Explain why getFiniteTypes() guard is needed in Pass 2 condition matching

Address reviewer question about why isSuperTypeOf cannot be used for all
types. Conditional expression holders come from multiple sources (param
conditional types, scope merging, assignment handlers, TypeSpecifier
boolean processing). Non-finite condition types from scope merging and
assignment handlers are too broad for isSuperTypeOf matching — e.g.
non-falsy-string incorrectly matches 'filter', or mixed~false matches
false, causing conflicting conditional expressions to produce *NEVER*.
The finite types check restricts Pass 2 to closed sets of concrete
values where subtype matching is safe.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Analyser/MutatingScope.php

@@ -3235,6 +3235,23 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 				// (e.g. 'value1') via equals(), but should match via isSuperTypeOf.
 				// Only attempted when pass 1 found no matches, to avoid conflicts with
 				// broader conditions that have lower certainty from scope merging.
+				//
+				// The getFiniteTypes() guard is necessary because conditional expression
+				// holders are created from multiple sources:
+				// 1. Conditional parameter types (@param conditional types) — these have
+				//    finite condition types like 'value1'|'value2' from TypeCombinator::intersect/remove
+				// 2. Scope merging (generateConditionalExpressions) — condition types can be
+				//    any type like mixed~null, object, non-falsy-string
+				// 3. Assignment handlers — condition types like mixed~false from falsey checks
+				// 4. TypeSpecifier boolean processing — condition types from BooleanAnd/Or
+				//
+				// Using isSuperTypeOf without the finite types guard causes regressions because
+				// non-finite condition types from sources 2-4 are too broad: e.g. a condition
+				// type of non-falsy-string would incorrectly match a narrowed type 'filter',
+				// or a condition type of mixed~false would match false, causing unrelated
+				// conditional expressions to activate and produce conflicting types (*NEVER*).
+				// The finite types check restricts Pass 2 to closed sets of concrete values
+				// (constant strings, booleans, enum cases, etc.) where subtype matching is safe.
 				if (!array_key_exists($conditionalExprString, $conditions)) {
 					foreach ($conditionalExpressions as $conditionalExpression) {
 						foreach ($conditionalExpression->getConditionExpressionTypeHolders() as $holderExprString => $conditionalTypeHolder) {