diff --git a/.env.example b/.env.example
index 71f3a4f..932bcec 100644
--- a/.env.example
+++ b/.env.example
@@ -1,7 +1,7 @@
 DATABASE_URL=mysql://user:password@localhost:3306/database
 
-# Optional: external AI SoH prediction service.
-# SOH_PREDICTION_API_BASE_URL=http://127.0.0.1:8000
+# Required: external AI SoH prediction service.
+SOH_PREDICTION_API_BASE_URL=http://127.0.0.1:8000
 # SOH_PREDICTION_CACHE_TTL_SECONDS=86400
 # SOH_PREDICTION_TIMEOUT_MS=10000
 
diff --git a/compose.yaml b/compose.yaml
index 1f2a40b..fab7fc8 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -26,6 +26,7 @@ services:
         condition: service_healthy
     environment:
       - DATABASE_URL=mysql://battery:battery@db:3306/battery_soh
+      - SOH_PREDICTION_API_BASE_URL=http://host.docker.internal:8000
     command: [ "bun", "run", "seed" ]
 
   app:
@@ -33,6 +34,8 @@ services:
     depends_on:
       seed:
         condition: service_completed_successfully
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     ports:
       - "3000:3000"
     environment:
diff --git a/src/env.ts b/src/env.ts
index ff614d1..4983a6c 100644
--- a/src/env.ts
+++ b/src/env.ts
@@ -7,7 +7,7 @@ export const env = createEnv({
     LOG_DB: z.stringbool().default(false),
     LOG_FORMAT: z.enum(['pretty', 'json']).optional(),
     LOG_LEVEL: z.enum(['trace', 'debug', 'info', 'warning', 'error', 'fatal']).default('info'),
-    SOH_PREDICTION_API_BASE_URL: z.url({ protocol: /^https?$/ }).optional(),
+    SOH_PREDICTION_API_BASE_URL: z.url({ protocol: /^https?$/ }),
     SOH_PREDICTION_CACHE_TTL_SECONDS: z.coerce.number().int().positive().default(86_400),
     SOH_PREDICTION_TIMEOUT_MS: z.coerce.number().int().positive().default(10_000),
   },