diff --git a/apps/server/src/provider/AntigravityInstallation.ts b/apps/server/src/provider/AntigravityInstallation.ts
index 24eb4e3d6df8..66094c7afa75 100644
--- a/apps/server/src/provider/AntigravityInstallation.ts
+++ b/apps/server/src/provider/AntigravityInstallation.ts
@@ -136,6 +136,33 @@ const installationError = (operation: string, detail: string, cause?: unknown) =
 const wrapFailure = (operation: string, detail: string) => (cause: unknown) =>
   isInstallationError(cause) ? cause : installationError(operation, detail, cause);
 
+const SIGNAL_INTERRUPT_PATTERN = /receipt of signal: '([A-Za-z0-9]+)'/;
+
+/**
+ * Walks a chained `cause` (as produced by effect/platform's child process
+ * spawner) looking for the signal that killed the process. Bounded so an
+ * unexpected cyclical cause cannot recurse forever.
+ * @internal
+ */
+export function findTerminatingSignal(cause: unknown, depth = 0): string | undefined {
+  if (depth > 8 || !(cause instanceof Error)) return undefined;
+  const match = SIGNAL_INTERRUPT_PATTERN.exec(cause.message);
+  if (match) return match[1];
+  return findTerminatingSignal((cause as { cause?: unknown }).cause, depth + 1);
+}
+
+const GENERIC_VALIDATION_FAILURE_DETAIL =
+  "The downloaded Antigravity runtime could not start in this environment.";
+const SIGILL_VALIDATION_FAILURE_DETAIL =
+  "The downloaded Antigravity runtime crashed on startup with an illegal instruction (SIGILL). This usually means the CPU is missing instructions (such as AVX/AVX2) that the Antigravity runtime requires.";
+
+/** @internal */
+export function describeValidationFailure(cause: unknown): string {
+  return findTerminatingSignal(cause) === "SIGILL"
+    ? SIGILL_VALIDATION_FAILURE_DETAIL
+    : GENERIC_VALIDATION_FAILURE_DETAIL;
+}
+
 function executableNames(platform: NodeJS.Platform) {
   return platform === "win32"
     ? { executable: "agy_acp_server.exe", harness: "localharness_external.exe" }
@@ -508,11 +535,10 @@ export const makeAntigravityInstallation = Effect.fn("AntigravityInstallation.ma
       Effect.provideService(Path.Path, path),
       Effect.provideService(ChildProcessSpawner.ChildProcessSpawner, spawner),
       Effect.provideService(Crypto.Crypto, crypto),
-      Effect.mapError(
-        wrapFailure(
-          "verify",
-          "The downloaded Antigravity runtime could not start in this environment.",
-        ),
+      Effect.mapError((cause) =>
+        isInstallationError(cause)
+          ? cause
+          : installationError("verify", describeValidationFailure(cause), cause),
       ),
     );
 
diff --git a/apps/server/src/provider/AntigravityInstallation.validationFailure.test.ts b/apps/server/src/provider/AntigravityInstallation.validationFailure.test.ts
new file mode 100644
index 000000000000..e489c3113111
--- /dev/null
+++ b/apps/server/src/provider/AntigravityInstallation.validationFailure.test.ts
@@ -0,0 +1,60 @@
+import * as NodeAssert from "node:assert/strict";
+
+import { describe, it } from "vite-plus/test";
+
+import { describeValidationFailure, findTerminatingSignal } from "./AntigravityInstallation.ts";
+
+describe("findTerminatingSignal", () => {
+  it("extracts the signal name from a child-process interrupt error", () => {
+    const cause = new Error("Process interrupted due to receipt of signal: 'SIGILL'");
+    NodeAssert.equal(findTerminatingSignal(cause), "SIGILL");
+  });
+
+  it("walks a chain of wrapped causes to find the signal", () => {
+    const signalError = new Error("Process interrupted due to receipt of signal: 'SIGILL'");
+    const platformError = new Error("Unknown: ChildProcess.exitCode (agy_acp_server.par)", {
+      cause: signalError,
+    });
+    const transportError = new Error("ACP transport operation read-process-exit-status failed.", {
+      cause: platformError,
+    });
+    NodeAssert.equal(findTerminatingSignal(transportError), "SIGILL");
+  });
+
+  it("returns undefined when no signal is present in the chain", () => {
+    const cause = new Error("The archive could not be read.", {
+      cause: new Error("ENOENT: no such file or directory"),
+    });
+    NodeAssert.equal(findTerminatingSignal(cause), undefined);
+  });
+
+  it("returns undefined for non-error causes", () => {
+    NodeAssert.equal(findTerminatingSignal(undefined), undefined);
+    NodeAssert.equal(findTerminatingSignal("SIGILL"), undefined);
+  });
+
+  it("does not recurse forever on a cyclical cause chain", () => {
+    const cause: Error & { cause?: unknown } = new Error("boom");
+    cause.cause = cause;
+    NodeAssert.equal(findTerminatingSignal(cause), undefined);
+  });
+});
+
+describe("describeValidationFailure", () => {
+  it("names AVX/AVX2 as the likely cause when the runtime is killed by SIGILL", () => {
+    const cause = new Error("ACP transport operation read-process-exit-status failed.", {
+      cause: new Error("Process interrupted due to receipt of signal: 'SIGILL'"),
+    });
+    const detail = describeValidationFailure(cause);
+    NodeAssert.match(detail, /SIGILL/);
+    NodeAssert.match(detail, /AVX/);
+  });
+
+  it("falls back to the generic message for other failures", () => {
+    const cause = new Error("The downloaded runtime did not identify as the expected release.");
+    NodeAssert.equal(
+      describeValidationFailure(cause),
+      "The downloaded Antigravity runtime could not start in this environment.",
+    );
+  });
+});