ONE vega_events row idea_abandoned when a member leaves the talk-build card after exactly one test (no second test, no deploy).

Sent by navigator.sendBeacon from pagehide / visibilitychange, so the body arrives as text/plain (a CORS-safelisted type — a beacon cannot make a preflight) and is parsed here as JSON.

• SESSION ONLY (the cookie): an API key or account pair gets 401 — this is the browser's own page lifecycle, nothing else sends it.
• user_id from the session, never the body.
• idea_text is cut to IDEA_TEXT_MAX chars; verdict/surface are whitelisted; the whole body is size-capped.
• IDEMPOTENT per page_session: a second beacon for the same page session (pagehide AND visibilitychange both fire on many browsers) writes nothing.
• Server-written only — deliberately NOT in _EVENT_NAMES, so the raw-text event cannot be forged anonymously through /v1/events. The raw words stay FIRST-PARTY: the web sends PostHog only the verdict, the length and a hash prefix.