeOptionalLowercaseString(normalizeTrimmedString(value));
  if (normalized === "inline" || normalized === "separate" || normalized === "both") {
    return normalized;
  }
@@ -144,7 +145,7 @@ function resolveDreamingPluginId(configValue: Record<string, unknown> | null): s
  const plugins = asRecord(configValue?.plugins);
  const slots = asRecord(plugins?.slots);
  const configuredSlot = normalizeTrimmedString(slots?.memory);
-  if (configuredSlot && configuredSlot.toLowerCase() !== "none") {
+  if (configuredSlot && normalizeOptionalLowercaseString(configuredSlot) !== "none") {
    return configuredSlot;
  }
  return DEFAULT_DREAMING_PLUGIN_ID;
--- a/ui/src/ui/controllers/logs.ts
+++ b/ui/src/ui/controllers/logs.ts
@@ -1,4 +1,5 @@
 import type { GatewayBrowserClient } from "../gateway.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { LogEntry, LogLevel } from "../types.ts";
 import {
  formatMissingOperatorReadScopeMessage,
@@ -45,7 +46,7 @@ function normalizeLevel(value: unknown): LogLevel | null {
  if (typeof value !== "string") {
    return null;
  }
-  const lowered = value.toLowerCase() as LogLevel;
+  const lowered = normalizeLowercaseStringOrEmpty(value) as LogLevel;
  return LEVELS.has(lowered) ? lowered : null;
 }

--- a/ui/src/ui/controllers/usage.ts
+++ b/ui/src/ui/controllers/usage.ts
@@ -1,5 +1,6 @@
 import { getSafeLocalStorage } from "../../local-storage.ts";
 import type { GatewayBrowserClient } from "../gateway.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { SessionsUsageResult, CostUsageSummary, SessionUsageTimeSeries } from "../types.ts";
 import type { SessionLogEntry } from "../views/usage.ts";
 import {
@@ -102,9 +103,9 @@ function normalizeGatewayCompatibilityKey(gatewayUrl?: string): string {
  try {
    const parsed = new URL(trimmed);
    const pathname = parsed.pathname === "/" ? "" : parsed.pathname;
-    return `${parsed.protocol}//${parsed.host}${pathname}`.toLowerCase();
+    return normalizeLowercaseStringOrEmpty(`${parsed.protocol}//${parsed.host}${pathname}`);
  } catch {
-    return trimmed.toLowerCase();
+    return normalizeLowercaseStringOrEmpty(trimmed);
  }
 }

--- a/ui/src/ui/external-link.ts
+++ b/ui/src/ui/external-link.ts
@@ -1,3 +1,5 @@
+import { normalizeOptionalLowercaseString } from "./string-coerce.ts";
+
 const REQUIRED_EXTERNAL_REL_TOKENS = ["noopener", "noreferrer"] as const;

 export const EXTERNAL_LINK_TARGET = "_blank";
@@ -7,7 +9,7 @@ export function buildExternalLinkRel(currentRel?: string): string {
  const seen = new Set<string>(REQUIRED_EXTERNAL_REL_TOKENS);

  for (const rawToken of (currentRel ?? "").split(/\s+/)) {
-    const token = rawToken.trim().toLowerCase();
+    const token = normalizeOptionalLowercaseString(rawToken);
    if (!token || seen.has(token)) {
      continue;
    }
--- a/ui/src/ui/gateway.ts
+++ b/ui/src/ui/gateway.ts
@@ -12,6 +12,7 @@ import {
 } from "../../../src/gateway/protocol/connect-error-details.js";
 import { clearDeviceAuthToken, loadDeviceAuthToken, storeDeviceAuthToken } from "./device-auth.ts";
 import { loadOrCreateDeviceIdentity, signDevicePayload } from "./device-identity.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 import { generateUUID } from "./uuid.ts";

 export type GatewayEventFrame = {
@@ -82,7 +83,7 @@ export function isNonRecoverableAuthError(error: GatewayErrorInfo | undefined):
 function isTrustedRetryEndpoint(url: string): boolean {
  try {
    const gatewayUrl = new URL(url, window.location.href);
-    const host = gatewayUrl.hostname.trim().toLowerCase();
+    const host = normalizeLowercaseStringOrEmpty(gatewayUrl.hostname);
    const isLoopbackHost =
      host === "localhost" || host === "::1" || host === "[::1]" || host === "127.0.0.1";
    const isLoopbackIPv4 = host.startsWith("127.");
--- a/ui/src/ui/markdown.ts
+++ b/ui/src/ui/markdown.ts
@@ -1,6 +1,7 @@
 import DOMPurify from "dompurify";
 import { marked } from "marked";
 import { truncateText } from "./format.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";

 const allowedTags = [
  "a",
@@ -116,7 +117,7 @@ function installHooks() {

    node.setAttribute("rel", "noreferrer noopener");
    node.setAttribute("target", "_blank");
-    if (href.toLowerCase().includes("tail")) {
+    if (normalizeLowercaseStringOrEmpty(href).includes("tail")) {
      node.classList.add(TAIL_LINK_BLUR_CLASS);
    }
  });
--- a/ui/src/ui/navigation.ts
+++ b/ui/src/ui/navigation.ts
@@ -1,5 +1,6 @@
 import { t } from "../i18n/index.ts";
 import type { IconName } from "./icons.js";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";

 export const TAB_GROUPS = [
  { label: "chat", tabs: ["chat"] },
@@ -122,7 +123,7 @@ export function tabFromPath(pathname: string, basePath = ""): Tab | null {
      path = path.slice(base.length);
    }
  }
-  let normalized = normalizePath(path).toLowerCase();
+  let normalized = normalizeLowercaseStringOrEmpty(normalizePath(path));
  if (normalized.endsWith("/index.html")) {
    normalized = "/";
  }
@@ -145,7 +146,7 @@ export function inferBasePathFromPathname(pathname: string): string {
    return "";
  }
  for (let i = 0; i < segments.length; i++) {
-    const candidate = `/${segments.slice(i).join("/")}`.toLowerCase();
+    const candidate = normalizeLowercaseStringOrEmpty(`/${segments.slice(i).join("/")}`);
    if (PATH_TO_TAB.has(candidate)) {
      const prefix = segments.slice(0, i);
      return prefix.length ? `/${prefix.join("/")}` : "";
--- a/ui/src/ui/open-external-url.ts
+++ b/ui/src/ui/open-external-url.ts
@@ -1,9 +1,11 @@
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
+
 const DATA_URL_PREFIX = "data:";
 const ALLOWED_EXTERNAL_PROTOCOLS = new Set(["http:", "https:", "blob:"]);
 const BLOCKED_DATA_IMAGE_MIME_TYPES = new Set(["image/svg+xml"]);

 function isAllowedDataImageUrl(url: string): boolean {
-  if (!url.toLowerCase().startsWith(DATA_URL_PREFIX)) {
+  if (!normalizeLowercaseStringOrEmpty(url).startsWith(DATA_URL_PREFIX)) {
    return false;
  }

@@ -13,7 +15,7 @@ function isAllowedDataImageUrl(url: string): boolean {
  }

  const metadata = url.slice(DATA_URL_PREFIX.length, commaIndex);
-  const mimeType = metadata.split(";")[0]?.trim().toLowerCase() ?? "";
+  const mimeType = normalizeLowercaseStringOrEmpty(metadata.split(";")[0]);
  if (!mimeType.startsWith("image/")) {
    return false;
  }
@@ -39,13 +41,15 @@ export function resolveSafeExternalUrl(
    return candidate;
  }

-  if (candidate.toLowerCase().startsWith(DATA_URL_PREFIX)) {
+  if (normalizeLowercaseStringOrEmpty(candidate).startsWith(DATA_URL_PREFIX)) {
    return null;
  }

  try {
    const parsed = new URL(candidate, baseHref);
-    return ALLOWED_EXTERNAL_PROTOCOLS.has(parsed.protocol.toLowerCase()) ? parsed.toString() : null;
+    return ALLOWED_EXTERNAL_PROTOCOLS.has(normalizeLowercaseStringOrEmpty(parsed.protocol))
+      ? parsed.toString()
+      : null;
  } catch {
    return null;
  }
--- a/ui/src/ui/session-key.ts
+++ b/ui/src/ui/session-key.ts
@@ -1,3 +1,8 @@
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "./string-coerce.ts";
+
 export type ParsedAgentSessionKey = {
  agentId: string;
  rest: string;
@@ -14,7 +19,7 @@ const TRAILING_DASH_RE = /-+$/;
 export function parseAgentSessionKey(
  sessionKey: string | undefined | null,
 ): ParsedAgentSessionKey | null {
-  const raw = (sessionKey ?? "").trim().toLowerCase();
+  const raw = normalizeLowercaseStringOrEmpty(sessionKey);
  if (!raw) {
    return null;
  }
@@ -31,8 +36,7 @@ export function parseAgentSessionKey(
 }

 export function normalizeMainKey(value: string | undefined | null): string {
-  const trimmed = (value ?? "").trim();
-  return trimmed ? trimmed.toLowerCase() : DEFAULT_MAIN_KEY;
+  return normalizeOptionalLowercaseString(value) ?? DEFAULT_MAIN_KEY;
 }

 export function normalizeAgentId(value: string | undefined | null): string {
@@ -41,11 +45,10 @@ export function normalizeAgentId(value: string | undefined | null): string {
    return DEFAULT_AGENT_ID;
  }
  if (VALID_ID_RE.test(trimmed)) {
-    return trimmed.toLowerCase();
+    return normalizeLowercaseStringOrEmpty(trimmed);
  }
  return (
-    trimmed
-      .toLowerCase()
+    normalizeLowercaseStringOrEmpty(trimmed)
      .replace(INVALID_CHARS_RE, "-")
      .replace(LEADING_DASH_RE, "")
      .replace(TRAILING_DASH_RE, "")
@@ -72,9 +75,9 @@ export function isSubagentSessionKey(sessionKey: string | undefined | null): boo
  if (!raw) {
    return false;
  }
-  if (raw.toLowerCase().startsWith("subagent:")) {
+  if (normalizeLowercaseStringOrEmpty(raw).startsWith("subagent:")) {
    return true;
  }
  const parsed = parseAgentSessionKey(raw);
-  return Boolean((parsed?.rest ?? "").toLowerCase().startsWith("subagent:"));
+  return normalizeLowercaseStringOrEmpty(parsed?.rest).startsWith("subagent:");
 }
--- a/ui/src/ui/string-coerce.ts
+++ b/ui/src/ui/string-coerce.ts
@@ -0,0 +1,15 @@
+export function normalizeOptionalString(value: unknown): string | undefined {
+  if (typeof value !== "string") {
+    return undefined;
+  }
+  const trimmed = value.trim();
+  return trimmed ? trimmed : undefined;
+}
+
+export function normalizeOptionalLowercaseString(value: unknown): string | undefined {
+  return normalizeOptionalString(value)?.toLowerCase();
+}
+
+export function normalizeLowercaseStringOrEmpty(value: unknown): string {
+  return normalizeOptionalLowercaseString(value) ?? "";
+}
--- a/ui/src/ui/thinking.ts
+++ b/ui/src/ui/thinking.ts
@@ -1,3 +1,5 @@
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
+
 export type ThinkingCatalogEntry = {
  provider: string;
  id: string;
@@ -13,7 +15,7 @@ export function normalizeThinkingProviderId(provider?: string | null): string {
  if (!provider) {
    return "";
  }
-  const normalized = provider.trim().toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(provider);
  if (normalized === "z.ai" || normalized === "z-ai") {
    return "zai";
  }
@@ -31,7 +33,7 @@ export function normalizeThinkLevel(raw?: string | null): string | undefined {
  if (!raw) {
    return undefined;
  }
-  const key = raw.trim().toLowerCase();
+  const key = normalizeLowercaseStringOrEmpty(raw);
  const collapsed = key.replace(/[\s_-]+/g, "");
  if (collapsed === "adaptive" || collapsed === "auto") {
    return "adaptive";
--- a/ui/src/ui/tool-display.ts
+++ b/ui/src/ui/tool-display.ts
@@ -7,6 +7,7 @@ import {
  type ToolDisplaySpec as ToolDisplaySpecBase,
 } from "../../../src/agents/tool-display-common.js";
 import type { IconName } from "./icons.ts";
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";

 type ToolDisplaySpec = ToolDisplaySpecBase & {
  icon?: string;
@@ -120,7 +121,7 @@ export function resolveToolDisplay(params: {
  meta?: string;
 }): ToolDisplay {
  const name = normalizeToolName(params.name);
-  const key = name.toLowerCase();
+  const key = normalizeLowercaseStringOrEmpty(name);
  const spec = TOOL_MAP[key];
  const icon = (spec?.icon ?? FALLBACK.icon ?? "puzzle") as IconName;
  const title = spec?.title ?? defaultTitle(name);
--- a/ui/src/ui/usage-helpers.ts
+++ b/ui/src/ui/usage-helpers.ts
@@ -51,7 +51,7 @@ const QUERY_KEYS = new Set([
  "maxmessages",
 ]);

-const normalizeQueryText = (value: string): string => value.trim().toLowerCase();
+const normalizeQueryText = (value: string): string => normalizeLowercaseStringOrEmpty(value);

 const globToRegex = (pattern: string): RegExp => {
  const escaped = pattern
@@ -62,7 +62,7 @@ const globToRegex = (pattern: string): RegExp => {
 };

 const parseQueryNumber = (value: string): number | null => {
-  let raw = value.trim().toLowerCase();
+  let raw = normalizeLowercaseStringOrEmpty(value);
  if (!raw) {
    return null;
  }
@@ -101,23 +101,25 @@ export const extractQueryTerms = (query: string): UsageQueryTerm[] => {

 const getSessionText = (session: UsageSessionQueryTarget): string[] => {
  const items: Array<string | undefined> = [session.label, session.key, session.sessionId];
-  return items.filter((item): item is string => Boolean(item)).map((item) => item.toLowerCase());
+  return items
+    .filter((item): item is string => Boolean(item))
+    .map((item) => normalizeLowercaseStringOrEmpty(item));
 };

 const getSessionProviders = (session: UsageSessionQueryTarget): string[] => {
  const providers = new Set<string>();
  if (session.modelProvider) {
-    providers.add(session.modelProvider.toLowerCase());
+    providers.add(normalizeLowercaseStringOrEmpty(session.modelProvider));
  }
  if (session.providerOverride) {
-    providers.add(session.providerOverride.toLowerCase());
+    providers.add(normalizeLowercaseStringOrEmpty(session.providerOverride));
  }
  if (session.origin?.provider) {
-    providers.add(session.origin.provider.toLowerCase());
+    providers.add(normalizeLowercaseStringOrEmpty(session.origin.provider));
  }
  for (const entry of session.usage?.modelUsage ?? []) {
    if (entry.provider) {
-      providers.add(entry.provider.toLowerCase());
+      providers.add(normalizeLowercaseStringOrEmpty(entry.provider));
    }
  }
  return Array.from(providers);
@@ -126,18 +128,18 @@ const getSessionProviders = (session: UsageSessionQueryTarget): string[] => {
 const getSessionModels = (session: UsageSessionQueryTarget): string[] => {
  const models = new Set<string>();
  if (session.model) {
-    models.add(session.model.toLowerCase());
+    models.add(normalizeLowercaseStringOrEmpty(session.model));
  }
  for (const entry of session.usage?.modelUsage ?? []) {
    if (entry.model) {
-      models.add(entry.model.toLowerCase());
+      models.add(normalizeLowercaseStringOrEmpty(entry.model));
    }
  }
  return Array.from(models);
 };

 const getSessionTools = (session: UsageSessionQueryTarget): string[] =>
-  (session.usage?.toolUsage?.tools ?? []).map((tool) => tool.name.toLowerCase());
+  (session.usage?.toolUsage?.tools ?? []).map((tool) => normalizeLowercaseStringOrEmpty(tool.name));

 const matchesUsageQuery = (session: UsageSessionQueryTarget, term: UsageQueryTerm): boolean => {
  const value = normalizeQueryText(term.value ?? "");
@@ -151,11 +153,11 @@ const matchesUsageQuery = (session: UsageSessionQueryTarget, term: UsageQueryTer
  const key = normalizeQueryText(term.key);
  switch (key) {
    case "agent":
-      return session.agentId?.toLowerCase().includes(value) ?? false;
+      return normalizeLowercaseStringOrEmpty(session.agentId).includes(value);
    case "channel":
-      return session.channel?.toLowerCase().includes(value) ?? false;
+      return normalizeLowercaseStringOrEmpty(session.channel).includes(value);
    case "chat":
-      return session.chatType?.toLowerCase().includes(value) ?? false;
+      return normalizeLowercaseStringOrEmpty(session.chatType).includes(value);
    case "provider":
      return getSessionProviders(session).some((provider) => provider.includes(value));
    case "model":
@@ -163,7 +165,7 @@ const matchesUsageQuery = (session: UsageSessionQueryTarget, term: UsageQueryTer
    case "tool":
      return getSessionTools(session).some((tool) => tool.includes(value));
    case "label":
-      return session.label?.toLowerCase().includes(value) ?? false;
+      return normalizeLowercaseStringOrEmpty(session.label).includes(value);
    case "key":
    case "session":
    case "id":
@@ -174,8 +176,8 @@ const matchesUsageQuery = (session: UsageSessionQueryTarget, term: UsageQueryTer
        );
      }
      return (
-        session.key.toLowerCase().includes(value) ||
-        (session.sessionId?.toLowerCase().includes(value) ?? false)
+        normalizeLowercaseStringOrEmpty(session.key).includes(value) ||
+        normalizeLowercaseStringOrEmpty(session.sessionId).includes(value)
      );
    case "has":
      switch (value) {
@@ -316,3 +318,4 @@ export function parseToolSummary(content: string) {
    cleanContent: nonToolLines.join("\n").trim(),
  };
 }
+import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
--- a/ui/src/ui/views/agents-panels-tools-skills.ts
+++ b/ui/src/ui/views/agents-panels-tools-skills.ts
@@ -1,6 +1,7 @@
 import { html, nothing } from "lit";
 import { normalizeToolName } from "../../../../src/agents/tool-policy-shared.js";
 import { t } from "../../i18n/index.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type {
  SkillStatusEntry,
  SkillStatusReport,
@@ -416,10 +417,12 @@ export function renderAgentSkills(params: {
  const usingAllowlist = allowlist !== undefined;
  const reportReady = Boolean(params.report && params.activeAgentId === params.agentId);
  const rawSkills = reportReady ? (params.report?.skills ?? []) : [];
-  const filter = params.filter.trim().toLowerCase();
+  const filter = normalizeLowercaseStringOrEmpty(params.filter);
  const filtered = filter
    ? rawSkills.filter((skill) =>
-        [skill.name, skill.description, skill.source].join(" ").toLowerCase().includes(filter),
+        normalizeLowercaseStringOrEmpty(
+          [skill.name, skill.description, skill.source].join(" "),
+        ).includes(filter),
      )
    : rawSkills;
  const groups = groupSkills(filtered);
--- a/ui/src/ui/views/agents-utils.ts
+++ b/ui/src/ui/views/agents-utils.ts
@@ -4,6 +4,7 @@ import {
  normalizeToolName,
  resolveToolProfilePolicy,
 } from "../../../../src/agents/tool-policy-shared.js";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type {
  AgentIdentityResult,
  AgentsFilesListResult,
@@ -586,7 +587,7 @@ export function buildModelOptions(
  const seen = new Set<string>();
  const options: ConfiguredModelOption[] = [];
  const addOption = (value: string, label: string) => {
-    const key = value.toLowerCase();
+    const key = normalizeLowercaseStringOrEmpty(value);
    if (seen.has(key)) {
      return;
    }
@@ -607,7 +608,7 @@ export function buildModelOptions(
    }
  }

-  if (current && !seen.has(current.toLowerCase())) {
+  if (current && !seen.has(normalizeLowercaseStringOrEmpty(current))) {
    options.unshift({ value: current, label: `Current (${current})` });
  }

--- a/ui/src/ui/views/chat.ts
+++ b/ui/src/ui/views/chat.ts
@@ -31,6 +31,7 @@ import {
 } from "../chat/slash-commands.ts";
 import { isSttSupported, startStt, stopStt } from "../chat/speech.ts";
 import { icons } from "../icons.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import { detectTextDirection } from "../text-direction.ts";
 import type { GatewaySessionRow, SessionsListResult } from "../types.ts";
 import type { ChatItem, MessageGroup } from "../types/chat-types.ts";
@@ -495,12 +496,12 @@ function updateSlashMenu(value: string, requestUpdate: () => void): void {
  // Arg mode: /command <partial-arg>
  const argMatch = value.match(/^\/(\S+)\s(.*)$/);
  if (argMatch) {
-    const cmdName = argMatch[1].toLowerCase();
-    const argFilter = argMatch[2].toLowerCase();
+    const cmdName = normalizeLowercaseStringOrEmpty(argMatch[1]);
+    const argFilter = normalizeLowercaseStringOrEmpty(argMatch[2]);
    const cmd = SLASH_COMMANDS.find((c) => c.name === cmdName);
    if (cmd?.argOptions?.length) {
      const filtered = argFilter
-        ? cmd.argOptions.filter((opt) => opt.toLowerCase().startsWith(argFilter))
+        ? cmd.argOptions.filter((opt) => normalizeLowercaseStringOrEmpty(opt).startsWith(argFilter))
        : cmd.argOptions;
      if (filtered.length > 0) {
        vs.slashMenuMode = "args";
@@ -1421,13 +1422,14 @@ function groupMessages(items: ChatItem[]): Array<ChatItem | MessageGroup> {

    const normalized = normalizeMessage(item.message);
    const role = normalizeRoleForGrouping(normalized.role);
-    const senderLabel = role.toLowerCase() === "user" ? (normalized.senderLabel ?? null) : null;
+    const senderLabel =
+      normalizeLowercaseStringOrEmpty(role) === "user" ? (normalized.senderLabel ?? null) : null;
    const timestamp = normalized.timestamp || Date.now();

    if (
      !currentGroup ||
      currentGroup.role !== role ||
-      (role.toLowerCase() === "user" && currentGroup.senderLabel !== senderLabel)
+      (normalizeLowercaseStringOrEmpty(role) === "user" && currentGroup.senderLabel !== senderLabel)
    ) {
      if (currentGroup) {
        result.push(currentGroup);
@@ -1486,7 +1488,7 @@ function buildChatItems(props: ChatProps): Array<ChatItem | MessageGroup> {
      continue;
    }

-    if (!props.showToolCalls && normalized.role.toLowerCase() === "toolresult") {
+    if (!props.showToolCalls && normalizeLowercaseStringOrEmpty(normalized.role) === "toolresult") {
      continue;
    }

--- a/ui/src/ui/views/command-palette.ts
+++ b/ui/src/ui/views/command-palette.ts
@@ -3,6 +3,7 @@ import { ref } from "lit/directives/ref.js";
 import { t } from "../../i18n/index.ts";
 import { SLASH_COMMANDS } from "../chat/slash-commands.ts";
 import { icons, type IconName } from "../icons.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";

 type PaletteItem = {
  id: string;
@@ -97,11 +98,11 @@ function filteredItems(query: string): PaletteItem[] {
  if (!query) {
    return PALETTE_ITEMS;
  }
-  const q = query.toLowerCase();
+  const q = normalizeLowercaseStringOrEmpty(query);
  return PALETTE_ITEMS.filter(
    (item) =>
-      item.label.toLowerCase().includes(q) ||
-      (item.description?.toLowerCase().includes(q) ?? false),
+      normalizeLowercaseStringOrEmpty(item.label).includes(q) ||
+      normalizeLowercaseStringOrEmpty(item.description).includes(q),
  );
 }

--- a/ui/src/ui/views/config-form.node.ts
+++ b/ui/src/ui/views/config-form.node.ts
@@ -1,6 +1,10 @@
 import { html, nothing, type TemplateResult } from "lit";
 import { formatUnknownText } from "../format.ts";
 import { icons as sharedIcons } from "../icons.ts";
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "../string-coerce.ts";
 import type { ConfigUiHints } from "../types.ts";
 import {
  defaultValue,
@@ -218,7 +222,7 @@ export function parseConfigSearchQuery(query: string): ConfigSearchCriteria {
  const seen = new Set<string>();
  const raw = query.trim();
  const stripped = raw.replace(/(^|\s)tag:([^\s]+)/gi, (_, leading: string, token: string) => {
-    const normalized = token.trim().toLowerCase();
+    const normalized = normalizeLowercaseStringOrEmpty(token);
    if (normalized && !seen.has(normalized)) {
      seen.add(normalized);
      tags.push(normalized);
@@ -226,7 +230,7 @@ export function parseConfigSearchQuery(query: string): ConfigSearchCriteria {
    return leading;
  });
  return {
-    text: stripped.trim().toLowerCase(),
+    text: normalizeLowercaseStringOrEmpty(stripped),
    tags,
  };
 }
@@ -245,7 +249,7 @@ function normalizeTags(raw: unknown): string[] {
    if (!tag) {
      continue;
    }
-    const key = tag.toLowerCase();
+    const key = normalizeLowercaseStringOrEmpty(tag);
    if (seen.has(key)) {
      continue;
    }
@@ -277,7 +281,7 @@ function matchesText(text: string, candidates: Array<string | undefined>): boole
    return true;
  }
  for (const candidate of candidates) {
-    if (candidate && candidate.toLowerCase().includes(text)) {
+    if (normalizeOptionalLowercaseString(candidate)?.includes(text)) {
      return true;
    }
  }
@@ -288,7 +292,7 @@ function matchesTags(filterTags: string[], fieldTags: string[]): boolean {
  if (filterTags.length === 0) {
    return true;
  }
-  const normalized = new Set(fieldTags.map((tag) => tag.toLowerCase()));
+  const normalized = new Set(fieldTags.map((tag) => normalizeLowercaseStringOrEmpty(tag)));
  return filterTags.every((tag) => normalized.has(tag));
 }

--- a/ui/src/ui/views/config-form.render.ts
+++ b/ui/src/ui/views/config-form.render.ts
@@ -1,5 +1,6 @@
 import { html, nothing } from "lit";
 import { icons } from "../icons.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { ConfigUiHints } from "../types.ts";
 import { matchesNodeSearch, parseConfigSearchQuery, renderNode } from "./config-form.node.ts";
 import { hintForPath, humanize, schemaType, type JsonSchema } from "./config-form.shared.ts";
@@ -342,9 +343,9 @@ function matchesSearch(params: {
  const meta = SECTION_META[params.key];
  const sectionMetaMatches =
    q &&
-    (params.key.toLowerCase().includes(q) ||
-      (meta?.label ? meta.label.toLowerCase().includes(q) : false) ||
-      (meta?.description ? meta.description.toLowerCase().includes(q) : false));
+    (normalizeLowercaseStringOrEmpty(params.key).includes(q) ||
+      (meta?.label ? normalizeLowercaseStringOrEmpty(meta.label).includes(q) : false) ||
+      (meta?.description ? normalizeLowercaseStringOrEmpty(meta.description).includes(q) : false));

  if (sectionMetaMatches && criteria.tags.length === 0) {
    return true;
--- a/ui/src/ui/views/config-form.shared.ts
+++ b/ui/src/ui/views/config-form.shared.ts
@@ -1,3 +1,4 @@
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { ConfigUiHint, ConfigUiHints } from "../types.ts";

 export type JsonSchema = {
@@ -125,7 +126,7 @@ function isEnvVarPlaceholder(value: string): boolean {
 }

 export function isSensitiveConfigPath(path: string): boolean {
-  const lowerPath = path.toLowerCase();
+  const lowerPath = normalizeLowercaseStringOrEmpty(path);
  const whitelisted = SENSITIVE_KEY_WHITELIST_SUFFIXES.some((suffix) => lowerPath.endsWith(suffix));
  return !whitelisted && SENSITIVE_PATTERNS.some((pattern) => pattern.test(path));
 }
--- a/ui/src/ui/views/logs.ts
+++ b/ui/src/ui/views/logs.ts
@@ -1,5 +1,6 @@
 import { html, nothing } from "lit";
 import { t } from "../../i18n/index.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { LogEntry, LogLevel } from "../types.ts";

 const LEVELS: LogLevel[] = ["trace", "debug", "info", "warn", "error", "fatal"];
@@ -36,15 +37,14 @@ function matchesFilter(entry: LogEntry, needle: string) {
  if (!needle) {
    return true;
  }
-  const haystack = [entry.message, entry.subsystem, entry.raw]
-    .filter(Boolean)
-    .join(" ")
-    .toLowerCase();
+  const haystack = normalizeLowercaseStringOrEmpty(
+    [entry.message, entry.subsystem, entry.raw].filter(Boolean).join(" "),
+  );
  return haystack.includes(needle);
 }

 export function renderLogs(props: LogsProps) {
-  const needle = props.filterText.trim().toLowerCase();
+  const needle = normalizeLowercaseStringOrEmpty(props.filterText);
  const levelFiltered = LEVELS.some((level) => !props.levelFilters[level]);
  const filtered = props.entries.filter((entry) => {
    if (entry.level && !props.levelFilters[entry.level]) {
--- a/ui/src/ui/views/overview-hints.ts
+++ b/ui/src/ui/views/overview-hints.ts
@@ -1,4 +1,5 @@
 import { ConnectErrorDetailCodes } from "../../../../src/gateway/protocol/connect-error-details.js";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";

 const AUTH_REQUIRED_CODES = new Set<string>([
  ConnectErrorDetailCodes.AUTH_REQUIRED,
@@ -40,7 +41,7 @@ export function shouldShowPairingHint(
  if (lastErrorCode === ConnectErrorDetailCodes.PAIRING_REQUIRED) {
    return true;
  }
-  return lastError.toLowerCase().includes("pairing required");
+  return normalizeLowercaseStringOrEmpty(lastError).includes("pairing required");
 }

 /**
@@ -66,7 +67,7 @@ export function resolveAuthHintKind(params: {
    return AUTH_REQUIRED_CODES.has(params.lastErrorCode) ? "required" : "failed";
  }

-  const lower = params.lastError.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(params.lastError);
  if (!lower.includes("unauthorized")) {
    return null;
  }
@@ -84,6 +85,6 @@ export function shouldShowInsecureContextHint(
  if (lastErrorCode) {
    return INSECURE_CONTEXT_CODES.has(lastErrorCode);
  }
-  const lower = lastError.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(lastError);
  return lower.includes("secure context") || lower.includes("device identity required");
 }
--- a/ui/src/ui/views/overview.ts
+++ b/ui/src/ui/views/overview.ts
@@ -6,6 +6,7 @@ import { formatRelativeTimestamp, formatDurationHuman } from "../format.ts";
 import type { GatewayHelloOk } from "../gateway.ts";
 import { icons } from "../icons.ts";
 import type { UiSettings } from "../storage.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type {
  AttentionItem,
  CronJob,
@@ -196,7 +197,7 @@ export function renderOverview(props: OverviewProps) {
    if (props.connected || !props.lastError || !props.warnQueryToken) {
      return null;
    }
-    const lower = props.lastError.toLowerCase();
+    const lower = normalizeLowercaseStringOrEmpty(props.lastError);
    const authFailed = lower.includes("unauthorized") || lower.includes("device identity required");
    if (!authFailed) {
      return null;
--- a/ui/src/ui/views/sessions.ts
+++ b/ui/src/ui/views/sessions.ts
@@ -4,6 +4,7 @@ import { formatRelativeTimestamp } from "../format.ts";
 import { icons } from "../icons.ts";
 import { pathForTab } from "../navigation.ts";
 import { formatSessionTokens } from "../presenter.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type {
  GatewaySessionRow,
  SessionCompactionCheckpoint,
@@ -82,7 +83,7 @@ function normalizeProviderId(provider?: string | null): string {
  if (!provider) {
    return "";
  }
-  const normalized = provider.trim().toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(provider);
  if (normalized === "z.ai" || normalized === "z-ai") {
    return "zai";
  }
@@ -144,15 +145,15 @@ function resolveThinkLevelPatchValue(value: string, isBinary: boolean): string |
 }

 function filterRows(rows: GatewaySessionRow[], query: string): GatewaySessionRow[] {
-  const q = query.trim().toLowerCase();
+  const q = normalizeLowercaseStringOrEmpty(query);
  if (!q) {
    return rows;
  }
  return rows.filter((row) => {
-    const key = (row.key ?? "").toLowerCase();
-    const label = (row.label ?? "").toLowerCase();
-    const kind = (row.kind ?? "").toLowerCase();
-    const displayName = (row.displayName ?? "").toLowerCase();
+    const key = normalizeLowercaseStringOrEmpty(row.key);
+    const label = normalizeLowercaseStringOrEmpty(row.label);
+    const kind = normalizeLowercaseStringOrEmpty(row.kind);
+    const displayName = normalizeLowercaseStringOrEmpty(row.displayName);
    return key.includes(q) || label.includes(q) || kind.includes(q) || displayName.includes(q);
  });
 }
--- a/ui/src/ui/views/skills.ts
+++ b/ui/src/ui/views/skills.ts
@@ -8,6 +8,7 @@ import type {
 } from "../controllers/skills.ts";
 import { clampText } from "../format.ts";
 import { resolveSafeExternalUrl } from "../open-external-url.ts";
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import type { SkillStatusEntry, SkillStatusReport } from "../types.ts";
 import { groupSkills } from "./skills-grouping.ts";
 import {
@@ -114,10 +115,12 @@ export function renderSkills(props: SkillsProps) {
      ? skills
      : skills.filter((s) => skillMatchesStatus(s, props.statusFilter));

-  const filter = props.filter.trim().toLowerCase();
+  const filter = normalizeLowercaseStringOrEmpty(props.filter);
  const filtered = filter
    ? afterStatus.filter((skill) =>
-        [skill.name, skill.description, skill.source].join(" ").toLowerCase().includes(filter),
+        normalizeLowercaseStringOrEmpty(
+          [skill.name, skill.description, skill.source].join(" "),
+        ).includes(filter),
      )
    : afterStatus;
  const groups = groupSkills(filtered);
--- a/ui/src/ui/views/usage-query.ts
+++ b/ui/src/ui/views/usage-query.ts
@@ -1,3 +1,4 @@
+import { normalizeLowercaseStringOrEmpty } from "../string-coerce.ts";
 import { extractQueryTerms } from "../usage-helpers.ts";
 import { CostDailyEntry, UsageAggregates, UsageSessionEntry } from "./usageTypes.ts";

@@ -138,8 +139,8 @@ const buildQuerySuggestions = (
    ? [lastToken.slice(0, lastToken.indexOf(":")), lastToken.slice(lastToken.indexOf(":") + 1)]
    : ["", ""];

-  const key = rawKey.toLowerCase();
-  const value = rawValue.toLowerCase();
+  const key = normalizeLowercaseStringOrEmpty(rawKey);
+  const value = normalizeLowercaseStringOrEmpty(rawValue);

  const unique = (items: Array<string | undefined>): string[] => {
    const set = new Set<string>();
@@ -181,7 +182,7 @@ const buildQuerySuggestions = (
  const suggestions: QuerySuggestion[] = [];
  const addValues = (prefix: string, values: string[]) => {
    for (const val of values) {
-      if (!value || val.toLowerCase().includes(value)) {
+      if (!value || normalizeLowercaseStringOrEmpty(val).includes(value)) {
        suggestions.push({ label: `${prefix}:${val}`, value: `${prefix}:${val}` });
      }
    }
@@ -227,7 +228,7 @@ const applySuggestionToQuery = (query: string, suggestion: string): string => {
  return `${tokens.join(" ")} `;
 };

-const normalizeQueryText = (value: string): string => value.trim().toLowerCase();
+const normalizeQueryText = (value: string): string => normalizeLowercaseStringOrEmpty(value);

 const addQueryToken = (query: string, token: string): string => {
  const trimmed = query.trim();