bubbles-config-bundle-per-train

Declare the owning train in the spec's state.json, add the flag as true in the owning train's bundle file, add it as false in every other train's bundle, and add a metadata entry. Then implement fail-fast env-var reading in code and let release-train-guard.sh verify at pre-push.

The CI config-bundle generator (G081) reads the train's feature-flags YAML file and emits a signed, immutable config artifact containing the resolved env file. Services read flags from environment variables at startup with no hardcoded defaults.

Flags use snake_case with verb-noun or feature-noun patterns, boolean semantics only, and no train name embedded in the flag. Version suffixes are avoided unless two versions must coexist, such as experimental_payment_flow_v2.

A flag is retired when release-train-flag-audit.sh marks it overdue, meaning its train graduated more than one cycle ago. The cleanup removes the conditional from code, deletes the flag from all bundles, and removes the env var reference.

Gate G111 enforces default-OFF outside the owning train so the same git SHA can ship to multiple slots safely. Omitting the flag from other bundles causes false positives and breaks bundle agreement during retirement.