test(#260): regression test — validator-rejected ingest creates no table

[LukasWodka]

Summary

#260 (orphaned table on validator rejection) is already fixed on develop — create_table was deferred out of __init__ to after validate_data passes (_table_schema stashed in __init__, table created in _ingest_with_lock). That fix shipped without the regression test its acceptance criteria called for. This adds it.

tests/test_ingest_atomicity.py pins the ordering:

• a validator-rejected ingest raises and leaves NO table — database.create_table is never called, so a rejected ingest is idempotent and doesn't block the next attempt with the "table already exists … drop it" guard (the original bug: validator-rejected ingest leaves an orphaned table; no rollback blocks the next ingest #260 symptom);
• a clean validation still creates the table — the deferral didn't break the happy path.

Both pass on develop. Independent of the open P5 refactor stack (new file, no overlap).

Closes #260.

🤖 Generated with Claude Code

[LukasWodka]

👋 Heads-up — Code review queue is at 17 / 8

Above the WIP limit. The team convention is to review existing PRs before opening new work.

Open PRs currently in Code review (oldest first):

• .github#57 — fix(fr-gate): pass items at or beyond the required stage · author: @aptracebloc · no reviewer assigned
• backend#806 — feat(#805): store & distribute contributor tokenizer as a model artifact (Task 1 — backend) · author: @shujaatTracebloc · reviewer: @aptracebloc
• backend#807 — Release: staging → master (16.06.2026) · author: @aptracebloc · no reviewer assigned
• backend#808 — fix(#731): edge-resources missing-hardware guard keys off effective memory · author: @aptracebloc · no reviewer assigned
• cli#78 — fix(dataset rm): delete staging files from a uid-65532 pod, not jobs-manager (Release v0.3.10 (ingestion hardening + path-traversal fix + single-label preflight) #259) · author: @LukasWodka · no reviewer assigned
• cli#79 — chore(schema): re-sync vendored ingest.v1.json from data-ingestors master · author: @LukasWodka · no reviewer assigned
• client-runtime#108 — fix(authz): match ingest table prefixes at a segment boundary (close cross-tenant straddle) · author: @LukasWodka · no reviewer assigned
• client-runtime#114 — fix(jobs): cap training Job backoffLimit to stop crashloops starving the cluster · author: @saadqbal · no reviewer assigned
• data-ingestors#270 — docs(releasing): correct ingestor rollout — floating tag + imagePullPolicy=Always, not INGESTOR_IMAGE_DIGEST rewrite · author: @saadqbal · no reviewer assigned
• data-ingestors#275 — refactor(P5b): extract the cross-ingest table lock into TableLock · author: @LukasWodka · no reviewer assigned

Pull from review before opening new work. (This is a nudge from the kanban WIP check, not a block.)