SNOW-2306184: config refactor - connection level overwrite for config merging

Author: sfc-gh-mraba

src/snowflake/cli/api/config_ng/__init__.py

@@ -16,6 +16,8 @@
 Enhanced Configuration System - Next Generation (NG)
 
 This package implements a simple, extensible configuration system with:
+- Two-phase resolution: file sources use connection-level replacement,
+  overlay sources (env/CLI) use field-level merging
 - List-order precedence (explicit ordering in source list)
 - Migration support (SnowCLI and SnowSQL compatibility)
 - Complete resolution history tracking
@@ -26,8 +28,10 @@
     ConfigValue,
     ResolutionEntry,
     ResolutionHistory,
+    SourceType,
     ValueSource,
 )
+from snowflake.cli.api.config_ng.presentation import ResolutionPresenter
 from snowflake.cli.api.config_ng.resolution_logger import (
     check_value_source,
     explain_configuration,
@@ -71,9 +75,11 @@
     "ResolutionEntry",
     "ResolutionHistory",
     "ResolutionHistoryTracker",
+    "ResolutionPresenter",
     "show_all_resolution_chains",
     "show_resolution_chain",
     "SnowSQLConfigFile",
     "SnowSQLEnvironment",
+    "SourceType",
     "ValueSource",
 ]

src/snowflake/cli/api/config_ng/core.py

@@ -26,9 +26,22 @@
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, field
 from datetime import datetime
+from enum import Enum
 from typing import Any, Callable, Dict, List, Literal, Optional
 
 
+class SourceType(Enum):
+    """
+    Classification of configuration sources by merging behavior.
+
+    FILE sources use connection-level replacement (later file replaces entire connection).
+    OVERLAY sources use field-level overlay (add/override individual fields).
+    """
+
+    FILE = "file"
+    OVERLAY = "overlay"
+
+
 @dataclass(frozen=True)
 class ConfigValue:
     """
@@ -104,6 +117,15 @@ def source_name(self) -> SourceName:
         """
         ...
 
+    @property
+    @abstractmethod
+    def source_type(self) -> SourceType:
+        """
+        Classification of this source for merging behavior.
+        FILE sources replace entire connections, OVERLAY sources merge per-field.
+        """
+        ...
+
     @abstractmethod
     def discover(self, key: Optional[str] = None) -> Dict[str, ConfigValue]:
         """