diff --git a/molecule_runtime/a2a_cli.py b/molecule_runtime/a2a_cli.py
index 9aae8f4..5fe97f6 100644
--- a/molecule_runtime/a2a_cli.py
+++ b/molecule_runtime/a2a_cli.py
@@ -24,7 +24,7 @@ import httpx
 from builtin_tools.validation import WorkspaceIdValidationError, get_validated_workspace_id
 
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")  # used for discover() headers only; URL uses validated version
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 
 
 async def discover(target_id: str) -> dict | None:
diff --git a/molecule_runtime/a2a_client.py b/molecule_runtime/a2a_client.py
index 76fb205..e9b2956 100644
--- a/molecule_runtime/a2a_client.py
+++ b/molecule_runtime/a2a_client.py
@@ -16,7 +16,7 @@ from .platform_auth import auth_headers
 logger = logging.getLogger(__name__)
 
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 
 # Cache workspace ID → name mappings (populated by list_peers calls)
 _peer_names: dict[str, str] = {}
diff --git a/molecule_runtime/a2a_mcp_server.py b/molecule_runtime/a2a_mcp_server.py
index 22a5497..33d93a7 100644
--- a/molecule_runtime/a2a_mcp_server.py
+++ b/molecule_runtime/a2a_mcp_server.py
@@ -14,7 +14,7 @@ the claude --print invocation.
 
 Environment variables (set by the workspace container):
   WORKSPACE_ID  — this workspace's ID
-  PLATFORM_URL  — platform API base URL (e.g. http://platform:8080)
+  PLATFORM_URL  — platform API base URL (default: http://host.docker.internal:8080)
 """
 
 import argparse
@@ -314,7 +314,7 @@ async def _handle_stdio():
                         "result": {
                             "protocolVersion": "2024-11-05",
                             "capabilities": {"tools": {"listChanged": False}},
-                            "serverInfo": {"name": "a2a-delegation", "version": "1.0.0"},
+                            "serverInfo": {"name": "molecule", "version": "1.0.0"},
                         },
                     })
 
@@ -361,15 +361,7 @@ _connection_queues: dict[str, asyncio.Queue] = {}
 _connection_lock = asyncio.Lock()
 
 
-async def _sse_broadcaster(request_id: str, response: dict, conn_id: str):
-    """Send a JSON-RPC response to a specific SSE connection."""
-    async with _connection_lock:
-        queue = _connection_queues.get(conn_id)
-    if queue is not None:
-        await queue.put(response)
-
-
-async def _handle_http_mcp(request) -> dict:
+async def _handle_http_mcp(request) -> dict | None:
     """Handle an incoming JSON-RPC request over HTTP. Returns the JSON-RPC response."""
     try:
         body = await request.json()
@@ -386,7 +378,7 @@ async def _handle_http_mcp(request) -> dict:
             "result": {
                 "protocolVersion": "2024-11-05",
                 "capabilities": {"tools": {"listChanged": False}},
-                "serverInfo": {"name": "a2a-delegation", "version": "1.0.0"},
+                "serverInfo": {"name": "molecule", "version": "1.0.0"},
             },
         }
 
@@ -440,7 +432,7 @@ async def _run_http_server(port: int):
 
     async def sse_handler(request):
         """GET endpoint — SSE stream for push-based responses."""
-        conn_id = str(uuid.uuid4())[:8]
+        conn_id = str(uuid.uuid4())  # full UUID to avoid collision across connections
         queue: asyncio.Queue = asyncio.Queue(maxsize=100)
 
         async with _connection_lock:
@@ -452,8 +444,9 @@ async def _run_http_server(port: int):
                 while True:
                     response = await asyncio.wait_for(queue.get(), timeout=300)
                     yield f"event: message\ndata: {json.dumps(response)}\n\n"
+                    # Emit a heartbeat when the queue is drained (connection alive but idle)
                     if queue.empty():
-                        yield "event: heartbeat\ndata: {}\n\n"
+                        yield "event: heartbeat\ndata: null\n\n"
             except asyncio.TimeoutError:
                 pass
             finally:
diff --git a/molecule_runtime/adapters/base.py b/molecule_runtime/adapters/base.py
index a1820e7..2c22b5a 100644
--- a/molecule_runtime/adapters/base.py
+++ b/molecule_runtime/adapters/base.py
@@ -229,7 +229,7 @@ class BaseAdapter(ABC):
         from builtin_tools.memory import commit_memory, search_memory
         from builtin_tools.sandbox import run_code
 
-        platform_url = os.environ.get("PLATFORM_URL", "http://platform:8080")
+        platform_url = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 
         # Load plugins from per-workspace dir first, then shared fallback
         workspace_plugins_dir = os.path.join(config.config_path, "plugins")
diff --git a/molecule_runtime/builtin_tools/a2a_tools.py b/molecule_runtime/builtin_tools/a2a_tools.py
index 61c21c1..ef15b53 100644
--- a/molecule_runtime/builtin_tools/a2a_tools.py
+++ b/molecule_runtime/builtin_tools/a2a_tools.py
@@ -11,7 +11,7 @@ import httpx
 
 from builtin_tools.validation import WorkspaceIdValidationError, get_validated_workspace_id
 
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")  # used only for tracing headers; URLs use validated version
 
 
diff --git a/molecule_runtime/builtin_tools/approval.py b/molecule_runtime/builtin_tools/approval.py
index 4a87b0c..790e844 100644
--- a/molecule_runtime/builtin_tools/approval.py
+++ b/molecule_runtime/builtin_tools/approval.py
@@ -32,7 +32,7 @@ RBAC denials emit an ``rbac / rbac.deny / denied`` event instead.
 
 Environment variables
 ---------------------
-PLATFORM_URL            Platform base URL            (default: http://platform:8080)
+PLATFORM_URL            Platform base URL            (default: http://host.docker.internal:8080)
 WORKSPACE_ID            This workspace's ID (validated at startup by platform_auth)
 APPROVAL_TIMEOUT        Max wait in seconds          (default: 300)
 APPROVAL_POLL_INTERVAL  Polling interval in seconds  (default: 5, polling path only)
@@ -55,7 +55,7 @@ from builtin_tools.validation import WorkspaceIdValidationError, get_validated_w
 
 logger = logging.getLogger(__name__)
 
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 from molecule_runtime.platform_auth import WORKSPACE_ID
 APPROVAL_POLL_INTERVAL = float(os.environ.get("APPROVAL_POLL_INTERVAL", "5"))
 APPROVAL_TIMEOUT = float(os.environ.get("APPROVAL_TIMEOUT", "300"))
diff --git a/molecule_runtime/builtin_tools/delegation.py b/molecule_runtime/builtin_tools/delegation.py
index 4e42438..e21c0e1 100644
--- a/molecule_runtime/builtin_tools/delegation.py
+++ b/molecule_runtime/builtin_tools/delegation.py
@@ -30,7 +30,7 @@ from builtin_tools.telemetry import (
     inject_trace_headers,
 )
 
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 from molecule_runtime.platform_auth import WORKSPACE_ID
 DELEGATION_RETRY_ATTEMPTS = int(os.environ.get("DELEGATION_RETRY_ATTEMPTS", "3"))
 DELEGATION_RETRY_DELAY = float(os.environ.get("DELEGATION_RETRY_DELAY", "5.0"))
diff --git a/molecule_runtime/builtin_tools/hitl.py b/molecule_runtime/builtin_tools/hitl.py
index d7bccc2..5335838 100644
--- a/molecule_runtime/builtin_tools/hitl.py
+++ b/molecule_runtime/builtin_tools/hitl.py
@@ -177,7 +177,7 @@ async def _notify_channels(
     Errors in individual channels are logged but never re-raised so that a
     misconfigured Slack webhook cannot block the approval flow.
     """
-    platform_url = os.environ.get("PLATFORM_URL", "http://platform:8080")
+    platform_url = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
     workspace_id = os.environ.get("WORKSPACE_ID", "")
 
     for channel in cfg.channels:
diff --git a/molecule_runtime/builtin_tools/memory.py b/molecule_runtime/builtin_tools/memory.py
index 268494b..1908684 100644
--- a/molecule_runtime/builtin_tools/memory.py
+++ b/molecule_runtime/builtin_tools/memory.py
@@ -42,7 +42,7 @@ try:  # pragma: no cover - optional runtime dependency in lightweight test envs
 except ImportError:  # pragma: no cover
     httpx = SimpleNamespace(AsyncClient=None)
 
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")
 
 
diff --git a/molecule_runtime/consolidation.py b/molecule_runtime/consolidation.py
index 6d6ef61..58c8d15 100644
--- a/molecule_runtime/consolidation.py
+++ b/molecule_runtime/consolidation.py
@@ -19,7 +19,7 @@ from .platform_auth import auth_headers
 
 logger = logging.getLogger(__name__)
 
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")
 CONSOLIDATION_INTERVAL = float(os.environ.get("CONSOLIDATION_INTERVAL", "300"))  # 5 min
 CONSOLIDATION_THRESHOLD = int(os.environ.get("CONSOLIDATION_THRESHOLD", "10"))  # min memories before consolidating
diff --git a/molecule_runtime/coordinator.py b/molecule_runtime/coordinator.py
index ce9d0cb..c1f28ee 100644
--- a/molecule_runtime/coordinator.py
+++ b/molecule_runtime/coordinator.py
@@ -23,7 +23,7 @@ from policies.routing import build_team_routing_payload
 
 logger = logging.getLogger(__name__)
 
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")
 
 
diff --git a/molecule_runtime/main.py b/molecule_runtime/main.py
index 77d6247..ce28eba 100644
--- a/molecule_runtime/main.py
+++ b/molecule_runtime/main.py
@@ -63,7 +63,7 @@ from transcript_auth import transcript_authorized as _transcript_authorized
 async def main():  # pragma: no cover
     workspace_id = os.environ.get("WORKSPACE_ID", "workspace-default")
     config_path = os.environ.get("WORKSPACE_CONFIG_PATH", "/configs")
-    platform_url = os.environ.get("PLATFORM_URL", "http://platform:8080")
+    platform_url = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
     awareness_config = get_awareness_config()
 
     # 0. Normalise LLM auth env vars based on token type.
diff --git a/molecule_runtime/molecule_ai_status.py b/molecule_runtime/molecule_ai_status.py
index f01b48f..03d4d96 100644
--- a/molecule_runtime/molecule_ai_status.py
+++ b/molecule_runtime/molecule_ai_status.py
@@ -25,7 +25,7 @@ import httpx
 from builtin_tools.validation import WorkspaceIdValidationError, get_validated_workspace_id
 
 WORKSPACE_ID = os.environ.get("WORKSPACE_ID", "")
-PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://platform:8080")
+PLATFORM_URL = os.environ.get("PLATFORM_URL", "http://host.docker.internal:8080")
 
 
 def set_status(task: str):