fix: remove orphaned snapshot exports at startup

[bmuddha]

What changed

An interrupted seal can leave a temporary AccountsDB export directory behind. Keeper now removes orphaned exports at startup, before archival begins, so a later seal can reuse the path.

Closes #157

Related: magicblock-labs/magicblock-validator#1731

Impact

Startup treats every snapshot-* entry under the AccountsDB root as an owned temporary export. Retained snapshots in the ledger are unaffected.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: magicblock-labs/magicblock-engine/.coderabbit.yaml

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 9f9773ac-a604-4afa-a828-9764f06e3bfb

📥 Commits

Reviewing files that changed from the base of the PR and between e1fb74f and 78141c2.

📒 Files selected for processing (3)

• accountsdb/README.md
• accountsdb/src/snapshot.rs
• keeper/src/builder.rs

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📝 Walkthrough

Walkthrough

AccountsDB now removes entries with the snapshot- prefix from its root directory. KeeperBuilder::build calls this cleanup before prepopulating accounts and caches, and propagates cleanup errors. The README describes snapshot export directories as temporary and states that retained snapshots live in the ledger.

Fixed issue severity: <fixed_issue_severity>Medium</fixed_issue_severity>

Priority: ➖ Normal

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 78141

The startup cleanup appears ready to merge after normal checks; no supported path was found that would prevent it from removing orphaned exports.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains that Keeper removes orphaned temporary AccountsDB snapshot exports at startup and preserves retained ledger snapshots.
Title check	✅ Passed	The title clearly and concisely states the main change: removing orphaned snapshot exports at startup.
Linked Issues check	✅ Passed	The changes satisfy issue #157. AccountsDB::cleanup_snapshots removes root entries whose names start with snapshot-. KeeperBuilder::build calls this method after opening AccountsDB and before pr…
Out of Scope Changes check	✅ Passed	The changes stay within issue #157 and PR #158. The README documents the temporary export lifecycle. The new AccountsDB cleanup method implements startup removal. The Keeper builder call places cleanu…
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files. (1 skipped: 1 …

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