nixos: add git-sync service for claude-history repo

Syncs ~/.claude to github.com/colonelpanic8/claude-history on
ryzen-shine and railbird-sf. Uses git-sync-rs in watch mode with
--new-files true and a 300s min-interval to handle active sessions
appending to transcripts without spamming pushes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dotfiles/claude/.gitignore

@@ -1,6 +0,0 @@
-*
-!.gitignore
-!CLAUDE.md
-!settings.json
-!settings.local.json
-!settings.local.json.example

nixos/git-sync.nix

@@ -1,9 +1,15 @@
 {
   pkgs,
   lib,
+  config,
   ...
 }: let
   gitSyncServicePath = lib.makeBinPath [pkgs.coreutils pkgs.git pkgs.openssh];
+  # ~/.claude history sync is being rolled out machine-by-machine; each new
+  # machine needs its existing history merged into the repo first (see
+  # github.com/colonelpanic8/claude-history).
+  claudeHistoryHosts = ["ryzen-shine" "railbird-sf"];
+  syncClaudeHistory = builtins.elem config.networking.hostName claudeHistoryHosts;
   mkGitSyncTrayOverrides = icon: {
     Service = {
       Environment = lib.mkMerge [
@@ -33,15 +39,31 @@ in {
           path = config.home.homeDirectory + "/.password-store";
           uri = "git@github.com:IvanMalison/.password-store.git";
         };
+      }
+      // lib.optionalAttrs syncClaudeHistory {
+        claude-history = {
+          path = config.home.homeDirectory + "/.claude";
+          uri = "git@github.com:colonelpanic8/claude-history.git";
+          interval = 600;
+        };
       };
     };
 
-    systemd.user.services =
-      lib.mapAttrs'
-      (name: _:
-        lib.nameValuePair "git-sync-${name}"
-        (mkGitSyncTrayOverrides (repoIcons.${name} or "git")))
-      config.services.git-sync.repositories;
+    systemd.user.services = lib.mkMerge [
+      (lib.mapAttrs'
+        (name: _:
+          lib.nameValuePair "git-sync-${name}"
+          (mkGitSyncTrayOverrides (repoIcons.${name} or "git")))
+        config.services.git-sync.repositories)
+      (lib.optionalAttrs syncClaudeHistory {
+        # Live sessions append to their transcript on every message; sync
+        # untracked session files and throttle event-driven syncs so an
+        # active session doesn't push once per append.
+        git-sync-claude-history.Service.ExecStart =
+          lib.mkForce
+          "${pkgs.git-sync-rs}/bin/git-sync-rs watch --new-files true --min-interval 300";
+      })
+    ];
   };
 
   home-manager.users.kat = {config, ...}: {