diff --git a/apps/api/src/modules/deployments/compose/deploy.service.ts b/apps/api/src/modules/deployments/compose/deploy.service.ts
index e24f60949..44d8903ae 100644
--- a/apps/api/src/modules/deployments/compose/deploy.service.ts
+++ b/apps/api/src/modules/deployments/compose/deploy.service.ts
@@ -434,13 +434,33 @@ export function mergeServiceDeployEnv(
   layers: ServiceEnvLayers,
   frozenWins: boolean,
 ): Record<string, string> {
-  return {
-    ...layers.project,
-    ...(frozenWins ? {} : layers.frozen),
-    ...layers.inline,
-    ...layers.service,
-    ...(frozenWins ? layers.frozen : {}),
-  };
+  const result: Record<string, string> = { ...layers.project };
+
+  if (!frozenWins && layers.frozen) {
+    Object.assign(result, layers.frozen);
+  }
+
+  // Layer inline compose environment.
+  // Non-empty inline values override project values (e.g. compose literals).
+  // Empty inline values (from compose passthrough placeholders like ${VAR:-}) do NOT
+  // clobber non-empty project values.
+  for (const [key, value] of Object.entries(layers.inline ?? {})) {
+    if (value === "" && result[key] !== undefined && result[key] !== "") {
+      continue;
+    }
+    result[key] = value;
+  }
+
+  // Layer service-scoped environment rows (explicit service overrides win)
+  for (const [key, value] of Object.entries(layers.service ?? {})) {
+    result[key] = value;
+  }
+
+  if (frozenWins && layers.frozen) {
+    Object.assign(result, layers.frozen);
+  }
+
+  return result;
 }
 
 /**
diff --git a/apps/api/test/modules/deployments/compose-env-passthrough.test.ts b/apps/api/test/modules/deployments/compose-env-passthrough.test.ts
new file mode 100644
index 000000000..cb8fc1d92
--- /dev/null
+++ b/apps/api/test/modules/deployments/compose-env-passthrough.test.ts
@@ -0,0 +1,128 @@
+import { describe, expect, it } from "vitest";
+
+import { parseComposeFile } from "../../../src/lib/compose-parser";
+import {
+  mergeServiceDeployEnv,
+  type ServiceEnvLayers,
+} from "../../../src/modules/deployments/compose/deploy.service";
+
+/**
+ * Fix for Issue #614:
+ * Compose passthrough environment variables (${VAR:-} / ${VAR}) must not clobber
+ * non-empty project-level environment variables during container deploy.
+ */
+describe("Issue #614 - Compose environment passthrough vs project env vars", () => {
+  it("imports compose passthrough variable (${VAR:-}) as empty string in service environment", () => {
+    const yaml = `
+services:
+  web:
+    image: node:20
+    environment:
+      CONFIG_VAR: \${CONFIG_VAR:-}
+      ANOTHER_VAR: \${ANOTHER_VAR}
+      WITH_DEFAULT: \${WITH_DEFAULT:-default_fallback}
+`;
+    const parsed = parseComposeFile(yaml);
+    const service = parsed.services[0];
+
+    expect(service).toBeDefined();
+    expect(service?.environment).toEqual({
+      CONFIG_VAR: "",
+      ANOTHER_VAR: "",
+      WITH_DEFAULT: "default_fallback",
+    });
+
+    expect(service?.environmentMeta?.CONFIG_VAR).toMatchObject({
+      source: "default",
+      variable: "CONFIG_VAR",
+      defaultValue: "",
+    });
+    expect(service?.environmentMeta?.ANOTHER_VAR).toMatchObject({
+      source: "missing",
+      variable: "ANOTHER_VAR",
+    });
+  });
+
+  it("preserves non-empty project-level env vars when compose specifies empty passthrough placeholders", () => {
+    const yaml = `
+services:
+  api:
+    image: my-app:latest
+    environment:
+      DATABASE_URL: \${DATABASE_URL:-}
+      API_SECRET: \${API_SECRET}
+      PORT: "3000"
+`;
+    const parsed = parseComposeFile(yaml);
+    const inlineEnv = parsed.services[0]?.environment ?? {};
+
+    // Project-level environment variables configured by the operator:
+    const projectEnv = {
+      DATABASE_URL: "postgresql://user:pass@db:5432/production_db",
+      API_SECRET: "super-secret-token-12345",
+      PORT: "8080",
+    };
+
+    const layers: ServiceEnvLayers = {
+      project: projectEnv,
+      frozen: {},
+      inline: inlineEnv,
+      service: {},
+    };
+
+    const merged = mergeServiceDeployEnv(layers, false);
+
+    // FIXED: Project-level environment variables are preserved
+    expect(merged.DATABASE_URL).toBe("postgresql://user:pass@db:5432/production_db");
+    expect(merged.API_SECRET).toBe("super-secret-token-12345");
+
+    // Literal inline value (PORT: "3000") still overrides project (PORT: "8080")
+    expect(merged.PORT).toBe("3000");
+  });
+
+  it("allows explicit service-scoped overrides to take precedence over project and inline", () => {
+    const projectEnv = {
+      DATABASE_URL: "postgresql://user:pass@db:5432/production_db",
+      API_SECRET: "global-secret",
+    };
+
+    const inlineEnv = {
+      DATABASE_URL: "",
+      API_SECRET: "",
+    };
+
+    const serviceEnv = {
+      DATABASE_URL: "postgresql://user:pass@db:5432/special_service_db",
+    };
+
+    const layers: ServiceEnvLayers = {
+      project: projectEnv,
+      frozen: {},
+      inline: inlineEnv,
+      service: serviceEnv,
+    };
+
+    const merged = mergeServiceDeployEnv(layers, false);
+
+    // Service-scoped override wins for DATABASE_URL
+    expect(merged.DATABASE_URL).toBe("postgresql://user:pass@db:5432/special_service_db");
+    // Project-level value is preserved for API_SECRET
+    expect(merged.API_SECRET).toBe("global-secret");
+  });
+
+  it("retains empty string when no project variable exists for the passthrough key", () => {
+    const inlineEnv = {
+      UNSET_PASSTHROUGH: "",
+    };
+
+    const layers: ServiceEnvLayers = {
+      project: {},
+      frozen: {},
+      inline: inlineEnv,
+      service: {},
+    };
+
+    const merged = mergeServiceDeployEnv(layers, false);
+    expect(merged.UNSET_PASSTHROUGH).toBe("");
+  });
+});