diff --git a/agents/hermes/start.sh b/agents/hermes/start.sh
index 4c605d93d04..aa109b5cc8a 100755
--- a/agents/hermes/start.sh
+++ b/agents/hermes/start.sh
@@ -230,6 +230,28 @@ start_gateway_log_stream() {
   GATEWAY_LOG_TAIL_PID=$!
 }
 
+retry_tirith_marker_if_needed() {
+  local marker="${HERMES_DIR}/.tirith-install-failed"
+  local reason
+
+  [ -e "$marker" ] || return 0
+  if [ -L "$marker" ] || [ ! -f "$marker" ]; then
+    echo "[tirith-bootstrap] WARNING: unsafe Tirith install marker at ${marker}; not reading it" >&2
+    return 0
+  fi
+
+  reason="$(head -n 1 "$marker" 2>/dev/null | tr -d '\r\n' || true)"
+  if [ "$reason" != "download_failed" ]; then
+    echo "[tirith-bootstrap] WARNING: Tirith install marker reason '${reason:-unknown}' is not retryable; Hermes gateway startup will continue" >&2
+    return 0
+  fi
+
+  echo "[tirith-bootstrap] download_failed marker present; letting Hermes runtime fallback retry Tirith" >&2
+  if ! rm -f "$marker" 2>/dev/null; then
+    echo "[tirith-bootstrap] WARNING: could not remove retryable Tirith marker; Hermes gateway startup will continue" >&2
+  fi
+}
+
 # ── socat forwarder ──────────────────────────────────────────────
 # Hermes API server binds to 127.0.0.1 regardless of config (upstream bug).
 # OpenShell needs the port accessible on 0.0.0.0 for port forwarding.
@@ -602,6 +624,8 @@ if [ "$(id -u)" -ne 0 ]; then
     exec "${NEMOCLAW_CMD[@]}"
   fi
 
+  retry_tirith_marker_if_needed
+
   prepare_restricted_log /tmp/gateway.log "" 600
 
   # Defence-in-depth: verify /tmp file permissions before launching services.
@@ -633,6 +657,7 @@ fi
 
 # ── Root path (full privilege separation via setpriv) ──────────
 
+export HERMES_HOME="${HERMES_DIR}"
 verify_config_integrity "${HERMES_DIR}" "${HERMES_HASH_FILE}"
 refresh_hermes_provider_placeholders
 install_configure_guard
@@ -642,6 +667,8 @@ if [ ${#NEMOCLAW_CMD[@]} -gt 0 ]; then
   exec "${STEP_DOWN_PREFIX_SANDBOX[@]}" "${NEMOCLAW_CMD[@]}"
 fi
 
+retry_tirith_marker_if_needed
+
 # SECURITY: Protect gateway log from sandbox user tampering
 prepare_restricted_log /tmp/gateway.log gateway:gateway 600
 
diff --git a/src/lib/agent/onboard.test.ts b/src/lib/agent/onboard.test.ts
index 67ce44f25d9..b71a82a83e0 100644
--- a/src/lib/agent/onboard.test.ts
+++ b/src/lib/agent/onboard.test.ts
@@ -3,7 +3,11 @@
 
 import { describe, it, expect, beforeEach, afterEach, afterAll, vi } from "vitest";
 // Import from compiled dist/ so coverage is attributed correctly.
-import { printDashboardUi, verifyAgentBinaryAvailable } from "../../../dist/lib/agent/onboard";
+import {
+  collectHermesStartupDiagnostics,
+  printDashboardUi,
+  verifyAgentBinaryAvailable,
+} from "../../../dist/lib/agent/onboard";
 import type { AgentDefinition } from "./defs";
 
 function makeAgent(overrides: Partial<AgentDefinition> = {}): AgentDefinition {
@@ -157,3 +161,60 @@ describe("handleAgentSetup guards", () => {
     expect(script).toContain("NEMOCLAW_AGENT_BINARY_CHECK:ok");
   });
 });
+
+describe("collectHermesStartupDiagnostics", () => {
+  it("includes Tirith marker content and binary state when the marker is present", () => {
+    const runCapture = vi.fn(() =>
+      [
+        "tirith marker: download_failed",
+        "tirith binary: missing (/sandbox/.hermes/bin/tirith)",
+        "--- tail: /tmp/nemoclaw-start.log ---",
+        "[tirith-bootstrap] Retrying Tirith install after download_failed marker",
+      ].join("\n"),
+    );
+
+    const diagnostics = collectHermesStartupDiagnostics("alpha", runCapture);
+
+    expect(runCapture).toHaveBeenCalledWith(
+      [
+        "sandbox",
+        "exec",
+        "-n",
+        "alpha",
+        "--",
+        "sh",
+        "-lc",
+        expect.stringContaining("/sandbox/.hermes/.tirith-install-failed"),
+      ],
+      { ignoreError: true },
+    );
+    expect(diagnostics.join("\n")).toContain("Hermes startup diagnostics:");
+    expect(diagnostics.join("\n")).toContain("tirith marker: download_failed");
+    expect(diagnostics.join("\n")).toContain(
+      "tirith binary: missing (/sandbox/.hermes/bin/tirith)",
+    );
+  });
+
+  it("returns no extra lines when the Tirith marker is absent", () => {
+    const runCapture = vi.fn(() => "tirith marker: absent\n");
+
+    expect(collectHermesStartupDiagnostics("alpha", runCapture)).toEqual([]);
+  });
+
+  it("redacts sensitive values from log tails", () => {
+    const slackToken = ["xoxb", "123456789012", "abcdefghijkl"].join("-");
+    const runCapture = vi.fn(() =>
+      [
+        "tirith marker: download_failed",
+        "tirith binary: present but not executable (/sandbox/.hermes/bin/tirith)",
+        "--- tail: /tmp/gateway.log ---",
+        `SLACK_BOT_TOKEN=${slackToken}`,
+      ].join("\n"),
+    );
+
+    const output = collectHermesStartupDiagnostics("alpha", runCapture).join("\n");
+
+    expect(output).toContain("SLACK_BOT_TOKEN=");
+    expect(output).not.toContain(slackToken);
+  });
+});
diff --git a/src/lib/agent/onboard.ts b/src/lib/agent/onboard.ts
index 359766646e8..2446108910a 100644
--- a/src/lib/agent/onboard.ts
+++ b/src/lib/agent/onboard.ts
@@ -209,6 +209,42 @@ type AgentBinaryAvailability =
     };
 
 const AGENT_BINARY_CHECK_PREFIX = "NEMOCLAW_AGENT_BINARY_CHECK:";
+const HERMES_TIRITH_MARKER_ABSENT = "tirith marker: absent";
+const HERMES_STARTUP_DIAGNOSTICS_SCRIPT = `
+set +e
+marker=/sandbox/.hermes/.tirith-install-failed
+if [ ! -e "$marker" ]; then
+  echo "${HERMES_TIRITH_MARKER_ABSENT}"
+  exit 0
+fi
+if [ -L "$marker" ]; then
+  echo "tirith marker: symlink (not read)"
+else
+  printf "tirith marker: "
+  head -c 200 "$marker" 2>/dev/null || printf "unreadable"
+  printf "\\n"
+fi
+
+tirith=/sandbox/.hermes/bin/tirith
+if [ -x "$tirith" ] && [ ! -L "$tirith" ]; then
+  echo "tirith binary: present executable ($tirith)"
+elif [ -e "$tirith" ]; then
+  echo "tirith binary: present but not executable ($tirith)"
+else
+  echo "tirith binary: missing ($tirith)"
+fi
+
+for log in /tmp/nemoclaw-start.log /tmp/gateway.log; do
+  if [ -f "$log" ] && [ ! -L "$log" ]; then
+    echo "--- tail: $log ---"
+    tail -n 40 "$log" 2>/dev/null || echo "(tail unavailable)"
+  elif [ -L "$log" ]; then
+    echo "--- tail: $log skipped (symlink) ---"
+  else
+    echo "--- tail: $log unavailable ---"
+  fi
+done
+`.trim();
 
 /**
  * Check whether the selected agent binary is available inside the sandbox.
@@ -285,12 +321,49 @@ function describeAgentBinaryFailure(
   return `${agent.displayName} binary '${executable}' is missing inside sandbox '${sandboxName}'`;
 }
 
+/**
+ * Collect read-only Hermes startup diagnostics for Step 7 health timeouts.
+ * Returns no extra lines when the Tirith marker is absent so non-Tirith
+ * failures keep the existing terse error shape.
+ */
+export function collectHermesStartupDiagnostics(
+  sandboxName: string,
+  runCaptureOpenshell: OnboardContext["runCaptureOpenshell"],
+): string[] {
+  const output = runCaptureOpenshell(
+    ["sandbox", "exec", "-n", sandboxName, "--", "sh", "-lc", HERMES_STARTUP_DIAGNOSTICS_SCRIPT],
+    { ignoreError: true },
+  );
+  const redactedOutput = String(redact(output ?? ""));
+  const lines = redactedOutput
+    .split(/\r?\n/)
+    .map((line) => line.trimEnd())
+    .filter((line) => line.length > 0);
+
+  const markerLine = lines.find((line) => line.startsWith("tirith marker:"));
+  if (!markerLine || markerLine === HERMES_TIRITH_MARKER_ABSENT) {
+    return [];
+  }
+  return ["Hermes startup diagnostics:", ...lines.slice(0, 140)];
+}
+
 /**
  * Record and print an agent setup failure before exiting the onboarding flow.
  */
-function failAgentSetup(sandboxName: string, agent: AgentDefinition, message: string): never {
-  onboardSession.markStepFailed("agent_setup", message);
+function failAgentSetup(
+  sandboxName: string,
+  agent: AgentDefinition,
+  message: string,
+  details: string[] = [],
+): never {
+  onboardSession.markStepFailed(
+    "agent_setup",
+    details.length > 0 ? `${message}\n${details.join("\n")}` : message,
+  );
   console.error(`  \u2717 ${message}`);
+  for (const line of details) {
+    console.error(`    ${line}`);
+  }
   console.error(`    Check: ${agentCliName(agent)} ${sandboxName} logs --follow`);
   process.exit(1);
 }
@@ -404,10 +477,15 @@ export async function handleAgentSetup(
     if (healthy) {
       console.log(`  \u2713 ${agent.displayName} gateway is healthy`);
     } else {
+      const diagnostics =
+        agent.name === "hermes"
+          ? collectHermesStartupDiagnostics(sandboxName, runCaptureOpenshell)
+          : [];
       failAgentSetup(
         sandboxName,
         agent,
         `${agent.displayName} gateway did not respond within ${timeoutSecs}s`,
+        diagnostics,
       );
     }
   } else {
diff --git a/test/e2e/docs/parity-map.yaml b/test/e2e/docs/parity-map.yaml
index 889c91e37bb..1516ce781b1 100644
--- a/test/e2e/docs/parity-map.yaml
+++ b/test/e2e/docs/parity-map.yaml
@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
 scripts:
   brev-e2e.test.ts:
     scenario: ''
diff --git a/test/hermes-start.test.ts b/test/hermes-start.test.ts
new file mode 100644
index 00000000000..261c5fb8780
--- /dev/null
+++ b/test/hermes-start.test.ts
@@ -0,0 +1,110 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { spawnSync } from "node:child_process";
+import { describe, expect, it } from "vitest";
+
+const START_SCRIPT = path.join(import.meta.dirname, "..", "agents", "hermes", "start.sh");
+
+function shellQuote(value: string): string {
+  return `'${value.replace(/'/g, "'\\''")}'`;
+}
+
+function escapeRegExp(value: string): string {
+  return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}
+
+function extractShellFunctionFromSource(src: string, name: string): string {
+  const escapedName = escapeRegExp(name);
+  const match = src.match(new RegExp(`${escapedName}\\(\\) \\{([\\s\\S]*?)^\\}`, "m"));
+  if (!match) {
+    throw new Error(`Expected ${name} in agents/hermes/start.sh`);
+  }
+  return `${name}() {${match[1]}\n}`;
+}
+
+function runTirithMarkerBootstrap(opts: {
+  markerReason?: string;
+  symlinkMarker?: boolean;
+}) {
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "nemoclaw-hermes-tirith-"));
+  const hermesHome = path.join(tmpDir, ".hermes");
+  const marker = path.join(hermesHome, ".tirith-install-failed");
+  const target = path.join(tmpDir, "marker-target");
+  const scriptPath = path.join(tmpDir, "run.sh");
+
+  fs.mkdirSync(hermesHome, { recursive: true });
+  if (opts.symlinkMarker) {
+    fs.writeFileSync(target, opts.markerReason ?? "download_failed");
+    fs.symlinkSync(target, marker);
+  } else if (opts.markerReason !== undefined) {
+    fs.writeFileSync(marker, opts.markerReason);
+  }
+
+  const src = fs.readFileSync(START_SCRIPT, "utf-8");
+  fs.writeFileSync(
+    scriptPath,
+    [
+      "#!/usr/bin/env bash",
+      "set -euo pipefail",
+      extractShellFunctionFromSource(src, "retry_tirith_marker_if_needed"),
+      `HERMES_DIR=${shellQuote(hermesHome)}`,
+      "retry_tirith_marker_if_needed",
+    ].join("\n"),
+    { mode: 0o700 },
+  );
+
+  try {
+    const result = spawnSync("bash", [scriptPath], {
+      encoding: "utf-8",
+      timeout: 5000,
+      env: process.env,
+    });
+    return {
+      result,
+      markerExists: fs.existsSync(marker),
+      markerIsSymlink: fs.existsSync(marker) && fs.lstatSync(marker).isSymbolicLink(),
+      markerContent: fs.existsSync(marker) ? fs.readFileSync(marker, "utf-8") : "",
+      targetContent: fs.existsSync(target) ? fs.readFileSync(target, "utf-8") : "",
+    };
+  } finally {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  }
+}
+
+describe("agents/hermes/start.sh Tirith marker bootstrap", () => {
+  it("removes a retryable download_failed marker so Hermes runtime fallback can retry", () => {
+    const run = runTirithMarkerBootstrap({ markerReason: "download_failed" });
+
+    expect(run.result.status).toBe(0);
+    expect(run.markerExists).toBe(false);
+    expect(run.result.stderr).toContain(
+      "download_failed marker present; letting Hermes runtime fallback retry Tirith",
+    );
+  });
+
+  it("leaves unknown marker reasons untouched", () => {
+    const run = runTirithMarkerBootstrap({ markerReason: "checksum_failed" });
+
+    expect(run.result.status).toBe(0);
+    expect(run.markerExists).toBe(true);
+    expect(run.markerContent).toBe("checksum_failed");
+    expect(run.result.stderr).toContain("is not retryable");
+  });
+
+  it("refuses to read or remove an unsafe symlink marker", () => {
+    const run = runTirithMarkerBootstrap({
+      markerReason: "download_failed",
+      symlinkMarker: true,
+    });
+
+    expect(run.result.status).toBe(0);
+    expect(run.markerExists).toBe(true);
+    expect(run.markerIsSymlink).toBe(true);
+    expect(run.targetContent).toBe("download_failed");
+    expect(run.result.stderr).toContain("unsafe Tirith install marker");
+  });
+});