[v1.0] Preserve correct provenance for nested configuration merges

[codeforester]

Goal

Make Context.config_provenance report the actual winning source for every nested leaf.

Background

The batteries-included profile promises recursive merging and dotted-path provenance. The recursive branch currently calls _merge_mapping() with the global provenance map but without the parent prefix, then updates the correctly-prefixed paths afterward:

base-cli/lib/python/base_cli/config.py

Lines 102 to 120 in 8a93d22

	def _merge_mapping(
	target: dict[str, Any],
	provenance: dict[str, str],
	incoming: Mapping[str, Any],
	source: str,
	) -> None:
	for key, value in incoming.items():
	if not isinstance(key, str):
	raise ConfigurationError("Configuration keys must be strings.")
	previous = target.get(key)
	if isinstance(previous, Mapping) and isinstance(value, Mapping):
	_merge_mapping(target[key], provenance, value, source)
	provenance.update(_leaf_provenance(value, source, key))
	continue
	for path in tuple(provenance):
	if path == key or path.startswith(f"{key}."):
	del provenance[path]
	target[key] = dict(value) if isinstance(value, Mapping) else value
	provenance.update(_leaf_provenance(value, source, key))

.

A merge of {"host": "top", "db": {"host": "one"}} from user, followed by {"db": {"host": "two"}} from project, leaves the value of top-level host unchanged but changes its provenance to project. The resulting map incorrectly reports host=project and db.host=project.

Scope

• Carry the complete dotted prefix through recursive merges.
• Remove stale provenance only inside the replaced subtree.
• Cover recursive mapping-to-mapping, mapping-to-scalar, scalar-to-mapping, and sibling keys with the same leaf name.

Acceptance Criteria

• The reproduction above keeps host=user and sets only db.host=project.
• Context.config_provenance agrees with the final value at every leaf.
• Existing precedence and consumer-owned configuration semantics do not change.
• Regression tests exercise at least three nested levels and repeated leaf names.

Validation

Run the batteries-included configuration tests and the full Python suite.

Non-Goals

Do not add a new precedence model or configuration source.

Project Fields

• Status: Backlog
• Priority: P1
• Area: Python
• Initiative: v1.0 Readiness
• Size: S

Ownership

• Assignee: @codeforester