diff --git a/opencode-sms-bridge/server.py b/opencode-sms-bridge/server.py
index 2279ba8..eda4647 100644
--- a/opencode-sms-bridge/server.py
+++ b/opencode-sms-bridge/server.py
@@ -480,18 +480,24 @@ def __init__(self, settings: Settings):
         basic = base64.b64encode(f"{settings.opencode_username}:{settings.opencode_password}".encode()).decode()
         self.headers = {"Authorization": f"Basic {basic}", "Content-Type": "application/json"}
 
-    def _request(self, path: str, payload: dict[str, Any]) -> dict[str, Any]:
+    def _request(self, path: str, payload: dict[str, Any] | None = None, method: str = "POST") -> dict[str, Any]:
         request = Request(
             f"{self.settings.opencode_base_url}{path}",
-            data=json.dumps(payload).encode(),
-            method="POST",
+            data=None if payload is None else json.dumps(payload).encode(),
+            method=method,
             headers=self.headers,
         )
         try:
             with build_opener(NoRedirect).open(request, timeout=self.settings.opencode_timeout_seconds) as response:
-                return json.loads(response.read().decode())
-        except (HTTPError, URLError, OSError, ValueError, json.JSONDecodeError) as error:
+                body = response.read()
+        except (HTTPError, URLError, OSError, ValueError) as error:
             raise BridgeError("OpenCode request failed") from error
+        if not body:
+            return {}
+        try:
+            return json.loads(body.decode())
+        except (UnicodeDecodeError, json.JSONDecodeError) as error:
+            raise BridgeError("OpenCode response was invalid") from error
 
     def create_session(self, agent: str) -> str:
         response = self._request("/api/session", {"agent": agent})
@@ -502,13 +508,34 @@ def create_session(self, agent: str) -> str:
         return session_id
 
     def prompt(self, session_id: str, parts: list[dict[str, str]]) -> str:
-        response = self._request(f"/session/{session_id}/message", {"parts": parts})
-        data = response.get("data", response)
-        candidates = data.get("parts", []) if isinstance(data, dict) else []
-        text = "".join(part.get("text", "") for part in candidates if part.get("type") == "text")
-        if not text.strip():
-            raise BridgeError("OpenCode response did not contain text")
-        return text.strip()
+        if any(part.get("type") != "text" for part in parts):
+            raise UnsupportedMedia("V2 file prompt mapping is not implemented")
+        text = "\n".join(part.get("text", "") for part in parts).strip()
+        if not text:
+            raise BridgeError("OpenCode prompt has no text")
+        admission = self._request(f"/api/session/{session_id}/prompt", {"prompt": {"text": text}})
+        data = admission.get("data")
+        if not isinstance(data, dict) or not isinstance(data.get("id"), str):
+            raise BridgeError("OpenCode prompt admission was invalid")
+        self._request(f"/api/session/{session_id}/wait")
+        response = self._request(f"/api/session/{session_id}/message?order=desc&limit=200", method="GET")
+        messages = response.get("data")
+        if not isinstance(messages, list):
+            raise BridgeError("OpenCode messages response was invalid")
+        for message in messages:
+            if not isinstance(message, dict) or message.get("type") != "assistant":
+                continue
+            content = message.get("content")
+            if not isinstance(content, list):
+                continue
+            reply = "".join(
+                part.get("text", "")
+                for part in content
+                if isinstance(part, dict) and part.get("type") == "text" and isinstance(part.get("text"), str)
+            )
+            if reply.strip():
+                return reply.strip()
+        raise BridgeError("OpenCode response did not contain text")
 
 
 def build_parts(settings: Settings, payload: dict[str, Any]) -> list[dict[str, str]]:
diff --git a/opencode-sms-bridge/test_server.py b/opencode-sms-bridge/test_server.py
index c2460d6..1ca6671 100644
--- a/opencode-sms-bridge/test_server.py
+++ b/opencode-sms-bridge/test_server.py
@@ -4,7 +4,7 @@
 import tempfile
 import unittest
 from pathlib import Path
-from unittest.mock import patch
+from unittest.mock import call, patch
 
 from cryptography.fernet import Fernet
 from fastapi.testclient import TestClient
@@ -17,6 +17,7 @@
     Routing,
     SQLiteStore,
     Settings,
+    UnsupportedMedia,
     create_ingress_app,
     load_routing,
     normalize_e164,
@@ -132,12 +133,31 @@ def test_ingress_ignores_unapproved_sender_before_queueing(self):
         enqueue.assert_not_called()
         self.assertIsNone(self.store.claim())
 
-    def test_prompt_uses_compatible_session_message_route(self):
-        parts = [{"type": "text", "text": "hello"}]
+    def test_prompt_uses_v2_admission_wait_and_message_flow(self):
         client = OpenCodeClient(self.settings)
-        with patch.object(client, "_request", return_value={"parts": [{"type": "text", "text": "reply"}]}) as request:
-            self.assertEqual(client.prompt("ses_123", parts), "reply")
-        request.assert_called_once_with("/session/ses_123/message", {"parts": parts})
+        with patch.object(
+            client,
+            "_request",
+            side_effect=[
+                {"data": {"id": "in_123"}},
+                {},
+                {"data": [{"type": "assistant", "content": [{"type": "text", "text": "reply"}]}]},
+            ],
+        ) as request:
+            self.assertEqual(client.prompt("ses_123", [{"type": "text", "text": "hello"}]), "reply")
+        request.assert_has_calls(
+            [
+                call("/api/session/ses_123/prompt", {"prompt": {"text": "hello"}}),
+                call("/api/session/ses_123/wait"),
+                call("/api/session/ses_123/message?order=desc&limit=200", method="GET"),
+            ]
+        )
+        self.assertEqual(request.call_count, 3)
+
+    def test_prompt_rejects_unmapped_file_parts(self):
+        client = OpenCodeClient(self.settings)
+        with self.assertRaises(UnsupportedMedia):
+            client.prompt("ses_123", [{"type": "file", "mime": "image/png", "filename": "image", "url": "data:image/png;base64,"}])
 
     def test_image_sanitization_removes_exif(self):
         image = Image.new("RGB", (8, 8), color="red")