v6.4.0-beta.1

The simplicity rule stops being a ranking. §1 put Simplicity third and §10
banned speculative features, but nothing was actionable: no clause told an agent
to prefer the least mechanism, no rubric row let a reviewer reject an
unnecessary abstraction, and no gate failed when the rule was diluted. Users saw
the result as code too complex to read and maintain. The rule is now sharp:
decidable tests for when structure has earned its place, and a counterweight so
that "simpler" never means "smaller diff."

Tagged as a beta: this is the same additive shape as v6.3.0, cut ahead of a
stable patch so the release path runs end-to-end before the change is advertised
as the latest download.

Added

• skills/craft — a Simplicity section (loaded on demand): the default is
  the least mechanism that works — the standard library before a dependency, a
  plain function before a class, a direct call before a layer. Four named classes
  of unintended complexity, each a defect: speculative abstraction (extract on
  the second concrete caller, never the first imagined one), dead configurability
  (a knob nobody turns), indirection the reader must decode (a wrapper that only
  forwards), and a dependency for the trivial. Flagged in review with the cost
  named — "this serves one caller and adds a file every change must cross" is a
  finding; "this feels complex" is not.
• A simplicity gate in scripts/check.py: the rule must be present on both
  canonical surfaces (the always-loaded manifesto clause and skills/craft), so
  neither can silently drop it. It shares a rule-presence helper with the
  comments gate rather than duplicating it, so a third such rule costs one
  dict entry.
• An eval case — simplicity-rule-survives-doctrine-edits — so a doctrine
  edit that drops the rule from either surface fails the suite.

Changed

• AGENTS.md §5 carries the always-loaded clause in place: least mechanism,
  complexity pays its way, no abstraction before a second real caller, no flag
  nobody sets, no forwarding wrapper, no dependency for what the standard library
  does — and simplicity never overrides correctness.
• AGENTS.md §10 extends the speculative-feature ban to a layer, flag,
  wrapper, or dependency that has not earned its cost.
• cmd-review gains a Simplicity rubric row: a finding must name a concrete
  cost or it is taste, not a defect, and a needed error path or clarifying name
  is never traded for a smaller diff.
• Doc drift swept: the gate count on the README verification table and
  validate.yml's gate list now include simplicity.