When an AI debug-message cooldown crosses the signed tick-counter boundary, DebugInterpolatedStringHandler can emit before the deadline or suppress a message after it. Both constructors compare absolute tick values.
Use subtraction-based deadline comparisons in both constructors, following dev-docs/tick-counts.md. This is a two-line production change; message formatting, cooldown duration, and gameplay behavior are unchanged.
Adds 35 regression cases exercising the actual handler and DebugSayFormatted:
- Both constructor overloads, with debugging enabled and disabled.
- Before/at/after deadlines on positive and negative clocks.
- Future and expired deadlines across signed wraparound.
- Cooldown rearming across wraparound and buffer clearing.
- A compiler-generated interpolated call through the public extension method.
Validation on Linux / .NET 10, based on clean upstream 35e3a31b4:
- Release build: 0 warnings, 0 errors.
- New tests against unchanged production code: 28 passed, 7 failed.
- With the fix: 35 passed, including without client map data (no skips).
- Selected AI/pet suites: 134 passed / 7 failed before; 141 passed / 0 failed after.
Tests use synthetic entities; no running shard or world saves. The faulty comparisons were reverified on upstream main before submission. Windows execution remains unverified. The tests exercise explicitly assigned deadlines; deadline initialization is outside this patch.
Addresses only the DebugInterpolatedStringHandler comparison item in #2627; it does not close the other audit items.
Two bugs found while reworking #2653.
**Custom flags throw.** `SyncStaticFlag` is a switch expression with no discard arm, so any key that has no static behind it throws `SwitchExpressionException`. `[FeatureFlag mykey create <category> <desc>` crashes in `CreateOrUpdateFlag`, and once such a key is in `flags.json`, every boot's `SyncAllStaticFlags()` throws mid-iteration — caught and logged as "Failed to load feature flags", but stock flags later in dictionary order never sync. Added `_ => enabled`.
**Removing a flag turns some features on.** `RemoveFlag` hardcoded `SyncStaticFlag(flagKey, true)`. For `speedhack_detection` and `insurance` the real default is `false` / `insurance.enable`, so deleting the flag enabled the feature. It now syncs the removed flag's `DefaultEnabled`, which #2653 seeds from the static.
Verified: `dotnet build Projects/UOContent/UOContent.csproj -c Release`, 0 `CS` diagnostics (post-build copy to `Distribution/` was blocked by a running server instance).
