- Add ConflictType enum for categorizing conflict types
- Add ConflictContext dataclass for storing conflict information
- Add ConflictReport dataclass for structured conflict reporting
- Add ConflictResolution enum for resolution strategies
- Implement ThreeWayMergeConflictDetector with standard three-way merge algorithm
- Add automatic conflict resolution heuristics
- Add comprehensive BDD test suite with 20+ test scenarios
- Update CHANGELOG.md and CONTRIBUTORS.md

ISSUES CLOSED: #9558

@@ -0,0 +38,4 @@
+        context.ancestor[field_name] = value
+
+
+@given("parent plan modifies field \"{field}\" to \"{value}\"")

@@ -4,0 +12,4 @@
+__all__ = [
+    "ConflictContext",
+    "ConflictReport",
+    "ConflictResolution",

@@ -0,0 +159,4 @@
+            return conflict.subplan_value
+        elif resolution == ConflictResolution.MERGED:
+            # For merged, return a merged value (implementation-specific)
+            return conflict.parent_value  # Default to parent

@@ -0,0 +174,4 @@
+        ancestor: dict[str, Any],
+        parent: dict[str, Any],
+        subplan: dict[str, Any],
+    ) -> ConflictReport:

@@ -0,0 +225,4 @@
+
+        Args:
+            field_path: Path to the field
+            ancestor_val: Value in ancestor

@@ -0,0 +262,4 @@
+            conflict_type = ConflictType.DELETE_MODIFY
+        elif subplan_deleted:
+            conflict_type = ConflictType.MODIFY_DELETE
+        else:

@@ -15,2 +15,4 @@
 
 ### Fixed
+
+### Added

@@ -0,0 +22,4 @@
+}
+
+
+@given('I create a detector with ancestor {ancestor:s}, parent {parent:d}, and subplan {subplan:d}')

@@ -0,0 +53,4 @@
+    assert k not in context.result.merged_config, f"Key '{k}' not in merged but found as {context.result.merged_config.get(k)!r}"
+
+
+@then('there should be one conflict of type "{t}" for key "{key}"')

@@ -4,0 +9,4 @@
+    "MergeResult",
+    "ThreeWayMergeConflictDetector",
+]
+

@@ -15,2 +15,4 @@
 
 ### Fixed
+
+### Added

@@ -0,0 +22,4 @@
+}
+
+
+@given('I create a detector with ancestor {ancestor:s}, parent {parent:d}, and subplan {subplan:d}')

@@ -0,0 +53,4 @@
+    assert k not in context.result.merged_config, f"Key '{k}' not in merged but found as {context.result.merged_config.get(k)!r}"
+
+
+@then('there should be one conflict of type "{t}" for key "{key}"')

@@ -4,0 +9,4 @@
+    "MergeResult",
+    "ThreeWayMergeConflictDetector",
+]
+

@@ -0,0 +11,4 @@
+  Scenario: ADD_ADD with differing values requires manual intervention
+    When I create a detector with ancestor {}, parent {{"editorCommand": "code"}}, and subplan {{"editorCommand": "vscode"}}
+    And I run conflict detection
+    Then there should be one conflict of type ADD_ADD for key "editorCommand"

@@ -0,0 +22,4 @@
+}
+
+
+@given('I create a detector with ancestor {ancestor:s}, parent {parent:d}, and subplan {subplan:d}')

@@ -0,0 +130,4 @@
+def _split_comma(s: str) -> list[str]:
+    parts, cur, in_q: list[str], str, bool = [], "", False
+    for ch in s:
+        if ch == '"':

@@ -4,0 +12,4 @@
+
+
+def _get_all_from_plan_config():
+    from .plan_config import AutoModeType, ConfigSetting, PlanConfig  # noqa: F401

@@ -0,0 +201,4 @@
+                ct = ConflictType.DELETE_MODIFY  # Subplan added/modified; parent accepted
+
+        return ConflictReport(key=key, conflict_type=ct,
+            context=ConflictContext(ancestor_value=ancestor_val, parent_value=parent_val, subplan_value=subplan_val))

@@ -15,2 +15,4 @@
 
 ### Fixed
+
+### Added

@@ -0,0 +22,4 @@
+}
+
+
+@given('I create a detector with ancestor {ancestor:s}, parent {parent:d}, and subplan {subplan:d}')

@@ -0,0 +104,4 @@
+    summary = context.detector.describe_all()
+    entries = [e for e in summary if e["key"] == key and e["status"] == "CONFLICT"]
+    assert len(entries) == 1, f"Expected one CONFLICT entry for {key}, found {len(entries)}"
+

@@ -0,0 +80,4 @@
+
+            conflict = self._analyse_field(
+                key,
+                str(ancestor_val) if ancestor_val is not None else None,

@@ -0,0 +182,4 @@
+            elif parent_val is None:
+                ct = ConflictType.DELETE_MODIFY  # parent deleted; subplan kept new value
+            elif subplan_val is None:
+                ct = ConflictType.MODIFY_DELETE  # subplan deleted; parent kept new value

@@ -0,0 +201,4 @@
+                ct = ConflictType.DELETE_MODIFY  # Subplan added/modified; parent accepted
+
+        return ConflictReport(key=key, conflict_type=ct,
+            context=ConflictContext(ancestor_value=ancestor_val, parent_value=parent_val, subplan_value=subplan_val))

@@ -14,6 +14,9 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   from the TDD test so both scenarios run as normal regression guards. (#988)
 
 ### Fixed
+

@@ -0,0 +11,4 @@
+  Scenario: ADD_ADD with differing values requires manual intervention
+    When I create a detector with ancestor {}, parent {{"editorCommand": "code"}}, and subplan {{"editorCommand": "vscode"}}
+    And I run conflict detection
+    Then there should be one conflict of type ADD_ADD for key "editorCommand"

@@ -0,0 +22,4 @@
+}
+
+
+@given('I create a detector with ancestor {ancestor:s}, parent {parent:d}, and subplan {subplan:d}')

@@ -0,0 +128,4 @@
+
+
+def _split_comma(s: str) -> list[str]:
+    parts, cur, in_q: list[str], str, bool = [], "", False

@@ -4,0 +11,4 @@
+]
+
+
+def _get_all_from_plan_config():

@@ -0,0 +69,4 @@
+
+    def detect(self) -> MergeResult:
+        """Run the three-way merge and return conflicts plus merged result."""
+        merged: dict[str, Any] = dict(self._get_non_conflicting_fields())