fix(ping): confirm a host is down before turning its dot red

src/hooks/useHostPingPolling.ts

@@ -5,7 +5,7 @@ import { allConnections } from "@/stores/connectionStore";
 import { useSessionStore } from "@/stores/sessionStore";
 import { buildPingTargets } from "@/services/ping/pingTargets";
 import { probeTarget } from "@/services/ping/probe";
-import { TICK_MS, selectDue } from "@/services/ping/schedule";
+import { DOWN_RETRY_MS, TICK_MS, confirmDown, selectDue } from "@/services/ping/schedule";
 
 export function useHostPingPolling() {
   const [enabled] = useToggle("reachability");
@@ -20,6 +20,7 @@ export function useHostPingPolling() {
     let cancelled = false;
     let dueAt: Record<string, number> = {};
     const inFlight = new Set<string>();
+    const failingSince = new Map<string, number>();
 
     // Stores are read through getState() rather than subscribed to: a write to
     // the connection store must not restart the schedule or trigger a probe.
@@ -34,9 +35,16 @@ export function useHostPingPolling() {
       for (const target of selected.due) {
         if (inFlight.has(target.key)) continue;
         inFlight.add(target.key);
+        const startedAt = Date.now();
         void probeTarget(target).then(({ status, latencyMs }) => {
           inFlight.delete(target.key);
           if (cancelled) return;
+          if (status !== "down") {
+            failingSince.delete(target.key);
+          } else if (!confirmDown(failingSince, target.key, startedAt)) {
+            dueAt[target.key] = Date.now() + DOWN_RETRY_MS;
+            return;
+          }
           for (const id of target.connectionIds) setStatus(id, status, latencyMs);
         });
       }

src/services/ping/schedule.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "vitest";
-import { STARTUP_SPREAD_MS, intervalFor, jitterFor, selectDue } from "./schedule";
+import { DOWN_CONFIRM_MS, DOWN_RETRY_MS, STARTUP_SPREAD_MS, confirmDown, intervalFor, jitterFor, selectDue } from "./schedule";
 import type { PingTarget } from "./pingTargets";
 
 const SESSION_MS = 5_000;
@@ -86,3 +86,32 @@ describe("selectDue", () => {
     expect(third.due).toHaveLength(0);
   });
 });
+
+describe("confirmDown", () => {
+  test("a single failed probe is not reported as down", () => {
+    expect(confirmDown(new Map(), "h1:22", 1_000)).toBe(false);
+  });
+
+  test("failures spanning the confirm window are reported as down", () => {
+    const failingSince = new Map<string, number>();
+    expect(confirmDown(failingSince, "h1:22", 0)).toBe(false);
+    expect(confirmDown(failingSince, "h1:22", DOWN_RETRY_MS)).toBe(false);
+    expect(confirmDown(failingSince, "h1:22", DOWN_CONFIRM_MS)).toBe(true);
+  });
+
+  test("once confirmed, later failures stay down", () => {
+    const failingSince = new Map([["h1:22", 0]]);
+    expect(confirmDown(failingSince, "h1:22", DOWN_CONFIRM_MS + IDLE_MS)).toBe(true);
+  });
+
+  test("a success in between restarts the window", () => {
+    const failingSince = new Map<string, number>();
+    confirmDown(failingSince, "h1:22", 0);
+    failingSince.delete("h1:22");
+    expect(confirmDown(failingSince, "h1:22", DOWN_CONFIRM_MS)).toBe(false);
+  });
+
+  test("retries well inside the confirm window", () => {
+    expect(DOWN_RETRY_MS * 2).toBeLessThanOrEqual(DOWN_CONFIRM_MS);
+  });
+});

src/services/ping/schedule.ts

@@ -2,6 +2,10 @@ import type { PingTarget } from "./pingTargets";
 
 export const TICK_MS = 1_000;
 export const STARTUP_SPREAD_MS = 5_000;
+/// One failed dial (lost SYN, network still waking from sleep) is not proof a
+/// host is down; retries stay under `ufw limit`'s 6 connections per 30s.
+export const DOWN_CONFIRM_MS = 15_000;
+export const DOWN_RETRY_MS = 7_500;
 
 /// FNV-1a over the target key: stable across ticks and app restarts, so a
 /// large host list does not fire on a single tick.
@@ -54,3 +58,9 @@ export function selectDue(
 
   return { due, dueAt: next };
 }
+
+export function confirmDown(failingSince: Map<string, number>, key: string, startedAt: number): boolean {
+  const since = failingSince.get(key) ?? startedAt;
+  failingSince.set(key, since);
+  return startedAt - since >= DOWN_CONFIRM_MS;
+}