ADR 0006: Auto-start UI API from Streamlit UI entrypoint

Date: 2026-01-06

Context: The Streamlit UI depends on the read-only UI API. Requiring users to start two processes manually adds friction and often leads to a confusing "API not reachable" experience. Decision: The UI entrypoint (run_ui) probes GET /api/v1/health and, when the configured API base URL is a local HTTP address, automatically starts the UI API as a subprocess. Decision: Auto-start is only attempted for http://127.0.0.1:<port>, http://localhost:<port>, and http://[::1]:<port> (no path prefix); non-local and non-HTTP base URLs never trigger auto-start. Decision: If the UI started the API subprocess, it owns its lifecycle and stops it when the UI exits (SIGTERM, Ctrl+C, or normal termination). Consequences: Local development becomes a single-command workflow; remote deployments keep explicit control over the API process; startup errors surface early with clear console messages and logs per role.