feat(agent): add subagents config for per-agent task tool filtering

Add a new 'subagents' configuration option that allows primary agents to
specify which subagents appear in their Task tool description. This reduces
token overhead when many subagents are configured but only a subset is
relevant to a particular agent.

- Add 'subagents' field to Agent config schema (supports glob patterns)
- Filter task tool description based on caller's subagents list
- Add tests for the new filtering behavior
- Update documentation with usage examples

Closes #7269

Author: marcusquinn

packages/opencode/src/agent/agent.ts

@@ -35,6 +35,7 @@ export namespace Agent {
       prompt: z.string().optional(),
       options: z.record(z.string(), z.any()),
       steps: z.number().int().positive().optional(),
+      subagents: z.array(z.string()).optional(),
     })
     .meta({
       ref: "Agent",
@@ -198,6 +199,7 @@ export namespace Agent {
       item.hidden = value.hidden ?? item.hidden
       item.name = value.name ?? item.name
       item.steps = value.steps ?? item.steps
+      item.subagents = value.subagents ?? item.subagents
       item.options = mergeDeep(item.options, value.options ?? {})
       item.permission = PermissionNext.merge(item.permission, PermissionNext.fromConfig(value.permission ?? {}))
     }

packages/opencode/src/config/config.ts

@@ -502,6 +502,12 @@ export namespace Config {
         .describe("Maximum number of agentic iterations before forcing text-only response"),
       maxSteps: z.number().int().positive().optional().describe("@deprecated Use 'steps' field instead."),
       permission: Permission.optional(),
+      subagents: z
+        .array(z.string())
+        .optional()
+        .describe(
+          "List of subagent names this agent can spawn via the Task tool. When set, only these subagents will appear in the task tool description. Supports glob patterns (e.g., 'explore', 'code-*'). If not set, all subagents are available.",
+        ),
     })
     .catchall(z.any())
     .transform((agent, ctx) => {
@@ -521,6 +527,7 @@ export namespace Config {
         "permission",
         "disable",
         "tools",
+        "subagents",
       ])
 
       // Extract unknown properties into options

packages/opencode/src/tool/task.ts

@@ -11,6 +11,7 @@ import { iife } from "@/util/iife"
 import { defer } from "@/util/defer"
 import { Config } from "../config/config"
 import { PermissionNext } from "@/permission/next"
+import { Wildcard } from "@/util/wildcard"
 
 const parameters = z.object({
   description: z.string().describe("A short (3-5 words) description of the task"),
@@ -23,11 +24,11 @@ const parameters = z.object({
 export const TaskTool = Tool.define("task", async (ctx) => {
   const agents = await Agent.list().then((x) => x.filter((a) => a.mode !== "primary"))
 
-  // Filter agents by permissions if agent provided
+  // Filter agents by permissions and subagents list if agent provided
   const caller = ctx?.agent
-  const accessibleAgents = caller
-    ? agents.filter((a) => PermissionNext.evaluate("task", a.name, caller.permission).action !== "deny")
-    : agents
+  const accessibleAgents = agents
+    .filter((a) => !caller || PermissionNext.evaluate("task", a.name, caller.permission).action !== "deny")
+    .filter((a) => !caller?.subagents?.length || caller.subagents.some((pattern) => Wildcard.match(a.name, pattern)))
 
   const description = DESCRIPTION.replace(
     "{agents}",

packages/opencode/test/tool/task-subagents.test.ts

@@ -0,0 +1,70 @@
+import { describe, test, expect } from "bun:test"
+import { Wildcard } from "../../src/util/wildcard"
+
+describe("Task tool subagents filtering", () => {
+  // These tests verify the filtering logic used in task.ts
+  // The actual filtering is: agents.filter(a => !caller?.subagents?.length || caller.subagents.some(pattern => Wildcard.match(a.name, pattern)))
+
+  const mockAgents = [
+    { name: "general", description: "General purpose agent" },
+    { name: "explore", description: "Codebase exploration" },
+    { name: "code-reviewer", description: "Code review agent" },
+    { name: "code-formatter", description: "Code formatting agent" },
+    { name: "test-runner", description: "Test execution agent" },
+    { name: "docs-generator", description: "Documentation generator" },
+  ]
+
+  const filterAgents = (agents: typeof mockAgents, subagents?: string[]) =>
+    agents.filter((a) => !subagents?.length || subagents.some((pattern) => Wildcard.match(a.name, pattern)))
+
+  test("returns all agents when subagents is undefined", () => {
+    const result = filterAgents(mockAgents, undefined)
+    expect(result).toHaveLength(6)
+  })
+
+  test("returns all agents when subagents is empty array", () => {
+    const result = filterAgents(mockAgents, [])
+    expect(result).toHaveLength(6)
+  })
+
+  test("filters to exact matches", () => {
+    const result = filterAgents(mockAgents, ["general", "explore"])
+    expect(result).toHaveLength(2)
+    expect(result.map((a) => a.name)).toEqual(["general", "explore"])
+  })
+
+  test("filters using wildcard patterns", () => {
+    const result = filterAgents(mockAgents, ["code-*"])
+    expect(result).toHaveLength(2)
+    expect(result.map((a) => a.name)).toEqual(["code-reviewer", "code-formatter"])
+  })
+
+  test("filters using mixed exact and wildcard patterns", () => {
+    const result = filterAgents(mockAgents, ["general", "code-*"])
+    expect(result).toHaveLength(3)
+    expect(result.map((a) => a.name)).toEqual(["general", "code-reviewer", "code-formatter"])
+  })
+
+  test("filters using global wildcard allows all", () => {
+    const result = filterAgents(mockAgents, ["*"])
+    expect(result).toHaveLength(6)
+  })
+
+  test("filters using suffix wildcard", () => {
+    const result = filterAgents(mockAgents, ["*-runner", "*-generator"])
+    expect(result).toHaveLength(2)
+    expect(result.map((a) => a.name)).toEqual(["test-runner", "docs-generator"])
+  })
+
+  test("returns empty when no patterns match", () => {
+    const result = filterAgents(mockAgents, ["nonexistent", "also-nonexistent"])
+    expect(result).toHaveLength(0)
+  })
+
+  test("handles single character wildcard", () => {
+    // ? matches single character
+    const result = filterAgents(mockAgents, ["code-?eviewer"])
+    expect(result).toHaveLength(1)
+    expect(result[0].name).toBe("code-reviewer")
+  })
+})

packages/web/src/content/docs/agents.mdx

@@ -566,6 +566,37 @@ Users can always invoke any subagent directly via the `@` autocomplete menu, eve
 
 ---
 
+### Subagents
+
+Control which subagents appear in the Task tool description with the `subagents` option. This is useful for reducing token overhead when you have many subagents configured but only want specific ones available to a particular agent.
+
+```json title="opencode.json"
+{
+  "agent": {
+    "build": {
+      "mode": "primary",
+      "subagents": ["explore", "general", "code-*"]
+    }
+  }
+}
+```
+
+When `subagents` is set, only the listed subagents will appear in the Task tool description. This reduces the token cost of the system prompt, which can be significant when you have many subagents configured.
+
+:::tip
+The `subagents` option supports glob patterns. Use `code-*` to match all subagents starting with `code-`, or `*-reviewer` to match all subagents ending with `-reviewer`.
+:::
+
+:::note
+If `subagents` is not set or is an empty array, all subagents are available (the default behavior).
+:::
+
+The `subagents` option works alongside `permission.task`:
+- `subagents` controls which subagents appear in the tool description (affects token usage)
+- `permission.task` controls runtime access (ask/allow/deny)
+
+---
+
 ### Additional
 
 Any other options you specify in your agent configuration will be **passed through directly** to the provider as model options. This allows you to use provider-specific features and parameters.