SEP-1727: Guard deep_dict_update against self-merge to prevent list doubling

[Copilot]

When the selected YAML profile is the base profile, YamlPrefixConfigSettingsSource passes the same dict object as both operands to deep_dict_update. Every list-valued leaf is concatenated with itself, doubling entries. Against sidecar/settings.yaml this prevents SEPSettings from constructing at all (duplicate resolution step validation error).

Changes

• app/core/utils/dict.py: Added is identity guard at the top of deep_dict_update. When both operands are the same object, the merge is a no-op — correct because every branch (scalar reassign, dict recurse, list concat) is already idempotent except list concat. The guard runs on each recursive step, so nested YAML anchors shared between two otherwise-distinct profiles are also covered.

def deep_dict_update(main_dict, update_dict):
    if main_dict is update_dict:
        return
    ...

• tests/app/core/utils/test_dict.py: Added test_deep_dict_update_self_merge_is_noop — passes the same dict as both arguments and asserts lists are not doubled.
• tests/app/core/test_config.py: Added test_yaml_prefix_config_settings_source_base_profile — selects the base profile through YamlPrefixConfigSettingsSource and asserts the resulting data matches the declared block exactly. Added a list field to the mock_yaml_data fixture to exercise the doubling path.

[Copilot]

Pull request overview

This PR addresses a configuration-loading edge case where YamlPrefixConfigSettingsSource can pass the same dict as both operands to deep_dict_update, causing list-valued leaves to be concatenated with themselves (doubling entries) and potentially preventing SEPSettings construction.

Changes:

• Add an identity (is) guard to deep_dict_update to make self-merges a no-op.
• Add a unit test ensuring deep_dict_update(d, d) does not double lists.
• Add a config-source regression test ensuring selecting the base YAML profile does not double list values.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
app/core/utils/dict.py	Adds a self-merge guard to prevent list doubling during recursive merges.
tests/app/core/utils/test_dict.py	Adds regression coverage for self-merge behavior in deep_dict_update.
tests/app/core/test_config.py	Adds regression coverage for base-profile selection in YamlPrefixConfigSettingsSource and exercises list handling.

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[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
app/core/utils
dict.py
app/sep
inventory.py
app/sep/sync/syncers
pmm.py
Project Total

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