fix(demo): move to a free port and stop cleanly on Ctrl-C - #23

Motivation

On a laptop the demo is started and stopped many times. A leftover run on :8080 made the next start fail, and state was kept in ~/Library/Caches, which macOS may clear.

Changes

• serve without --addr takes the first free port from 8080 to 8089 and prints the URL. An explicit --addr that is taken still fails.
• serve shuts down on Ctrl-C or SIGTERM and exits 0.
• Default state moves to the user config dir (~/Library/Application Support on macOS). Existing cache-folder state is not migrated; Reset rebuilds it.
• docs/troubleshooting.md row for the busy port updated.

This demo starts no child processes, so there is nothing to clean up beyond the server itself.

Tests

• make test vet: pass. go test -race ./internal/cli: pass.
• New tests: fallback only when the address was not chosen, serve stops cleanly on cancel, default state is not in a cache folder.
• Ran the built binary while another demo held :8080: it served on :8081, and exited 0 on SIGTERM.

Related

Independent of localstack-samples/localstack-app-emulators PR #22 (doctor). Both touch internal/cli/cli.go in different places.