fix: return error instead of silently discarding writes when storage batch is None (M3)

[QuantumExplorer]

Summary

• All 9 write operations in PrefixedRocksDbTransactionContext (put, put_aux, put_root, put_meta, delete, delete_aux, delete_root, delete_meta, commit_batch) now return Error::StorageError when self.batch is None, instead of silently returning Ok(())
• Fixed 4 merk tests that were unknowingly relying on the silent-discard behavior (writes were silently lost) — they now provide a StorageBatch
• Read operations continue to work correctly with None batch

Audit finding M3: All write operations silently succeeded and discarded data when no batch was provided. No legitimate code path writes through a batchless context — all batchless call sites only perform reads. The silent success made it impossible for callers to detect data loss.

Test plan

• test_write_operations_error_when_batch_is_none — verifies all 9 write operations return errors
• test_read_operations_succeed_when_batch_is_none — verifies reads still work with None batch
• 4 merk tests fixed to use proper StorageBatch
• All 2000+ workspace tests pass
• Clippy clean

🤖 Generated with Claude Code

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 9f8c24a5-fa74-4ecc-9909-62d3e5fb08b0

📥 Commits

Reviewing files that changed from the base of the PR and between 99a2ab0 and a49a934.

📒 Files selected for processing (4)

• merk/src/element/get.rs
• merk/src/merk/mod.rs
• storage/src/rocksdb_storage/storage_context/context_tx.rs
• storage/src/rocksdb_storage/tests.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/M3-silent-storage-data-loss

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[codecov]

Codecov Report

❌ Patch coverage is 98.01980% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.69%. Comparing base (ad90e2c) to head (a49a934).
⚠️ Report is 9 commits behind head on develop.

Files with missing lines	Patch %	Lines
.../src/rocksdb_storage/storage_context/context_tx.rs	97.61%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #604      +/-   ##
===========================================
+ Coverage    90.63%   90.69%   +0.06%     
===========================================
  Files          182      182              
  Lines        49801    49966     +165     
===========================================
+ Hits         45136    45318     +182     
+ Misses        4665     4648      -17     

Components	Coverage Δ
grovedb-core	88.78% <ø> (+0.03%)	⬆️
merk	92.06% <100.00%> (+0.11%)	⬆️
storage	86.37% <97.61%> (+0.87%)	⬆️
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]

Okay makes sense