diff --git a/packages/app/e2e/helpers/settings.ts b/packages/app/e2e/helpers/settings.ts
index 982731e54..254879456 100644
--- a/packages/app/e2e/helpers/settings.ts
+++ b/packages/app/e2e/helpers/settings.ts
@@ -249,6 +249,7 @@ export async function expectDirectHostUriHidden(page: Page): Promise<void> {
 }
 
 export async function expectDiagnosticsContent(page: Page): Promise<void> {
+  await expect(page.getByRole("button", { name: "Run" })).toBeVisible();
   await expect(page.getByRole("button", { name: "Play test" })).toBeVisible();
 }
 
diff --git a/packages/app/src/components/app-diagnostic-sheet.tsx b/packages/app/src/components/app-diagnostic-sheet.tsx
new file mode 100644
index 000000000..295910842
--- /dev/null
+++ b/packages/app/src/components/app-diagnostic-sheet.tsx
@@ -0,0 +1,439 @@
+import * as Clipboard from "expo-clipboard";
+import { useCallback, useEffect, useMemo, useRef, useState } from "react";
+import {
+  Platform,
+  Pressable,
+  ScrollView,
+  Text,
+  View,
+  type PressableStateCallbackType,
+} from "react-native";
+import { Copy, RotateCw } from "lucide-react-native";
+import { StyleSheet, withUnistyles } from "react-native-unistyles";
+import { useTranslation } from "react-i18next";
+
+import { AdaptiveModalSheet, type SheetHeader } from "@/components/adaptive-modal-sheet";
+import { LoadingSpinner } from "@/components/ui/loading-spinner";
+import { useToast } from "@/contexts/toast-context";
+import { getDesktopDaemonLogs, getDesktopDaemonStatus } from "@/desktop/daemon/desktop-daemon";
+import {
+  formatAppDiagnosticHeader,
+  formatDiagnosticSection,
+  formatHostRuntimeSection,
+  formatServerInfoSection,
+  redactAppDiagnosticReport,
+} from "@/diagnostics/app-diagnostic-report";
+import { getHostRuntimeStore, useHosts, type HostRuntimeSnapshot } from "@/runtime/host-runtime";
+import { settingsStyles } from "@/styles/settings";
+import { ICON_SIZE, type Theme } from "@/styles/theme";
+import type { HostProfile } from "@/types/host-connection";
+
+interface AppDiagnosticSheetProps {
+  visible: boolean;
+  onClose: () => void;
+  appVersion: string | null;
+  isDesktopApp: boolean;
+}
+
+type ProgressStatus = "pending" | "running" | "done" | "failed";
+
+interface ProgressRow {
+  id: string;
+  label: string;
+  status: ProgressStatus;
+}
+
+interface DiagnosticCollectionResult {
+  sections: string[];
+  status: ProgressStatus;
+}
+
+const SNAP_POINTS = ["55%", "88%"];
+const ThemedCopy = withUnistyles(Copy);
+const ThemedRotateCw = withUnistyles(RotateCw);
+const ThemedLoadingSpinner = withUnistyles(LoadingSpinner);
+const foregroundMutedColorMapping = (theme: Theme) => ({
+  color: theme.colors.foregroundMuted,
+});
+
+export function AppDiagnosticSheet({
+  visible,
+  onClose,
+  appVersion,
+  isDesktopApp,
+}: AppDiagnosticSheetProps) {
+  const { t } = useTranslation();
+  const toast = useToast();
+  const hosts = useHosts();
+  const [diagnostic, setDiagnostic] = useState<string | null>(null);
+  const [loading, setLoading] = useState(false);
+  const [progress, setProgress] = useState<ProgressRow[]>([]);
+  const runIdRef = useRef(0);
+
+  const updateProgress = useCallback((id: string, label: string, status: ProgressStatus) => {
+    setProgress((current) => {
+      const existing = current.find((row) => row.id === id);
+      if (existing) {
+        return current.map((row) => (row.id === id ? { ...row, label, status } : row));
+      }
+      return [...current, { id, label, status }];
+    });
+  }, []);
+
+  const runDiagnostics = useCallback(async () => {
+    const runId = runIdRef.current + 1;
+    runIdRef.current = runId;
+    const isCurrentRun = () => runIdRef.current === runId;
+    const updateRunProgress = (id: string, label: string, status: ProgressStatus) => {
+      if (isCurrentRun()) {
+        updateProgress(id, label, status);
+      }
+    };
+
+    setLoading(true);
+    setDiagnostic(null);
+    setProgress([]);
+
+    const sections: string[] = [];
+    try {
+      updateRunProgress("client", t("settings.diagnostics.app.progress.client"), "running");
+      sections.push(
+        formatAppDiagnosticHeader({
+          appVersion,
+          platform: Platform.OS,
+          isDesktopApp,
+          hostCount: hosts.length,
+        }),
+      );
+      updateRunProgress("client", t("settings.diagnostics.app.progress.client"), "done");
+
+      if (isDesktopApp) {
+        const desktopLabel = t("settings.diagnostics.app.progress.desktop");
+        updateRunProgress("desktop", desktopLabel, "running");
+        const desktopResult = await collectDesktopDiagnosticSections();
+        sections.push(...desktopResult.sections);
+        updateRunProgress("desktop", desktopLabel, desktopResult.status);
+      }
+
+      const store = getHostRuntimeStore();
+      for (const host of hosts) {
+        const hostProgressId = `host:${host.serverId}`;
+        updateRunProgress(hostProgressId, host.label, "running");
+        const snapshot = store.getSnapshot(host.serverId);
+        const hostResult = await collectHostDiagnosticSections(host, snapshot);
+        sections.push(...hostResult.sections);
+        updateRunProgress(hostProgressId, host.label, hostResult.status);
+      }
+
+      if (isCurrentRun()) {
+        setDiagnostic(redactAppDiagnosticReport(sections.join("\n\n"), hosts));
+      }
+    } finally {
+      if (isCurrentRun()) {
+        setLoading(false);
+      }
+    }
+  }, [appVersion, hosts, isDesktopApp, t, updateProgress]);
+
+  useEffect(() => {
+    if (visible) {
+      void runDiagnostics();
+    } else {
+      runIdRef.current += 1;
+      setLoading(false);
+      setDiagnostic(null);
+      setProgress([]);
+    }
+  }, [visible, runDiagnostics]);
+
+  const handleRefreshPress = useCallback(() => {
+    void runDiagnostics();
+  }, [runDiagnostics]);
+
+  const handleCopyPress = useCallback(() => {
+    if (!diagnostic) return;
+    void Clipboard.setStringAsync(diagnostic)
+      .then(() => toast.copied(t("settings.diagnostics.app.copyLabel")))
+      .catch(() => toast.error(t("settings.diagnostics.app.copyFailed")));
+  }, [diagnostic, t, toast]);
+
+  const iconButtonStyle = useCallback(
+    ({ hovered, pressed }: PressableStateCallbackType & { hovered?: boolean }) => [
+      styles.iconButton,
+      (Boolean(hovered) || pressed) && styles.iconButtonHovered,
+    ],
+    [],
+  );
+
+  const disabledIconButtonStyle = useCallback(
+    ({ hovered, pressed }: PressableStateCallbackType & { hovered?: boolean }) => [
+      styles.iconButton,
+      (Boolean(hovered) || pressed) && Boolean(diagnostic) && styles.iconButtonHovered,
+      diagnostic ? null : styles.disabled,
+    ],
+    [diagnostic],
+  );
+
+  const header = useMemo<SheetHeader>(
+    () => ({
+      title: t("settings.diagnostics.app.title"),
+      actions: (
+        <View style={styles.headerActions}>
+          <Pressable
+            onPress={handleCopyPress}
+            disabled={!diagnostic}
+            hitSlop={8}
+            style={disabledIconButtonStyle}
+            accessibilityRole="button"
+            accessibilityLabel={t("settings.diagnostics.app.copyAccessibility")}
+          >
+            <ThemedCopy size={ICON_SIZE.sm} uniProps={foregroundMutedColorMapping} />
+          </Pressable>
+          <Pressable
+            onPress={handleRefreshPress}
+            disabled={loading}
+            hitSlop={8}
+            style={iconButtonStyle}
+            accessibilityRole="button"
+            accessibilityLabel={
+              loading
+                ? t("settings.diagnostics.app.refreshingAccessibility")
+                : t("settings.diagnostics.app.refreshAccessibility")
+            }
+          >
+            {loading ? (
+              <ThemedLoadingSpinner size={ICON_SIZE.sm} uniProps={foregroundMutedColorMapping} />
+            ) : (
+              <ThemedRotateCw size={ICON_SIZE.sm} uniProps={foregroundMutedColorMapping} />
+            )}
+          </Pressable>
+        </View>
+      ),
+    }),
+    [
+      diagnostic,
+      disabledIconButtonStyle,
+      handleCopyPress,
+      handleRefreshPress,
+      iconButtonStyle,
+      loading,
+      t,
+    ],
+  );
+
+  return (
+    <AdaptiveModalSheet
+      header={header}
+      visible={visible}
+      onClose={onClose}
+      snapPoints={SNAP_POINTS}
+      scrollable={false}
+      testID="app-diagnostic-sheet"
+    >
+      <View style={DIAGNOSTIC_CARD_STYLE}>
+        {diagnostic ? (
+          <ScrollView style={styles.codeScroll} contentContainerStyle={styles.codeContent}>
+            <ScrollView horizontal showsHorizontalScrollIndicator>
+              <Text style={styles.codeText} selectable>
+                {diagnostic}
+              </Text>
+            </ScrollView>
+          </ScrollView>
+        ) : (
+          <View style={styles.progressContent}>
+            {progress.length === 0 ? (
+              <View style={styles.progressRow}>
+                <ThemedLoadingSpinner size={ICON_SIZE.sm} uniProps={foregroundMutedColorMapping} />
+                <Text style={styles.mutedText}>{t("settings.diagnostics.app.running")}</Text>
+              </View>
+            ) : (
+              progress.map((row) => (
+                <View key={row.id} style={styles.progressRow}>
+                  {row.status === "running" || row.status === "pending" ? (
+                    <ThemedLoadingSpinner
+                      size={ICON_SIZE.sm}
+                      uniProps={foregroundMutedColorMapping}
+                    />
+                  ) : (
+                    <View
+                      style={row.status === "failed" ? FAILED_STATUS_DOT_STYLE : styles.statusDot}
+                    />
+                  )}
+                  <Text
+                    style={styles.mutedText}
+                  >{`${row.label}: ${formatProgressStatus(row.status)}`}</Text>
+                </View>
+              ))
+            )}
+          </View>
+        )}
+      </View>
+    </AdaptiveModalSheet>
+  );
+}
+
+async function collectDesktopDiagnosticSections(): Promise<DiagnosticCollectionResult> {
+  try {
+    const [status, logs] = await Promise.all([getDesktopDaemonStatus(), getDesktopDaemonLogs()]);
+    return {
+      status: "done",
+      sections: [
+        formatDiagnosticSection("Desktop", [
+          { label: "Daemon status", value: status.status },
+          { label: "Desktop managed", value: String(status.desktopManaged) },
+          { label: "Daemon PID", value: status.pid === null ? "none" : String(status.pid) },
+          { label: "Daemon version", value: status.version ?? "unknown" },
+          { label: "Daemon home", value: status.home || "unknown" },
+          { label: "Log path", value: logs.logPath || "unknown" },
+          { label: "Error", value: status.error ?? "none" },
+        ]),
+        [
+          "Desktop daemon log tail",
+          logs.contents ? indentBlock(logs.contents) : "  No log lines found",
+        ].join("\n"),
+      ],
+    };
+  } catch (error) {
+    return {
+      status: "failed",
+      sections: [formatDiagnosticSection("Desktop", [{ label: "Error", value: toMessage(error) }])],
+    };
+  }
+}
+
+async function collectHostDiagnosticSections(
+  host: HostProfile,
+  snapshot: HostRuntimeSnapshot | null,
+): Promise<DiagnosticCollectionResult> {
+  const sections = [formatHostRuntimeSection({ host, snapshot })];
+  const client = snapshot?.client ?? null;
+  if (snapshot?.connectionStatus !== "online" || !client) {
+    sections.push(
+      formatDiagnosticSection(`Host diagnostics: ${host.label}`, [
+        { label: "Status", value: "host is not connected" },
+      ]),
+    );
+    return { sections, status: "done" };
+  }
+
+  try {
+    const serverInfo = client.getLastServerInfoMessage();
+    sections.push(formatServerInfoSection(serverInfo));
+
+    const rttMs = await client.measureLatency({ timeoutMs: 5000 });
+    sections.push(
+      formatDiagnosticSection(`Host latency: ${host.label}`, [
+        { label: "Active RTT", value: `${Math.round(rttMs)}ms` },
+      ]),
+    );
+
+    if (serverInfo?.features?.daemonDiagnostics === true) {
+      const result = await client.collectDiagnostics();
+      sections.push(result.diagnostic);
+    } else {
+      sections.push(
+        formatDiagnosticSection(`Daemon diagnostics: ${host.label}`, [
+          { label: "Status", value: "unsupported by this daemon" },
+        ]),
+      );
+    }
+
+    return { sections, status: "done" };
+  } catch (error) {
+    sections.push(
+      formatDiagnosticSection(`Host diagnostics: ${host.label}`, [
+        { label: "Error", value: toMessage(error) },
+      ]),
+    );
+    return { sections, status: "failed" };
+  }
+}
+
+function indentBlock(value: string): string {
+  return value
+    .split("\n")
+    .filter(Boolean)
+    .map((line) => `  ${line}`)
+    .join("\n");
+}
+
+function toMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}
+
+function formatProgressStatus(status: ProgressStatus): string {
+  switch (status) {
+    case "done":
+      return "done";
+    case "failed":
+      return "failed";
+    case "running":
+    case "pending":
+      return "running";
+  }
+}
+
+const styles = StyleSheet.create((theme) => ({
+  diagnosticCard: {
+    overflow: "hidden",
+  },
+  codeScroll: {
+    maxHeight: 520,
+  },
+  codeContent: {
+    paddingVertical: theme.spacing[3],
+    paddingHorizontal: theme.spacing[4],
+  },
+  codeText: {
+    fontFamily: theme.fontFamily.mono,
+    fontSize: theme.fontSize.code,
+    color: theme.colors.foreground,
+    lineHeight: 18,
+  },
+  progressContent: {
+    paddingVertical: theme.spacing[4],
+    paddingHorizontal: theme.spacing[4],
+    gap: theme.spacing[3],
+  },
+  progressRow: {
+    flexDirection: "row",
+    alignItems: "center",
+    gap: theme.spacing[2],
+    minHeight: 24,
+  },
+  mutedText: {
+    flex: 1,
+    fontSize: theme.fontSize.sm,
+    color: theme.colors.foregroundMuted,
+  },
+  headerActions: {
+    flexDirection: "row",
+    alignItems: "center",
+    gap: theme.spacing[1],
+  },
+  iconButton: {
+    width: 28,
+    height: 28,
+    borderRadius: theme.borderRadius.full,
+    alignItems: "center",
+    justifyContent: "center",
+  },
+  iconButtonHovered: {
+    backgroundColor: theme.colors.surface2,
+  },
+  disabled: {
+    opacity: 0.5,
+  },
+  statusDot: {
+    width: 8,
+    height: 8,
+    borderRadius: theme.borderRadius.full,
+    backgroundColor: theme.colors.success,
+  },
+  statusDotFailed: {
+    backgroundColor: theme.colors.destructive,
+  },
+}));
+
+const DIAGNOSTIC_CARD_STYLE = [settingsStyles.card, styles.diagnosticCard];
+const FAILED_STATUS_DOT_STYLE = [styles.statusDot, styles.statusDotFailed];
diff --git a/packages/app/src/diagnostics/app-diagnostic-report.test.ts b/packages/app/src/diagnostics/app-diagnostic-report.test.ts
new file mode 100644
index 000000000..1f437ce81
--- /dev/null
+++ b/packages/app/src/diagnostics/app-diagnostic-report.test.ts
@@ -0,0 +1,104 @@
+import { describe, expect, test } from "vitest";
+import { formatHostRuntimeSection, redactAppDiagnosticReport } from "./app-diagnostic-report";
+import type { HostRuntimeSnapshot } from "@/runtime/host-runtime";
+import type { HostProfile } from "@/types/host-connection";
+
+function makeHost(): HostProfile {
+  return {
+    serverId: "srv-secret",
+    label: "Secret host",
+    lifecycle: {},
+    preferredConnectionId: "direct:secret.example.test:6767",
+    createdAt: "2026-06-25T00:00:00.000Z",
+    updatedAt: "2026-06-25T00:00:00.000Z",
+    connections: [
+      {
+        id: "direct:secret.example.test:6767",
+        type: "directTcp",
+        endpoint: "secret.example.test:6767",
+        useTls: true,
+        password: "tcp-password",
+      },
+      {
+        id: "relay:relay.secret.test:443",
+        type: "relay",
+        relayEndpoint: "relay.secret.test:443",
+        useTls: true,
+        daemonPublicKeyB64: "daemon-public-key-secret",
+      },
+      {
+        id: "socket:/tmp/paseo-secret.sock",
+        type: "directSocket",
+        path: "/tmp/paseo-secret.sock",
+      },
+      {
+        id: "pipe:\\\\.\\pipe\\paseo-secret",
+        type: "directPipe",
+        path: "\\\\.\\pipe\\paseo-secret",
+      },
+    ],
+  };
+}
+
+describe("app diagnostics report", () => {
+  test("formats connection rows without raw connection details", () => {
+    const host = makeHost();
+    const snapshot: HostRuntimeSnapshot = {
+      serverId: host.serverId,
+      activeConnectionId: "relay:relay.secret.test:443",
+      activeConnection: {
+        type: "relay",
+        endpoint: "relay.secret.test:443",
+        display: "relay",
+      },
+      connectionStatus: "online",
+      client: null,
+      lastError: null,
+      lastOnlineAt: "2026-06-25T00:00:00.000Z",
+      agentDirectoryStatus: "ready",
+      agentDirectoryError: null,
+      hasEverLoadedAgentDirectory: true,
+      probeByConnectionId: new Map([
+        ["direct:secret.example.test:6767", { status: "available", latencyMs: 42 }],
+        ["relay:relay.secret.test:443", { status: "available", latencyMs: 8 }],
+      ]),
+      clientGeneration: 1,
+    };
+
+    const report = formatHostRuntimeSection({ host, snapshot });
+
+    expect(report).toContain("direct TCP");
+    expect(report).toContain("relay");
+    expect(report).toContain("local socket");
+    expect(report).toContain("local pipe");
+    expect(report).not.toContain("secret.example.test");
+    expect(report).not.toContain("relay.secret.test");
+    expect(report).not.toContain("daemon-public-key-secret");
+    expect(report).not.toContain("/tmp/paseo-secret.sock");
+    expect(report).not.toContain("tcp-password");
+  });
+
+  test("redacts saved connection secrets from collected daemon and desktop text", () => {
+    const host = makeHost();
+    const redacted = redactAppDiagnosticReport(
+      [
+        "secret.example.test:6767",
+        "relay.secret.test:443",
+        "daemon-public-key-secret",
+        "/tmp/paseo-secret.sock",
+        "\\\\.\\pipe\\paseo-secret",
+        "password=tcp-password",
+        "paseo://pairing-secret",
+      ].join("\n"),
+      [host],
+    );
+
+    expect(redacted).not.toContain("secret.example.test");
+    expect(redacted).not.toContain("relay.secret.test");
+    expect(redacted).not.toContain("daemon-public-key-secret");
+    expect(redacted).not.toContain("/tmp/paseo-secret.sock");
+    expect(redacted).not.toContain("\\\\.\\pipe\\paseo-secret");
+    expect(redacted).not.toContain("tcp-password");
+    expect(redacted).not.toContain("pairing-secret");
+  });
+});
diff --git a/packages/app/src/diagnostics/app-diagnostic-report.ts b/packages/app/src/diagnostics/app-diagnostic-report.ts
new file mode 100644
index 000000000..33aaad9e3
--- /dev/null
+++ b/packages/app/src/diagnostics/app-diagnostic-report.ts
@@ -0,0 +1,133 @@
+import type { ServerInfoStatusPayload } from "@getpaseo/protocol/messages";
+import type { HostRuntimeSnapshot } from "@/runtime/host-runtime";
+import type { HostConnection, HostProfile } from "@/types/host-connection";
+
+interface DiagnosticEntry {
+  label: string;
+  value: string;
+}
+
+export function formatDiagnosticSection(title: string, entries: DiagnosticEntry[]): string {
+  return [title, ...entries.map((entry) => `  ${entry.label}: ${entry.value}`)].join("\n");
+}
+
+export function formatAppDiagnosticHeader(input: {
+  appVersion: string | null;
+  platform: string;
+  isDesktopApp: boolean;
+  hostCount: number;
+}): string {
+  return formatDiagnosticSection("Paseo app diagnostics", [
+    { label: "Collected at", value: new Date().toISOString() },
+    { label: "App version", value: input.appVersion ?? "unknown" },
+    { label: "Platform", value: input.platform },
+    { label: "Desktop app", value: String(input.isDesktopApp) },
+    { label: "Saved hosts", value: String(input.hostCount) },
+  ]);
+}
+
+export function formatHostRuntimeSection(input: {
+  host: HostProfile;
+  snapshot: HostRuntimeSnapshot | null;
+}): string {
+  const { host, snapshot } = input;
+  const entries: DiagnosticEntry[] = [
+    { label: "Server ID", value: host.serverId },
+    { label: "Status", value: snapshot?.connectionStatus ?? "not started" },
+    {
+      label: "Active connection",
+      value: snapshot?.activeConnection
+        ? describeConnectionKind(snapshot.activeConnection.type)
+        : "none",
+    },
+    { label: "Last online", value: snapshot?.lastOnlineAt ?? "never" },
+    { label: "Last error", value: snapshot?.lastError ?? "none" },
+    {
+      label: "Agent directory",
+      value: snapshot?.agentDirectoryStatus ?? "unknown",
+    },
+  ];
+
+  const connectionRows = host.connections.map((connection, index) => {
+    const probe = snapshot?.probeByConnectionId.get(connection.id) ?? null;
+    const isActive = snapshot?.activeConnectionId === connection.id;
+    return {
+      label: `Connection ${index + 1}`,
+      value: [
+        describeConnectionKind(connection.type),
+        isActive ? "active" : "inactive",
+        probe ? `probe=${probe.status}` : "probe=unknown",
+        probe?.status === "available" ? `latency=${Math.round(probe.latencyMs)}ms` : null,
+      ]
+        .filter(Boolean)
+        .join(", "),
+    };
+  });
+
+  return formatDiagnosticSection(`Host: ${host.label}`, [...entries, ...connectionRows]);
+}
+
+export function formatServerInfoSection(serverInfo: ServerInfoStatusPayload | null): string {
+  if (!serverInfo) {
+    return formatDiagnosticSection("Server info", [{ label: "Status", value: "not received" }]);
+  }
+
+  const features = serverInfo.features ? Object.keys(serverInfo.features).sort() : [];
+  return formatDiagnosticSection("Server info", [
+    { label: "Server ID", value: serverInfo.serverId },
+    { label: "Hostname", value: serverInfo.hostname ?? "unknown" },
+    { label: "Version", value: serverInfo.version ?? "unknown" },
+    { label: "Features", value: features.length > 0 ? features.join(", ") : "none" },
+  ]);
+}
+
+export function describeConnectionKind(type: HostConnection["type"] | string): string {
+  switch (type) {
+    case "directTcp":
+      return "direct TCP";
+    case "directSocket":
+      return "local socket";
+    case "directPipe":
+      return "local pipe";
+    case "relay":
+      return "relay";
+    default:
+      return "unknown";
+  }
+}
+
+export function redactAppDiagnosticReport(report: string, hosts: HostProfile[]): string {
+  let redacted = report;
+  for (const value of collectSensitiveHostValues(hosts)) {
+    redacted = redacted.split(value).join("[redacted]");
+  }
+  return redacted
+    .replace(/paseo:\/\/\S+/gi, "paseo://[redacted]")
+    .replace(
+      /([?&](?:password|token|secret|key|publicKey|daemonPublicKeyB64)=)[^&\s"']+/gi,
+      "$1[redacted]",
+    )
+    .replace(
+      /((?:password|token|secret|authorization|api[_-]?key|daemonPublicKeyB64|relayKey)\s*[:=]\s*)("[^"]+"|'[^']+'|[^\s,}]+)/gi,
+      "$1[redacted]",
+    );
+}
+
+function collectSensitiveHostValues(hosts: HostProfile[]): string[] {
+  const values = new Set<string>();
+  for (const host of hosts) {
+    for (const connection of host.connections) {
+      values.add(connection.id);
+      if (connection.type === "directTcp") {
+        values.add(connection.endpoint);
+        if (connection.password) values.add(connection.password);
+      } else if (connection.type === "relay") {
+        values.add(connection.relayEndpoint);
+        values.add(connection.daemonPublicKeyB64);
+      } else if (connection.type === "directSocket" || connection.type === "directPipe") {
+        values.add(connection.path);
+      }
+    }
+  }
+  return [...values].filter((value) => value.trim().length > 0);
+}
diff --git a/packages/app/src/i18n/resources/ar.ts b/packages/app/src/i18n/resources/ar.ts
index 5b838f613..826a93294 100644
--- a/packages/app/src/i18n/resources/ar.ts
+++ b/packages/app/src/i18n/resources/ar.ts
@@ -1451,6 +1451,22 @@ export const ar: TranslationResources = {
       playTest: "لعب الاختبار",
       playing: "جارٍ اللعب...",
       playbackFailed: "فشل التشغيل:{{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "عن",
diff --git a/packages/app/src/i18n/resources/en.ts b/packages/app/src/i18n/resources/en.ts
index 4b907c4c5..bdaa7f86c 100644
--- a/packages/app/src/i18n/resources/en.ts
+++ b/packages/app/src/i18n/resources/en.ts
@@ -1457,6 +1457,22 @@ export const en = {
       playTest: "Play test",
       playing: "Playing...",
       playbackFailed: "Playback failed: {{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "About",
diff --git a/packages/app/src/i18n/resources/es.ts b/packages/app/src/i18n/resources/es.ts
index 41c094898..a8fbf7a64 100644
--- a/packages/app/src/i18n/resources/es.ts
+++ b/packages/app/src/i18n/resources/es.ts
@@ -1488,6 +1488,22 @@ export const es: TranslationResources = {
       playTest: "Prueba de juego",
       playing: "Jugando...",
       playbackFailed: "Error de reproducción:{{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "Acerca de",
diff --git a/packages/app/src/i18n/resources/fr.ts b/packages/app/src/i18n/resources/fr.ts
index 2c7c07ed3..5be82675c 100644
--- a/packages/app/src/i18n/resources/fr.ts
+++ b/packages/app/src/i18n/resources/fr.ts
@@ -1491,6 +1491,22 @@ export const fr: TranslationResources = {
       playTest: "Jouer à l'essai",
       playing: "Jouant...",
       playbackFailed: "Échec de la lecture:{{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "À propos",
diff --git a/packages/app/src/i18n/resources/ja.ts b/packages/app/src/i18n/resources/ja.ts
index 1f436fa9b..f6f7cbf42 100644
--- a/packages/app/src/i18n/resources/ja.ts
+++ b/packages/app/src/i18n/resources/ja.ts
@@ -1466,6 +1466,22 @@ export const ja: TranslationResources = {
       playTest: "テスト再生",
       playing: "再生中...",
       playbackFailed: "再生に失敗しました: {{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "アプリ情報",
diff --git a/packages/app/src/i18n/resources/pt-BR.ts b/packages/app/src/i18n/resources/pt-BR.ts
index 207e74ee1..e00c314f1 100644
--- a/packages/app/src/i18n/resources/pt-BR.ts
+++ b/packages/app/src/i18n/resources/pt-BR.ts
@@ -1473,6 +1473,22 @@ export const ptBR: TranslationResources = {
       playTest: "Reproduzir teste",
       playing: "Reproduzindo...",
       playbackFailed: "Falha na reprodução: {{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "Sobre",
diff --git a/packages/app/src/i18n/resources/ru.ts b/packages/app/src/i18n/resources/ru.ts
index 48159ebf8..e54dd030d 100644
--- a/packages/app/src/i18n/resources/ru.ts
+++ b/packages/app/src/i18n/resources/ru.ts
@@ -1478,6 +1478,22 @@ export const ru: TranslationResources = {
       playTest: "Игровой тест",
       playing: "Игра...",
       playbackFailed: "Ошибка воспроизведения:{{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "О",
diff --git a/packages/app/src/i18n/resources/zh-CN.ts b/packages/app/src/i18n/resources/zh-CN.ts
index 7db4b04b1..7cb3cb50b 100644
--- a/packages/app/src/i18n/resources/zh-CN.ts
+++ b/packages/app/src/i18n/resources/zh-CN.ts
@@ -1433,6 +1433,22 @@ export const zhCN: TranslationResources = {
       playTest: "播放测试",
       playing: "正在播放...",
       playbackFailed: "播放失败：{{message}}",
+      app: {
+        title: "App diagnostic",
+        rowTitle: "App diagnostic",
+        rowHint: "Collect connection, daemon, provider, desktop, and log details",
+        run: "Run",
+        running: "Running diagnostic...",
+        copyLabel: "diagnostic",
+        copyAccessibility: "Copy diagnostic",
+        copyFailed: "Failed to copy diagnostic",
+        refreshAccessibility: "Refresh diagnostic",
+        refreshingAccessibility: "Refreshing diagnostic",
+        progress: {
+          client: "Client",
+          desktop: "Desktop",
+        },
+      },
     },
     about: {
       title: "关于",
diff --git a/packages/app/src/screens/settings-screen.tsx b/packages/app/src/screens/settings-screen.tsx
index bd447bc8e..a29015647 100644
--- a/packages/app/src/screens/settings-screen.tsx
+++ b/packages/app/src/screens/settings-screen.tsx
@@ -44,6 +44,7 @@ import {
   SquareTerminal,
 } from "lucide-react-native";
 import { DropdownTrigger } from "@/components/ui/dropdown-trigger";
+import { AppDiagnosticSheet } from "@/components/app-diagnostic-sheet";
 import { ComboboxTrigger } from "@/components/ui/combobox-trigger";
 import { SidebarHeaderRow } from "@/components/sidebar/sidebar-header-row";
 import { SidebarSeparator } from "@/components/sidebar/sidebar-separator";
@@ -455,6 +456,8 @@ interface DiagnosticsSectionProps {
   isPlaybackTestRunning: boolean;
   playbackTestResult: string | null;
   handlePlaybackTest: () => Promise<void>;
+  appVersion: string | null;
+  isDesktopApp: boolean;
 }
 
 function DiagnosticsSection({
@@ -462,14 +465,28 @@ function DiagnosticsSection({
   isPlaybackTestRunning,
   playbackTestResult,
   handlePlaybackTest,
+  appVersion,
+  isDesktopApp,
 }: DiagnosticsSectionProps) {
   const { t } = useTranslation();
+  const [diagnosticSheetOpen, setDiagnosticSheetOpen] = useState(false);
   const handlePlayPress = useCallback(() => {
     void handlePlaybackTest();
   }, [handlePlaybackTest]);
+  const handleOpenDiagnostic = useCallback(() => setDiagnosticSheetOpen(true), []);
+  const handleCloseDiagnostic = useCallback(() => setDiagnosticSheetOpen(false), []);
   return (
     <SettingsSection title={t("settings.diagnostics.title")}>
       <View style={settingsStyles.card}>
+        <View style={settingsStyles.row} testID="app-diagnostic-row">
+          <View style={settingsStyles.rowContent}>
+            <Text style={settingsStyles.rowTitle}>{t("settings.diagnostics.app.rowTitle")}</Text>
+            <Text style={settingsStyles.rowHint}>{t("settings.diagnostics.app.rowHint")}</Text>
+          </View>
+          <Button variant="secondary" size="sm" onPress={handleOpenDiagnostic}>
+            {t("settings.diagnostics.app.run")}
+          </Button>
+        </View>
         <View style={settingsStyles.row}>
           <View style={settingsStyles.rowContent}>
             <Text style={settingsStyles.rowTitle}>{t("settings.diagnostics.testAudio")}</Text>
@@ -489,6 +506,12 @@ function DiagnosticsSection({
           </Button>
         </View>
       </View>
+      <AppDiagnosticSheet
+        visible={diagnosticSheetOpen}
+        onClose={handleCloseDiagnostic}
+        appVersion={appVersion}
+        isDesktopApp={isDesktopApp}
+      />
     </SettingsSection>
   );
 }
@@ -1533,6 +1556,8 @@ export default function SettingsScreen({ view }: SettingsScreenProps) {
               isPlaybackTestRunning={isPlaybackTestRunning}
               playbackTestResult={playbackTestResult}
               handlePlaybackTest={handlePlaybackTest}
+              appVersion={appVersion}
+              isDesktopApp={isDesktopApp}
             />
           );
         case "about":
diff --git a/packages/client/src/daemon-client.ts b/packages/client/src/daemon-client.ts
index 9439ce50e..f072d6a10 100644
--- a/packages/client/src/daemon-client.ts
+++ b/packages/client/src/daemon-client.ts
@@ -67,6 +67,7 @@ import type {
   ProviderUsageListResponseMessage,
   DaemonGetStatusResponse,
   DaemonGetPairingOfferResponse,
+  DiagnosticsResponse,
   AgentRewindResponseMessage,
   ListTerminalsResponse,
   CreateTerminalResponse,
@@ -351,6 +352,7 @@ type ProviderDiagnosticPayload = ProviderDiagnosticResponseMessage["payload"];
 type ProviderUsageListPayload = ProviderUsageListResponseMessage["payload"];
 type DaemonStatusPayload = DaemonGetStatusResponse["payload"];
 type DaemonPairingOfferPayload = DaemonGetPairingOfferResponse["payload"];
+type DiagnosticsPayload = DiagnosticsResponse["payload"];
 type ReadProjectConfigPayload = Extract<
   SessionOutboundMessage,
   { type: "read_project_config_response" }
@@ -3755,6 +3757,16 @@ export class DaemonClient {
     });
   }
 
+  async collectDiagnostics(requestId?: string): Promise<DiagnosticsPayload> {
+    return this.sendNamespacedCorrelatedSessionRequest({
+      requestId,
+      message: {
+        type: "diagnostics.request",
+      },
+      timeout: 30000,
+    });
+  }
+
   async patchDaemonConfig(
     config: MutableDaemonConfigPatch,
     requestId?: string,
diff --git a/packages/protocol/src/messages.test.ts b/packages/protocol/src/messages.test.ts
index ea5771f1a..f2247823f 100644
--- a/packages/protocol/src/messages.test.ts
+++ b/packages/protocol/src/messages.test.ts
@@ -220,6 +220,36 @@ describe("provider usage list message contract", () => {
   });
 });
 
+describe("diagnostics message contract", () => {
+  test("accepts the diagnostics request as a simple namespaced RPC", () => {
+    const parsed = SessionInboundMessageSchema.parse({
+      type: "diagnostics.request",
+      requestId: "diag-1",
+    });
+
+    expect(parsed).toEqual({
+      type: "diagnostics.request",
+      requestId: "diag-1",
+    });
+  });
+
+  test("accepts a copyable diagnostics response", () => {
+    const parsed = SessionOutboundMessageSchema.parse({
+      type: "diagnostics.response",
+      payload: {
+        requestId: "diag-2",
+        diagnostic: "Paseo diagnostics\n  Status: ok",
+      },
+    });
+
+    expect(parsed.type).toBe("diagnostics.response");
+    if (parsed.type !== "diagnostics.response") {
+      throw new Error("Expected diagnostics.response");
+    }
+    expect(parsed.payload.diagnostic).toContain("Status: ok");
+  });
+});
+
 describe("agent detach RPC", () => {
   test("parses the namespaced detach request", () => {
     const parsed = SessionInboundMessageSchema.parse({
diff --git a/packages/protocol/src/messages.ts b/packages/protocol/src/messages.ts
index 2757f4f58..db2f9d65b 100644
--- a/packages/protocol/src/messages.ts
+++ b/packages/protocol/src/messages.ts
@@ -1060,6 +1060,11 @@ export const DaemonGetPairingOfferRequestSchema = z.object({
   requestId: z.string(),
 });
 
+export const DiagnosticsRequestSchema = z.object({
+  type: z.literal("diagnostics.request"),
+  requestId: z.string(),
+});
+
 export const GetDaemonConfigRequestMessageSchema = z.object({
   type: z.literal("get_daemon_config_request"),
   requestId: z.string(),
@@ -2024,6 +2029,7 @@ export const SessionInboundMessageSchema = z.discriminatedUnion("type", [
   WaitForFinishRequestSchema,
   DaemonGetStatusRequestSchema,
   DaemonGetPairingOfferRequestSchema,
+  DiagnosticsRequestSchema,
   GetDaemonConfigRequestMessageSchema,
   SetDaemonConfigRequestMessageSchema,
   ReadProjectConfigRequestMessageSchema,
@@ -2319,6 +2325,8 @@ export const ServerInfoStatusPayloadSchema = z
         providerUsageList: z.boolean().optional(),
         // COMPAT(agentDetach): added in v0.1.98, remove gate after 2026-12-19 once daemon floor >= v0.1.98.
         agentDetach: z.boolean().optional(),
+        // COMPAT(daemonDiagnostics): added in v0.1.100, remove gate after 2026-12-25 once daemon floor >= v0.1.100.
+        daemonDiagnostics: z.boolean().optional(),
       })
       .optional(),
   })
@@ -3033,6 +3041,16 @@ export const DaemonGetPairingOfferResponseSchema = z.object({
     .passthrough(),
 });
 
+export const DiagnosticsResponseSchema = z.object({
+  type: z.literal("diagnostics.response"),
+  payload: z
+    .object({
+      requestId: z.string(),
+      diagnostic: z.string(),
+    })
+    .passthrough(),
+});
+
 export const SetDaemonConfigResponseMessageSchema = z.object({
   type: z.literal("set_daemon_config_response"),
   payload: z
@@ -4117,6 +4135,7 @@ export const SessionOutboundMessageSchema = z.discriminatedUnion("type", [
   SetVoiceModeResponseMessageSchema,
   DaemonGetStatusResponseSchema,
   DaemonGetPairingOfferResponseSchema,
+  DiagnosticsResponseSchema,
   GetDaemonConfigResponseMessageSchema,
   SetDaemonConfigResponseMessageSchema,
   ReadProjectConfigResponseMessageSchema,
@@ -4304,6 +4323,7 @@ export type ListProviderFeaturesResponseMessage = z.infer<
 export type ListAvailableProvidersResponse = z.infer<typeof ListAvailableProvidersResponseSchema>;
 export type DaemonGetStatusResponse = z.infer<typeof DaemonGetStatusResponseSchema>;
 export type DaemonGetPairingOfferResponse = z.infer<typeof DaemonGetPairingOfferResponseSchema>;
+export type DiagnosticsResponse = z.infer<typeof DiagnosticsResponseSchema>;
 export type GetProvidersSnapshotResponseMessage = z.infer<
   typeof GetProvidersSnapshotResponseMessageSchema
 >;
diff --git a/packages/server/src/server/loop-service.test.ts b/packages/server/src/server/loop-service.test.ts
index c8bbf7110..57d87b67d 100644
--- a/packages/server/src/server/loop-service.test.ts
+++ b/packages/server/src/server/loop-service.test.ts
@@ -635,6 +635,7 @@ describe("LoopService", () => {
 
   test("stops a running loop and cancels the active worker", async () => {
     let release: (() => void) | null = null;
+    const cancelledAgentIds: string[] = [];
     const blocker = new Promise<void>((resolve) => {
       release = resolve;
     });
@@ -653,6 +654,11 @@ describe("LoopService", () => {
       registry: storage,
       logger,
     });
+    const cancelAgentRun = manager.cancelAgentRun.bind(manager);
+    manager.cancelAgentRun = async (agentId) => {
+      cancelledAgentIds.push(agentId);
+      return cancelAgentRun(agentId);
+    };
     const service = new LoopService({
       paseoHome,
       agentManager: manager,
@@ -667,14 +673,26 @@ describe("LoopService", () => {
       verifyChecks: ["test -f never.txt"],
     });
 
-    await new Promise((resolve) => setTimeout(resolve, 25));
-    const stopped = await service.stopLoop(loop.id);
-    release?.();
+    const workerAgentId = await waitForActiveWorkerRun(service, manager, loop.id);
+    const stopPromise = service.stopLoop(loop.id);
+    let cancelWaitError: unknown;
+    try {
+      await waitForCancelledAgent(cancelledAgentIds, workerAgentId);
+    } catch (error) {
+      cancelWaitError = error;
+    } finally {
+      release?.();
+    }
+    const stopped = await stopPromise;
+    if (cancelWaitError) {
+      throw cancelWaitError;
+    }
 
     expect(stopped.status).toBe("stopped");
     const finalLoop = await service.inspectLoop(loop.id);
     expect(finalLoop.status).toBe("stopped");
     expect(finalLoop.iterations[0]?.status).toBe("stopped");
+    expect(cancelledAgentIds).toEqual([workerAgentId]);
     expect(finalLoop.logs.some((entry) => entry.text.includes("Stop requested"))).toBe(true);
   });
 });
@@ -692,3 +710,34 @@ async function waitForLoopCompletion(service: LoopService, loopId: string): Prom
     await new Promise((resolve) => setTimeout(resolve, 10));
   }
 }
+
+async function waitForActiveWorkerRun(
+  service: LoopService,
+  manager: AgentManager,
+  loopId: string,
+): Promise<string> {
+  const deadline = Date.now() + 2_000;
+  while (Date.now() < deadline) {
+    const loop = await service.inspectLoop(loopId);
+    const workerAgentId = loop.activeWorkerAgentId;
+    if (workerAgentId && manager.getAgent(workerAgentId)?.activeForegroundTurnId) {
+      return workerAgentId;
+    }
+    await new Promise((resolve) => setTimeout(resolve, 10));
+  }
+  throw new Error("Timed out waiting for loop worker run to start");
+}
+
+async function waitForCancelledAgent(
+  cancelledAgentIds: readonly string[],
+  agentId: string,
+): Promise<void> {
+  const deadline = Date.now() + 2_000;
+  while (Date.now() < deadline) {
+    if (cancelledAgentIds.includes(agentId)) {
+      return;
+    }
+    await new Promise((resolve) => setTimeout(resolve, 10));
+  }
+  throw new Error("Timed out waiting for loop worker cancellation");
+}
diff --git a/packages/server/src/server/session.ts b/packages/server/src/server/session.ts
index cfb1d568e..5b495a548 100644
--- a/packages/server/src/server/session.ts
+++ b/packages/server/src/server/session.ts
@@ -145,6 +145,7 @@ import { WorkspaceFilesSession } from "./session/files/workspace-files-session.j
 import { AgentConfigSession } from "./session/agent-config/agent-config-session.js";
 import { ProjectConfigSession } from "./session/project-config/project-config-session.js";
 import { DaemonSession, type DaemonRuntimeConfig } from "./session/daemon/daemon-session.js";
+import type { DaemonWebSocketRuntimeDiagnosticSnapshot } from "./session/daemon/diagnostics.js";
 import { DownloadTokenStore } from "./file-download/token-store.js";
 import { PushTokenStore } from "./push/token-store.js";
 import {
@@ -463,6 +464,7 @@ export interface SessionOptions {
   serverId?: string;
   daemonVersion?: string;
   daemonRuntimeConfig?: DaemonRuntimeConfig;
+  getWebSocketRuntimeMetrics?: () => DaemonWebSocketRuntimeDiagnosticSnapshot | null;
 }
 
 export type SessionLifecycleIntent =
@@ -632,6 +634,7 @@ export class Session {
       serverId,
       daemonVersion,
       daemonRuntimeConfig,
+      getWebSocketRuntimeMetrics,
     } = options;
     this.clientId = clientId;
     this.appVersion = appVersion ?? null;
@@ -779,7 +782,11 @@ export class Session {
       serverId,
       daemonVersion,
       daemonRuntimeConfig,
+      getWebSocketRuntimeMetrics,
       listProviderAvailability: () => this.agentManager.listProviderAvailability(),
+      listAgents: () => this.agentManager.listAgents(),
+      listProjects: () => this.projectRegistry.list(),
+      listWorkspaces: () => this.workspaceRegistry.list(),
       logger: this.sessionLogger,
     });
     this.daemonConfigStore = daemonConfigStore;
@@ -1501,6 +1508,8 @@ export class Session {
         return this.daemonSession.handleGetStatusRequest(msg);
       case "daemon.get_pairing_offer.request":
         return this.daemonSession.handleGetPairingOfferRequest(msg);
+      case "diagnostics.request":
+        return this.daemonSession.handleDiagnosticsRequest(msg);
       case "set_daemon_config_request":
         this.emit({
           type: "set_daemon_config_response",
diff --git a/packages/server/src/server/session/daemon/daemon-session.test.ts b/packages/server/src/server/session/daemon/daemon-session.test.ts
index dffae4646..856091d9e 100644
--- a/packages/server/src/server/session/daemon/daemon-session.test.ts
+++ b/packages/server/src/server/session/daemon/daemon-session.test.ts
@@ -1,4 +1,4 @@
-import { mkdtempSync, realpathSync, rmSync } from "node:fs";
+import { mkdtempSync, realpathSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, test } from "vitest";
@@ -8,6 +8,7 @@ import {
   type DaemonRuntimeConfig,
   type DaemonSessionHost,
 } from "./daemon-session.js";
+import type { DaemonWebSocketRuntimeDiagnosticSnapshot } from "./diagnostics.js";
 import type { ProviderAvailability } from "../../agent/agent-manager.js";
 import type { SessionOutboundMessage } from "../../messages.js";
 
@@ -25,24 +26,38 @@ function makeHome(): string {
   return home;
 }
 
+function restoreEnv(name: string, value: string | undefined): void {
+  if (value === undefined) {
+    delete process.env[name];
+    return;
+  }
+  process.env[name] = value;
+}
+
 function makeSubsystem(overrides: {
   serverId?: string;
   daemonVersion?: string;
   daemonRuntimeConfig?: DaemonRuntimeConfig;
   listProviderAvailability?: () => Promise<ProviderAvailability[]>;
+  getWebSocketRuntimeMetrics?: () => DaemonWebSocketRuntimeDiagnosticSnapshot | null;
 }) {
   const emitted: SessionOutboundMessage[] = [];
   const host: DaemonSessionHost = { emit: (msg) => emitted.push(msg) };
+  const paseoHome = makeHome();
   const subsystem = new DaemonSession({
     host,
-    paseoHome: makeHome(),
+    paseoHome,
     serverId: overrides.serverId,
     daemonVersion: overrides.daemonVersion,
     daemonRuntimeConfig: overrides.daemonRuntimeConfig,
+    listAgents: () => [],
+    listProjects: async () => [],
+    listWorkspaces: async () => [],
     listProviderAvailability: overrides.listProviderAvailability ?? (async () => []),
+    getWebSocketRuntimeMetrics: overrides.getWebSocketRuntimeMetrics,
     logger: pino({ level: "silent" }),
   });
-  return { subsystem, emitted };
+  return { subsystem, emitted, paseoHome };
 }
 
 describe("DaemonSession", () => {
@@ -168,4 +183,177 @@ describe("DaemonSession", () => {
     expect(message.payload.url.startsWith("https://app.example.test")).toBe(true);
     expect(typeof message.payload.qr).toBe("string");
   });
+
+  test("diagnostics includes a log tail and redacts connection secrets", async () => {
+    const { subsystem, emitted, paseoHome } = makeSubsystem({
+      serverId: "srv-1",
+      daemonVersion: "1.2.3",
+      daemonRuntimeConfig: {
+        listen: "127.0.0.1:6767",
+        relay: {
+          enabled: true,
+          endpoint: "relay.secret.test:443",
+          publicEndpoint: "relay.secret.test:443",
+          useTls: true,
+          publicUseTls: true,
+        },
+      },
+    });
+    writeFileSync(
+      join(paseoHome, "daemon.log"),
+      "first line\nrelay.secret.test:443 token=super-secret paseo://pairing-secret\n",
+    );
+
+    await subsystem.handleDiagnosticsRequest({ type: "diagnostics.request", requestId: "d-1" });
+
+    expect(emitted).toHaveLength(1);
+    const message = emitted[0];
+    expect(message.type).toBe("diagnostics.response");
+    if (message.type !== "diagnostics.response") {
+      throw new Error("expected diagnostics response");
+    }
+    expect(message.payload.requestId).toBe("d-1");
+    expect(message.payload.diagnostic).toContain("Daemon log tail");
+    expect(message.payload.diagnostic).toContain("first line");
+    expect(message.payload.diagnostic).not.toContain("relay.secret.test:443");
+    expect(message.payload.diagnostic).not.toContain("super-secret");
+    expect(message.payload.diagnostic).not.toContain("pairing-secret");
+  });
+
+  test("diagnostics includes the PATH and shell visible to the daemon", async () => {
+    const originalPath = process.env.PATH;
+    const originalShell = process.env.SHELL;
+    const originalComSpec = process.env.ComSpec;
+    const originalCOMSPEC = process.env.COMSPEC;
+    try {
+      process.env.PATH = "/opt/paseo-test/bin:/usr/bin";
+      process.env.SHELL = "/bin/paseo-test-shell";
+      delete process.env.ComSpec;
+      delete process.env.COMSPEC;
+
+      const { subsystem, emitted } = makeSubsystem({});
+
+      await subsystem.handleDiagnosticsRequest({ type: "diagnostics.request", requestId: "d-env" });
+
+      expect(emitted).toHaveLength(1);
+      const message = emitted[0];
+      expect(message.type).toBe("diagnostics.response");
+      if (message.type !== "diagnostics.response") {
+        throw new Error("expected diagnostics response");
+      }
+      expect(message.payload.diagnostic).toContain("PATH: /opt/paseo-test/bin:/usr/bin");
+      expect(message.payload.diagnostic).toContain("Shell: SHELL=/bin/paseo-test-shell");
+    } finally {
+      restoreEnv("PATH", originalPath);
+      restoreEnv("SHELL", originalShell);
+      restoreEnv("ComSpec", originalComSpec);
+      restoreEnv("COMSPEC", originalCOMSPEC);
+    }
+  });
+
+  test("diagnostics includes the last flushed websocket runtime metrics", async () => {
+    const { subsystem, emitted } = makeSubsystem({
+      getWebSocketRuntimeMetrics: () => ({
+        collectedAt: "2026-01-02T03:04:05.000Z",
+        windowMs: 30_000,
+        final: false,
+        sessions: {
+          activeConnections: 2,
+          externalSessionKeys: 3,
+          reconnectGraceSessions: 1,
+        },
+        sockets: {
+          activeSockets: 2,
+          pendingConnections: 1,
+        },
+        counters: {
+          connectedAwaitingHello: 1,
+          helloResumed: 0,
+          helloNew: 2,
+          pendingDisconnected: 0,
+          sessionDisconnectedWaitingReconnect: 0,
+          sessionSocketDisconnectedAttached: 0,
+          sessionCleanup: 0,
+          validationFailed: 0,
+          binaryBeforeHelloRejected: 0,
+          pendingMessageRejectedBeforeHello: 0,
+          missingConnectionForMessage: 0,
+          unexpectedHelloOnActiveConnection: 0,
+          relayExternalSocketAttached: 0,
+          originRejected: 0,
+          hostRejected: 0,
+        },
+        inboundMessageTypesTop: [["session", 4]],
+        inboundSessionRequestTypesTop: [["diagnostics.request", 2]],
+        outboundMessageTypesTop: [["session_message", 5]],
+        outboundSessionMessageTypesTop: [["diagnostics.response", 2]],
+        outboundAgentStreamTypesTop: [["timeline:message", 3]],
+        outboundAgentStreamAgentsTop: [["agent-1", 3]],
+        outboundBinaryFrameTypesTop: [["binary", 1]],
+        bufferedAmount: {
+          p95: 128,
+          max: 256,
+        },
+        eventLoopDelay: {
+          p50Ms: 1,
+          p99Ms: 4,
+          maxMs: 7,
+        },
+        runtime: {
+          inflightRequests: 1,
+          peakInflightRequests: 3,
+          terminalSubscriptionCount: 4,
+          terminalDirectorySubscriptionCount: 5,
+          checkoutDiffTargetCount: 6,
+          checkoutDiffSubscriptionCount: 7,
+          checkoutDiffWatcherCount: 8,
+          checkoutDiffFallbackRefreshTargetCount: 9,
+        },
+        latency: [
+          {
+            type: "diagnostics.request",
+            count: 2,
+            minMs: 3,
+            maxMs: 7,
+            p50Ms: 4,
+            totalMs: 11,
+          },
+        ],
+        agents: {
+          total: 10,
+          byLifecycle: {
+            idle: 8,
+            running: 2,
+          },
+          withActiveForegroundTurn: 2,
+          timelineStats: {
+            totalItems: 42,
+            maxItemsPerAgent: 12,
+          },
+        },
+      }),
+    });
+
+    await subsystem.handleDiagnosticsRequest({ type: "diagnostics.request", requestId: "d-2" });
+
+    expect(emitted).toHaveLength(1);
+    const message = emitted[0];
+    expect(message.type).toBe("diagnostics.response");
+    if (message.type !== "diagnostics.response") {
+      throw new Error("expected diagnostics response");
+    }
+    expect(message.payload.diagnostic).toContain("WebSocket runtime metrics");
+    expect(message.payload.diagnostic).toContain("Collected at: 2026-01-02T03:04:05.000Z");
+    expect(message.payload.diagnostic).toContain(
+      "Sessions: active=2, externalKeys=3, reconnectGrace=1",
+    );
+    expect(message.payload.diagnostic).toContain(
+      "Latency: diagnostics.request count=2 p50=4ms max=7ms total=11ms",
+    );
+    expect(message.payload.diagnostic).toContain("Inbound session requests: diagnostics.request=2");
+    expect(message.payload.diagnostic).toContain(
+      "Checkout diff: targets=6, subscriptions=7, watchers=8, fallbackRefreshTargets=9",
+    );
+    expect(message.payload.diagnostic).toContain("Agent lifecycle: idle=8, running=2");
+  });
 });
diff --git a/packages/server/src/server/session/daemon/daemon-session.ts b/packages/server/src/server/session/daemon/daemon-session.ts
index d0392f1f9..0c6781d29 100644
--- a/packages/server/src/server/session/daemon/daemon-session.ts
+++ b/packages/server/src/server/session/daemon/daemon-session.ts
@@ -3,6 +3,12 @@ import type { ProviderAvailability } from "../../agent/agent-manager.js";
 import type { SessionInboundMessage, SessionOutboundMessage } from "../../messages.js";
 import { getPidLockInfo } from "../../pid-lock.js";
 import { generateLocalPairingOffer } from "../../pairing-offer.js";
+import {
+  collectDaemonDiagnostics,
+  type DaemonWebSocketRuntimeDiagnosticSnapshot,
+} from "./diagnostics.js";
+import type { ManagedAgent } from "../../agent/agent-manager.js";
+import type { PersistedProjectRecord, PersistedWorkspaceRecord } from "../../workspace-registry.js";
 
 export interface DaemonRuntimeConfig {
   listen: string | null;
@@ -26,7 +32,11 @@ export interface DaemonSessionOptions {
   serverId: string | undefined;
   daemonVersion: string | undefined;
   daemonRuntimeConfig: DaemonRuntimeConfig | undefined;
+  listAgents: () => ManagedAgent[];
+  listProjects: () => Promise<PersistedProjectRecord[]>;
+  listWorkspaces: () => Promise<PersistedWorkspaceRecord[]>;
   listProviderAvailability: () => Promise<ProviderAvailability[]>;
+  getWebSocketRuntimeMetrics?: () => DaemonWebSocketRuntimeDiagnosticSnapshot | null;
   logger: pino.Logger;
 }
 
@@ -43,7 +53,11 @@ export class DaemonSession {
   private readonly serverId: string | undefined;
   private readonly daemonVersion: string | undefined;
   private readonly daemonRuntimeConfig: DaemonRuntimeConfig | undefined;
+  private readonly listAgents: () => ManagedAgent[];
+  private readonly listProjects: () => Promise<PersistedProjectRecord[]>;
+  private readonly listWorkspaces: () => Promise<PersistedWorkspaceRecord[]>;
   private readonly listProviderAvailability: () => Promise<ProviderAvailability[]>;
+  private readonly getWebSocketRuntimeMetrics: () => DaemonWebSocketRuntimeDiagnosticSnapshot | null;
   private readonly logger: pino.Logger;
 
   constructor(options: DaemonSessionOptions) {
@@ -52,7 +66,11 @@ export class DaemonSession {
     this.serverId = options.serverId;
     this.daemonVersion = options.daemonVersion;
     this.daemonRuntimeConfig = options.daemonRuntimeConfig;
+    this.listAgents = options.listAgents;
+    this.listProjects = options.listProjects;
+    this.listWorkspaces = options.listWorkspaces;
     this.listProviderAvailability = options.listProviderAvailability;
+    this.getWebSocketRuntimeMetrics = options.getWebSocketRuntimeMetrics ?? (() => null);
     this.logger = options.logger;
   }
 
@@ -136,4 +154,41 @@ export class DaemonSession {
       });
     }
   }
+
+  async handleDiagnosticsRequest(
+    msg: Extract<SessionInboundMessage, { type: "diagnostics.request" }>,
+  ): Promise<void> {
+    try {
+      const diagnostic = await collectDaemonDiagnostics({
+        paseoHome: this.paseoHome,
+        serverId: this.serverId,
+        daemonVersion: this.daemonVersion,
+        daemonRuntimeConfig: this.daemonRuntimeConfig,
+        listAgents: this.listAgents,
+        listProjects: this.listProjects,
+        listWorkspaces: this.listWorkspaces,
+        listProviderAvailability: this.listProviderAvailability,
+        getWebSocketRuntimeMetrics: this.getWebSocketRuntimeMetrics,
+        logger: this.logger,
+      });
+      this.host.emit({
+        type: "diagnostics.response",
+        payload: {
+          requestId: msg.requestId,
+          diagnostic,
+        },
+      });
+    } catch (error) {
+      this.logger.error({ err: error }, "Failed to handle diagnostics request");
+      this.host.emit({
+        type: "diagnostics.response",
+        payload: {
+          requestId: msg.requestId,
+          diagnostic: `Paseo diagnostics\n  Error: ${
+            error instanceof Error ? error.message : String(error)
+          }`,
+        },
+      });
+    }
+  }
 }
diff --git a/packages/server/src/server/session/daemon/diagnostics.ts b/packages/server/src/server/session/daemon/diagnostics.ts
new file mode 100644
index 000000000..468e1aac1
--- /dev/null
+++ b/packages/server/src/server/session/daemon/diagnostics.ts
@@ -0,0 +1,547 @@
+import { open, statfs } from "node:fs/promises";
+import { cpus, freemem, loadavg, platform, release, totalmem, type } from "node:os";
+import path from "node:path";
+
+import type pino from "pino";
+
+import type { ManagedAgent, ProviderAvailability } from "../../agent/agent-manager.js";
+import type { WebSocketRuntimeDiagnosticSnapshot } from "../../websocket/runtime-metrics.js";
+import type { PersistedProjectRecord, PersistedWorkspaceRecord } from "../../workspace-registry.js";
+import { execCommand } from "../../../utils/spawn.js";
+import type { DaemonRuntimeConfig } from "./daemon-session.js";
+
+interface DiagnosticEntry {
+  label: string;
+  value: string;
+}
+
+export interface DaemonDiagnosticsOptions {
+  paseoHome: string;
+  serverId: string | undefined;
+  daemonVersion: string | undefined;
+  daemonRuntimeConfig: DaemonRuntimeConfig | undefined;
+  listAgents: () => ManagedAgent[];
+  listProjects: () => Promise<PersistedProjectRecord[]>;
+  listWorkspaces: () => Promise<PersistedWorkspaceRecord[]>;
+  listProviderAvailability: () => Promise<ProviderAvailability[]>;
+  getWebSocketRuntimeMetrics: () => DaemonWebSocketRuntimeDiagnosticSnapshot | null;
+  logger: pino.Logger;
+}
+
+interface DiagnosticWebSocketRuntimeMetrics {
+  terminalDirectorySubscriptionCount: number;
+  terminalSubscriptionCount: number;
+  inflightRequests: number;
+  peakInflightRequests: number;
+  checkoutDiffTargetCount: number;
+  checkoutDiffSubscriptionCount: number;
+  checkoutDiffWatcherCount: number;
+  checkoutDiffFallbackRefreshTargetCount: number;
+}
+
+interface DiagnosticAgentRuntimeMetrics {
+  total: number;
+  byLifecycle: Record<string, number>;
+  withActiveForegroundTurn: number;
+  timelineStats: {
+    totalItems: number;
+    maxItemsPerAgent: number;
+  };
+}
+
+export type DaemonWebSocketRuntimeDiagnosticSnapshot = WebSocketRuntimeDiagnosticSnapshot<
+  DiagnosticWebSocketRuntimeMetrics,
+  DiagnosticAgentRuntimeMetrics
+>;
+
+const TOOL_TIMEOUT_MS = 3_000;
+const TOOL_OUTPUT_LIMIT = 512;
+const LOG_TAIL_LINES = 80;
+const LOG_TAIL_MAX_BYTES = 64 * 1024;
+
+export async function collectDaemonDiagnostics(options: DaemonDiagnosticsOptions): Promise<string> {
+  const sections: string[] = [
+    formatSection("Paseo diagnostics", [
+      { label: "Collected at", value: new Date().toISOString() },
+      { label: "Server ID", value: options.serverId ?? "unknown" },
+      { label: "Daemon version", value: options.daemonVersion ?? "unknown" },
+    ]),
+  ];
+
+  sections.push(
+    await safeSection("Daemon process", () => collectProcessEntries(options), options.logger),
+  );
+  sections.push(
+    await safeSection("Runtime config", () => collectRuntimeConfigEntries(options), options.logger),
+  );
+  sections.push(await safeSection("System", collectSystemEntries, options.logger));
+  sections.push(await safeSection("Disk", () => collectDiskEntries(options), options.logger));
+  sections.push(await safeSection("Agents", () => collectAgentEntries(options), options.logger));
+  sections.push(
+    await safeSection("Workspaces", () => collectWorkspaceEntries(options), options.logger),
+  );
+  sections.push(
+    await safeSection("Providers", () => collectProviderEntries(options), options.logger),
+  );
+  sections.push(
+    await safeSection(
+      "WebSocket runtime metrics",
+      () => collectWebSocketRuntimeEntries(options),
+      options.logger,
+    ),
+  );
+  sections.push(await safeSection("Tools", collectToolEntries, options.logger));
+  sections.push(await safeLogTailSection(options));
+
+  return redactDiagnostic(sections.filter(Boolean).join("\n\n"), options);
+}
+
+async function safeSection(
+  title: string,
+  collect: () => DiagnosticEntry[] | Promise<DiagnosticEntry[]>,
+  logger: pino.Logger,
+): Promise<string> {
+  try {
+    return formatSection(title, await collect());
+  } catch (error) {
+    logger.debug({ err: error, title }, "diagnostic section failed");
+    return formatSection(title, [{ label: "Error", value: toErrorMessage(error) }]);
+  }
+}
+
+function formatSection(title: string, entries: DiagnosticEntry[]): string {
+  return [title, ...entries.map((entry) => `  ${entry.label}: ${entry.value}`)].join("\n");
+}
+
+function collectProcessEntries(options: DaemonDiagnosticsOptions): DiagnosticEntry[] {
+  const memory = process.memoryUsage();
+  return [
+    { label: "PID", value: String(process.pid) },
+    { label: "Node", value: process.version },
+    { label: "Node path", value: process.execPath },
+    { label: "PATH", value: getEnvValue("PATH", "Path") ?? "unset" },
+    { label: "Shell", value: formatDaemonShell() },
+    { label: "Uptime", value: formatDurationMs(process.uptime() * 1000) },
+    { label: "Paseo home", value: options.paseoHome },
+    { label: "RSS", value: formatBytes(memory.rss) },
+    {
+      label: "Heap used",
+      value: `${formatBytes(memory.heapUsed)} / ${formatBytes(memory.heapTotal)}`,
+    },
+    { label: "External", value: formatBytes(memory.external) },
+  ];
+}
+
+function collectRuntimeConfigEntries(options: DaemonDiagnosticsOptions): DiagnosticEntry[] {
+  const relay = options.daemonRuntimeConfig?.relay ?? null;
+  return [
+    { label: "Listen", value: formatListenKind(options.daemonRuntimeConfig?.listen ?? null) },
+    { label: "Relay enabled", value: relay ? String(relay.enabled) : "false" },
+    { label: "Relay endpoint configured", value: relay?.endpoint ? "true" : "false" },
+    { label: "Relay public endpoint configured", value: relay?.publicEndpoint ? "true" : "false" },
+    { label: "Relay TLS", value: relay ? String(relay.useTls) : "n/a" },
+    { label: "Relay public TLS", value: relay ? String(relay.publicUseTls) : "n/a" },
+  ];
+}
+
+function collectSystemEntries(): DiagnosticEntry[] {
+  const loads = loadavg();
+  return [
+    { label: "OS", value: `${type()} ${release()}` },
+    { label: "Platform", value: `${platform()} ${process.arch}` },
+    { label: "CPU cores", value: String(cpus().length) },
+    { label: "Load avg", value: loads.map((value) => value.toFixed(2)).join(", ") },
+    { label: "Memory free", value: `${formatBytes(freemem())} / ${formatBytes(totalmem())}` },
+  ];
+}
+
+async function collectDiskEntries(options: DaemonDiagnosticsOptions): Promise<DiagnosticEntry[]> {
+  const stats = await statfs(options.paseoHome);
+  const freeBytes = stats.bavail * stats.bsize;
+  const totalBytes = stats.blocks * stats.bsize;
+  return [
+    { label: "Path", value: options.paseoHome },
+    { label: "Free", value: `${formatBytes(freeBytes)} / ${formatBytes(totalBytes)}` },
+  ];
+}
+
+function collectAgentEntries(options: DaemonDiagnosticsOptions): DiagnosticEntry[] {
+  const agents = options.listAgents();
+  return [
+    { label: "Total", value: String(agents.length) },
+    { label: "By provider", value: formatCountMap(countBy(agents, (agent) => agent.provider)) },
+    { label: "By lifecycle", value: formatCountMap(countBy(agents, (agent) => agent.lifecycle)) },
+    {
+      label: "Pending permissions",
+      value: String(
+        agents.reduce((total, agent) => total + (agent.pendingPermissions?.size ?? 0), 0),
+      ),
+    },
+  ];
+}
+
+async function collectWorkspaceEntries(
+  options: DaemonDiagnosticsOptions,
+): Promise<DiagnosticEntry[]> {
+  const [projects, workspaces] = await Promise.all([
+    options.listProjects(),
+    options.listWorkspaces(),
+  ]);
+  const activeProjects = projects.filter((project) => !project.archivedAt);
+  const activeWorkspaces = workspaces.filter((workspace) => !workspace.archivedAt);
+  return [
+    { label: "Projects", value: `${activeProjects.length} active / ${projects.length} total` },
+    {
+      label: "Workspaces",
+      value: `${activeWorkspaces.length} active / ${workspaces.length} total`,
+    },
+    {
+      label: "Workspaces by kind",
+      value: formatCountMap(countBy(activeWorkspaces, (workspace) => workspace.kind)),
+    },
+  ];
+}
+
+async function collectProviderEntries(
+  options: DaemonDiagnosticsOptions,
+): Promise<DiagnosticEntry[]> {
+  const providers = await options.listProviderAvailability();
+  return [
+    { label: "Total", value: String(providers.length) },
+    {
+      label: "Available",
+      value: String(providers.filter((provider) => provider.available).length),
+    },
+    {
+      label: "Unavailable",
+      value:
+        providers
+          .filter((provider) => !provider.available)
+          .map((provider) =>
+            provider.error ? `${provider.provider} (${provider.error})` : provider.provider,
+          )
+          .join(", ") || "none",
+    },
+  ];
+}
+
+async function collectToolEntries(): Promise<DiagnosticEntry[]> {
+  const [git, gh] = await Promise.all([
+    checkTool("git", ["--version"]),
+    checkTool("gh", ["--version"]),
+  ]);
+  return [
+    { label: "git", value: git },
+    { label: "gh", value: gh },
+  ];
+}
+
+function collectWebSocketRuntimeEntries(options: DaemonDiagnosticsOptions): DiagnosticEntry[] {
+  const snapshot = options.getWebSocketRuntimeMetrics();
+  if (!snapshot) {
+    return [{ label: "Status", value: "no runtime metrics window has been flushed yet" }];
+  }
+
+  const runtime = snapshot.runtime;
+  const agents = snapshot.agents;
+
+  return [
+    { label: "Collected at", value: snapshot.collectedAt },
+    { label: "Window", value: formatDurationMs(snapshot.windowMs) },
+    { label: "Final", value: String(snapshot.final) },
+    {
+      label: "Sessions",
+      value: [
+        `active=${snapshot.sessions.activeConnections}`,
+        `externalKeys=${snapshot.sessions.externalSessionKeys}`,
+        `reconnectGrace=${snapshot.sessions.reconnectGraceSessions}`,
+      ].join(", "),
+    },
+    {
+      label: "Sockets",
+      value: [
+        `active=${snapshot.sockets.activeSockets}`,
+        `pending=${snapshot.sockets.pendingConnections}`,
+      ].join(", "),
+    },
+    {
+      label: "Runtime requests",
+      value: [
+        `inflight=${formatNumberMetric(runtime.inflightRequests)}`,
+        `peakInflight=${formatNumberMetric(runtime.peakInflightRequests)}`,
+      ].join(", "),
+    },
+    {
+      label: "Terminal subscriptions",
+      value: [
+        `terminals=${formatNumberMetric(runtime.terminalSubscriptionCount)}`,
+        `directories=${formatNumberMetric(runtime.terminalDirectorySubscriptionCount)}`,
+      ].join(", "),
+    },
+    {
+      label: "Checkout diff",
+      value: [
+        `targets=${formatNumberMetric(runtime.checkoutDiffTargetCount)}`,
+        `subscriptions=${formatNumberMetric(runtime.checkoutDiffSubscriptionCount)}`,
+        `watchers=${formatNumberMetric(runtime.checkoutDiffWatcherCount)}`,
+        `fallbackRefreshTargets=${formatNumberMetric(
+          runtime.checkoutDiffFallbackRefreshTargetCount,
+        )}`,
+      ].join(", "),
+    },
+    {
+      label: "Buffered amount",
+      value: `p95=${formatBytes(snapshot.bufferedAmount.p95)}, max=${formatBytes(
+        snapshot.bufferedAmount.max,
+      )}`,
+    },
+    { label: "Event loop delay", value: formatEventLoopDelay(snapshot.eventLoopDelay) },
+    { label: "Latency", value: formatLatencyStats(snapshot.latency) },
+    { label: "Inbound messages", value: formatTopCounts(snapshot.inboundMessageTypesTop) },
+    {
+      label: "Inbound session requests",
+      value: formatTopCounts(snapshot.inboundSessionRequestTypesTop),
+    },
+    { label: "Outbound messages", value: formatTopCounts(snapshot.outboundMessageTypesTop) },
+    {
+      label: "Outbound session messages",
+      value: formatTopCounts(snapshot.outboundSessionMessageTypesTop),
+    },
+    { label: "Agent streams", value: formatTopCounts(snapshot.outboundAgentStreamTypesTop) },
+    { label: "Agent stream agents", value: formatTopCounts(snapshot.outboundAgentStreamAgentsTop) },
+    { label: "Binary frames", value: formatTopCounts(snapshot.outboundBinaryFrameTypesTop) },
+    { label: "Counters", value: formatNonZeroNumberRecord(snapshot.counters) },
+    {
+      label: "Agent metrics",
+      value: [
+        `total=${formatNumberMetric(agents.total)}`,
+        `activeForegroundTurns=${formatNumberMetric(agents.withActiveForegroundTurn)}`,
+      ].join(", "),
+    },
+    { label: "Agent lifecycle", value: formatNumberRecord(agents.byLifecycle) },
+    {
+      label: "Agent timelines",
+      value: [
+        `items=${formatNumberMetric(agents.timelineStats?.totalItems)}`,
+        `maxPerAgent=${formatNumberMetric(agents.timelineStats?.maxItemsPerAgent)}`,
+      ].join(", "),
+    },
+  ];
+}
+
+function formatTopCounts(counts: Array<[string, number]>): string {
+  if (counts.length === 0) return "none";
+  return counts.map(([key, count]) => `${key}=${count}`).join(", ");
+}
+
+function formatLatencyStats(stats: DaemonWebSocketRuntimeDiagnosticSnapshot["latency"]): string {
+  if (stats.length === 0) return "none";
+  return stats
+    .map(
+      (stat) =>
+        `${stat.type} count=${stat.count} p50=${formatMilliseconds(
+          stat.p50Ms,
+        )} max=${formatMilliseconds(stat.maxMs)} total=${formatMilliseconds(stat.totalMs)}`,
+    )
+    .join("; ");
+}
+
+function formatEventLoopDelay(
+  stats: DaemonWebSocketRuntimeDiagnosticSnapshot["eventLoopDelay"],
+): string {
+  if (!stats) return "unavailable";
+  return `p50=${formatMilliseconds(stats.p50Ms)}, p99=${formatMilliseconds(
+    stats.p99Ms,
+  )}, max=${formatMilliseconds(stats.maxMs)}`;
+}
+
+function formatNumberRecord(record: object | undefined): string {
+  if (!record) return "unknown";
+  const entries = Object.entries(record).filter(([, value]) => Number.isFinite(value));
+  if (entries.length === 0) return "none";
+  return entries
+    .sort(([left], [right]) => left.localeCompare(right))
+    .map(([key, value]) => `${key}=${value}`)
+    .join(", ");
+}
+
+function formatNonZeroNumberRecord(record: object): string {
+  const entries = Object.entries(record).filter(
+    ([, value]) => Number.isFinite(value) && value !== 0,
+  );
+  if (entries.length === 0) return "none";
+  return entries
+    .sort(([left], [right]) => left.localeCompare(right))
+    .map(([key, value]) => `${key}=${value}`)
+    .join(", ");
+}
+
+function formatNumberMetric(value: number | undefined): string {
+  if (typeof value !== "number" || !Number.isFinite(value)) return "unknown";
+  return String(value);
+}
+
+function formatMilliseconds(ms: number): string {
+  if (!Number.isFinite(ms) || ms < 0) return "unknown";
+  return `${Math.round(ms)}ms`;
+}
+
+async function checkTool(command: string, args: string[]): Promise<string> {
+  try {
+    const result = await execCommand(command, args, {
+      timeout: TOOL_TIMEOUT_MS,
+      maxBuffer: TOOL_OUTPUT_LIMIT * 2,
+    });
+    const output = truncateForDiagnostic(
+      (result.stdout || result.stderr).trim(),
+      TOOL_OUTPUT_LIMIT,
+    );
+    return output || "ok";
+  } catch (error) {
+    return `error: ${truncateForDiagnostic(toErrorMessage(error), TOOL_OUTPUT_LIMIT)}`;
+  }
+}
+
+async function safeLogTailSection(options: DaemonDiagnosticsOptions): Promise<string> {
+  const logPath = path.join(options.paseoHome, "daemon.log");
+  try {
+    const tail = await tailFile(logPath, LOG_TAIL_LINES, LOG_TAIL_MAX_BYTES);
+    return ["Daemon log tail", `  Path: ${logPath}`, tail ? tail : "  No log lines found"].join(
+      "\n",
+    );
+  } catch (error) {
+    options.logger.debug({ err: error, logPath }, "diagnostic log tail failed");
+    return ["Daemon log tail", `  Path: ${logPath}`, `  Error: ${toErrorMessage(error)}`].join(
+      "\n",
+    );
+  }
+}
+
+async function tailFile(filePath: string, lines: number, maxBytes: number): Promise<string> {
+  const handle = await open(filePath, "r");
+  try {
+    const stats = await handle.stat();
+    const length = Math.min(stats.size, maxBytes);
+    const buffer = Buffer.alloc(length);
+    await handle.read(buffer, 0, length, stats.size - length);
+    return buffer
+      .toString("utf8")
+      .split("\n")
+      .filter(Boolean)
+      .slice(-lines)
+      .map((line) => `  ${line}`)
+      .join("\n");
+  } finally {
+    await handle.close();
+  }
+}
+
+function formatListenKind(listen: string | null): string {
+  if (!listen) return "not configured";
+  if (listen.startsWith("unix://") || listen.startsWith("/")) return "local socket";
+  if (listen.startsWith("pipe://") || listen.startsWith("\\\\.\\pipe\\")) return "local pipe";
+  return "direct TCP";
+}
+
+function countBy<T>(
+  items: T[],
+  getKey: (item: T) => string | null | undefined,
+): Map<string, number> {
+  const counts = new Map<string, number>();
+  for (const item of items) {
+    const key = getKey(item) || "unknown";
+    counts.set(key, (counts.get(key) ?? 0) + 1);
+  }
+  return counts;
+}
+
+function formatCountMap(counts: Map<string, number>): string {
+  if (counts.size === 0) return "none";
+  return [...counts.entries()]
+    .sort(([left], [right]) => left.localeCompare(right))
+    .map(([key, count]) => `${key}=${count}`)
+    .join(", ");
+}
+
+function formatDurationMs(ms: number): string {
+  const seconds = Math.max(0, Math.round(ms / 1000));
+  const hours = Math.floor(seconds / 3600);
+  const minutes = Math.floor((seconds % 3600) / 60);
+  const remainingSeconds = seconds % 60;
+  if (hours > 0) return `${hours}h ${minutes}m ${remainingSeconds}s`;
+  if (minutes > 0) return `${minutes}m ${remainingSeconds}s`;
+  return `${remainingSeconds}s`;
+}
+
+function formatBytes(bytes: number): string {
+  if (!Number.isFinite(bytes) || bytes < 0) return "unknown";
+  const units = ["B", "KiB", "MiB", "GiB", "TiB"];
+  let value = bytes;
+  let unitIndex = 0;
+  while (value >= 1024 && unitIndex < units.length - 1) {
+    value /= 1024;
+    unitIndex += 1;
+  }
+  return `${value.toFixed(unitIndex === 0 ? 0 : 1)} ${units[unitIndex]}`;
+}
+
+function truncateForDiagnostic(value: string, maxLength: number): string {
+  const trimmed = value.trim();
+  if (trimmed.length <= maxLength) return trimmed;
+  return `${trimmed.slice(0, maxLength)}...(truncated)`;
+}
+
+function formatDaemonShell(): string {
+  const shell = getEnvValue("SHELL");
+  if (shell) return `SHELL=${shell}`;
+  const comspec = getEnvValue("ComSpec", "COMSPEC");
+  if (comspec) return `ComSpec=${comspec}`;
+  return "unset";
+}
+
+function getEnvValue(...names: string[]): string | null {
+  for (const name of names) {
+    const value = process.env[name];
+    if (value) return value;
+  }
+
+  const lowerNames = new Set(names.map((name) => name.toLowerCase()));
+  for (const [key, value] of Object.entries(process.env)) {
+    if (value && lowerNames.has(key.toLowerCase())) return value;
+  }
+
+  return null;
+}
+
+function toErrorMessage(error: unknown): string {
+  if (error instanceof Error) return error.message;
+  if (typeof error === "string") return error;
+  return String(error);
+}
+
+export function redactDiagnostic(
+  value: string,
+  options?: Partial<DaemonDiagnosticsOptions>,
+): string {
+  let redacted = value;
+  const sensitiveValues = [
+    options?.daemonRuntimeConfig?.listen,
+    options?.daemonRuntimeConfig?.relay?.endpoint,
+    options?.daemonRuntimeConfig?.relay?.publicEndpoint,
+  ].filter((item): item is string => Boolean(item));
+
+  for (const sensitive of sensitiveValues) {
+    redacted = redacted.split(sensitive).join("[redacted]");
+  }
+
+  return redacted
+    .replace(/paseo:\/\/\S+/gi, "paseo://[redacted]")
+    .replace(
+      /([?&](?:password|token|secret|key|publicKey|daemonPublicKeyB64)=)[^&\s"']+/gi,
+      "$1[redacted]",
+    )
+    .replace(
+      /((?:password|token|secret|authorization|api[_-]?key|daemonPublicKeyB64|relayKey)\s*[:=]\s*)("[^"]+"|'[^']+'|[^\s,}]+)/gi,
+      "$1[redacted]",
+    );
+}
diff --git a/packages/server/src/server/websocket-server.ts b/packages/server/src/server/websocket-server.ts
index 4290ad288..01e0b260f 100644
--- a/packages/server/src/server/websocket-server.ts
+++ b/packages/server/src/server/websocket-server.ts
@@ -3,7 +3,7 @@ import type { IncomingMessage, Server as HTTPServer } from "http";
 import { basename, join } from "path";
 import { hostname as getHostname } from "node:os";
 import { monitorEventLoopDelay } from "node:perf_hooks";
-import type { AgentManager } from "./agent/agent-manager.js";
+import type { AgentManager, AgentMetricsSnapshot } from "./agent/agent-manager.js";
 import type { AgentStorage } from "./agent/agent-storage.js";
 import type { DownloadTokenStore } from "./file-download/token-store.js";
 import type { TerminalManager } from "../terminal/terminal-manager.js";
@@ -60,6 +60,7 @@ import {
 import {
   WebSocketRuntimeMetricsWindow,
   type WebSocketRuntimeCounters,
+  type WebSocketRuntimeDiagnosticSnapshot,
 } from "./websocket/runtime-metrics.js";
 import { ProviderUsageService } from "../services/quota-fetcher/service.js";
 
@@ -81,6 +82,11 @@ interface WebSocketServerConfig {
 }
 
 type WebSocketRuntimeMetrics = SessionRuntimeMetrics & CheckoutDiffMetrics;
+type WebSocketRuntimeDiagnosticPayload = WebSocketRuntimeDiagnosticSnapshot<
+  WebSocketRuntimeMetrics,
+  AgentMetricsSnapshot
+>;
+type WebSocketRuntimeMetricsLogPayload = Omit<WebSocketRuntimeDiagnosticPayload, "collectedAt">;
 
 type TerminalAttentionReason = "finished" | "needs_input";
 
@@ -403,6 +409,7 @@ export class VoiceAssistantWebSocketServer {
     | null;
   private serverCapabilities: ServerCapabilities | undefined;
   private readonly runtimeMetrics = new WebSocketRuntimeMetricsWindow();
+  private lastRuntimeMetricsSnapshot: WebSocketRuntimeDiagnosticPayload | null = null;
   private runtimeMetricsInterval: ReturnType<typeof setInterval> | null = null;
   private eventLoopDelayMonitor: ReturnType<typeof monitorEventLoopDelay> | null = null;
   private unsubscribeSpeechReadiness: (() => void) | null = null;
@@ -1020,6 +1027,7 @@ export class VoiceAssistantWebSocketServer {
       serverId: this.serverId,
       daemonVersion: this.daemonVersion,
       daemonRuntimeConfig: this.daemonRuntimeConfig,
+      getWebSocketRuntimeMetrics: () => this.lastRuntimeMetricsSnapshot,
     });
 
     connection = {
@@ -1173,6 +1181,8 @@ export class VoiceAssistantWebSocketServer {
         providerUsageList: true,
         // COMPAT(agentDetach): added in v0.1.98, remove gate after 2026-12-19 once daemon floor >= v0.1.98.
         agentDetach: true,
+        // COMPAT(daemonDiagnostics): added in v0.1.100, remove gate after 2026-12-25 once daemon floor >= v0.1.100.
+        daemonDiagnostics: true,
       },
     };
   }
@@ -1719,36 +1729,38 @@ export class VoiceAssistantWebSocketServer {
     ).length;
     const sessionMetrics = this.collectSessionRuntimeMetrics();
     const agentSnapshot = this.agentManager.getMetricsSnapshot();
-
-    this.logger.info(
-      {
-        windowMs: runtimeMetrics.windowMs,
-        final: Boolean(options?.final),
-        sessions: {
-          activeConnections,
-          externalSessionKeys: this.externalSessionsByKey.size,
-          reconnectGraceSessions,
-        },
-        sockets: {
-          activeSockets,
-          pendingConnections,
-        },
-        counters: runtimeMetrics.counters,
-        inboundMessageTypesTop: runtimeMetrics.inboundMessageTypesTop,
-        inboundSessionRequestTypesTop: runtimeMetrics.inboundSessionRequestTypesTop,
-        outboundMessageTypesTop: runtimeMetrics.outboundMessageTypesTop,
-        outboundSessionMessageTypesTop: runtimeMetrics.outboundSessionMessageTypesTop,
-        outboundAgentStreamTypesTop: runtimeMetrics.outboundAgentStreamTypesTop,
-        outboundAgentStreamAgentsTop: runtimeMetrics.outboundAgentStreamAgentsTop,
-        outboundBinaryFrameTypesTop: runtimeMetrics.outboundBinaryFrameTypesTop,
-        bufferedAmount: runtimeMetrics.bufferedAmount,
-        eventLoopDelay: this.snapshotEventLoopDelay(),
-        runtime: sessionMetrics,
-        latency: runtimeMetrics.latency,
-        agents: agentSnapshot,
+    const loggedMetrics = {
+      windowMs: runtimeMetrics.windowMs,
+      final: Boolean(options?.final),
+      sessions: {
+        activeConnections,
+        externalSessionKeys: this.externalSessionsByKey.size,
+        reconnectGraceSessions,
       },
-      "ws_runtime_metrics",
-    );
+      sockets: {
+        activeSockets,
+        pendingConnections,
+      },
+      counters: runtimeMetrics.counters,
+      inboundMessageTypesTop: runtimeMetrics.inboundMessageTypesTop,
+      inboundSessionRequestTypesTop: runtimeMetrics.inboundSessionRequestTypesTop,
+      outboundMessageTypesTop: runtimeMetrics.outboundMessageTypesTop,
+      outboundSessionMessageTypesTop: runtimeMetrics.outboundSessionMessageTypesTop,
+      outboundAgentStreamTypesTop: runtimeMetrics.outboundAgentStreamTypesTop,
+      outboundAgentStreamAgentsTop: runtimeMetrics.outboundAgentStreamAgentsTop,
+      outboundBinaryFrameTypesTop: runtimeMetrics.outboundBinaryFrameTypesTop,
+      bufferedAmount: runtimeMetrics.bufferedAmount,
+      eventLoopDelay: this.snapshotEventLoopDelay(),
+      runtime: sessionMetrics,
+      latency: runtimeMetrics.latency,
+      agents: agentSnapshot,
+    } satisfies WebSocketRuntimeMetricsLogPayload;
+
+    this.lastRuntimeMetricsSnapshot = {
+      collectedAt: new Date().toISOString(),
+      ...loggedMetrics,
+    };
+    this.logger.info(loggedMetrics, "ws_runtime_metrics");
   }
 
   private getClientActivityState(session: Session): ClientPresenceState {
diff --git a/packages/server/src/server/websocket/runtime-metrics.ts b/packages/server/src/server/websocket/runtime-metrics.ts
index 76fbc39bd..214d7449a 100644
--- a/packages/server/src/server/websocket/runtime-metrics.ts
+++ b/packages/server/src/server/websocket/runtime-metrics.ts
@@ -42,6 +42,30 @@ export interface WebSocketRuntimeMetricsSnapshot {
   }>;
 }
 
+export interface WebSocketRuntimeDiagnosticSnapshot<
+  TRuntime = unknown,
+  TAgents = unknown,
+> extends WebSocketRuntimeMetricsSnapshot {
+  collectedAt: string;
+  final: boolean;
+  sessions: {
+    activeConnections: number;
+    externalSessionKeys: number;
+    reconnectGraceSessions: number;
+  };
+  sockets: {
+    activeSockets: number;
+    pendingConnections: number;
+  };
+  eventLoopDelay: {
+    p50Ms: number;
+    p99Ms: number;
+    maxMs: number;
+  } | null;
+  runtime: TRuntime;
+  agents: TAgents;
+}
+
 type Clock = () => number;
 
 export class WebSocketRuntimeMetricsWindow {