claude-config: add the highly-important-areas exception register with same-change criteria wiring

[claude]

Context

Signed-off decision Q2 of the context-engineering integration contract
(docs/topics/context-engineering-integration/PLAN.md, 2026-09-01): the article-derived
"except in highly important areas" carve-out has no incumbent encoding — the prior plan's own
coverage matrix marks it PARTIAL ("a trimming pass has no principled stopping point"). An
unconsumed register is inert, so the doc and its wiring land in one change.

Proposed work

• Author the register as a docs/conventions/ owner doc naming the domains where hard
  constraints stay (destructive operations, permission handling, publish/never-publish,
  secrets), explicitly NON-EXHAUSTIVE with a tighten-only clause: omission never licenses
  deletion.
• In the SAME change, name the register in consuming skills' criteria text
  (plugins/claude-config/skills/audit-instructions/reference/criteria.md deletion-class
  checks I4/I5 at minimum) so deletion recommendations consult it.
• Cross-reference from plugins/instruction-placement/context/routing-rubric.md (Gate 0) so
  one concern keeps one adjudication chain; state Gate 0 precedence inside the register.
• Respect the repo/product "two hats" boundary the unhobble skill records when wiring a
  repo-local doc into marketplace-shipped skill surfaces.

Acceptance criteria

• Register doc exists, is non-exhaustive, and states tighten-only + Gate 0 precedence.
• audit-instructions criteria text names the register in the same PR.
• routing-rubric.md cross-reference present; no duplicated hard-deny enumeration.

References

• docs/topics/context-engineering-integration/PLAN.md (Q2, validation record)
• docs/topics/context-engineering-claude-5/design/coverage-matrix.md:36
• plugins/instruction-placement/context/routing-rubric.md

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[kyle-sexton]

Done in #3588, merged to main as ae3aa802. All three acceptance criteria are satisfied:

• docs/conventions/instruction-exception-register/README.md exists, states non-exhaustive and
  tighten-only ("omission never licenses deletion"), and defers to Gate 0 on class membership.
• plugins/claude-config/skills/audit-instructions/reference/criteria.md names the register in
  the same change, on criteria I1, I4 and I5 rather than the I4/I5 minimum this issue asked for.
  I1 was added after the review lane caught the register's consumer table claiming wiring that did
  not exist.
• plugins/instruction-placement/context/routing-rubric.md carries the cross-reference, and the
  hard-deny class list is adopted by reference rather than re-enumerated, so the rubric stays its
  sole owner.

One thing landed beyond this issue's scope, for the same reason: unhobble Phase 4 previously
ended at "everything the ledger did not defend stays deleted", which would leave a protected rule
deleted on silence. It now restores a register-protected rule whether or not the ledger logged
against it.

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