docs: record constructor equality branch parse limitation

dag/gunbc/recurring_failure_mode/constructor_equality_consumes_the_branch_brace.dag

@@ -0,0 +1,19 @@
+module gunbc.recurring_failure_mode.constructor_equality_consumes_the_branch_brace
+
+import std.types { NonEmptyStr }
+import gunbc.recurring_failure_mode { RecurringFailureMode }
+
+data constructor_equality_consumes_the_branch_brace: RecurringFailureMode = RecurringFailureMode {
+  identity: "constructor_equality_consumes_the_branch_brace" as NonEmptyStr,
+  receipts: [
+    "HARM AND INVALID STATE: an if-condition ending in equality with a constructor name refuses valid nested-match and field-access branch bodies at a Dot token. Source inspection identifies an attempted record-literal parse of the branch brace before the conditional retry; this mechanism is distinct from any claim that a differently interpreted program is accepted. Parenthesizing the equality is a local workaround, not a parser repair. ",
+    "MEASUREMENT SUBJECT: installed arm64 /usr/local/bin/gunbc, SHA256 e713b7eece9b251a26347bcc1565e4d7c1178b7dfc9eb4a861371569600c42a6, observed 2026-09-05. Its source revision is not established; this receipt does not label it origin/main. Each isolated run resolves one source. With type Connective = Conj | NoConnective and type Item { connective: Connective, inferred: Int? }, fn probe(declaration: Item) -> Int { if declaration.connective == NoConnective { match declaration.inferred { Present { value: target } => target Absent => 0 } } else { 0 } } refuses expected expression, found Dot at the inferred field access, emitting zero files. Parenthesizing only the equality emits five files and zero diagnostics. ",
+    "PAIRED BODY VARIATIONS, SAME INSTALLED BINARY: replacing the then-body with literal 1 refuses expected LBrace, found keyword else; replacing it with declaration.inferred ?? 0 refuses expected expression, found Dot. Each corresponding parenthesized equality emits five files with zero diagnostics. None of these three unparenthesized specimens produces an Accepted program with different meaning; this is a bounded observation, not a claim that every related shape refuses. ",
+    "REF-BOUND PAIRED MEASUREMENT: archived release seed built from 03a3b91fb4c1ea7e408df2cb484f475d75080a7f, executable SHA256 8692902cd6540b0cd1bd5f73701c6a3910bb3c87a73110f8125b0c00cdbfa02b, invocation https://app.buildbuddy.io/invocation/5b341ce2-2377-471f-a1ac-47128df431e8. Isolated repository-local fixtures resolve one source. Unparenthesized nested-match and field-access bodies refuse at Dot; each paired parenthesized equality accepts with six emitted files and zero diagnostics. The literal-1 body accepts with or without parentheses on this seed, unlike the separately identified installed binary above. The measured class is therefore the body-token parse failure, not every constructor equality. No differently interpreted Accepted program is established. Earlier /tmp fixtures were rejected by entry admission and provide no parser evidence. ",
+    "AUTHORING LIMIT, NOT A MEASURED REGRESSION: both identified seeds refuse the nested-match and field-access shapes. Unwritable form: fn probe(declaration: Item) -> Int { if declaration.connective == NoConnective { declaration.inferred ?? 0 } else { 0 } }. Accepted replacement: fn probe(declaration: Item) -> Int { if (declaration.connective == NoConnective) { declaration.inferred ?? 0 } else { 0 } }. The searchable diagnostic is expected expression, found Dot. Parentheses allow the author to proceed while preserving the intended condition. ",
+    "RUNG FOUND AT AND CURRENT RUNG: Mitigatable at the measured source-to-Rust boundary: these specimens refuse rather than emit a differently interpreted accepted program, and author-side parentheses avoid the refusal. No parser repair or enrolled prevention is claimed. CEILING: correct parser handling of this measured source grain is decidable; parse_expr_bp_no_brace already carries a branch retry, but parse_prefix errors return before it. A repair must preserve legitimate record-valued conditions. This source trace identifies the missed retry, not a proof that a particular grammar change is correct. ",
+    "NEXT-RUNG TRIGGER: v1.compiler.parse parse_expr_bp_no_brace distinguishes the branch brace before an attempted record parse can abort at a body token. On 03a3b91fb4c1, parse_prefix errors return before the existing swallowed-branch retry. Repair and execute both the constructor-equality conditional and genuine record-literal condition controls; a blanket ban on record expressions in conditions would lose valid syntax. ",
+    "DISPOSITION: filed separately from the generic-inhabitance repair that encountered it. That producer uses parentheses explicitly while this parser deficit remains; the parentheses are not evidence of parser correctness.",
+  ],
+  evidence: [],
+}

dag/gunbc/recurring_failure_mode/roster.dag

@@ -150,6 +150,8 @@ import gunbc.recurring_failure_mode.comparison_keyed_on_part_of_the_identity_it_
 import gunbc.recurring_failure_mode.edit_range_bounded_by_a_neighbour_rather_than_the_target { edit_range_bounded_by_a_neighbour_rather_than_the_target }
 import gunbc.recurring_failure_mode.one_disposition_defined_jointly_by_independent_matches { one_disposition_defined_jointly_by_independent_matches }
 
+import gunbc.recurring_failure_mode.constructor_equality_consumes_the_branch_brace { constructor_equality_consumes_the_branch_brace }
+
 data recurring_failure_mode_roster: List<RecurringFailureMode> = [
   a_type_name_asserts_an_algebra_the_arithmetic_does_not_carry,
   censored_estimator_drops_its_own_tail,
@@ -289,4 +291,5 @@ data recurring_failure_mode_roster: List<RecurringFailureMode> = [
   comparison_keyed_on_part_of_the_identity_it_compares,
   edit_range_bounded_by_a_neighbour_rather_than_the_target,
   one_disposition_defined_jointly_by_independent_matches,
+  constructor_equality_consumes_the_branch_brace,
 ]