refactor(kt-graph,worker-nodes): route auto_build through WorkerGraphEngine

[charlie83Gs]

Summary

• auto_build_graph was reaching into WriteNode/Edge/Dimension repos and Qdrant directly, duplicating key derivation, edge-rekey logic and Qdrant plumbing. The rest of the worker-nodes pipeline already goes through WorkerGraphEngine — auto_build was the lone divergent path and risked silently bypassing future engine side-effects (hooks, counters, telemetry).
• Add batch + lifecycle methods on WorkerGraphEngine so the engine remains the single source of write-routing truth, then route auto_build through them.

New on WorkerGraphEngine (libs/kt-graph/src/kt_graph/worker_engine.py)

• bulk_create_nodes(specs) — accepts list[NodeCreateSpec], upserts each into write-db, populates the in-memory node cache, returns BulkCreateResult per spec. No commit, no Qdrant.
• bulk_upsert_nodes_to_qdrant(items) — single batched Qdrant call (chunked at 200 internally by QdrantNodeRepository.upsert_batch).
• delete_node(node_id) / delete_node_qdrant(node_uuid) — write-db node delete + best-effort Qdrant cleanup.
• delete_edge_by_key(edge_key) — write-db edge delete with cache eviction.
• absorb_node(loser_id, winner_id) — composite: dimension transfer, edge re-key, fact merge, loser delete. Returns AbsorbResult so caller can do Qdrant cleanup outside any savepoint.

All new methods leave transaction control to the caller (no commit, no begin_nested) and keep Qdrant calls non-transactional — matches the per-seed semantics auto_build was already relying on.

auto_build (services/worker-nodes/src/kt_worker_nodes/workflows/auto_build.py)

• _promote_seeds builds a NodeCreateSpec per active seed, calls bulk_create_nodes inside a per-seed savepoint, marks the seed promoted, then issues one batched bulk_upsert_nodes_to_qdrant outside savepoints. Drops direct imports of WriteNodeRepository, make_node_key, key_to_uuid, QdrantNodeRepository.
• _absorb_merged_nodes resolves loser/winner UUIDs and calls engine.absorb_node inside a savepoint, then engine.delete_node_qdrant outside. Drops direct imports of WriteEdgeRepository, WriteDimensionRepository, make_edge_key.
• _check_fact_stale_nodes unchanged.

Seed lifecycle (get_promotable_seeds, mark_seed_promoted, get_merged_promoted_seeds, clear_promoted_node_key, get_seed_fact_ids) stays in WriteSeedRepository — seeds are not graph entities.

Tests

• New libs/kt-graph/tests/test_worker_engine_bulk.py — 17 unit tests covering all 6 new methods, including absorb-node happy path, missing loser/winner, self-edge, no-commit / no-Qdrant invariants.
• services/worker-nodes/tests/test_merge_absorption.py rewritten — mocks the engine seam (WorkerGraphEngine.absorb_node, delete_node_qdrant) instead of three repo classes. Engine internals are now covered by the engine's own tests.

Test plan

• uv run --project libs/kt-graph pytest libs/kt-graph/tests/ --ignore=libs/kt-graph/tests/integration — 43 passed
• uv run --project services/worker-nodes pytest services/worker-nodes/tests/ --ignore=services/worker-nodes/tests/integration — 122 passed
• ruff check + ruff format clean on changed files
• CI green

🤖 Generated with Claude Code

[charlie83Gs]

Merged locally; switching to local-iteration mode (no remote PRs for now).

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