Split ssh config into common plus a host layer

Putting the whole ssh config in common/ was wrong twice over. It mapped
git.rcjohnstone.com to localhost:2222, which is only true on mainframe
where Gitea runs -- on system76 it broke git entirely. And it replaced a
77-line file holding 13 personal host aliases (storagebox, several
forwarded localhost ports, older work hosts) with a five-entry fleet list.

common/ssh/config now Includes ~/.ssh/config.local first, so host entries
win on the first-value-obtained rule, and carries only the fleet aliases.
Each host keeps its own list; system76's is restored verbatim.

common/ssh/config

@@ -1,11 +1,8 @@
-# Host aliases only. No keys, no secrets.
-
-Host git.rcjohnstone.com
-    HostName localhost
-    Port 2222
-    User connor
-    IdentityFile ~/.ssh/id_ed25519
+# Host-specific aliases come first: ssh takes the FIRST value it obtains for
+# each keyword, so anything in config.local wins over the fleet defaults below.
+Include ~/.ssh/config.local
 
+# --- the fleet -------------------------------------------------------------
 Host nas
     HostName 10.0.0.3
     User connor
@@ -13,6 +10,8 @@ Host nas
 Host mainframe
     HostName 10.0.0.2
     User connor
+    ServerAliveInterval 30
+    ServerAliveCountMax 6
 
 Host system76
     HostName 10.0.0.4
@@ -21,3 +20,11 @@ Host system76
 Host work_laptop
     HostName 10.0.0.8
     User connorjohnstone
+
+# Correct from every machine except mainframe itself, which overrides it in
+# hosts/mainframe/ssh/config.local — there, Gitea is a local port.
+Host git.rcjohnstone.com
+    HostName 10.0.0.2
+    Port 2222
+    User connor
+    IdentityFile ~/.ssh/id_ed25519

hosts/mainframe/ssh/config.local

@@ -0,0 +1,6 @@
+# Gitea runs on this machine; reach it on the loopback rather than out and back.
+Host git.rcjohnstone.com
+    HostName localhost
+    Port 2222
+    User connor
+    IdentityFile ~/.ssh/id_ed25519

hosts/nas/ssh/config.local

@@ -0,0 +1 @@
+# No machine-specific ssh aliases on the NAS.

hosts/sctfw004/ssh/config.local

@@ -0,0 +1,5 @@
+# Work-specific hosts.
+Host framework1
+    HostName 100.100.61.12
+    User scout-dev
+    IdentityFile ~/.ssh/id_ed25519

hosts/system76/ssh/config.local

@@ -0,0 +1,75 @@
+# Personal host aliases for this machine. Kept verbatim from the
+# pre-refit ~/.ssh/config; common/ssh/config Includes this first.
+
+Host gitserver.idm.orionspace.com
+    PreferredAuthentications publickey
+    IdentityFile ~/.ssh/id_ed25519
+
+# Host gitlab.arcfield.com
+#     PreferredAuthentications publickey
+#     IdentityFile ~/.ssh/id_rsa
+
+Host github.com
+    HostName github.com
+    User git
+    PreferredAuthentications publickey
+    IdentityFile ~/.ssh/id_ed25519
+
+Host tiny
+    Hostname 192.168.1.188
+    User connor
+    IdentityFile ~/.ssh/id_ed25519
+
+Host devboard
+    HostName localhost
+    Port 9004
+
+Host rfbr
+    HostName localhost
+    User rfbr
+    Port 9003
+
+Host work
+    HostName localhost
+    Port 9000
+    User connor.johnstone@arcfield.com
+    IdentityFile ~/.ssh/id_ed25519
+
+Host traccs
+    HostName localhost
+    Port 9012
+    User azureuser
+    IdentityFile ~/.ssh/tracss-demo_key.pem
+
+Host orbitiq.space
+    Port 8001
+    User ubuntu
+    IdentityFile ~/.ssh/tracss.pem
+
+Host 18.188.195.42
+    Port 8001
+    User ubuntu
+    IdentityFile ~/.ssh/tracss.pem
+
+Host 3.31.241.208
+    Port 8001
+    User ubuntu
+    IdentityFile ~/.ssh/tracss.pem
+
+Host reverse.diff
+    HostName localhost
+    User ubuntu
+    Port 9005
+    IdentityFile ~/.ssh/ConnorKey.pem
+
+Host edu
+    HostName localhost
+    User rroci
+    Port 9007
+
+Host box
+    HostName u491382.your-storagebox.de
+    Port 23
+    User u491382
+    PreferredAuthentications publickey
+

meta/hosts/mainframe.conf.yaml

@@ -10,6 +10,7 @@
       force: true
 
 - link:
+    ~/.ssh/config.local:    hosts/mainframe/ssh/config.local
     ~/.config/git/identity:     hosts/mainframe/git/identity
     ~/.config/paru:             common/paru
     ~/.config/rbw:              common/rbw

meta/hosts/nas.conf.yaml

@@ -10,5 +10,6 @@
       force: true
 
 - link:
+    ~/.ssh/config.local:    hosts/nas/ssh/config.local
     ~/.config/git/identity: hosts/nas/git/identity
     ~/.config/paru:         common/paru

meta/hosts/sctfw004.conf.yaml

@@ -10,6 +10,7 @@
       force: true
 
 - link:
+    ~/.ssh/config.local:    hosts/sctfw004/ssh/config.local
     ~/.config/wallust:       common/wallust
     ~/.config/hypr/colors.conf:  hosts/sctfw004/hypr/colors.conf
     ~/.config/waybar/colors.css: hosts/sctfw004/waybar/colors.css

meta/hosts/system76.conf.yaml

@@ -9,6 +9,7 @@
       force: true
 
 - link:
+    ~/.ssh/config.local:    hosts/system76/ssh/config.local
     ~/.config/wallust:       common/wallust
     ~/.config/hypr/colors.conf:  hosts/system76/hypr/colors.conf
     ~/.config/waybar/colors.css: hosts/system76/waybar/colors.css