fix: batch DeleteTree now enforces emptiness check and cleans up subtree storage (H1, H2)

[QuantumExplorer]

Summary

Two related fixes for batch DeleteTree operations:

H2 — Emptiness check: Before apply_body runs, each DeleteTree op is now checked for subtree emptiness when allow_deleting_non_empty_trees is false. Standard Merk trees use is_empty_tree_except(batch_deleted_keys) to correctly account for sibling deletes in the same batch. Non-Merk trees use element.non_merk_entry_count(). When a non-empty tree is found and deleting_non_empty_trees_returns_error is true, returns Error::DeletingNonEmptyTree; otherwise silently skips the op.

H1 — Storage cleanup: After apply_body completes, for each standard Merk tree deletion, find_subtrees recursively discovers all nested subtrees and storage.clear() is applied to each. This matches the non-batch delete behavior in delete_internal_on_transaction. Previously, only the parent key was removed, leaving orphaned storage data that could corrupt a later re-insert at the same path.

Both fixes apply to the full batch and partial batch paths.

Test plan

• test_batch_delete_tree_non_empty_should_fail_when_not_allowed — H2: error on non-empty tree delete
• test_batch_delete_tree_non_empty_succeeds_when_allowed — H2: success when allowed
• test_batch_delete_empty_tree_succeeds — H2: empty tree always works
• test_batch_delete_tree_cleans_up_subtree_storage — H1: no orphaned storage after delete
• test_batch_delete_tree_then_reinsert_produces_clean_tree — H1: clean re-insertion after delete
• 3 existing tests updated to set allow_deleting_non_empty_trees: true (they intentionally delete non-empty trees)
• All 1295 tests pass

🤖 Generated with Claude Code

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e5a3fc80-142f-4bc0-b3d8-bf380440ebf9

📥 Commits

Reviewing files that changed from the base of the PR and between 99a2ab0 and e581ce6.

📒 Files selected for processing (3)

• grovedb/src/batch/mod.rs
• grovedb/src/tests/batch_delete_tree_tests.rs
• grovedb/src/tests/mod.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/H1-H2-batch-delete-tree-cleanup

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[codecov]

Codecov Report

❌ Patch coverage is 85.43897% with 68 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.62%. Comparing base (99a2ab0) to head (e581ce6).
⚠️ Report is 13 commits behind head on develop.

Files with missing lines	Patch %	Lines
grovedb/src/batch/mod.rs	85.43%	68 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #599      +/-   ##
===========================================
- Coverage    90.67%   90.62%   -0.05%     
===========================================
  Files          182      182              
  Lines        49913    50534     +621     
===========================================
+ Hits         45258    45797     +539     
- Misses        4655     4737      +82     

Components	Coverage Δ
grovedb-core	88.75% <85.43%> (-0.04%)	⬇️
merk	91.99% <ø> (-0.06%)	⬇️
storage	85.50% <ø> (ø)
commitment-tree	96.41% <ø> (ø)
mmr	96.72% <ø> (ø)
bulk-append-tree	90.85% <ø> (ø)
element	97.55% <ø> (ø)

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[QuantumExplorer]

Approved, this would cause Platform to no longer work, but PR dashpay/platform#3210 will solve that on Platform side.