docs: document config environment listing

content/docs/ai/mcp.mdx

@@ -80,6 +80,10 @@ The configuration file must be in the `toml` format. By default, the server look
 
 Each setting can also be overridden using `IGGY_MCP_<SECTION>_<KEY>`, for example `IGGY_MCP_IGGY_USERNAME` or `IGGY_MCP_HTTP_ADDRESS`. Nested settings use the same underscore convention, such as `IGGY_MCP_IGGY_TLS_ENABLED`. Set `IGGY_MCP_ENV_PATH` to load a particular dotenv file; otherwise `.env` is searched for in the current directory and its parents. Existing environment variables take precedence over dotenv values.
 
+Run `iggy-mcp --list-config-env-vars` to print every supported MCP configuration variable and exit before loading dotenv or configuration files or creating the Tokio runtime. The output is sorted and contains names only. If a configuration field is an indexed vector, its template uses `<N>` for indices from `0` through `255`; whole-value vectors are listed once without a placeholder.
+
+`iggy-mcp` rejects unknown command-line arguments with exit code 2. Keep client and container argument lists empty unless they contain a supported flag.
+
 The `token` value can be either a literal PAT or a `file:` reference such as `token = "file:/run/secrets/iggy_pat"`, in which case the token is read from the given file and surrounding whitespace is removed (`~/` is expanded to the home directory). A non-empty token takes precedence over the username and password.
 
 ## Available tools

content/docs/connectors/runtime.mdx

@@ -23,6 +23,12 @@ The [docker image](https://hub.docker.com/r/apache/iggy-connect) is available, a
 - On startup the runtime loads environment variables from the first `.env` file found in the working directory or its parents, or from the file pointed to by `IGGY_CONNECTORS_ENV_PATH`.
 - Supported scalar fields and indexed list entries can be overridden by environment variables using the `IGGY_CONNECTORS_<SECTION>_<KEY>` convention (nested keys joined by underscores), e.g. `IGGY_CONNECTORS_IGGY_USERNAME` or `IGGY_CONNECTORS_HTTP_ADDRESS`.
 
+Run `iggy-connectors --list-config-env-vars` to print the supported names and templates, then exit before dotenv and configuration loading, runtime creation, plugin loading, or other startup activity. The output is sorted and uses these placeholders:
+
+- `<N>` is a vector index from `0` through `255` for connector stream fields. Whole-value vectors are listed once without a placeholder.
+- `<KEY>` is the configured connector key, uppercased. These per-connector overrides are available only with the local configuration provider.
+- `<FIELD>` sets one lowercased top-level plugin configuration key. Underscores are preserved (`A_B` becomes `a_b`, not nested `a.b`), and nested plugin configuration keys cannot be set through environment variables. `FORMAT` is reserved and is listed separately as `..._PLUGIN_CONFIG_FORMAT`; the passthrough template does not guarantee that a plugin accepts every field.
+
 ## How plugins are resolved
 
 The `path` field of a connector configuration accepts both `plugin.so` and `plugin` - the OS-specific extension (`.so` / `.dylib` / `.dll`) is appended when missing. Absolute paths are checked at the literal location. Relative paths are searched in order:

content/docs/server/configuration.mdx

@@ -51,6 +51,8 @@ export IGGY_SHARDING_CPU_ALLOCATION=4        # [sharding] cpu_allocation
 
 Two variables live outside the config schema: `IGGY_ROOT_USERNAME` and `IGGY_ROOT_PASSWORD` set the root credentials, always as a pair. They initialize the root user **only at first creation**. On an existing data directory the stored root user is recovered unchanged, but supplied environment credentials must still pass validation.
 
+Run `iggy-server --list-config-env-vars` to print every supported server variable and exit before loading dotenv or configuration files or creating runtime state. The output is sorted, contains names only, and uses `<N>` for indexed vector entries. Most indexed fields accept `0` through `255`; `cluster.nodes.<N>.advertised_addresses.<N>` accepts `0` through `15` for its inner index. Whole-value vector fields are listed once without a placeholder.
+
 ### Secrets
 
 Five values are secret-flagged: `http.jwt.encoding_secret`, `http.jwt.decoding_secret`, `encryption.key`, `cluster.auth.shared_secret`, and `cluster.auth.previous_shared_secret`. Prefer setting them through their environment variables (`IGGY_HTTP_JWT_ENCODING_SECRET`, `IGGY_ENCRYPTION_KEY`, `IGGY_CLUSTER_AUTH_SHARED_SECRET`, and so on) instead of storing them in a file. Secret values are masked in logs and **never serialized** into `runtime/current_config.toml`.
@@ -65,10 +67,11 @@ Five values are secret-flagged: `http.jwt.encoding_secret`, `http.jwt.decoding_s
 
 ## Command-line flags
 
-`iggy-server` accepts these three startup options, plus `--help` (`-h`) and `--version` (`-V`):
+`iggy-server` accepts these four startup options, plus `--help` (`-h`) and `--version` (`-V`):
 
 | Flag | Description |
 |------|-------------|
+| `--list-config-env-vars` | Print the supported configuration environment-variable names and templates, then exit without starting the server. See [Environment variables](#environment-variables). |
 | `--fresh`, `-f` | Delete the configured data directory (`local_data` by default, see `IGGY_PATH`) before boot and start on empty state. In cluster mode this wipes **this replica only**; it rejoins and refills by state transfer from the others. Wiping a quorum at the same time can destroy committed data. Do not put `--fresh` in a service unit: it would re-transfer the whole dataset on every restart. |
 | `--with-default-root-credentials` | Set `IGGY_ROOT_USERNAME` and `IGGY_ROOT_PASSWORD` to `iggy` unless they are already present in the environment. These values initialize the root user only at first creation. Development only. |
 | `--replica-id <N>` | Identify this node within `cluster.nodes`. Required when `cluster.enabled = true`; the value must match exactly one `replica_id` in the roster. |