## Summary
Hardens the **Advanced Search** engine (`Projects/UOContent/Engines/Advanced Search/`) — the GM entity finder that fans searches across background worker threads. A code review surfaced 14 defects (A–N), including a shard-crasher reachable from a single admin typo and a path that silently disables autosave for the rest of the shard's uptime. Each behavioral fix ships with a test.
Full `UOContent.Tests` suite: **530/530 green** (21 new AdvancedSearch tests).
## Fixes
### Crash / data-loss
- **A — Shard crash on a malformed Property Test.** `AdvancedSearchThreadWorker.Execute` had no `try/catch` and the worker `Thread` is foreground, so a parse throw (`Hits>abc`, `Layer=onehanded` — `Enum.Parse` was case-sensitive, `Hits>1@` — empty sub-expression indexing) terminated the process. Now: `ParseValue`/`CompareValues` use `TryParse`/`Enum.TryParse(ignoreCase)` and return no-match instead of throwing; the per-entity filter is wrapped in `try/catch` (logs + skips); empty expressions are guarded.
- **C — Overlapping searches corrupt state + brick autosave.** `_threadWorkers`/`_threadId` were `static` but `DoSearch` is an instance method; a second search (double-click / two admins) stomped shared worker state and could leave a drain waiting forever on the shared `AutoResetEvent`, so `AutoSave.SavesEnabled` was never restored. Now: an `Interlocked` re-entrancy guard rejects concurrent searches.
- **G — Autosave restore not guaranteed.** The restore lived only in the success callback. Now it's in a `finally` (plus an outer `catch` covering the synchronous setup and a `catch` on the drain body), so autosave + the guard are always released.
### Wrong results
- **D — `@`/`|` operator precedence.** `a@b|c` evaluated as `a && (b || c)` instead of `(a && b) || c`. OR now binds looser than AND (`AdvancedSearchUtilities.EvaluateBoolean`, unit-tested).
- **E — Descending sort, partial last page rendered blank** (the index decreased in descending mode and the `break` early-out killed the loop). Now a bounded `VisibleCount`-driven loop renders the last page in both directions.
- **F — Deleted entities** were not skipped (ghost rows). Now `DoEntitySearch` skips `entity.Deleted`.
- **N — Reference-type comparisons** threw (`Comparer<T>.Default.Compare` on non-`IComparable`) and compared references to a string. Now equality is by value and ordering is guarded to `IComparable` (no throw).
### Worker perf / hardening
- **H** busy-spin → `Thread.Yield()` in the drain; **I** `GetProperties()` cached per `Type`; **J** `HandleValidInternal` moved behind the cheap map/range/region filters; **K** worker threads are `IsBackground` + `Exit()` tolerates an already-terminated worker; **L** `_filter == null` guard; **M** consistent `Volatile` access on `_pause`/`_exit`.
### Documented
- **B** — the residual worker/event-loop read race is documented on `AdvancedSearchThreadWorker`: workers read live entity state concurrently with the loop, so value-type reads may be stale-but-safe and getter exceptions are swallowed; fully eliminating it would require snapshotting entity fields on the main thread (deferred).
## Notes
- New test-only seams (`TryBeginSearch`/`EndSearch`/`IsSearchInProgress`/`VisibleCount`/`TryParseValue`/`EvaluateBoolean`) are `internal` via the existing `InternalsVisibleTo("UOContent.Tests")`.
- Dead `public ParseValue<T>` removed.
- `ConcurrentDictionary` for the reflection cache is intentional — these workers are genuinely parallel.
## Summary
Adds a custom `:L` format specifier to `RawInterpolatedStringHandler`. When the format string is `"L"`, the handler lowercases the formatted value's chars in-place after the underlying `ISpanFormattable.TryFormat` / `IFormattable.ToString` path completes. Zero allocation, single-pass.
## Usage
```csharp
mob.SendMessage($"You earned a {rank:L} trophy!"); // "gold"
mob.SendMessage($"Welcome, {playerName:L}"); // lowercased
mob.SendMessage($"{count:L} kills"); // ints unchanged ("42")
```
## Motivation
Eliminates the `value.ToString().ToLowerInvariant()` two-allocation idiom that appears across the codebase for any type that goes through an interpolation handler. After this lands, content code can use the `:L` specifier directly instead of helper extensions or per-enum lookup tables.
## Coverage
- `AppendFormatted<T>(T value, string? format)` — generic path (covers IFormattable, ISpanFormattable, .ToString fallback)
- `AppendFormatted(ReadOnlySpan<char> value, int alignment, string? format)` — span path with alignment-aware lowercase range (only the value range is lowercased, not padding)
- `AppendFormatted<T>(T value, int alignment, string? format)` and `AppendFormatted(string? value, int alignment, string? format)` and `AppendFormatted(object? value, int alignment, string? format)` — inherit via delegation
The `format == "L"` comparison is case-sensitive — `:l` (lowercase L) is NOT recognized. `:L` matches the convention of e.g. `:N0` / `:F2` (numeric format specifiers traditionally use uppercase). `char.ToLowerInvariant` is used (not locale-dependent) for predictable game text.
## Future cleanup
Phase 3.3 (#2438) introduced a per-enum `TrophyRank.LowerName()` extension to eliminate `rank.ToString().ToLower()` allocations at 10 ConPVP sites. Once this PR lands, those sites can be simplified to `{rank:L}` and the `TrophyRankExtensions` helper can be removed. Tracked as a follow-up.
Kamron Batman