fix(searxng): update to 2026.9.18 — all four engines restored

searxng had been answering from google cse alone for at least a day, with
brave and startpage suspended and duckduckgo returning CAPTCHA. Updating the
image from 2026.9.3+a1144dda3 to 2026.9.18+c0042add3 restored all four
engines immediately, and they held across 11 consecutive queries run after the
change specifically to rule out a freshly-reset circuit breaker flattering the
first measurement.

  before  searxng/searxng@sha256:3602e6ddbeba037f5d800d1ed9d296a8b93c9f5b3cf9d05fa179d0e766dd59a1
  after   searxng/searxng@sha256:e0027a772aeeea55bf642256aae6fb3344ffa5f25ca665898c2ea821101334c4

The image stays on :latest rather than being digest-pinned. For this stack that
is deliberate and now demonstrated: upstream ships engine-handler fixes as
providers change their bot gating, so being current is the mitigation, and a
pin would have frozen the breakage in place. The post office is pinned for the
opposite reason — it is the fleet message bus and must not move under us.

README corrected. It had carried two successive wrong diagnoses, both blaming
egress, and now records the real cause plus the two measurements that
falsified them: reverting to direct NH3 egress reproduced the failure exactly,
and a live !ddg probe on a freshly restarted container also CAPTCHA'd, ruling
out a stale suspension timer. Both wrong claims asserted causation from
correlation without a baseline.

The health-script blind spot is unchanged and still called out:
scripts/searxng-health.sh reports the same passing result whether four engines
answer or one.

stacks/searxng/README.md

@@ -11,41 +11,59 @@ Hosting and egress are both nh3-docker. Outbound search requests leave from
 This is the configuration that works; the section below records why, and the
 one after it records an attempt to change it that failed.
 
+## The 2026-09-18 engine outage — cause was the build, not egress
+
+For at least a day, searxng answered from **one engine**: brave and startpage
+suspended, duckduckgo CAPTCHA, google cse alone returning results. **Fixed by
+updating the image** — `2026.9.3+a1144dda3` → `2026.9.18+c0042add3`. All four
+engines came back immediately and held across 11 consecutive queries.
+
+Upstream ships engine-handler fixes constantly, because search providers change
+their bot gating constantly. **That is why this stack tracks `:latest` rather
+than pinning a digest**: for searxng specifically, being current *is* the
+mitigation, and a pin would have frozen the breakage in place.
+
+⚠ **Two wrong diagnoses were published before the right one. Read this before
+theorising about egress again.**
+
+1. The failures were first blamed on the ESH egress move (below), on the
+   strength of a 2026-09-03 comment claiming NH3's residential address avoided
+   CAPTCHAs. Reverting to direct NH3 egress produced a **byte-identical**
+   result — same three engines down — which falsified it.
+2. A live `!ddg` bang probe on a freshly restarted container also returned
+   CAPTCHA, ruling out a stale circuit-breaker timer as the explanation.
+
+Both claims asserted causation from correlation without measuring a baseline.
+The version bump was the only change that moved the number.
+
+⚠ **Neither health check can see this class of failure.** `/healthz` cannot,
+and `scripts/searxng-health.sh` prints `✓ searching` whether four engines
+answer or one, because it gates on "did any results come back" and treats
+failed engines as informational — it prints them, then passes anyway. Search
+ran on one engine for a day with every instrument green. **Make the script fail
+on blocked engines before trusting it again.**
+
 ## The ESH egress experiment (2026-09-17 → reverted 2026-09-18)
 
 Search egress was moved to `socks5h://10.0.50.65:1080` on **esh-scale**
 (CT 108 on esh-pve) — an application-level proxy, no host route or exit-node
-changes. **Reverted after one day: it cost three of the four engines.**
+changes. Reverted after one day.
 
-Measured 2026-09-18 across five queries (two ad-hoc plus all three in
-`scripts/searxng-health.sh`), identical every time:
+It did **not** cause the engine outage above, and it did not fix anything
+either: engine behaviour was identical with it and without it. It was reverted
+on its own merits — it bought no measurable improvement while making all fleet
+search depend on ESH WAN and mesh availability, and the simpler configuration
+is the better one.
 
-    brave       Suspended: too many requests
-    duckduckgo  CAPTCHA
-    startpage   Suspended: CAPTCHA
-    google cse  20 results   <- the only engine answering
-
-The cause is the one this stack already knew about. SearXNG runs at NH3
-*because* its residential egress avoids the CAPTCHA gating that gets applied
-to datacenter ranges; routing out through ESH (`128.177.138.182` when
-measured, `154.50.58.126` at cutover — ESH's WAN address moves) gave that
-property up. The Dependency note written at cutover called the risk and it
-materialised.
-
-⚠ **The failure was invisible to both health checks.** `/healthz` cannot see
-it, and `scripts/searxng-health.sh` — the script this README told you to run
-instead — prints `✓ searching` in this exact state, because it gates on "did
-any results come back" and treats failed engines as informational. Search ran
-on one engine for a day with every instrument reporting healthy. If egress is
-ever changed again, fix the script to fail on blocked engines *first*, or the
-next regression is equally silent.
+ESH egress measured `128.177.138.182` in use and `154.50.58.126` at cutover;
+ESH's WAN address moves and nothing pins it.
 
 The proxy side was built correctly and none of this was its fault: microsocks
 ran as `nobody` under `searxng-egress.service`, bound `10.0.50.65:1080` only,
 and allowed source `10.100.50.40` alone. The canonical unit is kept at
 [`configs/esh-scale/searxng-egress.service`](../../configs/esh-scale/searxng-egress.service)
-in case a future egress experiment wants it; the service is disabled on
-esh-scale.
+in case a future egress experiment wants it; the service is stopped and
+disabled on esh-scale, and tailscaled there was not touched.
 
 ## Historical placement: NH3 rather than the colo