feat: add synclaude, Claude Code on synthetic.new

Binds the opus/sonnet/haiku aliases to Kimi K3, GLM-5.2 and Qwen3.6 so
they can be swapped mid-session, and registers the wrapper as an aoe agent.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

home/common/programs/claude/default.nix

@@ -12,7 +12,10 @@ let
   };
 in
 {
-  imports = [ inputs.agent-skills.homeModules.default ];
+  imports = [
+    inputs.agent-skills.homeModules.default
+    ./synthetic.nix
+  ];
 
   # Shared UI-scale knob for the Electron AI desktop apps (Claude Desktop, T3 Code).
   # Set per-host (e.g. konishi's 4K@1x monitors want ~"1.5"); null = native scale.

home/common/programs/claude/synthetic.nix

@@ -0,0 +1,64 @@
+{
+  pkgs,
+  inputs,
+  ...
+}:
+# Claude Code pointed at synthetic.new. The three model aliases below are bound
+# to three Synthetic models, so `/model opus|sonnet|haiku` swaps between them
+# live; anything else there is reachable by full id (`/model hf:...`).
+let
+  claude = inputs.claude-code.packages.${pkgs.stdenv.hostPlatform.system}.default;
+
+  # `hf:` ids pin one exact model. The `syn:large:*` aliases in Synthetic's own
+  # docs move under you whenever they rotate what "large" means.
+  kimi = "hf:moonshotai/Kimi-K3";
+  glm = "hf:zai-org/GLM-5.2";
+  qwen = "hf:Qwen/Qwen3.6-27B";
+in
+{
+  home.packages = [
+    (pkgs.writeShellScriptBin "synclaude" ''
+      set -euo pipefail
+
+      if [ -z "''${SYNTHETIC_API_KEY:-}" ] && [ -r "$HOME/.env.claude" ]; then
+        set +u
+        # Silenced: the file greets missing tooling on stderr, which would
+        # otherwise print before every session.
+        . "$HOME/.env.claude" >/dev/null 2>&1
+        set -u
+      fi
+
+      if [ -z "''${SYNTHETIC_API_KEY:-}" ]; then
+        echo "synclaude: SYNTHETIC_API_KEY is not set" >&2
+        exit 1
+      fi
+
+      export ANTHROPIC_BASE_URL="https://api.synthetic.new/anthropic"
+      export ANTHROPIC_AUTH_TOKEN="$SYNTHETIC_API_KEY"
+      export ANTHROPIC_DEFAULT_OPUS_MODEL="${kimi}"
+      export ANTHROPIC_DEFAULT_SONNET_MODEL="${glm}"
+      export ANTHROPIC_DEFAULT_HAIKU_MODEL="${qwen}"
+      export CLAUDE_CODE_SUBAGENT_MODEL="${glm}"
+      export CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1
+      export CLAUDE_CODE_ATTRIBUTION_HEADER=0
+
+      # ~/.env.claude exports both. ANTHROPIC_MODEL outranks the DEFAULT_* trio
+      # above, and ANTHROPIC_API_KEY would send Anthropic's credential to
+      # Synthetic.
+      unset ANTHROPIC_MODEL ANTHROPIC_API_KEY
+
+      # ~/.claude/settings.json pins model "opus[1m]". The [1m] context-window
+      # suffix survives alias resolution and reaches Synthetic as part of the id,
+      # which 404s there — so pick the alias explicitly unless the caller did.
+      for arg in "$@"; do
+        case "$arg" in
+        --model | --model=*)
+          exec ${claude}/bin/claude "$@"
+          ;;
+        esac
+      done
+
+      exec ${claude}/bin/claude --model sonnet "$@"
+    '')
+  ];
+}