## Summary
After #2670, `BaseCreature` stores one master. Callers still reached it through three differently gated names plus hand-rolled combinations of the `Controlled`/`Summoned` flags. Each gate is now one named view:
| Member | Definition | Meaning |
|---|---|---|
| `Master` | the reference; its setter does the follower bookkeeping; serialized as before | whoever the creature answers to |
| `ControlMaster` | `Controlled ? Master : null` | the owner |
| `SummonMaster` | `Summoned ? Master : null` | the summoner |
| `GetMaster()` | `ControlMaster ?? SummonMaster` | who answers for the creature |
`ControlMaster` and `SummonMaster` stay settable so custom code keeps compiling: both setters assign `Master`. There is no guard, so a write through either one can read back as null until the matching flag is set.
An enraged creature is the one shape with a master and neither flag. It keeps its meer through `Master`, while `GetMaster()` stays null, so the meer never answers for it (notoriety, kill credit).
Readers move onto the view they mean:
- "Owner or summoner" pairs and `ControlMaster ?? SummonMaster` collapse into `GetMaster()`: pack instinct, familiars, golem, house access, mounts, pack horse, Solen friendship, spell target and guild checks, and the `[` pet command.
- Checks such as `Controlled && ControlMaster == from` drop the flag the view already applies. Checks that don't reduce keep it: `Controlled && ControlMaster != from`, a possibly-null `from`, and `MageAI.CanDispel`'s `Summoned &&`.
**No behavior change, save format unchanged** (the schema generator produces no diff). Edge cases for custom code and shard operators:
- `SummonMaster = x` on a plain pet now replaces its owner (#2670 made that a no-op), and `ControlMaster = null` on an uncontrolled summon now clears its caster (it did nothing before).
- `SpellHelper.GetGuildFor` no longer falls back to an enraged creature's meer. Meer mages have no guild.
## Docs
- `dev-docs/content-patterns.md` § Masters: which view answers which question, how to set a master, and which flag checks are redundant.
- `dev-docs/runuo-migration-docs/09-items-mobiles-creatures.md` § Masters: RunUO's two-field reads mapped onto the views, plus the gotcha for creatures that set `SummonMaster` without `Summoned` (the write compiles, the read now returns null; use `Master`).
- The `modernuo-content-patterns` and `migrate-items-mobiles` skills point at both.
## Test plan
- [x] `MasterViewsTests`: all four views across wild, pet, controlled summon, uncontrolled summon and enraged shapes; reassigning `Master` moves follower slots; `SetControlMaster(null)` keeps an uncontrolled summon's caster; deleting a summon returns the caster's slots
- [x] Serialization tests updated to the new views (round-trip, legacy v22, v23 migration)
- [x] UOContent.Tests (1178 passed, 2 skipped) and Server.Tests (907) green
#2132 let a player's energy vortex or blade spirits in pre-AOS Felucca target their own caster, gated by `FollowsAcquireRules`. #2232's AI overhaul moved the summon checks into `IsInvalidSummonTarget`, which excluded the caster in every era, and dropped the gate. Since then `FollowsAcquireRules` has had no readers and summons have never turned on their caster.
## Changes
- `IsInvalidSummonTarget` reads `FollowsAcquireRules` again. A summon that follows the acquire rules spares its caster and anyone the caster's harmful spells would spare. The vortex and blade spirits don't follow them in pre-AOS Felucca when a player summoned them.
- The animated-dead restrictions (no players, no other animated dead, no pets) apply to every animated summon regardless of that setting.
- `AcquireNewFocusMob` sets a berserk summon's caster aside and targets them only when nobody else is available. #2132 meant to prefer others, but its check only worked when the caster was scanned before the other candidates, and the vortex's Int-plus-Magery ranking usually puts a nearby caster first.
- The AOS summon-target check no longer dereferences a missing `SummonMaster`. A summon whose caster was deleted before a reload comes back without one.
Controlled summons are unaffected: since #2665 they target through `HandleControlled` and never reach this scan.
## Tests
`SummonAcquireRulesTests` has 6 cases, skipped without client map data. Pre-AOS Felucca: a vortex and blade spirits each target their caster when the caster is alone, and a vortex targets a bystander even when the caster ranks higher. Pre-AOS Trammel and AOS Felucca: the caster is still spared. An AOS scan next to a summon with no master doesn't throw. `UOContent.Tests`: 1148 passed, 2 skipped, 0 failed on Windows.
