date_posted column was added to db.py CREATE TABLE but had no migration
file, so existing user DBs were missing it. The list_jobs endpoint queries
this column, causing 500 errors and empty Apply/Review queues for all
existing cloud users while job_counts (which doesn't touch date_posted)
continued to work — making the home page show correct counts but tabs show
empty data.
Fixes:
- migrations/006_date_posted.sql: ALTER TABLE to add date_posted to existing DBs
- dev_api.py lifespan: on startup in cloud mode, sweep all user DBs in
CLOUD_DATA_ROOT and apply pending migrations — ensures schema changes land
for every user on each deploy, not only on their first post-deploy request
