Encrypted DNS health, comparing a zone's views, --local everywhere

jarld checks the DoT and DoH listeners every 10 minutes as a client would (page, dashboard, jarl encrypted-dns health, jarl_encrypted_dns_up). The Compare views tab and jarl zone diff show what differs between a zone's views, with Use this version. --local works on unlinked zones. A changed certificates.dir is followed by encrypted DNS's tls statements. Sharing an already shared version replaces other views' overrides.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/encrypted-dns.md

@@ -113,6 +113,31 @@ Clients check the certificate against the host name, so the name must
 resolve to this server for them: the setup adds it to your private views.
 Open the ports in the server's firewall for your own networks only.
 
+## Health
+
+jarld checks the listeners itself, a minute after it starts and then
+every 10 minutes, the way a client would: it connects to each, checks the
+certificate named serves (for the host name, current, and the one Jarl
+last wrote, so a renewal named hasn't reread shows up) and asks for the
+host name. The Encrypted DNS page shows the result per listener (**Check
+now** checks again), the dashboard a card and the problems, Prometheus
+`jarl_encrypted_dns_up{kind,address,port}`:
+
+```sh
+jarl encrypted-dns health        # check now; exit 1 when a listener doesn't work
+```
+
+What it can say:
+
+| | |
+|--|--|
+| nothing listens on ADDR port P | named couldn't bind the port: look in named's log (ports below 1024 need named to start as root, as the Debian service does) |
+| no answer within 5s | a firewall on the server |
+| a certificate for X, not HOST | named serves another certificate |
+| an older certificate | named hasn't reread the renewed files (`rndc reconfig`) |
+| not from a CA this server trusts (warning) | a staging or test CA: clients reject it unless they trust it |
+| REFUSED (warning) | it works, but this server's own address gets a view that doesn't answer for the host name |
+
 ## What Jarl checks
 
 * A `tls` statement whose files don't exist is an error
@@ -129,3 +154,4 @@ Open the ports in the server's firewall for your own networks only.
 | POST | `/encrypted-dns/check` | `{"addresses", "dot", "doh", "dot_port", "doh_port"}`: `conflicts` (address, port, what) and `free_doh_port` |
 | POST | `/encrypted-dns` | `{"hostname", "certificate", "addresses", "dot", "doh", "dot_port", "doh_port", "views"}`: staged or applied like any change; 409 while the certificate hasn't been obtained |
 | DELETE | `/encrypted-dns` | Turns it off |
+| POST | `/encrypted-dns/health` | Checks the listeners now: `checked`, `probes` (kind, address, port, `ok`, `problem`, `warning`, certificate names, expiry and serial, `trusted`, `rcode`, `ms`). `GET /encrypted-dns` has the last check as `health` |