Summary

• Relaxes the "no comments inside methods" rule: why-comments (constraints, invariants,
  rationale) are now allowed; narration/what-comments and section headers inside methods
  stay banned. The test-method comment rule is unchanged.
• Sweeps src/ for narration-style comments and one LLM leftover; ~90 existing comments were
  reviewed and either kept as legitimate why-comments or judged out of scope (field/type-level,
  not inside a method body).
• Moves two file pairs to match their already-declared namespace (namespace changes on public
  types are breaking, so the files move instead): Partitioner.cs/PartitionSpec.cs out of a
  Partitioning/ subfolder, and two Infrastructure.Relational files into a new OutboxProcessing/
  folder mirroring the sibling provider projects.
• Splits a file that packed four public types (plus one internal helper) into one file per type.
• Adds a missing null-guard to one provider extension whose siblings already had it, with a
  matching test.

Verification

• Full solution build: clean, 0 warnings/errors.
• Targeted test projects for every touched src project, both TFMs: all passing (116/116, 2/2,
  10/10 including the new guard test).
• PublicAPI*.txt / CompatibilitySuppressions.xml: byte-identical (empty diff).

Backport to v1.0: no — convention sweep ships with the next release.