diff --git a/crates/tinymemory-module/src/config.rs b/crates/tinymemory-module/src/config.rs
index 0dd8b54..0009836 100644
--- a/crates/tinymemory-module/src/config.rs
+++ b/crates/tinymemory-module/src/config.rs
@@ -164,6 +164,22 @@ pub struct ModuleConfig {
     /// a no-sync nobody can, this picks the one that can be noticed.
     pub memory_sync_interval_secs: Option<u64>,
 
+    /// Base URL of the OpenHuman backend, for proxied ("backend") Composio.
+    ///
+    /// A field rather than a seam member, unlike the session bearer beside it,
+    /// and the difference is what each thing is. A bearer is a credential that
+    /// expires and gets refreshed, so a snapshot of it goes stale and has to be
+    /// asked for per call. A base URL is routing configuration: it changes when
+    /// an operator points the host at a different backend, which is a restart,
+    /// not a mid-session event.
+    ///
+    /// Empty means the host named none. The proxied branch of `composio_config`
+    /// then builds its request against an empty base and fails inside the HTTP
+    /// client with a builder error that names no cause — so a host that intends
+    /// proxied mode must send this.
+    #[serde(default)]
+    pub backend_api_url: String,
+
     /// How the host routes Composio calls: `backend` or `direct`.
     ///
     /// Empty means the host stated no mode — an older host, or one with no
@@ -204,6 +220,7 @@ impl Default for ModuleConfig {
             local_ai: LocalAiConfig::default(),
             embeddings_provider: None,
             memory_provider: None,
+            backend_api_url: String::new(),
             default_model: None,
             default_temperature: 0.0,
             output_language: None,
diff --git a/crates/tinymemory-module/src/provider.rs b/crates/tinymemory-module/src/provider.rs
index a48734b..4aeb437 100644
--- a/crates/tinymemory-module/src/provider.rs
+++ b/crates/tinymemory-module/src/provider.rs
@@ -33,6 +33,7 @@ impl From<&ModuleConfig> for EngineRuntimeConfig {
             // mode, and both of those skip work rather than fail it.
             memory_sync_interval_secs: config.memory_sync_interval_secs,
             composio_mode: config.composio_mode.clone(),
+            backend_api_url: config.backend_api_url.clone(),
             composio_entity_id: config.composio_entity_id.clone(),
         }
     }
diff --git a/crates/tinymemory-tinycortex/src/engine/mod.rs b/crates/tinymemory-tinycortex/src/engine/mod.rs
index dd3c92d..7f9a55a 100644
--- a/crates/tinymemory-tinycortex/src/engine/mod.rs
+++ b/crates/tinymemory-tinycortex/src/engine/mod.rs
@@ -118,6 +118,10 @@ pub struct EngineRuntimeConfig {
     /// answer backend mode gets, which is what an unset Composio integration
     /// should look like.
     pub composio_mode: String,
+    /// Base URL of the host's backend, for proxied Composio. Empty when the
+    /// host named none — see `effective_backend_api_url` below for why that is
+    /// a refusal rather than a default.
+    pub backend_api_url: String,
     /// The Composio entity the host authenticates as.
     ///
     /// An identifier, not a credential: it selects whose connected accounts a
@@ -200,8 +204,15 @@ impl MemoryHostConfig for EngineRuntimeConfig {
     fn api_url(&self) -> Option<&str> {
         None
     }
+    /// The host's backend base URL, verbatim.
+    ///
+    /// No default is substituted for an empty one. Guessing a URL here would
+    /// send a user's memory at whichever backend this crate happened to hard-code
+    /// — including, for a self-hosted operator, one they do not control. An
+    /// empty string fails inside the HTTP client instead, which is a bad error
+    /// message and the right outcome.
     fn effective_backend_api_url(&self) -> String {
-        String::new()
+        self.backend_api_url.clone()
     }
     /// Always the named refusal, never `Ok(None)`.
     ///
diff --git a/crates/tinymemory-tinycortex/src/engine/test.rs b/crates/tinymemory-tinycortex/src/engine/test.rs
index 1caeb18..a2aa311 100644
--- a/crates/tinymemory-tinycortex/src/engine/test.rs
+++ b/crates/tinymemory-tinycortex/src/engine/test.rs
@@ -55,6 +55,7 @@ fn runtime_config() -> EngineRuntimeConfig {
     EngineRuntimeConfig {
         workspace_dir: "/workspace".into(),
         config_path: "/workspace/config.toml".into(),
+        backend_api_url: String::new(),
         memory: Default::default(),
         memory_tree: Default::default(),
         scheduler_gate: Default::default(),
@@ -253,6 +254,7 @@ fn the_sync_cadence_is_answered_from_the_host_and_not_from_a_constant() {
 fn an_unstated_composio_mode_is_not_direct() {
     let config = EngineRuntimeConfig {
         composio_mode: String::new(),
+        backend_api_url: String::new(),
         composio_entity_id: String::new(),
         ..runtime_config()
     };
diff --git a/crates/tinymemory-tinycortex/tests/full_provider_conformance.rs b/crates/tinymemory-tinycortex/tests/full_provider_conformance.rs
index 95b487c..e977a9e 100644
--- a/crates/tinymemory-tinycortex/tests/full_provider_conformance.rs
+++ b/crates/tinymemory-tinycortex/tests/full_provider_conformance.rs
@@ -118,6 +118,7 @@ fn provider_config(
         // sends.
         memory_sync_interval_secs: None,
         composio_mode: String::new(),
+        backend_api_url: String::new(),
         composio_entity_id: String::new(),
     }
 }