## Why
Delta world saves (only changed entities re-serialized during the freeze) need two things from content: `Serialize` must be pure, and an unchanged entity must produce identical bytes on every save. An audit of the tree found the places that break this today. This PR fixes them and adds a diagnostic that measures byte stability in a running world over real time. No wire format changes, no version bumps.
## What
- **Guild**: `Serialize` ran the daily guildmaster recalculation (dictionary-order tie breaks, random picks, mutates another entity), war expiry, and the alliance leadership check on every save. That work now runs from `GuildMaintenanceTimer` (the former `WarTimer`, now started for both guild systems; the war and alliance checks are no-ops without the new guild system).
- **BaseHouse**: the `DecayLevel` getter wrote `LastRefreshed` and advanced the dynamic decay stage on every read, so any undecayable house changed its persisted bytes whenever a sign, gump, or `[Props` looked at it. It is now a pure read; `UpdateDecay()` on the decay tick advances the stage and refreshes a house that leaves the undecayable state.
- **Locked-down container contents decay through `DecayScheduler`** instead of a sweep inside `BaseHouse.Serialize`. `Item.CanDecay` now accepts a parent container whose new `Container.ContentsDecay` is true (locked down and not secure) when the content item is not itself locked down or secured; the `IsLockedDown`/`IsSecure` setters re-evaluate a container and its direct contents; `OnDecay` resolves the region from the world location. `BaseBoard`, `Aquarium` and `FishBowl` override `ContentsDecay` to false, matching the exclusions of the old sweep. Items already inside such containers are picked up at load, where every item re-evaluates its registration. The per-save O(all locked-down items) walk is gone; the work is now event driven.
- **BraceletOfBinding**: the `Bound` getter nulled its backing field for a deleted target; it now returns null for a missing or deleted target without writing.
- **`[SaveStability [delaySeconds=60] [sampleStride=1]`** (Administrator): hashes the serialized bytes of every entity in every registered entity persistence (`Persistence.EntityPersistences`, new), waits the delay in real time, hashes again, and reports per type how many records changed. Both passes are chunked under a 20 ms per-tick budget. Serializing twice inside one tick cannot see drift derived from `Core.Now`, which is frozen within a tick; the real-time wait is the point. On an idle shard the only legitimate churn is NPC movement and regeneration, so a static type with a high changed fraction is a serialization bug. `[SaveStability cancel` stops a run.
Engine additions: `Container.ContentsDecay` / `UpdateContentsDecayRegistration()`, the `CanDecay`/`OnDecay` change above, and diagnostic-facing `IGenericEntityPersistence.Name`, `EntityCount`, `EnumerateEntities()`, and `Persistence.EntityPersistences`.
## Behaviour notes
- Fealty recalculation now happens on the minute timer for both guild systems instead of at save time.
- A house that becomes decayable is refreshed on its next decay tick rather than at the exact moment of transition (at most one minute later).
- Contents of locked-down containers now decay on their own schedule (same `LastMoved + DecayTime` rule) instead of at the next world save after becoming due.
## Testing
- New tests: `GuildSerializePurityTests`, `HouseDecayPurityTests`, `SaveStabilityTests` (stable entities hash identically after the clock advances; a clock-stamped record is reported by type only after the clock advances; the snapshot covers Items, Mobiles and Guilds).
- `LockedDownContainerDecayTests` (Server.Tests): registration on drop, lock/secure/release transitions, excluded containers, nested containers, and decay on schedule through the scheduler.
- Full suites: Server.Tests 855 passed, UOContent.Tests 765 passed.
## Summary
- Removes allocation of a `List<ContextMenuEntry>` every time a context menu is created.
- Moves packet/context menu creation logic out of the core
- Fixes tame entry
## BREAKING CHANGE
> [!Important]
> **Developer Note**
> ```cs
> public virtual void GetContextMenuEntries(Mobile from, List<ContextMenuEntry> list)
> ```
> and similar functions changed to
> ```cs
> public virtual void GetContextMenuEntries(Mobile from, ref PooledRefList<ContextMenuEntry> list)
> ```
## Changes
- [X] Adds OPL convenience methods
- `opl.Add(cliloc, value)` and `opl.Add(value)` - value as an integer or string works just like `opl.Add(cliloc, $"{value}")`
- `opl.AddLocalized(cliloc, clilocValue)` - works the same as `opl.Add(cliloc, $"#{clilocValue}");`
- [X] Simplifies basic `list.Add()` situations
- [X] Changes cliloc as an argument so it works with custom IPropertyList implementations (HTML)
- [X] Fixes plants so they support the old localization and new (changed in 7.0.12.0+)
- [X] Exposes more methods to override for Item to make creating custom OPL possible.
## Important Notes
* Using a ternary as an argument, like this `opl.Add(number, showType ? $"{type}\t{value}" : $"{value}");` _will not use the correct string interpolation_. This means if you use a custom PropertyList (for HTML or some other purpose), the property list won't be localized properly.
* All localization values must be interpolated, even if they are literal strings, or integers. Example: `opl.Add(number, $"{"Charges"}\t{m_Charges}");` is correct. Using the following: `$"Charges\t{m_Charges}"` will not work for custom PropertyList implementations!
## Breaking Changes (New API)
ObjectPropertyList supports the following API:
```cs
list.Add(500000);
list.Add(500001, stringArgument);
list.Add("Some text");
list.Add($"Some text with {argument}");
list.Add(500002, $"{arg1}\t{arg2}");
```
## Notes
1. All API uses that require a formatter like this:
```cs
list.Add(500002, "{0}\t{1}", arg1, arg2);
```
Should be changed to use string interpolation, for example:
```cs
list.Add(500002, $"{arg1}\t{arg2}");
```
2. The following paradigm should no longer be used:
```cs
list.Add(1061170, prop.ToString()); // strength requirement ~1_val~
```
The new string interpolation API will avoid having to convert the argument to a string before writing it to the packet. Instead use the following:
```cs
list.Add(1061170, $"{prop}"); // strength requirement ~1_val~
```
### Benchmarks
```cs
| Method | Mean | Error | StdDev | Gen 0 | Allocated |
|------------------------------- |---------:|--------:|--------:|-------:|----------:|
| BenchmarkOldOPL | 241.0 ns | 0.56 ns | 0.47 ns | 0.0105 | 88 B |
| BenchmarkStringInterpolatedOPL | 199.9 ns | 2.44 ns | 2.39 ns | - | - |
```
### Changes
- [X] Removes crash in STArray.Return when array is null.
- [X] Fixes NPE in OPL when entity is null. Serial in packet will be 0 when entity is null.
- [X] Fixes NPE in AosAttributes when Parent is null.
- [X] Changes OPL to use string interpolation.
- [X] Introduces `IPropertyList` to allow extending PropertyList for other uses.
