Shell: tls, ntp and netstat (#90)

The rest of the issue's list. tls makes a handshake that checks nothing,
then says the certificate in words: who it is for, who signed it, until
when, and whether this device's roots and the name asked for accept it,
with the reason when they don't. ntp compares a time server's clock with
the device's. netstat lists what listens and what is connected.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

docs/milestones/N1.md

@@ -1,6 +1,6 @@
 # N1 — Network tools
 
-**Status:** in progress. The WireGuard tunnel (issue #8) shipped as **v0.19.0**. The first network troubleshooting commands (issue #90) shipped as **v0.20.0**: `ping`, `nslookup`, `port`, `traceroute`, `ifconfig`, `arp`; `tls`, `ntp` and `netstat` are still to do. SSH (#2) is not started.
+**Status:** in progress. The WireGuard tunnel (issue #8) shipped as **v0.19.0**. The network troubleshooting commands (issue #90) shipped in two parts: `ping`, `nslookup`, `port`, `traceroute`, `ifconfig` and `arp` as **v0.20.0**; `tls`, `ntp` and `netstat` after it. SSH (#2) is not started.
 
 **Goal:** reach things from the device that aren't on the Wi-Fi it happens to be on, and keep its traffic private on a network that isn't yours.
 
@@ -121,3 +121,23 @@ With a tunnel, fixed addresses and a file server on the device, "is it the netwo
 **Not checked:** without the VPN (every check went through the tunnel, or to the local network); a network that drops ICMP; the commands in Safe Mode, where they are not offered.
 
 **Found on the way:** a refused connection is reported by lwIP as "reset", not "refused"; the first version called it "no route". And the header for the tested half was first given the same name as the service's, which makes a file include itself: the same mistake as an hour before, in the same way.
+
+### The rest of the list: `tls`, `ntp`, `netstat` (2026-10-08)
+
+- **`tls <host> [port]`** makes a handshake that checks nothing, so that a bad certificate can be looked at, and then checks it itself: against this device's roots (`ca_roots.h`, the ones the Update Service trusts) and the name asked for. It says who the certificate is for, who signed it, from when to when with the days left, the verdict with its reasons, and the SHA-256 that a Gemini pin is. It runs on a 12 KB task and isn't tried with less than 70 KB free: a handshake peaks at about 52 KB.
+- **`ntp [server]`** sends one SNTP request and compares the answer with the device's clock, allowing for half the round trip. With no server it asks the first one in Settings.
+- **`netstat`** reads lwIP's own lists: what listens, labelled where the firmware knows what it is, what is connected, and the UDP ports in use.
+- Host tests: the NTP packet and the year 2036, the offset in words, a certificate's name (an old string type that mbedTLS prints as hex included), days between dates. 7 tests in `test/test_net_probe` in all.
+
+| Check on the device | Result |
+|---|---|
+| `tls git.twis.la` | 709 ms; for git.twis.la, 67 days left, "this device trusts it", the SHA-256 |
+| `tls geminiprotocol.net 1965` | "NOT trusted here: not signed by a root this device has": a capsule signs its own |
+| `tls expired.badssl.com` | "EXPIRED 4197 days ago" |
+| `tls wrong.host.badssl.com` | "NOT trusted here: not for that name" |
+| `tls` to a port that isn't TLS | "no handshake ... An invalid SSL record was received" |
+| `ntp` | The server, its stratum, 50 ms away; "this clock is right, to 0.1 s" |
+| `netstat` | The update port and the Debug Console listening, the console's own connection, the UDP ports |
+| Memory during a `tls` | 44.5 KB free at the lowest, from 104 KB |
+
+**Not checked:** `tls` with IRC connected (it should refuse for lack of memory); `ntp` against a clock that is wrong; `netstat` while sharing.