Docs, ticks, working app

tickets/019-default-port-zero.md

@@ -0,0 +1,29 @@
+# 019 — Default port should be 0
+
+## Summary
+
+`--port` currently defaults to `8420` (`Args` in `main.rs`). The wishlist asks for a
+default of `0`, i.e. let the OS assign an ephemeral free port rather than colliding
+with whatever else is running on a fixed port.
+
+## Scope
+
+- Change `Args::port`'s default to `0`.
+- After `TcpListener::bind` succeeds, read back the actual bound port (via
+  `listener.local_addr()`) since binding to `0` means the requested port and the
+  real one differ.
+- Print the real bound port in the startup log line (it already prints
+  `args.port`, which would otherwise always read `0`).
+- Consider whether the actual port needs to be surfaced anywhere else (e.g. a
+  `GET /api/stats`-style endpoint) — not required unless something already depends
+  on knowing it programmatically today; check before adding.
+
+## Acceptance criteria
+
+- Running `ottyl` with no `--port` binds an OS-assigned free port instead of a fixed
+  one, and the startup message prints that actual port.
+- `--port <n>` still binds the requested fixed port as before.
+
+## Depends on
+
+None.