diff --git a/src/components/automations/composer-invocations.tsx b/src/components/automations/composer-invocations.tsx
index 7c191145e0..45ef7316a0 100644
--- a/src/components/automations/composer-invocations.tsx
+++ b/src/components/automations/composer-invocations.tsx
@@ -87,7 +87,7 @@ export interface ComposerInvocations {
  * `isExternalMenuOpen`/`onExternalMenuKeyDown` escape hatch; a selected item
  * becomes a badge that serializes to its literal `/cmd` / `$skill` token on save.
  * Antigravity's and OpenCode's skills, which their servers never advertise,
- * join their commands under `/`.
+ * and a custom agent's declared skills join their commands under `/`.
  */
 export function useComposerInvocations({
   editorRef,
diff --git a/src/components/chat/composer/invocation-reference.test.ts b/src/components/chat/composer/invocation-reference.test.ts
index ade3877ac7..0baf35c074 100644
--- a/src/components/chat/composer/invocation-reference.test.ts
+++ b/src/components/chat/composer/invocation-reference.test.ts
@@ -130,8 +130,16 @@ describe("diskSkillTrigger", () => {
     expect(diskSkillTrigger("open_code")).toBe("/")
   })
 
+  // Custom ACP agents (e.g. user-configured Antigravity, or agents with declared
+  // skill directories) do not advertise skills as ACP commands; their skills
+  // live on disk and are invoked via `/`.
+  it("lists custom ACP agents' disk skills under `/`", () => {
+    expect(diskSkillTrigger("custom:antigravity-b")).toBe("/")
+    expect(diskSkillTrigger("custom:my-agent")).toBe("/")
+  })
+
   it("scans nothing for an agent that advertises its skills as commands", () => {
-    for (const agent of ["claude_code", "kimi_code", "gemini", "custom:x"]) {
+    for (const agent of ["claude_code", "kimi_code", "gemini"]) {
       expect(diskSkillTrigger(agent)).toBeNull()
     }
     expect(diskSkillTrigger(null)).toBeNull()
diff --git a/src/components/chat/composer/invocation-reference.ts b/src/components/chat/composer/invocation-reference.ts
index 977df932aa..65fcd9c287 100644
--- a/src/components/chat/composer/invocation-reference.ts
+++ b/src/components/chat/composer/invocation-reference.ts
@@ -1,8 +1,9 @@
 import type { KnownInvocations } from "@/lib/invocation-token"
-import type {
-  AgentSkillItem,
-  AgentType,
-  AvailableCommandInfo,
+import {
+  isCustomAgentType,
+  type AgentSkillItem,
+  type AgentType,
+  type AvailableCommandInfo,
 } from "@/lib/types"
 
 import type { ReferenceAttrs } from "./types"
@@ -36,12 +37,27 @@ export type InvocationPrefix = "/" | "$"
  *   configured and MCP-prompt ones), while it still loads every skill, names
  *   each to the model and gives the model a `skill` tool to load one by id. A
  *   `/<skill>` the user sends reaches the model as written.
+ * - Custom ACP agents (`custom:<id>`): `/`. codeg cannot tell whether an
+ *   arbitrary ACP server advertises its skills (Antigravity's
+ *   `agy_acp_server` run as a custom agent never does), so the scan follows the
+ *   user's own declaration instead: a custom agent that declares a dedicated
+ *   skills directory or the shared `.agents/skills` store lists those skills,
+ *   and one that declares neither gets `supported: false` and an empty list. A
+ *   declared skill the agent also advertises as a command is dropped by
+ *   {@link skillsForMenu}, so it is not listed twice.
  */
 export function diskSkillTrigger(
   agentType: AgentType | null | undefined
 ): InvocationPrefix | null {
+  if (!agentType) return null
   if (agentType === "codex") return "$"
-  if (agentType === "antigravity" || agentType === "open_code") return "/"
+  if (
+    agentType === "antigravity" ||
+    agentType === "open_code" ||
+    isCustomAgentType(agentType)
+  ) {
+    return "/"
+  }
   return null
 }
 
diff --git a/src/components/chat/message-input.test.tsx b/src/components/chat/message-input.test.tsx
index 1391fb4c23..3cef470850 100644
--- a/src/components/chat/message-input.test.tsx
+++ b/src/components/chat/message-input.test.tsx
@@ -1970,6 +1970,27 @@ describe("MessageInput slash menu for skills an agent does not advertise", () =>
     expect(agentSkills).toHaveBeenCalledWith("antigravity", null)
   })
 
+  it("lists custom ACP agents' skills from disk after their commands", async () => {
+    agentSkills.mockReturnValue([DEPLOY, SHADOWED])
+    await mountAndType({
+      agentType: "custom:antigravity-b",
+      availableCommands: COMMANDS,
+    })
+
+    const menu = await screen.findByTestId("slash-menu")
+    const rows = within(menu)
+      .getAllByRole("button")
+      .map((row) => row.textContent)
+    expect(rows).toEqual([
+      expect.stringMatching(/^\/plan/),
+      expect.stringMatching(/^\/logout/),
+      expect.stringMatching(/^\/usage/),
+      "DeployShip the build",
+    ])
+    expect(within(menu).queryByText("Plan skill")).toBeNull()
+    expect(agentSkills).toHaveBeenCalledWith("custom:antigravity-b", null)
+  })
+
   it("inserts a picked Antigravity skill as its `/` token", async () => {
     agentSkills.mockReturnValue([DEPLOY])
     const { editor } = await mountAndType(
diff --git a/src/components/chat/message-input.tsx b/src/components/chat/message-input.tsx
index eaf650c401..519b3ab593 100644
--- a/src/components/chat/message-input.tsx
+++ b/src/components/chat/message-input.tsx
@@ -381,9 +381,11 @@ export function MessageInput({
   // Skills read from disk feed the menu only for an agent that does not
   // advertise them itself: Codex under `$` (its native command set is very
   // small), Antigravity and OpenCode under `/` beside their commands (their
-  // ACP servers list only commands, never a skill). Every other agent surfaces
-  // its skills through ACP `availableCommands`, so a disk scan would only
-  // repeat them — skip it.
+  // ACP servers list only commands, never a skill), and custom agents under `/`
+  // from the skill directories their user declared (codeg cannot know what an
+  // arbitrary ACP server advertises). Every other built-in agent surfaces its
+  // skills through ACP `availableCommands`, so a disk scan would only repeat
+  // them — skip it.
   const skillTrigger = diskSkillTrigger(agentType)
   // Pass the working dir so we see both global skills and folder-scoped
   // project skills (e.g. `{folder}/.codex/skills`). Without this, users