opencode/packages/opencode/test/agent/plan-mode-subagent-bypass.test.ts

/**
 * Reproducer for opencode issue #26514:
 *
 * In Plan Mode (the `plan` agent), the main agent's edit/write tools are
 * blocked by the plan agent's permission ruleset (`edit: { "*": "deny" }`).
 * However, when the plan agent spawns a subagent via the `task` tool, the
 * subagent retains full file modification capabilities — a security bypass.
 *
 * This test replicates the permission ruleset that would govern a
 * `general` subagent when launched from a `plan` parent session, mirroring
 * the logic in `src/tool/task.ts` (filtered parent permissions ++ runtime
 * subagent agent permissions, evaluated as in `session/prompt.ts`).
 *
 * The expected (secure) behavior is that the subagent inherits the plan
 * mode read-only restriction and `edit`/`write` resolve to `deny`. On
 * origin/dev this assertion fails because the parent **agent** permissions
 * are not propagated to the subagent — only the parent **session**
 * permissions are passed through, and Plan Mode's restrictions live on the
 * agent, not the session.
 */
import { expect } from "bun:test"
import { Effect } from "effect"
import { Agent } from "../../src/agent/agent"
import { deriveSubagentSessionPermission } from "../../src/agent/subagent-permissions"
import { Permission } from "../../src/permission"
import { testEffect } from "../lib/effect"

const it = testEffect(Agent.defaultLayer)

// `deriveSubagentSessionPermission` is imported from production. The test
// exercises the actual helper that task.ts uses to build the subagent's
// session permission, so any regression in that helper trips this test.

it.instance("[#26514] subagent spawned from plan mode inherits read-only restriction (edit denied)", () =>
  Effect.gen(function* () {
    const planAgent = yield* Agent.Service.use((svc) => svc.get("plan"))
    const generalAgent = yield* Agent.Service.use((svc) => svc.get("general"))

    expect(planAgent).toBeDefined()
    expect(generalAgent).toBeDefined()
    // Sanity: the plan agent itself blocks edit. (Note: `write` and
    // `apply_patch` route through the `edit` permission at the runtime
    // tool layer — see Permission.disabled / EDIT_TOOLS.)
    expect(Permission.evaluate("edit", "/some/file.ts", planAgent!.permission).action).toBe("deny")

    // Simulate the plan-mode parent session: in real flow the plan
    // session's `permission` field is empty (Plan Mode lives on the agent
    // ruleset, not the session). So we pass [] through as the parent
    // session permission, exactly like the actual code path.
    const parentSessionPermission: Permission.Ruleset = []

    const subagentSessionPermission = deriveSubagentSessionPermission({
      parentSessionPermission,
      parentAgent: planAgent,
      subagent: generalAgent!,
    })

    // Mirror the runtime evaluation in session/prompt.ts (~line 410, 639):
    //   ruleset: Permission.merge(agent.permission, session.permission ?? [])
    const effective = Permission.merge(generalAgent!.permission, subagentSessionPermission)

    expect(Permission.evaluate("edit", "/some/file.ts", effective).action).toBe("deny")
    expect(Permission.evaluate("edit", "/another/path/index.tsx", effective).action).toBe("deny")
  }),
)

it.instance("[#26514] explore subagent launched from plan mode also stays read-only", () =>
  // Sibling check: even though `explore` is intrinsically read-only, the
  // bug surface is the same. Including this case to document that the fix
  // should propagate the parent **agent** permissions, not just deny edit
  // when the subagent happens to already deny it.
  Effect.gen(function* () {
    const planAgent = yield* Agent.Service.use((svc) => svc.get("plan"))
    const explore = yield* Agent.Service.use((svc) => svc.get("explore"))
    expect(planAgent).toBeDefined()
    expect(explore).toBeDefined()

    const parentSessionPermission: Permission.Ruleset = []
    const subagentSessionPermission = deriveSubagentSessionPermission({
      parentSessionPermission,
      parentAgent: planAgent,
      subagent: explore!,
    })
    const effective = Permission.merge(explore!.permission, subagentSessionPermission)

    // Already deny — sanity check.
    expect(Permission.evaluate("edit", "/x.ts", effective).action).toBe("deny")
  }),
)

it.instance(
  "[#26514] custom user subagent launched from plan mode bypasses Plan Mode read-only",
  // The most damaging case: a user-defined subagent with default
  // permissions (allow-by-default, like `general`). The subagent must NOT
  // be able to edit when the parent agent is `plan`.
  () =>
    Effect.gen(function* () {
      const planAgent = yield* Agent.Service.use((svc) => svc.get("plan"))
      const my = yield* Agent.Service.use((svc) => svc.get("my_subagent"))
      expect(planAgent).toBeDefined()
      expect(my).toBeDefined()

      const parentSessionPermission: Permission.Ruleset = []
      const subagentSessionPermission = deriveSubagentSessionPermission({
        parentSessionPermission,
        parentAgent: planAgent,
        subagent: my!,
      })
      const effective = Permission.merge(my!.permission, subagentSessionPermission)

      // BUG: on origin/dev edit resolves to "allow" because the plan
      // agent's `edit: deny *` rule never reaches the subagent.
      expect(Permission.evaluate("edit", "/some/file.ts", effective).action).toBe("deny")
    }),
  {
    config: {
      agent: {
        my_subagent: {
          description: "A user-defined subagent",
          mode: "subagent",
        },
      },
    },
  },
)