docs: clarify custom endpoint support

.claude-plugin/README.md

@@ -3,3 +3,15 @@
 If you plan to edit `.claude-plugin/plugin.json`, be aware that the Claude plugin validator enforces several **undocumented but strict constraints** that can cause installs to fail with vague errors (for example, `agents: Invalid input`). In particular, component fields must be arrays, `agents` must use explicit file paths rather than directories, and a `version` field is required for reliable validation and installation.
 
 These constraints are not obvious from public examples and have caused repeated installation failures in the past. They are documented in detail in `.claude-plugin/PLUGIN_SCHEMA_NOTES.md`, which should be reviewed before making any changes to the plugin manifest.
+
+### Custom Endpoints and Gateways
+
+ECC does not override Claude Code transport settings. If Claude Code is configured to run through an official LLM gateway or a compatible custom endpoint, the plugin continues to work because hooks, commands, and skills execute locally after the CLI starts successfully.
+
+Use Claude Code's own environment/configuration for transport selection, for example:
+
+```bash
+export ANTHROPIC_BASE_URL=https://your-gateway.example.com
+export ANTHROPIC_AUTH_TOKEN=your-token
+claude
+```