The three operations, exact
Repair
re-lays missing/corrupt components using cached source; does not change versions, does not re-run your tweaks
Upgrade (major)
new package+product codes, stable UpgradeCode; RemoveExistingProducts unwinds old product — file-overwrite rules decide what's replaced
Fresh install
clean slate; old product was removed first, so no costing logic applies
The two installer gotchas worth memorizing
- Equal file version = not overwritten. MSI's costing engine compares
FileVersion; same versions skip replacement even if bytes differ. Teams that forget to bump FileVersion ship no-op upgrades and wonder why bugs “still repro.” - Dual mode by feature flags. Default
REINSTALLMODE=omuspresumes versioned-file delta; installers that forcev(rewrite from cache) can resurrect buggy cached copies on genuinely-fresh artifacts.
Evidence pattern: the preview pipeline stamps every build with distinct FileVersion precisely so upgrades land — the Win32 versioning principle the installer respects is the versioning principle the build discipline preserves.
ProofTune ProjectEngineering notes — every claim here names the bytes a real tool touches. Verify first, install second.