diff --git a/src/infra/diagnostic-flags.test.ts b/src/infra/diagnostic-flags.test.ts
index 7c4c3b0a62d..868b4c56c2f 100644
--- a/src/infra/diagnostic-flags.test.ts
+++ b/src/infra/diagnostic-flags.test.ts
@@ -18,17 +18,29 @@ describe("resolveDiagnosticFlags", () => {
     expect(resolveDiagnosticFlags(cfg, env)).toEqual(["telegram.http", "cache.*", "foo"]);
   });
 
-  it("treats false-like env values as no extra flags", () => {
+  it("treats blank env values as no extra flags", () => {
     const cfg = {
       diagnostics: { flags: ["telegram.http"] },
     } as OpenClawConfig;
 
-    for (const raw of ["0", "false", "off", "none", "   "]) {
+    expect(
+      resolveDiagnosticFlags(cfg, {
+        OPENCLAW_DIAGNOSTICS: "   ",
+      } as NodeJS.ProcessEnv),
+    ).toEqual(["telegram.http"]);
+  });
+
+  it("treats false-like env values as disable overrides", () => {
+    const cfg = {
+      diagnostics: { flags: ["telegram.http"] },
+    } as OpenClawConfig;
+
+    for (const raw of ["0", "false", "off", "none"]) {
       expect(
         resolveDiagnosticFlags(cfg, {
           OPENCLAW_DIAGNOSTICS: raw,
         } as NodeJS.ProcessEnv),
-      ).toEqual(["telegram.http"]);
+      ).toEqual([]);
     }
   });
 });
diff --git a/src/infra/diagnostic-flags.ts b/src/infra/diagnostic-flags.ts
index 36c8625fc2c..7e6dfda211e 100644
--- a/src/infra/diagnostic-flags.ts
+++ b/src/infra/diagnostic-flags.ts
@@ -3,25 +3,33 @@ import { normalizeLowercaseStringOrEmpty } from "../shared/string-coerce.js";
 
 const DIAGNOSTICS_ENV = "OPENCLAW_DIAGNOSTICS";
 
-function parseEnvFlags(raw?: string): string[] {
+type ParsedEnvFlags = {
+  flags: string[];
+  disablesAll: boolean;
+};
+
+function parseEnvFlags(raw?: string): ParsedEnvFlags {
   if (!raw) {
-    return [];
+    return { flags: [], disablesAll: false };
   }
   const trimmed = raw.trim();
   const lowered = normalizeLowercaseStringOrEmpty(trimmed);
   if (!lowered) {
-    return [];
+    return { flags: [], disablesAll: false };
   }
   if (["0", "false", "off", "none"].includes(lowered)) {
-    return [];
+    return { flags: [], disablesAll: true };
   }
   if (["1", "true", "all", "*"].includes(lowered)) {
-    return ["*"];
+    return { flags: ["*"], disablesAll: false };
   }
-  return trimmed
-    .split(/[,\s]+/)
-    .map((value) => normalizeLowercaseStringOrEmpty(value))
-    .filter(Boolean);
+  return {
+    flags: trimmed
+      .split(/[,\s]+/)
+      .map((value) => normalizeLowercaseStringOrEmpty(value))
+      .filter(Boolean),
+    disablesAll: false,
+  };
 }
 
 function uniqueFlags(flags: string[]): string[] {
@@ -44,7 +52,10 @@ export function resolveDiagnosticFlags(
 ): string[] {
   const configFlags = Array.isArray(cfg?.diagnostics?.flags) ? cfg?.diagnostics?.flags : [];
   const envFlags = parseEnvFlags(env[DIAGNOSTICS_ENV]);
-  return uniqueFlags([...configFlags, ...envFlags]);
+  if (envFlags.disablesAll) {
+    return [];
+  }
+  return uniqueFlags([...configFlags, ...envFlags.flags]);
 }
 
 export function matchesDiagnosticFlag(flag: string, enabledFlags: string[]): boolean {
diff --git a/src/infra/diagnostics-timeline.test.ts b/src/infra/diagnostics-timeline.test.ts
index 7ba11252876..d391cdae2fa 100644
--- a/src/infra/diagnostics-timeline.test.ts
+++ b/src/infra/diagnostics-timeline.test.ts
@@ -86,6 +86,18 @@ describe("diagnostics timeline", () => {
     ).toBe(false);
   });
 
+  it("lets false-like env diagnostics disable config-enabled timeline output", async () => {
+    const { env } = await createTimelineEnv();
+    const configWithTimeline = { diagnostics: { flags: ["timeline"] } } as OpenClawConfig;
+
+    expect(
+      isDiagnosticsTimelineEnabled({
+        config: configWithTimeline,
+        env: { ...env, OPENCLAW_DIAGNOSTICS: "0" },
+      }),
+    ).toBe(false);
+  });
+
   it("writes JSONL diagnostic events with the stable envelope", async () => {
     const { env, path } = await createTimelineEnv();