docs: add is_leading_title() gotcha to AGENTS.md

The leading period-abbreviation title inference (#109, docs/usage.rst)
was undocumented in AGENTS.md's Gotchas section despite being a subtle,
position-dependent rule distinct from is_title().

Author: derek73

AGENTS.md

@@ -128,6 +128,8 @@ Add a dedicated `copy.deepcopy()` round-trip test for it too (see `test_regexes_
 
 **Titles permanently shadow first names — be conservative** — any word in `TITLES` is always consumed as a title and can never be parsed as a first name. `"Dean"` is the canonical example: it's a common academic title *and* a common given name, so it is intentionally absent from the default titles (see `docs/customize.rst` — users who need it add it via opt-in `Constants`). Before adding a word to `TITLES`, ask: "Could this plausibly be someone's given name in any culture?" If yes, don't add it globally; it belongs in caller-supplied `Constants` instead. This same caution applies to international honorifics — `Prince`, `Sheikh`, `Frau` are all first names in some contexts.
 
+**`is_leading_title()` infers titles beyond the `TITLES` set, but only in leading position** — an unrecognized multi-letter word ending in a single trailing period (matched via the `period_abbreviation` regex, `{2,}` letters) is treated as a title when it appears before the first name is set, e.g. `"Major. Dona Smith"` → `title='Major.'`. It's distinct from `is_title()` and does not mutate `C.titles`, so the periodless form (`"Major"`) is unaffected elsewhere. The `{2,}` length requirement — not a separate initials check — is what excludes single-letter initials like `"J."` from being swallowed as titles; the same word after the first name is left as a middle name. (#109; see `docs/usage.rst` "Leading Period-Abbreviation Titles")
+
 **Cyrillic suffix regexes need `re.I` even when the pattern is suffix-only** — a Latin title-cased word (`Ivanovich`) keeps its suffix lowercase, so `re.I` seemed skippable; but an irregular Cyrillic suffix can be nearly the whole word (`ильич`), so title-casing capitalizes into the suffix itself (`Ильич`). `east_slavic_patronymic_cyrillic` shipped without `re.I` on the Latin reasoning and silently failed on capitalized irregular forms — don't assume Latin's title-case safety transfers to Cyrillic. (#185)
 
 **`suffix_not_acronyms` vs `is_an_initial` tension** — single-letter roman numeral suffixes (`i`, `v`) are in `suffix_not_acronyms` but also match the `is_an_initial` regex (single uppercase letter), so `is_suffix()` rejects them. Two separate code paths need context-aware workarounds: (1) suffix-comma detection uses `are_suffixes_after_comma()` which bypasses `is_suffix()` for `suffix_not_acronyms` members; (2) lastname-comma post-comma parsing uses `is_suffix_at_lastname_comma_end()` which only fires when `nxt is None` and `len(parts)==2` (no `parts[2]` suffix segment). See issues #136, #144.