Hub redeploys can reset msexports and raw retention

Roland Krummenacher (@RolandKrummenacher)

🤖 [AI][Claude Code]

Follow-up to #2206 and #2288, which keep stored ingestion and final retention on redeploy. Two retention settings are still not protected.

msexports.days: stored in config/settings.json and read by the exports app (Exports/app.bicep) to decide whether export files are deleted after ingestion. A redeploy that omits exportRetentionInDays writes 0, so files start being deleted again.
Raw retention (dataExplorerRawRetentionInDays): raw.days in settings.json has no reader. The effective value is baked into the Data Explorer policy at deploy time (Analytics/app.bicep: .alter-merge table ActualCosts_raw policy retention softdelete = <days>d recoverability = disabled). With the default of 0, a redeploy that omits the parameter reapplies softdelete = 0d recoverability = disabled to the *_raw tables, which is an immediate purge that can't be recovered.

To do

Decide how a redeploy tells an explicit value from an omitted one (for example read the stored/current value first, or make the Bicep parameters nullable).
Guard msexports.days the same way as ingestion and final.
Read the current softdelete policy before reapplying it, or skip the alter when no value was requested.
Document how to change each value afterward.