Beside every TypeScript entrypoint the builder writes an executable launcher; the runtime is told it (hq ADR 0193)

The runtime knows no language: the build makes each served entrypoint executable. For a TypeScript
bundle that is <entry>.serve.mjs, which imports the entrypoint and serves what it registered over
MCP on stdio through the bundle's own SDK. The build records its launchers on the bundle, and the
composer names the launcher where a build wrote one and the entrypoint where it did not, so bundles
built before this keep serving until they are rebuilt.

internal/catalogue/runtime.go

@@ -169,6 +169,11 @@ func (r Resolution) runtimeProcess(with Rendering) (map[string]any, error) {
 				continue
 			}
 			for _, load := range b.Loads {
+				// What the runtime starts: the launcher the build wrote beside the entrypoint, where
+				// it wrote one (ADR 0193); the entrypoint itself for a build from before them.
+				if launcher, has := b.Launchers[load]; has {
+					load = launcher
+				}
 				served = append(served, m.Module+"="+BundlePath(m.Module, b.Name)+"/"+load)
 			}
 			restartOn = append(restartOn, m.Module+"."+BundleID(b.Name))