[emme1t]

Description

Fixes #23679.

SimplePropertyGraphStore.upsert_relations() currently ignores updated properties when a relation's (source, label, target) already exists. For example, upserting a KNOWS relation with confidence 0.1 and then 0.9 still returns 0.1.

Remove the early return in LabelledPropertyGraph.add_triplet() so node/relation mappings receive the latest objects. The existing triplet set continues to prevent duplicates, including repeated identical upserts. add_node() already replaces nodes by identity.

Validation

• Unchanged main 619d74664: 2 failed, 8 passed in tests/graph_stores/test_simple_lpg.py; both new sync/async update cases return the stale confidence.
• After the fix: PYTHONPATH=$PWD python -m pytest tests/graph_stores -q --tb=short: 10 passed.
• Tests cover updated relation properties, preserved endpoint properties, unrelated relations between the same endpoints, stable relation/triplet counts, and replay of the updated relation.
• Ruff check/format check and git diff --check: passed.
• Targeted mypy with --follow-imports=skip on both changed files: passed. Full repository typechecking/CI was not run locally.

No dependency or core version change. Separate from shared-endpoint deletion (#23347) and relation-key collisions (#23437).

AI assistance was used for investigation, implementation and regression tests. Verified both baseline failures, reviewed the set/mapping update behavior, and ran the checks above. Submitted as draft for human review.