Correct AGENTS.md's particles.py bullet to rules.md#P1's one-site fold

AGENTS.md

@@ -275,7 +275,7 @@ Most modules define a `frozenset` of known name pieces; `capitalization.py` and
 
 - `titles.py` — `TITLES` (prenominals) and `GIVEN_NAME_TITLES` (e.g. "Sir", which treat the following name as given, not family)
 - `suffixes.py` — `SUFFIX_ACRONYMS` (with periods, e.g. "M.D.") and `SUFFIX_WORDS` (e.g. "Jr."), plus `GLUED_HONORIFICS` (#308), the subset of `SUFFIX_WORDS` the peel may split off the END of a name token — a separate, harsher set, since the glued position has no writer-drawn boundary to lean on
-- `particles.py` — `PARTICLES` (family-name particles, e.g. "de", "van") and `NON_GIVEN_NAME_PARTICLES`, the curated subset that is *never* a standalone given name (a name whose opening PIECE is one of them, standing alone, is all surname — "de Mesnil" — under EVERY `name_order` since #359, and the degenerate bare "de" with nothing to fold into still stays as it is. What post_rules rule 1b enforces is one clause wider than the leading shape, and reading it as leading-only is how the FAMILY_FIRST bug got in: where a member stands ALONE as a piece, either opening the name or in the given position, the name is left with no given name at all — the given and the middles fold into the family. Two shapes, one repair — opening the name it pulls the rest in, and in the given position (`"Mesnil de"` under `FAMILY_FIRST`, where the given position is the trailing piece) it folds into the family beside it. So the rule asks by opening POSITION, read off `pieces`, as well as by the GIVEN role; the role test alone caught both shapes only because under the default order the opening piece IS the given. It is a lone PIECE throughout, and stating it any wider is false: under `FAMILY_FIRST` the given position of `Juan de la Vega` holds the whole chain `de la Vega`, a three-token piece rather than a lone particle, so 1b declines and reports it — #359 records that case as working as intended — and the degenerate bare `de` keeps given `de` because it has nothing to fold into. (`Sir de Mesnil` reported given `de Mesnil` and no family at all in the default order, which was the same guard declining on a chained piece; #367 removed the chain rather than touching this rule — a title is now transparent to the leading-particle exception, so the piece is lone again, 1b fires, and the name reads family `de Mesnil` like the untitled form.) A leading particle OUTSIDE the set is genuinely order-dependent and still splits — "van Gogh" is family "van", given "Gogh" under both family-first orders — since a word that CAN be a given name leaves `name_order` a real question to answer; what the set decides under any of the three orders is that such a leading particle records a `PARTICLE_OR_GIVEN` ambiguity and one inside it records none); `Lexicon.particles_ambiguous` is its complement within `PARTICLES`, so the two mark OPPOSITE sets — see the flip warning in `docs/migrate.rst` before translating either
+- `particles.py` — `PARTICLES` (family-name particles, e.g. "de", "van") and `NON_GIVEN_NAME_PARTICLES`, the curated subset that is *never* a standalone given name. What the subset licenses is rules.md#P1's fold in `post_rules` (the "rule 1b" of older issue comments — decisions.md maps the old numbers), and the fold has ONE site: the piece that OPENS the name. A lone never-given particle there, with at least one more name word behind it, starts the family. Titles do not move the opening position (rules.md#P4), so `Sir de Mesnil` reads family `de Mesnil` under every `name_order`, as `de Mesnil` does. How far the fold reaches depends on the order the name was read under: by default it takes the rest of the name (`de Mesnil Jean` → family `de Mesnil Jean`); under either family-first order it takes the particle run plus ONE name unit and lays the rest out by the order (`de Mesnil Jean` → family `de Mesnil`, given `Jean`); after a family comma it takes the rest of that part whatever the order (`Smith, de Mesnil Jean` → family `Smith de Mesnil Jean`). The leading particle stays a lone piece for the fold to find — `group` does not chain it forward, and the fold walks the particles after it itself — so `de la Vega` reads family `de la Vega` under all three orders. The GIVEN position is not a site. It was a second one until #467, which removed it because under a family-first order that slot holds what the caller DECLARED to be the given name: `Mesnil de` under `FAMILY_FIRST` or `FAMILY_FIRST_GIVEN_LAST` reads given `de`, family `Mesnil`. Nor is a particle inside the name: `Juan de la Vega` under a family-first order reads family `Juan`, given `de la Vega`, with no ambiguity recorded — what the vocabulary forbids is the bare particle as a given name, not a name part that begins with one. A bare `de` has nothing to fold into and is placed by position like any one-word name: given `de` by default, family `de` under both family-first orders. A leading particle OUTSIDE the set is left to position — `van Gogh` is given `van`, family `Gogh` by default and family `van`, given `Gogh` under both family-first orders — and records a `PARTICLE_OR_GIVEN` ambiguity under all three; a never-given particle opening the name records none (`de Mesnil`), and neither does an ambiguous one inside it (`Vincent van Gogh`). `Lexicon.particles_ambiguous` is its complement within `PARTICLES`, so the two mark OPPOSITE sets — see the flip warning in `docs/migrate.rst` before translating either
 - `bound_given_names.py` — `BOUND_GIVEN_NAMES` (bound given-name prefixes, e.g. "abdul", "abu"); a group-stage rule joins the first non-title piece to its following piece before roles are assigned, reserving a family word unless a family comma has already fixed it or a given-name title stands ahead (#369, rules.md#P5) (v1's `_join_bound_first_name`, ported into `_pipeline/_group.py` and gone from the tree — the v1 descriptions further down are history, not current code)
 - `conjunctions.py` — `CONJUNCTIONS` (e.g. "and", "of") used to chain multi-word titles and to join name parts (rules.md#P3), plus `CONJUNCTIONS_AMBIGUOUS` (#383/#479), the subset of single cased letters that read as an INITIAL in a name written wholly in one case — a marker set with no v1 `Constants` attribute of its own, so the only v1 knob that reaches it is deleting the conjunction
 - `maiden_markers.py` — `MAIDEN_MARKERS` (e.g. "née", "geb.") routing the following name to `maiden`