diff --git a/src/config/io.ts b/src/config/io.ts
index fba17f253aa..9f7183e072e 100644
--- a/src/config/io.ts
+++ b/src/config/io.ts
@@ -1,10 +1,11 @@
+import JSON5 from "json5";
+import { ensureOwnerDisplaySecret } from "../agents/owner-display.js";
+import type { OpenClawConfig, ConfigFileSnapshot, LegacyConfigIssue } from "./types.js";
 import crypto from "node:crypto";
 import fs from "node:fs";
 import os from "node:os";
 import path from "node:path";
 import { isDeepStrictEqual } from "node:util";
-import JSON5 from "json5";
-import { ensureOwnerDisplaySecret } from "../agents/owner-display.js";
 import { loadDotEnv } from "../infra/dotenv.js";
 import { resolveRequiredHomeDir } from "../infra/home-dir.js";
 import {
@@ -47,8 +48,8 @@ import { normalizeExecSafeBinProfilesInConfig } from "./normalize-exec-safe-bin.
 import { normalizeConfigPaths } from "./normalize-paths.js";
 import { resolveConfigPath, resolveDefaultConfigCandidates, resolveStateDir } from "./paths.js";
 import { isBlockedObjectKey } from "./prototype-keys.js";
+import { REDACTED_SENTINEL } from "./redact-snapshot.js";
 import { applyConfigOverrides } from "./runtime-overrides.js";
-import type { OpenClawConfig, ConfigFileSnapshot, LegacyConfigIssue } from "./types.js";
 import {
   validateConfigObjectRawWithPlugins,
   validateConfigObjectWithPlugins,
@@ -1188,6 +1189,19 @@ export function createConfigIO(overrides: ConfigIoDeps = {}) {
     // explicitly set values. Runtime defaults are applied when loading (issue #6070).
     const stampedOutputConfig = stampConfigVersion(outputConfig);
     const json = JSON.stringify(stampedOutputConfig, null, 2).trimEnd().concat("\n");
+
+    if (json.includes(REDACTED_SENTINEL)) {
+      deps.logger.error(
+        `Config write blocked: redaction sentinel "${REDACTED_SENTINEL}" found in output — ` +
+          `writing would destroy credentials. Config file was NOT modified.`,
+      );
+      throw new Error(
+        `Refusing to write config: found redaction sentinel "${REDACTED_SENTINEL}". ` +
+          `This is a bug — credentials would be permanently lost. ` +
+          `The config file on disk was not changed.`,
+      );
+    }
+
     const nextHash = hashConfigRaw(json);
     const previousHash = resolveConfigSnapshotHash(snapshot);
     const changedPathCount = changedPaths?.size;
diff --git a/src/config/io.write-config.test.ts b/src/config/io.write-config.test.ts
index 68709725d83..5d00d54c40e 100644
--- a/src/config/io.write-config.test.ts
+++ b/src/config/io.write-config.test.ts
@@ -4,6 +4,7 @@ import path from "node:path";
 import { afterAll, beforeAll, describe, expect, it, vi } from "vitest";
 import { createConfigIO } from "./io.js";
 import type { OpenClawConfig } from "./types.js";
+import { REDACTED_SENTINEL } from "./redact-snapshot.js";
 
 describe("config io write", () => {
   let fixtureRoot = "";
@@ -548,4 +549,35 @@ describe("config io write", () => {
       expect(last.watchCommand).toBe("gateway --force");
     });
   });
+
+  it("refuses to write config containing redaction sentinel (issue #18102)", async () => {
+    await withSuiteHome(async (home) => {
+      const initialConfig = {
+        gateway: { port: 18789 },
+        channels: { telegram: { botToken: "real-bot-token-123" } },
+      };
+      const errorFn = vi.fn();
+      const { configPath, io, snapshot } = await writeConfigAndCreateIo({
+        home,
+        initialConfig,
+        logger: { warn: vi.fn(), error: errorFn },
+      });
+
+      const poisoned = structuredClone(snapshot.config);
+      (poisoned as Record<string, unknown>).channels = {
+        ...poisoned.channels,
+        telegram: {
+          ...poisoned.channels?.telegram,
+          botToken: REDACTED_SENTINEL,
+        },
+      };
+
+      await expect(io.writeConfigFile(poisoned)).rejects.toThrow(/redaction sentinel/i);
+
+      const ondisk = JSON.parse(await fs.readFile(configPath, "utf-8")) as Record<string, unknown>;
+      expect(JSON.stringify(ondisk)).not.toContain(REDACTED_SENTINEL);
+      expect(ondisk).toEqual(initialConfig);
+      expect(errorFn).toHaveBeenCalled();
+    });
+  });
 });