diff --git a/docs/contracts/issues/17.contract.md b/docs/contracts/issues/17.contract.md
index 9fb16ca..1a5329a 100644
--- a/docs/contracts/issues/17.contract.md
+++ b/docs/contracts/issues/17.contract.md
@@ -1,7 +1,7 @@
 ---
 contract_version: "2.1"
 target_module: "ratatoskr.sessions + ratatoskr.provider (+ cli/tui/web trigger surfaces)"
-scope: "Issue #17 v1 — make the canary chat client self-drive AND observe its own Bifrost provider. Two parts. (1) BIND: `create_session` gains an optional single-plane Bifrost binding (`BifrostBinding{endpoint_url, scope}`) authenticated with a DISTINCT consumer Heimdall key; Worldtree runs the handshake synchronously at POST /sessions, so handshake failure is a session-create failure (502), surfaced on the create path. A plane selector (`memory`→:8391 / `affect`→:8390) + the consumer key thread through CLI / TUI / web; bound-state is visible. (2) OBSERVE: a structured op-feed in the provider, instrumented at the DISPATCH/ASGI layer (where the JWT ctx / session_id lives — bifrost passes ctx to upsert_many but NOT to search/get/delete, so the existing store-method stdout shim cannot see session_id), emitting JSONL {session_id, plane, op, req_summary, resp_summary, status, ts}. OPERATOR DECISIONS LOCKED: single-plane-per-session for v1 (composite endpoint fronting both planes is PARKED — vNext); op-feed with session-level correlation for v1 (turn-correlated debug-pane UI is PARKED — needs turn_id, TBD). Provider store scope semantics MUST NOT change (AND-parity with bifrost's reference store is a hard constraint). Direct in-session TDD; live-smoke against personal Worldtree is the load-bearing acceptance gate."
+scope: "Issue #17 v1 — make the canary chat client self-drive AND observe its own Bifrost provider. Two parts. (1) BIND: `create_session` gains an optional single-plane Bifrost binding (`BifrostBinding{endpoint_url, scope}`) authenticated with a DISTINCT consumer Heimdall key; Worldtree runs the handshake synchronously at POST /sessions, so handshake failure is a session-create failure (502), surfaced on the create path. A plane selector (`memory`→:8391 / `affect`→:8390; `combined`→:8392 added post-#17 — the #18 composite, the web default) + the consumer key thread through CLI / TUI / web; bound-state is visible. (2) OBSERVE: a structured op-feed in the provider, instrumented at the DISPATCH/ASGI layer (where the JWT ctx / session_id lives — bifrost passes ctx to upsert_many but NOT to search/get/delete, so the existing store-method stdout shim cannot see session_id), emitting JSONL {session_id, plane, op, req_summary, resp_summary, status, ts}. OPERATOR DECISIONS LOCKED: single-plane-per-session for v1 (composite endpoint fronting both planes was PARKED at #17 — later shipped as #18 and surfaced in the web bind as the `combined` plane); op-feed with session-level correlation for v1 (turn-correlated debug-pane UI is PARKED — needs turn_id, TBD). Provider store scope semantics MUST NOT change (AND-parity with bifrost's reference store is a hard constraint). Direct in-session TDD; live-smoke against personal Worldtree is the load-bearing acceptance gate."
 depends_on:
   - "httpx"
   - "ratatoskr.sessions"
@@ -92,8 +92,8 @@ async def create_session(
 
 
 def endpoint_for_plane(plane: str, base_host: str) -> str:
-    """'memory'->:8391, 'affect'->:8390 → f'http://{base_host}:{port}'. The
-    Worldtree-visible base URL. See FN endpoint_for_plane."""
+    """'memory'->:8391, 'affect'->:8390, 'combined'->:8392 (#18 composite) →
+    f'http://{base_host}:{port}'. The Worldtree-visible base URL. See FN endpoint_for_plane."""
 ```
 
 ```python
@@ -218,12 +218,12 @@ STEPS:
 
 ```contract
 FN endpoint_for_plane(plane: str, base_host: str) -> str
-BRIEF: Map a plane name to the Worldtree-visible provider base URL (memory->:8391, affect->:8390).
+BRIEF: Map a plane name to the Worldtree-visible provider base URL (memory->:8391, affect->:8390, combined->:8392 — the #18 composite both-plane endpoint, surfaced post-#17).
 
-PRE: [PRE-001 hard] plane in {"memory", "affect"} -- else ValueError
-POST: [POST-001 return_value] returns f"http://{base_host}:{port}", port 8391 (memory) / 8390 (affect) -- assert
+PRE: [PRE-001 hard] plane in {"memory", "affect", "combined"} -- else ValueError
+POST: [POST-001 return_value] returns f"http://{base_host}:{port}", port 8391 (memory) / 8390 (affect) / 8392 (combined) -- assert
 STEPS:
-  1. port = 8391 if plane == "memory" else 8390
+  1. port = {"memory": 8391, "affect": 8390, "combined": 8392}[plane]
   2. return the Worldtree-VISIBLE base URL (not client loopback); HTTPS relaxation is allowlist-side, not a URL concern
 ```
 
diff --git a/pyproject.toml b/pyproject.toml
index 070f191..b89c13e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "ratatoskr"
-version = "0.18.0"
+version = "0.18.1"
 description = "Worldtree Conversation API debug TUI — multi-pane observability dashboard"
 readme = "README.md"
 requires-python = ">=3.12"
diff --git a/src/ratatoskr/sessions.py b/src/ratatoskr/sessions.py
index 83c3945..0d626ec 100644
--- a/src/ratatoskr/sessions.py
+++ b/src/ratatoskr/sessions.py
@@ -227,19 +227,21 @@ async def list_sessions(
 def endpoint_for_plane(plane: str, base_host: str) -> str:
     """Map a provider plane name to its Worldtree-VISIBLE base URL.
 
-    Issue #17 dev helper: `memory` → :8391, `affect` → :8390. Returns the
-    Worldtree-visible base (e.g. `http://10.100.10.50:8391`), NOT the client's
-    loopback — Worldtree must reach the provider over the network. `http://` is
-    deliberate: the HTTPS relaxation is allowlist-side (Worldtree's
-    BIFROST_CLIENT_ALLOWED_HOSTS), not a URL concern. A production HTTPS endpoint
-    is supplied directly, bypassing this helper.
+    Issue #17 dev helper: `memory` → :8391, `affect` → :8390, `combined` → :8392
+    (the #18 composite both-plane endpoint). Returns the Worldtree-visible base
+    (e.g. `http://10.100.10.50:8391`), NOT the client's loopback — Worldtree must
+    reach the provider over the network. `http://` is deliberate: the HTTPS
+    relaxation is allowlist-side (Worldtree's BIFROST_CLIENT_ALLOWED_HOSTS), not a
+    URL concern. A production HTTPS endpoint is supplied directly, bypassing this
+    helper.
     """
-    if plane not in ("memory", "affect"):
+    ports = {"memory": 8391, "affect": 8390, "combined": 8392}
+    if plane not in ports:
         raise ValueError(
-            f"unknown plane: {plane!r} (expected 'memory' or 'affect')"
+            f"unknown plane: {plane!r} "
+            "(expected 'memory', 'affect', or 'combined')"
         )
-    port = 8391 if plane == "memory" else 8390
-    return f"http://{base_host}:{port}"
+    return f"http://{base_host}:{ports[plane]}"
 
 
 def _bifrost_error_from(resp: httpx.Response) -> str | None:
diff --git a/src/ratatoskr/web/server.py b/src/ratatoskr/web/server.py
index 3668d07..850d3ac 100644
--- a/src/ratatoskr/web/server.py
+++ b/src/ratatoskr/web/server.py
@@ -138,7 +138,7 @@ async def _create_session_endpoint(request: Request) -> JSONResponse:
     consumer_key = request.app.state.bifrost_consumer_key
     visible_host = request.app.state.bifrost_visible_host
     if bifrost_plane:
-        if bifrost_plane not in ("memory", "affect"):
+        if bifrost_plane not in ("memory", "affect", "combined"):
             return JSONResponse(
                 {"error_code": "invalid_bifrost_plane"}, status_code=400
             )
diff --git a/src/ratatoskr/web/static/index.html b/src/ratatoskr/web/static/index.html
index 8c881ce..5be3a22 100644
--- a/src/ratatoskr/web/static/index.html
+++ b/src/ratatoskr/web/static/index.html
@@ -513,6 +513,7 @@ body {
     <label class="field-label" for="bifrost-plane">Bifrost binding (Tier-3 provider)</label>
     <div class="select-wrap">
       <select id="bifrost-plane">
+        <option value="combined" selected>combined (:8392) — PAD + memory in one session</option>
         <option value="">none — observe only</option>
         <option value="memory">memory (:8391) — durable recall</option>
         <option value="affect">affect (:8390) — persona / PAD</option>
diff --git a/tests/test_sessions.py b/tests/test_sessions.py
index 917a677..dd21c65 100644
--- a/tests/test_sessions.py
+++ b/tests/test_sessions.py
@@ -384,6 +384,13 @@ class TestEndpointForPlane:
             == "http://10.100.10.50:8390"
         )
 
+    def test_combined_plane_maps_to_8392(self) -> None:
+        """combined [#18 composite]: 'combined' → http://<host>:8392 (POST-001)."""
+        assert (
+            endpoint_for_plane("combined", "10.100.10.50")
+            == "http://10.100.10.50:8392"
+        )
+
     def test_unknown_plane_raises_value_error(self) -> None:
         """unknown_plane [adversarial]: any other plane → ValueError (PRE-001)."""
         with pytest.raises(ValueError):
diff --git a/tests/test_web_server.py b/tests/test_web_server.py
index dec7887..641065e 100644
--- a/tests/test_web_server.py
+++ b/tests/test_web_server.py
@@ -837,6 +837,50 @@ class TestWebBifrostBind:
         }
         assert upstream.headers["Authorization"] == "Bearer server-ck"
 
+    @respx.mock
+    def test_combined_plane_binds_to_8392(self) -> None:
+        """combined [#18 composite]: a 'combined' plane from the browser → the server
+        binds the :8392 both-plane endpoint; bound-state echoes plane='combined'."""
+        import json as _json
+
+        from ratatoskr.web.server import create_app
+
+        route = respx.post("https://w.example/sessions").mock(
+            return_value=httpx.Response(201, json=_CREATE_OK)
+        )
+        app = create_app(
+            _mock_client_factory(),
+            bifrost_consumer_key="server-ck",
+            bifrost_visible_host="10.100.10.50",
+        )
+        resp = TestClient(app).post(
+            "/api/sessions",
+            json={"agent_id": "ratatoskr:sindra", "bifrost_plane": "combined"},
+        )
+        assert resp.status_code == 201
+        assert resp.json()["bifrost"] == {
+            "plane": "combined",
+            "endpoint": "http://10.100.10.50:8392",
+            "status": "bound",
+        }
+        upstream = route.calls[0].request
+        body = _json.loads(upstream.content)
+        assert body["bifrost"] == {
+            "endpoint_url": "http://10.100.10.50:8392",
+            "scope": None,
+        }
+
+    def test_dropdown_offers_combined_as_default(self) -> None:
+        """(a)+default: the SPA plane dropdown offers a 'combined' (:8392) option,
+        it is the DEFAULT-selected one, and single-plane memory/affect remain."""
+        from pathlib import Path
+
+        import ratatoskr.web as web_pkg
+
+        html = (Path(web_pkg.__file__).parent / "static" / "index.html").read_text()
+        assert '<option value="combined" selected>' in html
+        assert 'value="memory"' in html and 'value="affect"' in html
+
     @respx.mock
     def test_plane_without_server_config_is_400(self) -> None:
         """A plane requested but no server-held key/host → bifrost_not_configured."""
diff --git a/uv.lock b/uv.lock
index 54c4247..6967301 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1052,7 +1052,7 @@ wheels = [
 
 [[package]]
 name = "ratatoskr"
-version = "0.18.0"
+version = "0.18.1"
 source = { editable = "." }
 dependencies = [
     { name = "httpx" },