diff --git a/docker/app/start.sh b/docker/app/start.sh
index 5062b5b4b..533612369 100644
--- a/docker/app/start.sh
+++ b/docker/app/start.sh
@@ -3,7 +3,7 @@ set -e
 
 MODE="${1:-server}"
 
-echo "Starting Owletto backend (Node + tsx)"
+echo "Starting Owletto backend (Bun)"
 echo "================================"
 
 echo "Environment:"
@@ -41,16 +41,15 @@ else
   run_migrations
 fi
 
-# Run under Node so V8 native addons (isolated-vm) load.
-# Bun uses JavaScriptCore and cannot link the V8 ABI surface that
-# isolated-vm requires; the execute MCP tool silently degrades to
-# RuntimeUnavailable under bun. tsx provides the TS loader so the
-# source layout stays uncompiled.
-#
-# Keep cwd=/app — gateway services and embedded agent routes resolve
-# bundled config (`config/providers.json`) relative to process.cwd().
-# Use the absolute tsx loader path so the resolution doesn't depend
-# on cwd or PATH.
-exec node \
-  --import "file:///app/packages/owletto-backend/node_modules/tsx/dist/loader.mjs" \
-  /app/packages/owletto-backend/src/server.ts
+# NOTE: prod runs under Bun. The execute MCP tool requires V8
+# (isolated-vm), which Bun's JSC ABI shim cannot load. PR #430 attempted
+# to switch the runtime to `node --import tsx`, but exposed a CJS/ESM
+# interop gap: Node's cjs-module-lexer doesn't detect new named exports
+# of @lobu/core's CJS dist when the static import follows certain
+# reachability paths (e.g. the full server.ts boot chain hits
+# `SyntaxError: ... does not provide an export named 'createBuiltinSecretRef'`,
+# even though a same-imports test entry resolves fine). Reverted on the
+# understanding that fixing properly means making @lobu/core (and other
+# workspace packages) ship dual ESM+CJS output instead of CJS-only with
+# an `import` condition. Tracked separately.
+exec bun /app/packages/owletto-backend/src/server.ts