fix(823): three cleanups from the coherence pass — a wrong witness, a wrong because, a duplicated paths:

Round-five review confirmed the decision record is coherent with no third
survivor of the empty reading, and returned three LOW findings. All are in
prose I wrote in the last two commits.

- The comment defending `(IsAbstract && !IsSealed)` cited
  AlternateScheduleSelectorTests as an in-repo static-fixture witness. That
  class IS static, but it merely NESTS its [TestFixture]es and declares no test
  of its own, so it would fail the sibling "declares no runnable test" assertion
  rather than demonstrating the point. The rule is right and the witness was
  wrong, which is the worse of the two failures because a wrong example is what
  a reader checks the rule against. No witness is cited now, and why is stated.

- A mis-bound `because` in `rule:`: "assigning a null and calling SaveChanges
  SUCCEEDS ... because only the HTTP request records normalize with `?? []`".
  The `?? []` clause explains how a null could REACH the entity; what makes the
  save succeed is the column being nullable. A right observation with a wrong
  cause attached. Split into the two claims.

- `signals:` carried the literal token `paths:` twice, an artifact of appending
  the #823 path list to the existing one. It degrades the field the discovery
  surface parses.

Also recorded from that review, and NOT changed: `MonthsOfYear ?? AllDaysOfMonth()`
survives the selector fixture and no date can kill it -- 1..31 contains every
valid month, so it is an EQUIVALENT mutant there rather than a coverage gap.
Its non-equivalent twin at the DTO boundary is pinned per-dimension by
RecurrenceLimitsMapperNullTests. Left alone deliberately: chasing an equivalent
mutant with a contrived date would buy nothing and cost the fixture's
readability.

Local gate: ErsatzTV.Tests 2091 passed / 6 skipped, Core.Tests 697/1 -- 0
failures. Format clean, no BOM. decisions_validate OK.

Refs #823
Refs #824

Decisions-Edit: yes
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019zUmJZHhVP7kXg5DV237TW

ErsatzTV.Tests/Integration/SearchIndexMutationCoverageTests.cs

@@ -112,9 +112,12 @@ public class SearchIndexMutationCoverageTests
             // class NUnit will not instantiate, and [Explicit]/[Ignore]. The indexer population at the top
             // of this method already filters IsAbstract; the fixture side needs the mirror of that.
             // `IsAbstract` ALONE is wrong here and would have been a false red: a C# `static class`
-            // compiles to `abstract sealed`, and NUnit runs tests declared in one -- this repo already has
-            // such a fixture (`AlternateScheduleSelectorTests`). What must be rejected is an abstract BASE
-            // (abstract and NOT sealed), which NUnit cannot instantiate.
+            // compiles to `abstract sealed`, and NUnit runs a test declared in one. What must be rejected
+            // is an abstract BASE (abstract and NOT sealed), which NUnit cannot instantiate. Deliberately
+            // no in-repo witness is cited: `AlternateScheduleSelectorTests` is a static class, but it
+            // merely NESTS its `[TestFixture]`es and declares no test of its own, so it would fail the
+            // sibling assertion above instead -- naming it here would have been a wrong example attached
+            // to a right rule.
             (fixture.IsAbstract && !fixture.IsSealed).ShouldBeFalse(
                 $"{fixture.Name} is named as the mutation fixture for {indexer.Name} but is an abstract "
                 + "base class, so NUnit never runs it");