Fallback when region_order is unsatisfiable for lvl2 assembly and add warning

[Gonza10V]

Motivation

• Make lvl2 assembly more robust when a provided region_order constraint cannot be satisfied by trying a relaxed search and continuing if a compatible route exists.

Description

• If CompatibilitySelector returns no route due to region_order, attempt a second selection without the region_order constraint and proceed if that returns a route, collecting a warning in warning_logs when this fallback is used.
• Include warning_logs in the returned StageResult logs for blocked, missing-input, and success outcomes so the user is informed of the relaxed ordering decision.
• Stop treating region_order specially in _extract_region_identities so region identities are discovered from constraints or the module definition consistently.
• Add unit test test_assembly_lvl2_incomplete_region_order_falls_back_with_warning to verify the fallback occurs and a warning is emitted.

Testing

• Ran the lvl2 assembly unit tests in tests/unit/stages/test_assembly_lvl2.py including the new test_assembly_lvl2_incomplete_region_order_falls_back_with_warning test, and they all passed.
• The new test asserts that the stage succeeds, a route is selected, and a warning containing "Unable to satisfy region_order constraint" appears in the logs.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle empty region_order in fallback check

The new fallback only runs when constraints.get("region_order") is truthy, so a provided but empty region_order ([]) skips the relaxed retry and still returns BLOCKED even when a compatible route exists without ordering constraints. Since this commit’s behavior change is to recover from unsatisfiable region_order values, the empty-list case is an unsatisfied constraint that should also trigger the fallback path and warning.

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