fly launch overwrites a hand-written fly.toml (drops [[mounts]]/[env], changes region)

Problem

After committing a hand-written fly.toml, running `fly launch` regenerated it and silently dropped the [[mounts]] (volume) and [env] blocks and changed primary_region. The app then deployed to the wrong region WITHOUT the volume, so SQLite/model data was ephemeral, two machines ran, and `fly scale`/`fly deploy` hit `failed to obtain lease`.

Symptoms

• fly.toml lost its [[mounts]] and [env] after fly launch
• machines created in the wrong region (e.g. sin) while the volume is in another (nrt)
• volume shows no ATTACHED VM; data is ephemeral
• fly scale/deploy: failed to obtain lease ... lease currently held by ...
• two machines for an app that must be single-instance

Likely causes

• fly launch treats fly.toml as scaffolding and regenerates it
• a Fly Volume is region-locked and attaches to exactly one machine

Verified fix

Verification

• fly machine list shows 1 machine in the volume region with VOLUME attached and checks passing
• fly volumes list shows ATTACHED VM set
• curl /api/health returns 200

Agent hint

Fly volume region-locked + single SQLite file => exactly one machine in the volume`s region. If fly launch ran, diff fly.toml against git first.

Related cards (semantic)