diff --git a/packages/app/src/composer/agent-controls/mode-control.tsx b/packages/app/src/composer/agent-controls/mode-control.tsx
index d9ffbb642..79c7ee151 100644
--- a/packages/app/src/composer/agent-controls/mode-control.tsx
+++ b/packages/app/src/composer/agent-controls/mode-control.tsx
@@ -1,4 +1,12 @@
-import { memo, useCallback, useMemo, useRef, useState, type ReactElement } from "react";
+import {
+  memo,
+  useCallback,
+  useMemo,
+  useRef,
+  useState,
+  type ComponentType,
+  type ReactElement,
+} from "react";
 import { Pressable, Text, View, type PressableStateCallbackType } from "react-native";
 import { StyleSheet, useUnistyles } from "react-native-unistyles";
 import { useShallow } from "zustand/shallow";
@@ -33,13 +41,18 @@ function shouldRenderForPlacement(placement: AgentModeControlPlacement, isCompac
   return placement === "footer" ? isCompact : !isCompact;
 }
 
-const MODE_ICONS = {
+interface ModeIconProps {
+  size?: number;
+  color?: string;
+}
+
+const MODE_ICONS: Record<string, ComponentType<ModeIconProps>> = {
   Bot,
   ShieldCheck,
   ShieldAlert,
   ShieldOff,
   ShieldQuestionMark,
-} as const;
+};
 
 interface ModePalette {
   blue: { 500: string };
@@ -87,9 +100,9 @@ function ModeComboboxOption({
   iconColor,
 }: ModeComboboxOptionProps) {
   const visuals = getModeVisuals(provider, option.id, providerDefinitions);
-  const IconComponent = visuals?.icon ? MODE_ICONS[visuals.icon] : ShieldCheck;
+  const IconComponent = visuals?.icon ? MODE_ICONS[visuals.icon] : undefined;
   const leadingSlot = useMemo(
-    () => <IconComponent size={16} color={iconColor} />,
+    () => (IconComponent ? <IconComponent size={16} color={iconColor} /> : null),
     [IconComponent, iconColor],
   );
   return (
@@ -137,7 +150,7 @@ function AgentModeControlView({
   const visuals = selectedMode
     ? getModeVisuals(provider, selectedMode.id, providerDefinitions)
     : undefined;
-  const Icon = visuals?.icon ? MODE_ICONS[visuals.icon] : ShieldCheck;
+  const Icon = visuals?.icon ? MODE_ICONS[visuals.icon] : undefined;
   const iconColor = getModeIconColor(visuals?.colorTier, theme.colors.palette);
   const selectedModeLabel = selectedMode ? formatAgentModeLabel(selectedMode) : "";
 
@@ -224,7 +237,7 @@ function AgentModeControlView({
         accessibilityLabel={`Select agent mode (${selectedModeLabel})`}
         testID="mode-control"
       >
-        <Icon size={theme.iconSize.md} color={iconColor} />
+        {Icon ? <Icon size={theme.iconSize.md} color={iconColor} /> : null}
         <Text style={labelStyle}>{selectedModeLabel}</Text>
         <ChevronDown size={theme.iconSize.sm} color={iconColor} />
       </Pressable>
diff --git a/packages/server/src/client/daemon-client.ts b/packages/server/src/client/daemon-client.ts
index 481d06f1a..602ee14a9 100644
--- a/packages/server/src/client/daemon-client.ts
+++ b/packages/server/src/client/daemon-client.ts
@@ -4264,6 +4264,7 @@ export class DaemonClient {
           protocolVersion: 1,
           capabilities: {
             [CLIENT_CAPS.reasoningMergeEnum]: true,
+            [CLIENT_CAPS.customModeIcons]: true,
           },
           ...(this.config.appVersion ? { appVersion: this.config.appVersion } : {}),
         }),
diff --git a/packages/server/src/server/agent/provider-manifest.ts b/packages/server/src/server/agent/provider-manifest.ts
index e4b1161aa..2b94745ff 100644
--- a/packages/server/src/server/agent/provider-manifest.ts
+++ b/packages/server/src/server/agent/provider-manifest.ts
@@ -2,12 +2,10 @@ import { z } from "zod";
 import type { AgentMode } from "./agent-sdk-types.js";
 
 export type AgentModeColorTier = "safe" | "moderate" | "dangerous" | "planning" | `#${string}`;
-export type AgentModeIcon =
-  | "Bot"
-  | "ShieldCheck"
-  | "ShieldAlert"
-  | "ShieldOff"
-  | "ShieldQuestionMark";
+// Open string by design: the client looks icons up in a registry and falls back
+// to a default for unknown values. Daemon downgrades unknown icons for clients
+// that pre-date the open-string contract (see CLIENT_CAPS.customModeIcons).
+export type AgentModeIcon = string;
 
 export interface AgentModeVisuals {
   icon: AgentModeIcon;
diff --git a/packages/server/src/server/session.ts b/packages/server/src/server/session.ts
index 460d62c2e..d5d88c64c 100644
--- a/packages/server/src/server/session.ts
+++ b/packages/server/src/server/session.ts
@@ -324,6 +324,14 @@ type GitMutationRefreshReason =
 // Clients before 0.1.45 validate providers with z.enum(["claude", "codex", "opencode"]) and reject
 // the entire session message if they encounter an unknown provider.
 const LEGACY_PROVIDER_IDS = new Set(["claude", "codex", "opencode"]);
+// COMPAT(customModeIcons): the only mode icons known to clients before v0.1.84. Any
+// other icon name is downgraded to "ShieldCheck" for those clients.
+const LEGACY_MODE_ICONS = new Set<string>([
+  "ShieldCheck",
+  "ShieldAlert",
+  "ShieldOff",
+  "ShieldQuestionMark",
+]);
 const MIN_VERSION_ALL_PROVIDERS = "0.1.45";
 const MIN_VERSION_FLEXIBLE_EDITOR_IDS = "0.1.50";
 
@@ -994,6 +1002,25 @@ export class Session {
     return this.clientCapabilities.has(capability);
   }
 
+  // COMPAT(customModeIcons): rewrite icons unknown to v0.1.83 clients (whose MODE_ICONS
+  // map is a closed enum and would render `undefined`, crashing in render). Drop
+  // this and the cap gate when floor >= v0.1.84.
+  private downgradeModeIconsForClient<T extends { icon?: string }>(modes: T[]): T[] {
+    if (this.supports(CLIENT_CAPS.customModeIcons)) return modes;
+    return modes.map((mode) =>
+      mode.icon && !LEGACY_MODE_ICONS.has(mode.icon) ? { ...mode, icon: "ShieldCheck" } : mode,
+    );
+  }
+
+  private downgradeEntryModesForClient<T extends { modes?: { icon?: string }[] }>(
+    entries: T[],
+  ): T[] {
+    if (this.supports(CLIENT_CAPS.customModeIcons)) return entries;
+    return entries.map((entry) =>
+      entry.modes ? { ...entry, modes: this.downgradeModeIconsForClient(entry.modes) } : entry,
+    );
+  }
+
   async syncWorkspaceGitObserverForWorkspace(workspace: PersistedWorkspaceRecord): Promise<void> {
     const descriptor = await this.describeWorkspaceRecordWithGitData(workspace);
     this.syncWorkspaceGitObservers([descriptor]);
@@ -1244,7 +1271,7 @@ export class Session {
           type: "providers_snapshot_update",
           payload: {
             ...(snapshotCwd ? { cwd: snapshotCwd } : {}),
-            entries: visibleEntries,
+            entries: this.downgradeEntryModesForClient(visibleEntries),
             generatedAt: new Date().toISOString(),
           },
         });
@@ -3800,7 +3827,7 @@ export class Session {
           type: "list_provider_modes_response",
           payload: {
             provider: msg.provider,
-            modes: entry.modes ?? [],
+            modes: this.downgradeModeIconsForClient(entry.modes ?? []),
             error: null,
             fetchedAt: entry.fetchedAt ?? fetchedAt,
             requestId: msg.requestId,
@@ -3841,7 +3868,7 @@ export class Session {
         type: "list_provider_modes_response",
         payload: {
           provider: msg.provider,
-          modes,
+          modes: this.downgradeModeIconsForClient(modes),
           error: null,
           fetchedAt,
           requestId: msg.requestId,
@@ -4065,7 +4092,7 @@ export class Session {
     this.emit({
       type: "get_providers_snapshot_response",
       payload: {
-        entries,
+        entries: this.downgradeEntryModesForClient(entries),
         generatedAt: new Date().toISOString(),
         requestId: msg.requestId,
       },
diff --git a/packages/server/src/shared/client-capabilities.ts b/packages/server/src/shared/client-capabilities.ts
index d7d3ba6ec..0b602c137 100644
--- a/packages/server/src/shared/client-capabilities.ts
+++ b/packages/server/src/shared/client-capabilities.ts
@@ -1,5 +1,10 @@
 export const CLIENT_CAPS = {
   reasoningMergeEnum: "reasoning_merge_enum",
+  // COMPAT(customModeIcons): added in v0.1.84. Old clients pin AgentModeIcon to
+  // a closed enum and crash rendering unknown values; daemon downgrades icons
+  // outside the legacy set to "ShieldCheck" when this cap is absent. Drop the
+  // gate when floor >= v0.1.84.
+  customModeIcons: "custom_mode_icons",
 } as const;
 
 export type ClientCapability = (typeof CLIENT_CAPS)[keyof typeof CLIENT_CAPS];
diff --git a/packages/server/src/shared/messages.ts b/packages/server/src/shared/messages.ts
index f50ec22f7..d7894503f 100644
--- a/packages/server/src/shared/messages.ts
+++ b/packages/server/src/shared/messages.ts
@@ -4053,6 +4053,7 @@ export const WSHelloMessageSchema = z.object({
       voice: z.boolean().optional(),
       pushNotifications: z.boolean().optional(),
       [CLIENT_CAPS.reasoningMergeEnum]: z.boolean().optional(),
+      [CLIENT_CAPS.customModeIcons]: z.boolean().optional(),
     })
     .passthrough()
     .optional(),