From 6d3c6aec7c613ee7e688a5410e84334846b59fae Mon Sep 17 00:00:00 2001
From: arunpshankar <141447424+arunpshankar@users.noreply.github.com>
Date: Mon, 10 Aug 2026 14:36:30 -0500
Subject: [PATCH] fix(a2a): declare a2a-sdk[http-server] so the a2a extra can
 serve

The `a2a` extra installs `a2a-sdk` with no extras, which is enough to
import the package but not to run the server. `sse-starlette` is only
declared under a2a-sdk's `http-server`, `fastapi` and `all` extras, and
every server dispatcher imports it at module level:

    a2a.server.routes.jsonrpc_dispatcher
    a2a.server.routes.rest_dispatcher
    a2a.compat.v0_3.jsonrpc_adapter

`to_a2a()` builds an `A2AStarletteApplication`, which routes through the
first of these, so a clean install of `google-adk[a2a]` raises
ModuleNotFoundError: No module named 'sse_starlette' at startup.

This is invisible during development because `mcp` requires
sse-starlette, so any environment that has ever installed the `mcp`
extra already satisfies it by accident. It surfaces on the first clean
install - typically a container - and the runtime reports a failed
startup probe on the port rather than the missing module.

Repro, from an empty venv:

    pip install "a2a-sdk>=0.3.4,<2"          # what the a2a extra installs
    python -c "import a2a.server.routes.jsonrpc_dispatcher"
    # ModuleNotFoundError: No module named 'sse_starlette'

    pip install "a2a-sdk[http-server]>=0.3.4,<2"
    python -c "import a2a.server.routes.jsonrpc_dispatcher"   # ok

`http-server` rather than a direct `sse-starlette` pin because it states
the intent - ADK serves the A2A HTTP application - and leaves the
transitive set to a2a-sdk. The extra exists at the pinned floor (0.3.4)
and carries sse-starlette through the current 1.1.2, so it holds across
the whole `>=0.3.4,<2` range.

This is not the lazy-import case: the import is inside a2a-sdk, and it
is needed to serve, not merely to import. It also leaves
test_constructing_agent_defers_optional_mcp_server_stack unaffected -
that asserts sse_starlette is not imported when constructing an Agent,
which installing it does not change.
---
 pyproject.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index da19c11bef..d14db5d0bd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -58,7 +58,7 @@ dependencies = [
   "websockets>=15.0.1,<16",
 ]
 optional-dependencies.a2a = [
-  "a2a-sdk>=0.3.4,<2",
+  "a2a-sdk[http-server]>=0.3.4,<2",
 ]
 optional-dependencies.agent-identity = [
   "google-cloud-agentidentitycredentials>=0.1,<0.2",