Slimefun Legacy 4.1.51 - v1.0 - (1.21.11->26.3)

java 21->java 26

Slimefun Legacy 4.1.51 is a major maintenance and compatibility release focused on safer data migration, storage reliability, Minecraft 26.3 compatibility, addon support, and long-term stability.

This release brings together the work completed since 4.1.50 and continues the goal of keeping the classic Slimefun experience working reliably on modern Minecraft servers.

Minecraft 1.21.11 → 26.3 Compatibility

Slimefun Legacy continues to support modern Paper-family servers while maintaining Minecraft 1.21.11 as the compatibility floor.

A major focus of this release was preparing Slimefun Legacy for Minecraft 26.3.

Several dependencies on Paper implementation internals have been removed, including:

• Removed legacy Paper PlayerProfile casting from old ItemMeta/skull recovery.
• Removed reflection into Paper's internal MCUtil.MAIN_EXECUTOR.
• Preserved the normal Bukkit/Slimefun scheduler path on Paper.
• Preserved the global-region scheduler implementation for Folia.
• Reduced dependency on implementation details that may change between Paper versions.

Paper 26.2 remains the current production baseline, while 26.3 compatibility is being actively validated through the compatibility and pre-release testing paths.

Doctor & Legacy Data Migration Improvements

A substantial amount of work went into making /slimefun doctor safer and more useful when upgrading servers with years of existing Slimefun data.

Migration support now covers more of Slimefun's persisted storage system, including:

• Persisted BLOCK_RECORD Slimefun IDs.
• Persisted UNIVERSAL_RECORD IDs.
• Serialized ItemStacks stored inside block inventories.
• Serialized ItemStacks stored inside universal inventories.
• Persisted Backpack Item IDs.
• Addon-provided loaded machine migrations.
• Safer handling of unloaded Slimefun storage.

Migration operations now use fingerprints and stale-data validation so a migration cannot blindly modify a record that has changed since it was scanned.

Migration plans are also intentionally short-lived and single-use.

Backpack & Storage Safety

Backpack migration received additional protections around live player data.

Doctor maintenance now coordinates with:

• Backpack caches.
• Profile storage.
• Cache misses.
• Active maintenance operations.
• Direct database access.

If Slimefun cannot prove that a backpack can be modified safely, the migration fails closed instead of risking live inventory data.

Additional regression coverage was added for:

• Backpack cache installation.
• Maintenance locking.
• Rollback behavior.
• Empty ItemStack serialization.
• Migration fingerprints.
• Concurrent storage activity.

Safer Migration Behavior

Slimefun Legacy now takes a deliberately conservative approach to legacy storage.

The migration system will not guess when it encounters data that is:

• Unknown
• Ambiguous
• Unreadable
• Currently loaded
• Modified since scanning
• Otherwise unsafe to automatically migrate

Those records are left untouched and reported for review.

Doctor storage scans also avoid unnecessarily forcing chunks to load.

Migration Coverage Protection

New CI checks now verify that structured Slimefun persistence fields containing Slimefun IDs or serialized ItemStacks have an explicit migration strategy.

This helps prevent future storage changes from silently introducing data that Doctor does not understand.

Coverage includes the supported persistence implementations for:

• SQLite
• MySQL
• PostgreSQL

Addon-owned opaque key/value storage is intentionally excluded from generic Item-ID rewriting.

Rollback & Failure Protection

Storage migrations now include stronger rollback handling.

If part of a migration operation cannot complete safely, Slimefun attempts to restore the affected storage instead of leaving a partially migrated record.

This is especially important for older servers with large databases and data spanning multiple generations of Slimefun.

Slimefun Legacy Addons

Alongside the core Slimefun Legacy release, there is now a maintained compatibility bundle containing the Slimefun Legacy addon collection.

Download the Addon Bundle & HotFixes:

SF_Addons_1.21.11-26 https://github.com/wickidcow/Slimefun-Legacy/releases