fix: scope workflow credentials to callers

modules/capabilities/ai.nix

@@ -7,6 +7,18 @@ in
   flake.modules.nixos.ai =
     { pkgs, ... }:
     let
+      context7Headers = pkgs.writeShellScript "context7-http-headers" ''
+        set -euo pipefail
+
+        CONTEXT7_KEY_FILE="''${XDG_CONFIG_HOME:-$HOME/.config}/context7/api-key"
+        [[ -r "$CONTEXT7_KEY_FILE" ]]
+        CONTEXT7_KEY="$(< "$CONTEXT7_KEY_FILE")"
+
+        exec ${pkgs.jq}/bin/jq --null-input --compact-output \
+          --arg authorization "Bearer $CONTEXT7_KEY" \
+          '{ Authorization: $authorization }'
+      '';
+
       codexConfig = (pkgs.formats.toml { }).generate "codex-config.toml" {
         model = "gpt-5.6-sol";
         model_reasoning_effort = "high";
@@ -29,7 +41,7 @@ in
         mcp_servers = {
           context7 = {
             url = "https://mcp.context7.com/mcp";
-            env_http_headers.CONTEXT7_API_KEY = "CONTEXT7_API_KEY";
+            http_headers_helper = "${context7Headers}";
           };
           nixos = {
             command = "${pkgs.uv}/bin/uvx";