Add shared OTLP telemetry and propagate command traces across agents

docs/openwrt-uci.md

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+# OpenWrt UCI for Wakey
+
+Wakey's OpenWrt init script reads `/etc/config/wakey` for the log filter and
+OTLP authorization header, then passes them to the agent through procd.
+The agent's application settings remain in `/etc/wakey-agent/config.toml`.
+The previous `/etc/wakey-agent/environment` file is no longer read.
+
+## The three names
+
+```sh
+uci set wakey.main.otlp_authorization='Basic BASE64_OF_USERNAME_COLON_PASSWORD'
+```
+
+| Part | Meaning |
+| --- | --- |
+| `wakey` | Package: `/etc/config/wakey` |
+| `main` | Named section inside that package |
+| `otlp_authorization` | Option inside the section |
+
+Quotes keep the complete `Basic ...` value together despite its space.
+The credential is the Base64 encoding of `username:password`.
+It is not the htpasswd hash, and Base64 is not encryption.
+
+## Create and save
+
+Run as root on the router. `touch` does not truncate an existing file:
+
+```sh
+touch /etc/config/wakey
+chown root:root /etc/config/wakey
+chmod 600 /etc/config/wakey
+
+uci set wakey.main=service
+uci set wakey.main.log_filter='info'
+uci set wakey.main.otlp_authorization='Basic BASE64_OF_USERNAME_COLON_PASSWORD'
+uci commit wakey
+chmod 600 /etc/config/wakey
+```
+
+`wakey.main=service` creates a named section of type `service`. The type is our
+chosen label, not a built-in Wakey feature. Existing options are not cleared.
+`set` stages changes; `commit wakey` writes that package to disk. Committing does
+not restart a service.
+
+The resulting file looks like:
+
+```text
+config service 'main'
+    option log_filter 'info'
+    option otlp_authorization 'Basic BASE64_OF_USERNAME_COLON_PASSWORD'
+```
+
+The example above uses a placeholder. Avoid typing real credentials into a
+command that your shell will save in history. On OpenWrt's ash, you can instead
+read the Basic header without echoing it and send it to UCI over stdin:
+
+```sh
+read -r -s -p 'Complete Basic authorization header: ' authorization
+printf '\n'
+printf "set wakey.main.otlp_authorization='%s'\ncommit wakey\n" "$authorization" | uci batch
+unset authorization
+chmod 600 /etc/config/wakey
+```
+
+Use a normal `Basic <base64>` header here, without quotes/newlines inside the value.
+The shell's builtin `printf` avoids passing the secret in `uci`'s command arguments.
+UCI is not a secret vault: committed files, staged changes, router backups, and
+root access can expose these credentials. Do not paste their output into logs/chat.
+
+## Inspect, change, delete
+
+Inspect the non-secret option:
+
+```sh
+uci get wakey.main.log_filter
+```
+
+`uci show wakey`, `uci export wakey`, `uci changes wakey`, and
+`uci get wakey.main.otlp_authorization` **print the credential**. Use them only
+when you deliberately want to see it.
+
+Change an option:
+
+```sh
+uci set wakey.main.log_filter='wakey_agent=debug,wakey=debug,opentelemetry=warn'
+uci commit wakey
+```
+
+Delete just the authorization option:
+
+```sh
+uci -q delete wakey.main.otlp_authorization
+uci commit wakey
+```
+
+If TOML still requires `authorization_env`, removing the variable makes startup
+fail. Remove that TOML field too only when the receiver no longer requires auth.
+
+Discard all uncommitted changes to this package:
+
+```sh
+uci revert wakey
+```
+
+## How the service reads it
+
+`config_load` and `config_get` are shell helpers from `/lib/functions.sh`, available
+in the normal `/etc/rc.common` init-script environment. They are not standalone
+commands to run directly in your SSH shell.
+
+```sh
+config_load wakey
+config_get authorization main otlp_authorization
+```
+
+`config_get` arguments are **destination variable, section, option, optional default**.
+The line above puts the option into the shell variable `authorization`. It does
+not export it to the agent automatically; procd must receive it explicitly.
+
+The checked-in [init script](../scripts/init/openwrt/wakey) uses these helpers.
+Its configuration handling is:
+
+```sh
+start_service() {
+    local authorization='' log_filter='info'
+    if [ -f /etc/config/wakey ]; then
+        config_load wakey || return 1
+        config_get authorization main otlp_authorization
+        config_get log_filter main log_filter 'info'
+    fi
+
+    procd_open_instance
+    procd_set_param command "$BIN" serve --config "$CONFIG"
+    procd_set_param file "$CONFIG"
+    [ ! -f /etc/config/wakey ] || procd_append_param file /etc/config/wakey
+    procd_set_param env "RUST_LOG=$log_filter"
+    [ -z "$authorization" ] || procd_append_param env "WAKEY_OTLP_AUTHORIZATION=$authorization"
+    procd_set_param respawn 5 1 0
+    procd_set_param stdout 1
+    procd_set_param stderr 1
+    procd_close_instance
+}
+```
+
+Keep these fields in the agent's TOML:
+
+```toml
+[telemetry]
+otlp_endpoint = "http://10.5.0.1:4317"
+authorization_env = "WAKEY_OTLP_AUTHORIZATION"
+```
+
+UCI stores the header; procd passes the environment variable; Rust reads it using
+the name in TOML. The application does not parse UCI itself.
+
+After installing the updated init script and committing settings:
+
+```sh
+/etc/init.d/wakey restart
+```
+
+Use **restart**, not the existing HUP-based reload: a running process cannot receive
+changed environment variables that way. UCI is only for the router; the CC's
+systemd environment file remains unchanged. See [telemetry.md](telemetry.md).
+
+## References
+
+- [OpenWrt UCI CLI source and command usage](https://github.com/openwrt/uci/blob/master/cli.c)
+- [OpenWrt config_load/config_get helpers](https://github.com/openwrt/openwrt/blob/main/package/base-files/files/lib/functions.sh)