feat(sidecar): make the sidecar installable — CLI, --print-config, anchored data paths

Phase 0.2 of the installer plan (docs/installer/PLAN.md §5). The installer has to
drive this binary non-interactively, and today it cannot: the auth token is only
readable by scraping the startup log, the config path can only be named through an
environment variable, and a relative db path follows the process working directory —
which a service manager, not the operator, chooses.

- Add a four-flag CLI (cli.rs): --print-config, --config <PATH>, --version, --help.
  Hand-rolled; an argument-parsing dependency would be larger than the code it
  replaced. An unrecognized flag exits 2 rather than starting a sidecar that is not
  the one that was asked for.
- --print-config resolves the configuration exactly as a normal start does —
  including writing a missing config file and generating a blank auth token — and
  prints it as JSON on stdout: versions, protocol, both bind addresses, ws path,
  resolved db path, and the token. config_created / token_generated let a re-run
  tell "read an existing install" from "provisioned a new one". The log subscriber
  is deliberately not started in this mode, so the document is the whole output.
- Anchor a relative [store].path to the config file's directory instead of the CWD,
  and report resolved absolute paths. A unit pinning UOLINK_CONFIG now keeps its
  database beside its config rather than in %SystemRoot%\System32 or a VirtualStore
  redirect. Development is unaffected: under cargo run the two directories are the
  same. :memory: and file: URIs are left alone.
- Hand the db path to sqlx as a filesystem path instead of formatting it into a
  sqlite:// URL, which percent-decodes it and splits it on '?'. An installed path
  containing %20 previously opened a different file; verified it now does not.
- Create the config's and the database's parent directories when missing, so a
  service can name /var/lib/runicgateway on a host where nothing made it yet.
- 22 unit tests covering argument parsing, path anchoring, token persistence, the
  generated config template, and the --print-config document.

No protocol change: PROTOCOL_VERSION stays 3.

Co-Authored-By: Claude <noreply@anthropic.com>

sidecar/src/cli.rs

@@ -0,0 +1,172 @@
+//! Command-line surface.
+//!
+//! The sidecar is configured by file and environment (see [`crate::config`]); this is deliberately
+//! not a second configuration mechanism. It exists so the binary can be *driven by an installer*
+//! rather than only by a human reading its logs:
+//!
+//! - `--print-config` resolves the configuration exactly as a normal start would — including
+//!   generating the auth token on first run — and prints it as JSON on stdout. That is the
+//!   supported way to obtain the token for the website's Admin → Shard form. Before this existed,
+//!   the only way to read it back was to scrape the startup log or parse `sidecar.toml`.
+//! - `--config <PATH>` names the config file without having to export `UOLINK_CONFIG`, so a
+//!   diagnostic run can point at an installed config from any working directory.
+//!
+//! Hand-rolled rather than pulled from a crate: four flags, no subcommands, no completions. A
+//! dependency here would be larger than the code it replaced.
+
+/// What this invocation should do. Everything except `Run` prints and exits.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Mode {
+    /// Normal operation: bind the shard listener and the web server.
+    Run,
+    /// Resolve config, print it as JSON, exit.
+    PrintConfig,
+    Help,
+    Version,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Cli {
+    pub mode: Mode,
+    /// `--config <PATH>`, which outranks `$UOLINK_CONFIG`.
+    pub config: Option<String>,
+}
+
+pub const USAGE: &str = "\
+uo-link sidecar — bridges a ServUO shard to the Runic Gateway website.
+
+Usage: uo-link-sidecar [OPTIONS]
+
+Options:
+      --print-config     Resolve the configuration, print it as JSON, and exit.
+                         Runs first-run setup like a normal start does: if the
+                         config file is missing it is written, and a blank auth
+                         token is generated and saved. The JSON CONTAINS THE
+                         AUTH TOKEN in clear text.
+      --config <PATH>    Path to sidecar.toml. Overrides $UOLINK_CONFIG;
+                         defaults to ./sidecar.toml.
+  -V, --version          Print the sidecar and protocol versions and exit.
+  -h, --help             Print this help and exit.
+
+Configuration lives in sidecar.toml; environment variables override the file:
+  UOLINK_CONFIG, UOLINK_SHARD_BIND, UOLINK_WEB_BIND, UOLINK_WEB_TOKEN,
+  UOLINK_DB_PATH
+";
+
+/// Parses arguments **without** the program name.
+///
+/// Returns the message to print on stderr when the arguments are unusable; the caller exits `2`.
+pub fn parse<I: IntoIterator<Item = String>>(args: I) -> Result<Cli, String> {
+    let mut mode = Mode::Run;
+    let mut config = None;
+    let mut it = args.into_iter();
+
+    while let Some(arg) = it.next() {
+        match arg.as_str() {
+            "--print-config" => mode = Mode::PrintConfig,
+            "-h" | "--help" => {
+                return Ok(Cli {
+                    mode: Mode::Help,
+                    config,
+                })
+            }
+            "-V" | "--version" => {
+                return Ok(Cli {
+                    mode: Mode::Version,
+                    config,
+                })
+            }
+            "--config" => {
+                // `--config` with nothing after it would otherwise silently fall through and start
+                // the sidecar against the default config — the opposite of what was asked for.
+                let path = it
+                    .next()
+                    .ok_or_else(|| "--config requires a path".to_string())?;
+                config = Some(path);
+            }
+            _ => match arg.strip_prefix("--config=") {
+                Some("") => return Err("--config requires a path".into()),
+                Some(path) => config = Some(path.to_string()),
+                None => return Err(format!("unrecognized argument: {arg}")),
+            },
+        }
+    }
+
+    Ok(Cli { mode, config })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn parse_str(args: &[&str]) -> Result<Cli, String> {
+        parse(args.iter().map(|s| s.to_string()))
+    }
+
+    #[test]
+    fn no_arguments_runs_the_sidecar() {
+        let cli = parse_str(&[]).unwrap();
+        assert_eq!(cli.mode, Mode::Run);
+        assert_eq!(cli.config, None);
+    }
+
+    #[test]
+    fn print_config_is_recognized() {
+        assert_eq!(
+            parse_str(&["--print-config"]).unwrap().mode,
+            Mode::PrintConfig
+        );
+    }
+
+    #[test]
+    fn config_accepts_both_spellings() {
+        let spaced = parse_str(&["--config", "/etc/runicgateway/sidecar.toml"]).unwrap();
+        let equals = parse_str(&["--config=/etc/runicgateway/sidecar.toml"]).unwrap();
+        assert_eq!(
+            spaced.config.as_deref(),
+            Some("/etc/runicgateway/sidecar.toml")
+        );
+        assert_eq!(spaced, equals);
+    }
+
+    #[test]
+    fn config_combines_with_print_config() {
+        let cli = parse_str(&["--config", "c.toml", "--print-config"]).unwrap();
+        assert_eq!(cli.mode, Mode::PrintConfig);
+        assert_eq!(cli.config.as_deref(), Some("c.toml"));
+    }
+
+    #[test]
+    fn a_path_is_never_swallowed_as_a_flag() {
+        // `--config --print-config` takes the next token as the path, wrong as that path is. The
+        // alternative — treating it as a missing value — guesses at intent.
+        let cli = parse_str(&["--config", "--print-config"]).unwrap();
+        assert_eq!(cli.mode, Mode::Run);
+        assert_eq!(cli.config.as_deref(), Some("--print-config"));
+    }
+
+    #[test]
+    fn config_without_a_value_is_an_error() {
+        assert!(parse_str(&["--config"]).is_err());
+        assert!(parse_str(&["--config="]).is_err());
+    }
+
+    #[test]
+    fn unknown_arguments_are_rejected() {
+        // Silently ignoring a typo'd flag would start a sidecar that is not what was asked for.
+        let err = parse_str(&["--pirnt-config"]).unwrap_err();
+        assert!(err.contains("--pirnt-config"), "{err}");
+        assert!(parse_str(&["/etc/runicgateway/sidecar.toml"]).is_err());
+    }
+
+    #[test]
+    fn help_and_version_win_immediately() {
+        assert_eq!(parse_str(&["--help", "--bogus"]).unwrap().mode, Mode::Help);
+        assert_eq!(parse_str(&["-h"]).unwrap().mode, Mode::Help);
+        assert_eq!(
+            parse_str(&["--version", "--bogus"]).unwrap().mode,
+            Mode::Version
+        );
+        assert_eq!(parse_str(&["-V"]).unwrap().mode, Mode::Version);
+    }
+}