Set $callers in tool and prompt handler processes

CHANGELOG.md

@@ -1,3 +1,10 @@
+## Unreleased
+
+- Tool and prompt handlers run with the dispatching process in `$callers`, as
+  in a `Task`. Mocking and stubbing libraries and the Ecto SQL sandbox, which
+  find their owner through `$callers`, now reach handlers called with
+  `Phantom.Test` without global or shared mode.
+
 ## 0.7.1 (2026-10-08)
 
 - A GET SSE stream for a session that already has one replaces it instead of

lib/phantom/router.ex

@@ -2028,9 +2028,11 @@ defmodule Phantom.Router do
     request_id = request.id
     parent_pid = session.pid
     task_session = %{session | request: %{request | spec: spec}}
+    callers = [self() | Process.get(:"$callers", [])]
 
     worker =
       spawn(fn ->
+        Process.put(:"$callers", callers)
         # The isolated handler uses these process keys to return its eventual
         # result to the transport process that owns the current request.
         Process.put(:phantom_adopter, parent_pid)

test/phantom/handler_callers_test.exs

@@ -0,0 +1,43 @@
+defmodule Phantom.HandlerCallersTest do
+  use ExUnit.Case, async: true
+
+  defmodule Router do
+    use Phantom.Router, name: "HandlerCallers", vsn: "1.0"
+
+    require Phantom.Prompt, as: Prompt
+    alias Phantom.Tool
+
+    tool :stubbed_tool, description: "Replies with a stubbed HTTP response"
+    prompt :stubbed_prompt, description: "Replies with a stubbed HTTP response"
+
+    def stubbed_tool(_params, session) do
+      {:reply, Tool.text(fetch_stub()), session}
+    end
+
+    def stubbed_prompt(_params, session) do
+      {:reply, Prompt.response(user: Prompt.text(fetch_stub())), session}
+    end
+
+    defp fetch_stub, do: Req.get!(plug: {Req.Test, __MODULE__}, retry: false).body
+  end
+
+  import Phantom.Test
+
+  setup do
+    Phantom.Test.start(router: Router)
+    Req.Test.stub(Router, &Req.Test.text(&1, "stubbed"))
+    {:ok, session: build_session(Router)}
+  end
+
+  test "a tool handler can use stubs owned by the calling test", %{session: session} do
+    session
+    |> call_tool(:stubbed_tool, %{})
+    |> assert_tool_text("stubbed")
+  end
+
+  test "a prompt handler can use stubs owned by the calling test", %{session: session} do
+    session
+    |> get_prompt(:stubbed_prompt, %{})
+    |> assert_prompt_message(text: "stubbed")
+  end
+end