Second round for the flat-alias deprecation. `pr-commits` and
`pr-assign-reviewer` are back-compat aliases with an exact scoped
equivalent, and they were missed by all three buckets of the original
accounting -- which was wrong in both terms: `reopen`/`dependency`/
`reaction` appear only in the doc-comment prose listing the scoped
surface and are not Verb variants at all, so the real count is 17
(7 + 2 + 7 + 1), not 18.
The test for "pure rename" is that an exact scoped form exists AND the
verb is PR-only, so a caller holding just a number can be sent somewhere
unambiguous. Verified rather than assumed: `pr commits` and
`pr assign-reviewer` exit 0, while `issue commits` and
`issue assign-reviewer` exit 2 -- the same code a deliberately bogus
verb returns, which is what makes those 2s mean "no such verb".
That is also why the seven kind-agnostic aliases are untouched here:
each exists as both `issue <verb>` and `pr <verb>`, so refusing them
would remove a capability rather than rename one.
Both run functions are still called from pr_cmd.rs, so nothing becomes
dead code. The enum's block comment enumerates the pure renames by name
and is extended to match -- left alone it would be a stale claim naming
seven of nine.
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