fix(parser): match block continuation parsing

CHANGELOG.md

@@ -7,7 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-Nothing yet.
+### Fixed
+
+- Treat more-indented plain scalar continuation lines that start with `-` as
+  text unless they appear at a known sequence-entry indentation. This fixes
+  OpenAPI-style `allOf` descriptions while preserving nested block sequences
+  such as `- - 123`.
+- Parse explicit scalar keys whose `:` value starts a same-line mapping and
+  continues with indented mapping siblings, matching large OpenAPI schema keys.
 
 ## [0.1.0] - 2026-06-05
 

Sources/Parsing/Scanner.Helpers.swift

@@ -138,14 +138,14 @@ extension PureYAML.Parsing.Scanner {
             guard !probe.isAtEnd, !isLineBreak(probe.peek()), probe.peek() != "#" else {
                 return value
             }
-            guard !isBlockEntry(probe) else {
-                return value
-            }
 
             let baseIndentation = plainScalarContinuationBaseIndentation(state: state)
             guard indentationWidth > baseIndentation else {
                 return value
             }
+            if isBlockEntry(probe), state.validImplicitIndentation.contains(indentationWidth) {
+                return value
+            }
 
             var continuationState = state
             continuationState.reader = probe

Sources/Parsing/TokenEventParser.Helpers.swift

@@ -30,6 +30,13 @@ extension PureYAML.Parsing.TokenEventParser {
         if properties == .none, canParsePlainScalarWithContinuation(after: valueIndicator) {
             return try parsePlainScalarWithContinuation(properties: properties)
         }
+        if cursor.current?.kind.isMappingKey == true, hasNodeOnSameLine(after: valueIndicator) {
+            return try parseBlockMapping(
+                properties: properties,
+                includeIndentedContinuation: true,
+                minimumColumn: cursor.current?.mark.column,
+            )
+        }
         if properties != .none || hasNodeOnSameLine(after: valueIndicator) {
             return try parseNode(properties: properties)
         }

Tests/CollectionCompatibilityFixtures.swift

@@ -166,6 +166,39 @@ enum CollectionCompatibilityFixtures {
                 ]))),
             ])),
         ),
+        SuccessCase(
+            name: "mapping value with indentless sequence of inline mappings",
+            yaml: """
+            schema:
+              allOf:
+              - $ref: '#/components/schemas/ErrorCategory'
+              - description: An integer value that specifies the category of a query
+                  failure error. Values include 1 - System, 2 - User, and 3
+                  - Other.
+            """,
+            expected: .mapping(.init([
+                .init(key: "schema", value: .mapping(.init([
+                    .init(key: "allOf", value: .sequence([
+                        .mapping(.init([
+                            .init(
+                                key: "$ref",
+                                value: .string("#/components/schemas/ErrorCategory"),
+                            ),
+                        ])),
+                        .mapping(.init([
+                            .init(
+                                key: "description",
+                                value: .string(
+                                    "An integer value that specifies the category of a query "
+                                        + "failure error. Values include 1 - System, 2 - User, and 3 "
+                                        + "- Other.",
+                                ),
+                            ),
+                        ])),
+                    ])),
+                ]))),
+            ])),
+        ),
     ]
 
     static let parseErrors: [ParseErrorCase] = [

Tests/ComplexMappingKeyParsingTests.swift

@@ -84,6 +84,34 @@ struct ComplexMappingKeyParsingTests {
         #expect(value.rootMapping?["[\"a\", \"b\"]"] == nil)
     }
 
+    @Test("Parses explicit scalar keys with same-line mapping values")
+    func test_parsesExplicitScalarKeysWithSameLineMappingValues() throws {
+        let value = try PureYAML.parse("""
+        ? __stringMin14PatternS3Captions
+        : minLength: 14
+          pattern: ^((s3://(.*?)\\.(srt|SRT))|(https?://(.*?)\\.(srt|SRT)))$
+          type: string
+        next: done
+        """)
+        let key = PureYAML.Model.Key.string("__stringMin14PatternS3Captions")
+
+        #expect(value == .mapping(.init([
+            .init(keyNode: key, value: .mapping(.init([
+                .init(key: "minLength", value: .int(14)),
+                .init(
+                    key: "pattern",
+                    value: .string("^((s3://(.*?)\\.(srt|SRT))|(https?://(.*?)\\.(srt|SRT)))$"),
+                ),
+                .init(key: "type", value: .string("string")),
+            ]))),
+            .init(key: "next", value: .string("done")),
+        ])))
+        #expect(value.rootMapping?[key]?.rootMapping?["minLength"] == .int(14))
+        #expect(value.rootMapping?[key]?.rootMapping?["type"] == .string("string"))
+        #expect(value.rootMapping?["next"] == .string("done"))
+        #expect(value.rootMapping?["minLength"] == nil)
+    }
+
     @Test("Expands merged mappings with complex-key local overrides")
     func test_expandsMergedMappingsWithComplexKeyLocalOverrides() throws {
         let value = try PureYAML.parse("""

docs/rules/research-compatibility.md

@@ -43,3 +43,24 @@ Every compatibility test must pin at least one of:
 - exact validation issue;
 - exact path-aware decoding or encoding error;
 - exact required absence check for fields that must not appear.
+
+## Parser Compatibility Lessons
+
+YAML compatibility is parser-state compatibility, not only value-model
+compatibility. Indicator characters such as `-`, `?`, and `:` are meaningful
+only after indentation, flow depth, and the current parser production are taken
+into account.
+
+When fixing scanner or parser behavior:
+
+- preserve tests for the exact production corpus shape that failed, not only a
+  smaller feature in isolation;
+- combine interacting YAML features in one regression fixture when the bug
+  requires their interaction;
+- keep implementation fixes grammar-level and content-independent; never branch
+  on corpus file names, OpenAPI field names, vendor names, schema prefixes, or
+  other production-data fingerprints;
+- for plain scalar continuation bugs, cover both sides explicitly:
+  - a more-indented continuation line that starts with an indicator but remains
+    text;
+  - a same-context indicator line that must remain a collection item.