Give each restated rule one owner

[alanhc]

Eight rules were written out in two skills each, which is the shape
references/prose-register.md warns about: a rule copied to a second place is
a rule that can drift. Each now sits with the skill that owns the mechanism,
and the second site names that skill rather than restating it.

What moved

Rule	Kept by	Routes from
The GDB stub's refusal of x86_64	elfuse-debug	elfuse-guest-abi
What check-atomics.py cannot see	elfuse-conventions	elfuse-security
A proof binds the arithmetic, not its callers	elfuse-verify	elfuse-security
The lock ordering record	elfuse-syscall	elfuse-conventions, elfuse-refactor, elfuse-security
The change-area-to-command table	elfuse-verify	elfuse-syscall, elfuse-refactor
Recompute a number, take the baseline first, name the lane that could not run	elfuse-verify	elfuse-refactor
Where a new file or shared declaration goes	elfuse-conventions	elfuse-syscall

Two skills also stated a rule twice inside themselves: elfuse-security on the
lock record, once in the shared-pages rule and once in the gate list beneath
it, and elfuse-refactor on make lint never having been clean.

What this does not do

It does not make the skills shorter. 2234 lines to 2229, because a pointer
costs about what the restatement cost. The saving is one home per rule rather
than bytes.

The volume is in elfuse-conventions at 402 lines, elfuse-security at 310
and elfuse-guest-abi at 291, and there it is subject matter rather than
repetition. Cutting it means merging skills or dropping sections, which changes
which skill fires on which task, so it is a different change from this one.

One candidate is left in place deliberately. "This skill is a working summary.
These are tracked and survive a fresh clone, so prefer them when the two
disagree:" appears verbatim in five skills, and looks like the clearest
boilerplate in the set. Skills load independently, so a reader who loaded only
elfuse-debug would lose what its authoritative sources list is for.

Verification

make check-skill-refs resolves every path, target, section and
cross-reference across the 12 files, and scripts/check-commit-log.sh accepts
all five commits. Documentation only: no build or test target reads these
files.

---

Summary by cubic

Consolidates duplicated rules so each has a single owning skill. Eight rules were written out in two skills each, and two skills stated a rule twice within themselves; now each rule sits with the skill that owns its mechanism, and other sites name that skill instead of restating it, so a rule can no longer drift between copies.

• elfuse-syscall keeps the lock ordering record, elfuse-verify keeps the validation table, proof limits, and reporting rules, elfuse-conventions keeps file placement and the check-atomics.py blind spot, and elfuse-debug keeps the GDB stub refusal.
• Skills stay nearly the same length (2234 → 2229 lines) because a pointer costs about what the restatement did; the win is one home per rule, not fewer bytes.
• One boilerplate block ("This skill is a working summary...") deliberately remains in five skills since skills load independently and a reader of only one would lose what its sources list is for.
• Documentation only; make check-skill-refs resolves every path, target, section, and cross-reference across the 12 files.

^{Written for commit a7f6cac. Summary will update on new commits.}

[alanhc]

Rebased onto main; the conflicts were in elfuse-refactor/SKILL.md, which Record what this refactor pass taught (3bcd930) rewrote wholesale. Resolved by re-landing this PR's edits against the new structure: the lock bullet in "Preserve the boundaries" now routes to elfuse-syscall instead of restating the ordering-comment rule, and the obsolete "Three cases where I only moved code is wrong" list is dropped since "Route the change first" already covers it.

cubic's two findings, both folded into Give the lock ordering record one owner:

1. elfuse-security:164 — reworded to "which the gate below fails for being missing".
2. elfuse-conventions:237 — dropped the restated "before its second module" condition, which was weaker than elfuse-syscall's actual rule (a lock enters the record as soon as it exists). Now routes to elfuse-syscall for the condition too, not just the record's location.

[jserv]

I defer to @henrybear327 for confirmation.