Prevent building fragments from hitting their source

[WhiteGiverMa]

Additions

• None.

Changes

• Mark fragments emitted from a damaged building with their source building.
• Exclude that source building from the fragment projectile's collision candidates.
• Serialize the exclusion reference so a fragment saved in flight retains the rule after loading.

References

• Reproduction symptom: Tried to destroy already-destroyed thing Turret_AutoChargeBlaster...
• No upstream issue opened; the causal chain is documented below.

Reasoning

• Harmony_DamageWorker_Apply emits building fragments before the original damage worker runs.
• CompFragments.FragRoutine ticks each emitted fragment immediately. A fragment can collide with the building that emitted it, destroy it, and return to the outer damage worker.
• The outer vanilla damage worker then reaches Kill() for the same, already-destroyed building and emits a false duplicate-destroy error.
• Excluding only the emission source preserves fragment damage to every other target and leaves ordinary fragment generation unchanged.

Alternatives

• Disable Fragments from walls globally:
  • Avoids the error, but removes the feature instead of fixing it.
• Use the source building as the projectile launcher:
  • Reuses existing self-collision logic, but misattributes fragment damage and combat logs.
• Defer all building fragments until after damage resolution:
  • Avoids synchronous re-entry, but changes timing and allows surviving buildings to be hit by their own delayed fragments.

Testing

• Compiles without warnings: dotnet build Source\CombatExtended\CombatExtended.csproj -c Release --no-restore
• Existing test suite: dotnet test Source\Tests\Tests.csproj -c Release --no-restore (1 passed)
• Game runs without errors: pending deployment after RimWorld closes
• Playtested a colony: pending developer-mode high-damage hit against an auto charge turret with Fragments from walls enabled. Local gameplay validation uses a combined branch containing this and my other unmerged CE PRs, so it verifies integration behavior rather than this change in isolation. (Fix NRE in CompSuppressable.IsHunkering when pawn.CurJob is null #4652 Fix TendSelf/TendPatient reservation conflict in CompTend #4653 Fix InvalidCastException in StatPart_NaturalArmorDurability #4649 Downgrade NumCellsInRadius overflow from Log.Error to Log.Warning #4645 )

[github-actions]

You can download the rebuilt assembly for this PR here: https://combatextended.lp-programming.com/CombatExtended-29182189983.zip