diff --git a/AGENTS.md b/AGENTS.md
index d4fee67a..42c7e313 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -99,6 +99,7 @@ fail-closed and only pauses when the agent actually proposed a reviewed output.
 │   │   │   ├── github.rs # Always-on GitHub MCP extension
 │   │   │   ├── safe_outputs.rs # Always-on SafeOutputs MCP extension
 │   │   │   ├── ado_script.rs # Always-on ado-script extension (gate evaluator + runtime-import resolver + execution-context precomputes, per-job downloads)
+│   │   │   ├── container_runtime.rs # Typed Docker runtime configuration for MCPG stdio servers (mount modes, container args)
 │   │   │   ├── exec_context/ # Always-on execution-context extension (issue #860)
 │   │   │   │   ├── mod.rs    # ExecContextExtension; CompilerExtension impl; contributor fan-out
 │   │   │   │   ├── contributor.rs # Internal ContextContributor trait + Contributor enum
diff --git a/docs/ir.md b/docs/ir.md
index 1c9263de..3135391a 100644
--- a/docs/ir.md
+++ b/docs/ir.md
@@ -224,7 +224,11 @@ The extension trait lives in `src/compile/extensions/mod.rs` and now has exactly
 pub trait CompilerExtension {
     fn name(&self) -> &str;
     fn phase(&self) -> ExtensionPhase;
-    fn declarations(&self, ctx: &CompileContext) -> Result<Declarations>;
+    /// Default returns `Ok(Declarations::default())` — override when the
+    /// extension contributes steps, hosts, tools, or other signals.
+    fn declarations(&self, ctx: &CompileContext) -> Result<Declarations> {
+        Ok(Declarations::default())
+    }
 }
 ```