Share P6's particle tail and the maiden take's candidates as one predicate each (#610)

[derek73]

Closes #610.

Summary

• _pieces.particle_tail: P6's walk, read off roles, now asked by both post_rules' attachment and assign's given-part credential run (Should a name word after a credential join the suffix? John Smith PhD Jones reads middle Smith PhD #602). Before, these were two walks that agreed only through the run's roles. No reading moves, and family-comma parses get slightly cheaper (Smith, John 183 → 180 frames).

• _pieces.trailing_candidates: the maiden take's choice of clause words, now written beside the peel whose admissions it has to cover. It replaces _group._clause_tail_word and an inline numeral clause.

• A bug the shared predicate fixed. The fork recognizes a numeral in no wordlist (VI) by its shape, as the walk's last piece. A period title or the merged Ph. D. standing behind it leaves it last without standing at the end of the name. The old copy admitted the numeral only as the clause's last word, so:

  Input	master	this PR
  Jane Doe nee Smith VI Prof.	maiden Smith VI, title Prof.	maiden Smith, suffix VI, title Prof.
  Jane Doe nee Smith VI Ph. D.	maiden Smith VI	maiden Smith, suffix VI Ph. D.

  Both now match the clause-free name (John Smith VI Prof. gives suffix VI), as rules.md#M2 says they should. V and III already worked because they're in the vocabulary.

How it's guarded

• A sweep test checks, at the take itself on the unjoined pieces it's handed, that every word tail_reading takes from the clause-free view is at or after the candidates' cut. 37,044 clauses, 0 misses. The recorded negative control is the loop Rethink the maiden-marker rule (M2): a marker stands after the current name and takes words up to the trailing suffix run #601 shipped: 432 misses, all this numeral class.
• Equivalence against master over 95,813 texts under three policies (every field, ambiguity and initials string): 10 readings moved, all this class. The review's own fuzz, 1.3M parses across 36 parser configurations including custom lexicons, found 0 differences from particle_tail. Its 200k random fuzz moved 11 readings, all the numeral class.

Docs

• rules.md M2 gains the VI Prof. example. decisions.md#M2 gains a Two stages hand-copy each other's trailing-word logic after #601/#602; share one predicate each #610 entry. mechanisms.md#ONE-PREDICATE-PER-QUESTION names both new instances, and its Field notes record the review's catch: the first sweep test ran on post-join pieces the take never sees.
• AGENTS.md gains two Workflow-level paragraphs:
  • record the check that would have caught a defect, in the same PR, where the next session meets it, with where each kind of lesson goes;
  • sweep spellings as well as comma shapes and orders: a class reached by vocabulary is also reached by shape. Roman numerals are the case: ii–iv are listed, i/v are listed but initial-shaped, vi and up are in no list.

Test plan

• uv run pytest (11,393 passed), also run without namedivider
• uv run mypy, uv run ruff check
• sphinx-build -b doctest docs, python -m doctest README.rst
• differential gate at 1.4.0, 2.0.0, 2.1.0, 2.2.0 and 2.3.0, all exit 0, no moved shapes
• review pass, with its finding fixed in 2db7ae0

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.98%. Comparing base (8a8459a) to head (2db7ae0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #612   +/-   ##
=======================================
  Coverage   98.97%   98.98%           
=======================================
  Files          45       45           
  Lines        4214     4227   +13     
=======================================
+ Hits         4171     4184   +13     
  Misses         43       43           

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