fix: synthetic dataset generation for ≥200 rows

[Copilot]

Gemini (free tier) reliably generates ≤100 rows per call but returns only ~71–76% of rows for larger requests, exhausting all retries. A second bug caused the exhausted-retry path (no exception) to return [] instead of data, producing "Batch 1 complete: 0/200 total rows".

Changes

src/synthetic/generator.py

• Auto sub-batching: requests above _LLM_MAX_ROWS_PER_CALL = 100 are split into sequential sub-batches of ≤100 rows. A 200-row request now makes 2 reliable calls instead of 3 failing ones, reducing quota burn.
• Fixed empty-return bug: tracks best_rows across retry attempts; when the retry loop exhausts without an exception, fills from the best partial LLM result + mock data rather than returning [].

# Before — silent data loss
return [], logs  # hit when all retries got < 80% rows with no exception

# After — always returns requested count
if best_rows:
    records = self._coerce_types(best_rows, schema)
    ...
    if len(records) < num_rows:
        records.extend(self._generate_mock_data(schema, num_rows - len(records)))
    return records[:num_rows], logs
return self._generate_mock_data(schema, num_rows), logs

tests/backend/api/test_synthetic_backend.py

• Added TestGenerateBatchLargeRowHandling with 6 tests covering: sub-batch triggering, single-call at threshold, mock-fill fallback, no-empty-return guarantee, and best-partial-rows retention.

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Project	Deployment	Actions	Updated (UTC)
data-forge-test	Ready	Preview, Comment	Mar 11, 2026 3:48am

[github-actions]

🧪 PR Test Summary

Suite	Status
Backend — Unit	✅ success
Backend — API	✅ success
Backend — Security	✅ success
Frontend — Coverage	✅ success

Coverage thresholds: Statements 80% · Branches 70% · Functions 75% · Lines 80%

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updated for commit: bb66b01 by action🐍