diff --git a/extensions/acpx/src/acpx-runtime-compat.d.ts b/extensions/acpx/src/acpx-runtime-compat.d.ts
index 646871b5888..a7d97fad294 100644
--- a/extensions/acpx/src/acpx-runtime-compat.d.ts
+++ b/extensions/acpx/src/acpx-runtime-compat.d.ts
@@ -30,6 +30,7 @@ declare module "acpx/runtime" {
     permissionMode?: unknown;
     nonInteractivePermissions?: unknown;
     timeoutMs?: number;
+    probeAgent?: string;
   };
 
   export class AcpxRuntime {
diff --git a/extensions/acpx/src/config-schema.ts b/extensions/acpx/src/config-schema.ts
index 306f58f0cc7..0b390363d51 100644
--- a/extensions/acpx/src/config-schema.ts
+++ b/extensions/acpx/src/config-schema.ts
@@ -34,7 +34,6 @@ export type AcpxPluginConfig = {
   strictWindowsCmdWrapper?: boolean;
   timeoutSeconds?: number;
   queueOwnerTtlSeconds?: number;
-  probeAgent?: string;
   mcpServers?: Record<string, McpServerConfig>;
   agents?: Record<string, { command: string }>;
 };
@@ -50,7 +49,6 @@ export type ResolvedAcpxPluginConfig = {
   strictWindowsCmdWrapper: boolean;
   timeoutSeconds?: number;
   queueOwnerTtlSeconds: number;
-  probeAgent?: string;
   legacyCompatibilityConfig: {
     strictWindowsCmdWrapper?: boolean;
     queueOwnerTtlSeconds?: number;
@@ -109,7 +107,6 @@ export const AcpxPluginConfigSchema = z.strictObject({
     .number({ error: "queueOwnerTtlSeconds must be a number >= 0" })
     .min(0, { error: "queueOwnerTtlSeconds must be a number >= 0" })
     .optional(),
-  probeAgent: nonEmptyTrimmedString("probeAgent must be a non-empty string").optional(),
   mcpServers: z.record(z.string(), McpServerConfigSchema).optional(),
   agents: z
     .record(
diff --git a/extensions/acpx/src/config.ts b/extensions/acpx/src/config.ts
index a77a36e117c..76e26cef430 100644
--- a/extensions/acpx/src/config.ts
+++ b/extensions/acpx/src/config.ts
@@ -260,12 +260,16 @@ export function resolveAcpxPluginConfig(params: {
     ]),
   );
 
-  const probeAgent = normalized.probeAgent?.trim();
+  // Lowercase probeAgent so lookups match the registry keys built above, which
+  // also go through normalizeLowercaseStringOrEmpty. Without this, a user who
+  // writes `probeAgent: "OpenCode"` would silently miss the stored "opencode"
+  // key.
+  const probeAgent = normalizeLowercaseStringOrEmpty(normalized.probeAgent) || undefined;
 
   return {
     cwd,
     stateDir,
-    probeAgent: normalized.probeAgent,
+    probeAgent,
     permissionMode: normalized.permissionMode ?? DEFAULT_PERMISSION_MODE,
     nonInteractivePermissions:
       normalized.nonInteractivePermissions ?? DEFAULT_NON_INTERACTIVE_POLICY,
@@ -275,7 +279,6 @@ export function resolveAcpxPluginConfig(params: {
       normalized.strictWindowsCmdWrapper ?? DEFAULT_STRICT_WINDOWS_CMD_WRAPPER,
     timeoutSeconds: normalized.timeoutSeconds ?? DEFAULT_ACPX_TIMEOUT_SECONDS,
     queueOwnerTtlSeconds: normalized.queueOwnerTtlSeconds ?? DEFAULT_QUEUE_OWNER_TTL_SECONDS,
-    probeAgent: probeAgent && probeAgent.length > 0 ? probeAgent : undefined,
     legacyCompatibilityConfig: {
       strictWindowsCmdWrapper: normalized.strictWindowsCmdWrapper,
       queueOwnerTtlSeconds: normalized.queueOwnerTtlSeconds,
diff --git a/extensions/acpx/src/service.ts b/extensions/acpx/src/service.ts
index 576e4072f19..27175434b9a 100644
--- a/extensions/acpx/src/service.ts
+++ b/extensions/acpx/src/service.ts
@@ -53,7 +53,6 @@ function createDefaultRuntime(params: AcpxRuntimeFactoryParams): AcpxRuntimeLike
     mcpServers: toAcpMcpServers(params.pluginConfig.mcpServers),
     permissionMode: params.pluginConfig.permissionMode,
     nonInteractivePermissions: params.pluginConfig.nonInteractivePermissions,
-    probeAgent: params.pluginConfig.probeAgent,
     timeoutMs:
       params.pluginConfig.timeoutSeconds != null
         ? params.pluginConfig.timeoutSeconds * 1_000