Fix blockchain integrity cache advancing before DB commit

[Copilot]

Description

blockchain_last_hash_cache was updated with the new integrity_hash before save_issue_db was called. A failed DB commit would leave the cache pointing to a hash that was never persisted, causing subsequent issues to chain off a phantom hash and silently corrupting the blockchain integrity chain.

Fix:

• Move blockchain_last_hash_cache.set(...) to after save_issue_db succeeds — cache only advances on confirmed persist
• Add blockchain_last_hash_cache.invalidate("last_hash") in the except block — forces a fresh DB lookup on the next request instead of chaining off a stale/uncommitted value

# Before (broken): cache updated before DB write
integrity_hash = hashlib.sha256(hash_content.encode()).hexdigest()
blockchain_last_hash_cache.set(data=integrity_hash, key="last_hash")  # ← too early
await run_in_threadpool(save_issue_db, db, new_issue)

# After (fixed): cache updated only on success, invalidated on failure
integrity_hash = hashlib.sha256(hash_content.encode()).hexdigest()
await run_in_threadpool(save_issue_db, db, new_issue)
blockchain_last_hash_cache.set(data=integrity_hash, key="last_hash")  # ← after commit
# ...
except Exception as e:
    blockchain_last_hash_cache.invalidate("last_hash")  # ← force re-fetch from DB

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🎨 Code style update (formatting, renaming)
• ♻️ Refactoring (no functional changes)
• ⚡ Performance improvement
• ✅ Test update

Related Issue

Closes #

Testing Done

• Tested locally
• Added/updated tests
• All tests passing

Screenshots (if applicable)

N/A

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Co-Authors

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Summary by cubic

Strengthens blockchain integrity and speeds up Admin Stats. Tightens validation, fixes the last-hash cache race, and adds fast, indexed rollups with short-lived caching to cut query load and fix incorrect counts.

• Bug Fixes

  • Block acceptance now checks prev-hash continuity and transaction merkle root before commit to prevent orphan/invalid blocks.
  • Fixed last-hash cache race: update only after a successful DB commit and invalidate on errors to avoid stale reads.
  • Admin Stats totals corrected by reading from the canonical chain state and excluding pending/orphaned records.

• Refactors

  • Centralized validation into small utilities with a startup integrity pass for the existing chain.
  • Admin Stats now use aggregated queries with new DB indexes and a 60s cache (stale-while-revalidate).

^{Written for commit 59daf4c. Summary will update on new commits.}