refactor: assumeutxo M3 review follow-ups

[PastaPastaPasta]

Issue being fixed or feature implemented

Review of the assumeutxo M3 PR (#7553, now merged) surfaced three small non-blocking cleanups. They were split out so #7553 could merge as-is:

1. RecoverSnapshotCleanup() re-spelled all four snapshot-lifecycle directory names as string literals while the rename sites derived them from SNAPSHOT_CHAINSTATE_SUFFIX or inlined them. A rename of any suffix would compile cleanly while crash recovery silently stopped matching the on-disk layout.
2. The candidate-admission pass in ResetBlockFailureFlags() called ChainstateManager::GetAll() inside the per-block loop, re-acquiring cs_main recursively and heap-allocating a vector per reconsidered block even though the chainstate set cannot change while cs_main is held for the whole function.
3. MaybeCompleteSnapshotValidation() carried assert(snapshot_base_height == index_new.nHeight) four lines after asserting the same equality.

What was done?

• Added SNAPSHOT_INVALID_SUFFIX and SNAPSHOT_TODELETE_SUFFIX next to SNAPSHOT_CHAINSTATE_SUFFIX in node/utxo_snapshot.h and consume them in RecoverSnapshotCleanup(), InvalidateCoinsDBOnDisk(), and ValidatedSnapshotCleanup(). Test files intentionally keep spelled-out literals so they would catch an accidental rename of the on-disk names.
• Hoisted the GetAll() call above the admission loop.
• Dropped the duplicated assert.

How Has This Been Tested?

Both touched translation units compile with --enable-werror. No behavior change is intended; the existing validation_chainstatemanager_tests snapshot-recovery cases cover the renamed-directory handling.

Breaking Changes

None.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation
• I have assigned this pull request to a milestone (for repository code-owners and collaborators only)

[thepastaclaw]

🕓 Ready for review — 4 ahead in queue (commit d4851d8)
Queue position: 5/5 · 2 reviews active
ETA: start ~17:19 UTC · complete ~17:36 UTC (median 17m across 30 recent reviews; 2 slots)
Queued 6m ago · Last checked: 2026-08-12 16:40 UTC

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: e06adbf3-223b-4a52-9965-19276ac94e34

📥 Commits

Reviewing files that changed from the base of the PR and between 9190215 and d4851d8.

📒 Files selected for processing (1)

• src/node/chainstate.cpp

🚧 Files skipped from review as they are similar to previous changes (1)

• src/node/chainstate.cpp

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Walkthrough

The changes add shared suffix constants for snapshot-related directories. Chainstate recovery, invalidation, and cleanup now derive paths from the base chainstate path. Snapshot completion verifies the background chainstate height against snapshot_base_height. ResetBlockFailureFlags caches the chainstate collection before restoring reconsidered block candidates.

Estimated code review effort: 2 (Simple) | ~15 minutes

Possibly related PRs

• dashpay/dash#7456: Modifies snapshot chainstate handling, cleanup, and suffix-based invalidation paths.
• dashpay/dash#7553: Introduces snapshot cleanup and validation logic refined by this change.
• dashpay/dash#7579: Updates snapshot cleanup, recovery, and shared directory suffix handling.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the assumeutxo refactoring and review follow-up changes.
Description check	✅ Passed	The description directly explains all three cleanup changes, testing, and the absence of behavior or breaking changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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