fix(firms): retry over IPv4 when every address fails to connect

Node's network-family auto-selection gives each resolved address a short
attempt timeout. On hosts where IPv6 is unreachable, a slow IPv4 handshake
is abandoned for the IPv6 address, which fails at once, and the request
reports only `fetch failed`. Retry such failures once with a single IPv4
connection within the same deadline, and log the per-address connection
errors (never the keyed URL). Node 26 wraps the AggregateError one level
deeper, so both shapes are recognised.

Fixes #68

src/data/firmsProxy.test.mjs

@@ -2,6 +2,12 @@ import assert from 'node:assert/strict';
 import fs from 'node:fs';
 import test from 'node:test';
 import { filterTrailing24h, parseFirmsCsv } from './firmsCsv.js';
+import net from 'node:net';
+import {
+  describeFetchError,
+  fetchFirms,
+  fetchIpv4,
+} from '../../server/providers/firms.js';
 
 const config = fs.readFileSync(new URL('../../server/providers/firms.js', import.meta.url), 'utf8');
 const start = config.indexOf('  async function refreshUpstream(key) {');
@@ -17,8 +23,8 @@ const recent = { acqDate: '2026-09-11', acqTime: '1100' };
 // Inject only its upstream, clock and filter dependencies; keep its aggregation
 // and source-status code intact, including failures while consuming records.
 function createRefresh(fetchSource, filter = filterTrailing24h) {
-  return new Function('SOURCES', 'fetchSource', 'filterTrailing24h', 'Date', 'console',
-    `return (${refreshSource});`)(SOURCES, fetchSource, filter, { now: () => NOW }, { warn() {} });
+  return new Function('SOURCES', 'fetchSource', 'filterTrailing24h', 'describeFetchError', 'Date', 'console',
+    `return (${refreshSource});`)(SOURCES, fetchSource, filter, describeFetchError, { now: () => NOW }, { warn() {} });
 }
 
 test('FIRMS retains large sources in order and filters expired rows', async () => {
@@ -78,3 +84,111 @@ test('FIRMS distinguishes all-source failure from successful empty sources', asy
   assert.deepEqual(result.fires, []);
   assert.deepEqual(result.sources, SOURCES.map(source => ({ source, count: 0, ok: true })));
 });
+
+// #68: Node's network-family auto-selection gives each address a short attempt
+// timeout, abandons a slow IPv4 handshake for an unreachable IPv6 address, and
+// reports only `fetch failed`. This is the shape Node 24 throws for it.
+function addressSelectionFailure() {
+  const v4 = Object.assign(new Error('connect ETIMEDOUT 198.118.194.34:443'), { code: 'ETIMEDOUT' });
+  const v6 = Object.assign(new Error('connect ENETUNREACH 2001:4d0:241a:40c0::34:443'), { code: 'ENETUNREACH' });
+  const cause = Object.assign(new AggregateError([v4, v6]), { code: 'ETIMEDOUT' });
+  return new TypeError('fetch failed', { cause });
+}
+// Node 26's fetch wraps the same AggregateError in a ConnectTimeoutError.
+function wrappedAddressSelectionFailure() {
+  const inner = addressSelectionFailure().cause;
+  const cause = Object.assign(new Error('Connect Timeout Error (attempted addresses: 198.118.194.34:443, 2001:4d0:241a:40c0::34:443, timeout: 10000ms)'),
+    { name: 'ConnectTimeoutError', code: 'UND_ERR_CONNECT_TIMEOUT', cause: inner });
+  return new TypeError('fetch failed', { cause });
+}
+const URL_WITH_KEY = 'https://firms.modaps.eosdis.nasa.gov/api/area/csv/SECRET/VIIRS_SNPP_NRT/world/2';
+
+test('FIRMS failures log the socket cause, never the keyed URL', () => {
+  const described = describeFetchError(addressSelectionFailure());
+  assert.equal(described,
+    'fetch failed (connect ETIMEDOUT 198.118.194.34:443; connect ENETUNREACH 2001:4d0:241a:40c0::34:443)');
+  assert.ok(!described.includes('SECRET'));
+  assert.equal(describeFetchError(wrappedAddressSelectionFailure()), described, 'Node 26 reports the same attempts');
+  const single = new TypeError('fetch failed', { cause: Object.assign(new Error('getaddrinfo ENOTFOUND x'), { code: 'ENOTFOUND' }) });
+  assert.equal(describeFetchError(single), 'fetch failed (getaddrinfo ENOTFOUND x)');
+  assert.equal(describeFetchError(new Error('HTTP 503')), 'HTTP 503');
+});
+
+test('FIRMS retries once over IPv4 when every address fails to connect', async () => {
+  for (const shape of [addressSelectionFailure, wrappedAddressSelectionFailure]) {
+    const retried = [];
+    await fetchFirms(URL_WITH_KEY, {}, {
+      fetchImpl: async () => { throw shape(); },
+      fetchIpv4Impl: async (url) => { retried.push(url); return new Response('csv'); },
+      warn() {},
+    });
+    assert.deepEqual(retried, [URL_WITH_KEY], `${shape.name} is retried`);
+  }
+  const signal = new AbortController().signal;
+  const ok = new Response('csv');
+  const retried = [];
+  const warnings = [];
+  const response = await fetchFirms(URL_WITH_KEY, { signal }, {
+    fetchImpl: async () => { throw addressSelectionFailure(); },
+    fetchIpv4Impl: async (url, options) => { retried.push([url, options]); return ok; },
+    warn: (message) => warnings.push(message),
+  });
+  assert.equal(response, ok);
+  assert.deepEqual(retried, [[URL_WITH_KEY, { signal }]], 'one retry, same URL and deadline');
+  assert.equal(warnings.length, 1);
+  assert.match(warnings[0], /ETIMEDOUT 198\.118\.194\.34:443; .*ENETUNREACH .* retrying over IPv4/);
+  assert.ok(!warnings[0].includes('SECRET'));
+
+  const failure = new Error('connect ETIMEDOUT 198.118.194.34:443');
+  await assert.rejects(fetchFirms(URL_WITH_KEY, {}, {
+    fetchImpl: async () => { throw addressSelectionFailure(); },
+    fetchIpv4Impl: async () => { throw failure; },
+    warn() {},
+  }), (err) => err === failure, 'a failed retry reports its own error');
+});
+
+test('FIRMS does not retry anything but an address-selection failure', async () => {
+  const deps = (fetchImpl) => ({
+    fetchImpl,
+    fetchIpv4Impl: async () => assert.fail('must not retry'),
+    warn: () => assert.fail('must not warn'),
+  });
+  const serverError = new Response('down', { status: 503 });
+  assert.equal(await fetchFirms(URL_WITH_KEY, {}, deps(async () => serverError)), serverError);
+  for (const thrown of [
+    new TypeError('fetch failed', { cause: Object.assign(new Error('getaddrinfo ENOTFOUND x'), { code: 'ENOTFOUND' }) }),
+    new TypeError('fetch failed', { cause: new AggregateError([]) }),
+    new TypeError('fetch failed'),
+    new DOMException('The operation was aborted due to timeout', 'TimeoutError'),
+  ]) {
+    await assert.rejects(fetchFirms(URL_WITH_KEY, {}, deps(async () => { throw thrown; })), (err) => err === thrown);
+  }
+  const controller = new AbortController();
+  controller.abort();
+  const aborted = addressSelectionFailure();
+  await assert.rejects(fetchFirms(URL_WITH_KEY, { signal: controller.signal },
+    deps(async () => { throw aborted; })), (err) => err === aborted, 'an expired deadline is not retried');
+});
+
+test('the IPv4 retry connects to an IPv4 address only', async (t) => {
+  // `localhost` resolves to both ::1 and 127.0.0.1. Listen on both with the
+  // same port and record which one the retry reaches; the TLS handshake then
+  // fails against a plain socket, which is fine — only the connection matters.
+  const reached = [];
+  const listen = (host, port) => new Promise((resolve, reject) => {
+    const server = net.createServer((socket) => { reached.push(host); socket.destroy(); });
+    server.once('error', reject).listen(port, host, () => resolve(server));
+  });
+  const v4 = await listen('127.0.0.1', 0);
+  t.after(() => v4.close());
+  const { port } = v4.address();
+  let v6 = null;
+  try {
+    v6 = await listen('::1', port);
+    t.after(() => v6.close());
+  } catch {
+    // No IPv6 loopback on this host; the IPv4 assertion still holds.
+  }
+  await assert.rejects(fetchIpv4(`https://localhost:${port}/`, { signal: AbortSignal.timeout(5_000) }));
+  assert.deepEqual(reached, ['127.0.0.1']);
+});