diff --git a/src/lib/build-context.ts b/src/lib/build-context.ts
index 2407f2ebba3..e67a7e693a6 100644
--- a/src/lib/build-context.ts
+++ b/src/lib/build-context.ts
@@ -72,6 +72,12 @@ export function printSandboxCreateRecoveryHints(output = ""): void {
     );
     return;
   }
+  if (failure.kind === "tls_cert_mismatch") {
+    console.error("  Hint: TLS certificate mismatch — the gateway certificate changed since the CLI last trusted it.");
+    console.error("  Fix:  openshell gateway trust -g nemoclaw");
+    console.error("  Then: nemoclaw onboard --resume");
+    return;
+  }
   console.error("  Recovery: nemoclaw onboard --resume");
   console.error("  Or:      nemoclaw onboard");
 }
diff --git a/src/lib/validation.test.ts b/src/lib/validation.test.ts
index 9bd4a521879..a81639387c0 100644
--- a/src/lib/validation.test.ts
+++ b/src/lib/validation.test.ts
@@ -182,6 +182,49 @@ describe("classifySandboxCreateFailure", () => {
     const result = classifySandboxCreateFailure("something else happened");
     expect(result.kind).toBe("unknown");
   });
+
+  it("detects TLS cert error from 'invalid peer certificate: BadSignature'", () => {
+    const result = classifySandboxCreateFailure("invalid peer certificate: BadSignature");
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
+
+  it("detects TLS cert error from 'handshake verification failed'", () => {
+    const result = classifySandboxCreateFailure("handshake verification failed");
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
+
+  it("detects TLS cert error from 'certificate verify failed'", () => {
+    const result = classifySandboxCreateFailure("certificate verify failed");
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
+
+  it("detects TLS cert error from 'SSL certificate problem'", () => {
+    const result = classifySandboxCreateFailure("SSL certificate problem: unable to get local issuer certificate");
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
+
+  it("detects TLS cert error from 'x509: certificate'", () => {
+    const result = classifySandboxCreateFailure("x509: certificate signed by unknown authority");
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
+
+  it("detects TLS cert error from 'unknown authority'", () => {
+    const result = classifySandboxCreateFailure("failed: unknown authority");
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
+
+  it("does NOT classify generic TLS transport errors as tls_cert_mismatch", () => {
+    expect(classifySandboxCreateFailure("TLS error: connection refused by proxy").kind).toBe("unknown");
+    expect(classifySandboxCreateFailure("SSL error: unsupported protocol version").kind).toBe("unknown");
+    expect(classifySandboxCreateFailure("TLS error later during notify").kind).toBe("unknown");
+    expect(classifySandboxCreateFailure("ssl error: peer closed connection").kind).toBe("unknown");
+  });
+
+  it("classifies tls_cert_mismatch even when 'Created sandbox:' is also present", () => {
+    const output = "Created sandbox: test-sandbox\nError: handshake verification failed";
+    const result = classifySandboxCreateFailure(output);
+    expect(result.kind).toBe("tls_cert_mismatch");
+  });
 });
 
 describe("validateNvidiaApiKeyValue", () => {
diff --git a/src/lib/validation.ts b/src/lib/validation.ts
index 7125abc77cf..5e030f5d5c6 100644
--- a/src/lib/validation.ts
+++ b/src/lib/validation.ts
@@ -13,7 +13,7 @@ export interface ValidationClassification {
 }
 
 export interface SandboxCreateFailure {
-  kind: "image_transfer_timeout" | "image_transfer_reset" | "sandbox_create_incomplete" | "unknown";
+  kind: "image_transfer_timeout" | "image_transfer_reset" | "sandbox_create_incomplete" | "tls_cert_mismatch" | "unknown";
   uploadedToGateway: boolean;
 }
 
@@ -72,6 +72,9 @@ export function classifySandboxCreateFailure(output = ""): SandboxCreateFailure
   if (/Connection reset by peer/i.test(text)) {
     return { kind: "image_transfer_reset", uploadedToGateway };
   }
+  if (/invalid peer certificate|BadSignature|handshake verification failed|certificate verify failed|SSL certificate problem|x509: certificate|unknown authority/i.test(text)) {
+    return { kind: "tls_cert_mismatch", uploadedToGateway };
+  }
   if (/Created sandbox:/i.test(text)) {
     return { kind: "sandbox_create_incomplete", uploadedToGateway: true };
   }