diff --git a/openhands-agent-server/openhands/agent_server/docker/Dockerfile b/openhands-agent-server/openhands/agent_server/docker/Dockerfile
index b857f7b221..72020191e4 100644
--- a/openhands-agent-server/openhands/agent_server/docker/Dockerfile
+++ b/openhands-agent-server/openhands/agent_server/docker/Dockerfile
@@ -93,14 +93,40 @@ RUN set -eux; \
     rm -rf /var/lib/apt/lists/*
 
 # Pre-install ACP servers for ACPAgent support (Claude Code, Codex, Gemini CLI)
-# Install Node.js/npm if not present (SWE-bench base images may lack them)
+# Install Node.js 22 to a dedicated prefix so ACP packages get a modern runtime
+# WITHOUT overwriting the repo-specific Node.js that test suites depend on.
+# SWE-bench images ship NVM/apt-managed Node 8-14 which cannot run ACP packages.
+ENV ACP_NODE_DIR=/opt/acp-node
 RUN set -eux; \
-    if ! command -v npm >/dev/null 2>&1; then \
-        curl -fsSL https://deb.nodesource.com/setup_22.x | bash - && \
-        apt-get install -y --no-install-recommends nodejs && \
-        rm -rf /var/lib/apt/lists/*; \
-    fi; \
-    npm install -g @zed-industries/claude-agent-acp @zed-industries/codex-acp @google/gemini-cli
+    ARCH=$(dpkg --print-architecture); \
+    case "$ARCH" in \
+      amd64) NARCH=x64; NODE_SHA256=69b09dba5c8dcb05c4e4273a4340db1005abeafe3927efda2bc5b249e80437ec;; \
+      arm64) NARCH=arm64; NODE_SHA256=08bfbf538bad0e8cbb0269f0173cca28d705874a67a22f60b57d99dc99e30050;; \
+      *) echo "Unsupported architecture for ACP Node install: $ARCH" >&2; exit 1;; \
+    esac; \
+    NODE_TARBALL="/tmp/node-v22.14.0-linux-${NARCH}.tar.xz"; \
+    mkdir -p "$ACP_NODE_DIR"; \
+    curl -fsSL "https://nodejs.org/dist/v22.14.0/node-v22.14.0-linux-${NARCH}.tar.xz" -o "$NODE_TARBALL"; \
+    echo "$NODE_SHA256  $NODE_TARBALL" | sha256sum -c -; \
+    tar -xJ --strip-components=1 -C "$ACP_NODE_DIR" -f "$NODE_TARBALL"; \
+    rm -f "$NODE_TARBALL"; \
+    PATH="$ACP_NODE_DIR/bin:$PATH"; \
+    node --version; \
+    npm install -g \
+      @zed-industries/claude-agent-acp \
+      @zed-industries/codex-acp \
+      @google/gemini-cli; \
+    # Create wrappers in /usr/local/bin that prepend ACP's Node 22 to PATH.
+    # This ensures the ACP binary's #!/usr/bin/env node shebang resolves to
+    # Node 22, while the repo's own node (NVM/system) stays untouched for tests.
+    for bin in claude-agent-acp codex-acp gemini; do \
+      if [ -e "$ACP_NODE_DIR/bin/$bin" ]; then \
+        printf '#!/bin/sh\nPATH="%s/bin:$PATH" exec "%s/bin/%s" "$@"\n' \
+          "$ACP_NODE_DIR" "$ACP_NODE_DIR" "$bin" \
+          > /usr/local/bin/"$bin"; \
+        chmod +x /usr/local/bin/"$bin"; \
+      fi; \
+    done
 
 # Configure Claude Code managed settings for headless operation:
 # Allow all tool permissions (no human in the loop to approve).
diff --git a/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py b/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
index 9113c4ecd9..a171a3576f 100644
--- a/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
+++ b/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
@@ -3,6 +3,7 @@
 from collections.abc import Mapping
 from pathlib import Path
 
+from openhands.sdk.agent.acp_agent import ACPAgent
 from openhands.sdk.agent.base import AgentBase
 from openhands.sdk.context.prompts.prompt import render_template
 from openhands.sdk.conversation.base import BaseConversation
@@ -484,6 +485,16 @@ def _ensure_agent_ready(self) -> None:
 
             self._agent_ready = True
 
+    def _should_initialize_agent_on_send_message(self) -> bool:
+        """Return whether send_message() should eagerly initialize the agent.
+
+        ACPAgent startup is substantially heavier than regular agent
+        initialization because it launches and handshakes with an external ACP
+        subprocess. Deferring that work to run() keeps send_message() fast and
+        avoids HTTP client read timeouts on the remote conversation endpoint.
+        """
+        return not isinstance(self.agent, ACPAgent)
+
     def switch_profile(self, profile_name: str) -> None:
         """Switch the agent's LLM to a named profile.
 
@@ -520,8 +531,12 @@ def send_message(self, message: str | Message, sender: str | None = None) -> Non
                    one agent delegates to another, the sender can be set to
                    identify which agent is sending the message.
         """
-        # Ensure agent is fully initialized (loads plugins and initializes agent)
-        self._ensure_agent_ready()
+        # ACPAgent startup can take much longer than a normal send_message()
+        # round-trip because it launches and initializes a subprocess-backed
+        # session. Defer that work to run() so enqueueing the user message
+        # remains fast for remote callers.
+        if self._should_initialize_agent_on_send_message():
+            self._ensure_agent_ready()
 
         if isinstance(message, str):
             message = Message(role="user", content=[TextContent(text=message)])
diff --git a/tests/sdk/conversation/local/test_conversation_send_message.py b/tests/sdk/conversation/local/test_conversation_send_message.py
index e19f87c334..b43c4c7e7b 100644
--- a/tests/sdk/conversation/local/test_conversation_send_message.py
+++ b/tests/sdk/conversation/local/test_conversation_send_message.py
@@ -1,8 +1,14 @@
+from unittest.mock import patch
+
 from pydantic import SecretStr
 
+from openhands.sdk.agent.acp_agent import ACPAgent
 from openhands.sdk.agent.base import AgentBase
 from openhands.sdk.conversation import Conversation, LocalConversation
-from openhands.sdk.conversation.state import ConversationState
+from openhands.sdk.conversation.state import (
+    ConversationExecutionStatus,
+    ConversationState,
+)
 from openhands.sdk.conversation.types import (
     ConversationCallbackType,
     ConversationTokenCallbackType,
@@ -153,3 +159,45 @@ def test_send_message_with_message_object():
     assert len(user_event.llm_message.content) == 1
     assert isinstance(user_event.llm_message.content[0], TextContent)
     assert user_event.llm_message.content[0].text == test_text
+
+
+def test_acp_send_message_defers_initialization_until_run(tmp_path):
+    """ACP conversations should enqueue messages before starting ACP bootstrap."""
+
+    agent = ACPAgent(acp_command=["echo", "test"])
+    conversation = LocalConversation(agent=agent, workspace=str(tmp_path))
+    test_text = "Hello from ACP"
+
+    def _finish_immediately(self, conv, on_event, on_token=None):
+        conv.state.execution_status = ConversationExecutionStatus.FINISHED
+
+    with (
+        patch.object(ACPAgent, "init_state", autospec=True) as mock_init_state,
+        patch.object(
+            ACPAgent,
+            "step",
+            autospec=True,
+            side_effect=_finish_immediately,
+        ) as mock_step,
+    ):
+        conversation.send_message(test_text)
+
+        assert mock_init_state.call_count == 0
+        assert mock_step.call_count == 0
+        assert len(conversation.state.events) == 1
+        user_event = conversation.state.events[-1]
+        assert isinstance(user_event, MessageEvent)
+        assert user_event.source == "user"
+        assert user_event.llm_message.role == "user"
+        assert len(user_event.llm_message.content) == 1
+        assert isinstance(user_event.llm_message.content[0], TextContent)
+        assert user_event.llm_message.content[0].text == test_text
+
+        conversation.run()
+
+        assert mock_init_state.call_count == 1
+        assert mock_step.call_count == 1
+        assert (
+            conversation.state.execution_status == ConversationExecutionStatus.FINISHED
+        )
+        assert conversation.state.events[-1] == user_event