docs(rules): say what a boundary example is, and unmark a contrast

"Juan y Garcia" reads oddly as a boundary — y is inside P3's carve-out,
not outside the rule. Surveying all 39 markers shows that is the
convention rather than a slip: H1's boundary is "Sir John" (its
given-name-title exception), H2's is "J. Smith" (bare initials, which
its statement excludes), H3's is a title word mid-name. The marker
means the rule's effect does not occur, and the informative case is
almost always the rule's own exception. The preamble now says so.

What was genuinely wrong is that P3 carried two markers meaning
different things. "Mr. Jack Jill" is the contrast half of the H1
one-word pair — no connective is present at all — so it is not a
limit of P3 and no longer claims to be.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: derek73

docs/design/rules.md

@@ -11,7 +11,7 @@ Every example line is EXECUTABLE. The grammar (its executable definition is `tes
     "INPUT" [annotation] →  field="value"  [· boundary]
                             [deviates: #N (today: field="value")]
 
-An `annotation` names a policy, locale (`[ru]`), or extras gate (`[ja+segmenter]`) in the registry beside the test. `· boundary` marks the non-firing example every rule must carry — or the rule declares `no-boundary: <reason>` instead, so skipping the boundary is a recorded decision. `deviates:` states the INTENDED output on the example line while the marker records TODAY's output and the tracking issue; the runner asserts today's output strictly, so a parser change that closes the gap fails the suite until the marker is removed in the same PR. `grep deviates:` on this file is the deviation backlog (deviations from statable rules — coverage gaps are a separate, larger category no grep can see, and contested vocabulary memberships a third, tracked as Open blocks keyed to the vocabulary set in decisions.md).
+An `annotation` names a policy, locale (`[ru]`), or extras gate (`[ja+segmenter]`) in the registry beside the test. `· boundary` marks the non-firing example every rule must carry: an input shaped like the rule's subject where its effect does NOT occur. That is usually the rule's OWN stated exception — H1's given-name title, P3's single-letter carve-out — not an input the rule never reaches, so the exception is executable rather than merely asserted. Or the rule declares `no-boundary: <reason>` instead, so skipping the boundary is a recorded decision. `deviates:` states the INTENDED output on the example line while the marker records TODAY's output and the tracking issue; the runner asserts today's output strictly, so a parser change that closes the gap fails the suite until the marker is removed in the same PR. `grep deviates:` on this file is the deviation backlog (deviations from statable rules — coverage gaps are a separate, larger category no grep can see, and contested vocabulary memberships a third, tracked as Open blocks keyed to the vocabulary set in decisions.md).
 
 ## Not in scope
 
@@ -159,7 +159,7 @@ P3. Rationale: connective words ("y", "of the") bind name words into
       "Juan and Garcia"           →  given="Juan and Garcia"
       "Juan & Garcia"             →  given="Juan & Garcia"
       "Mr. Jack and Jill"         →  family="Jack and Jill"
-      "Mr. Jack Jill"             →  given="Jack"  · boundary
+      "Mr. Jack Jill"             →  given="Jack"
     Both exceptions are about the written FORM, not the word: the
     three-word carve-out counts letters, so a symbol connective joins
     at any length, and it reaches every single-letter connective the