diff --git a/server/src/routes/agents.ts b/server/src/routes/agents.ts
index 2ad85e63..c2cacfe4 100644
--- a/server/src/routes/agents.ts
+++ b/server/src/routes/agents.ts
@@ -1772,6 +1772,18 @@ export function agentRoutes(db: Db) {
         rawEffectiveAdapterConfig = { ...existingAdapterConfig, ...requestedAdapterConfig };
       }
       if (changingAdapterType) {
+        // Preserve adapter-agnostic keys (env, cwd, etc.) from the existing config
+        // when the adapter type changes. Without this, a PATCH that includes
+        // adapterConfig but omits these keys would silently drop them.
+        const ADAPTER_AGNOSTIC_KEYS = [
+          "env", "cwd", "timeoutSec", "graceSec",
+          "promptTemplate", "bootstrapPromptTemplate",
+        ] as const;
+        for (const key of ADAPTER_AGNOSTIC_KEYS) {
+          if (rawEffectiveAdapterConfig[key] === undefined && existingAdapterConfig[key] !== undefined) {
+            rawEffectiveAdapterConfig = { ...rawEffectiveAdapterConfig, [key]: existingAdapterConfig[key] };
+          }
+        }
         rawEffectiveAdapterConfig = preserveInstructionsBundleConfig(
           existingAdapterConfig,
           rawEffectiveAdapterConfig,