[makspll]

First of the stacked script system PRs (stabilise → access → scheduling → queries → perf).

Lifecycle

• A script system is identified by (attachment, callback label). Adding it again replaces the old one, with a warn!.
• Systems are removed when their script unloads or reloads. They are removed from remove_script_systems_when_unloaded observers, which always run, independent of the unload callback setting.
• ScriptSystemSet(u32) holds a slot in the new ScriptSystems resource. Slots are recycled, so the interning leak (one per distinct set value) is bounded by the peak number of live script systems.
• Sets are never removed from schedules, only their systems (RemoveSystemsOnlyAllowBreakages). In Bevy 0.20, SystemSets::remove keeps the set in its ids map, so adding to a removed set panics. A slot that a live script system orders against is not recycled.
• Changes to running schedules (e.g. PreUpdate, where the pipeline runs) are queued, together with later changes to the same schedule, and applied by apply_script_system_changes in First and Last. Removed systems stop running right away through an alive flag. When the add is deferred, world.add_system returns a ReflectSystem without a node id.

Robustness

• Errors are sent as ScriptErrorMessages (collected in ScriptSystems, sent by the same system). Invalid params are reported once, after which the system no longer runs; previously the init errors were popped once per frame and the system then ran anyway.
• No panics:
  • an uninitialised system, or one run in another world, is Skipped
  • scope_schedule's assert! is now an error, and the schedule is re-inserted even if Schedules was removed
• The ScriptContexts read lock is released before P::handle. Previously a callback that loaded or unloaded a script could deadlock.

Soundness

Bevy schedules a script system by its FilteredAccess, so query(C):with(A) runs in parallel with Query<&mut C, Without<A>>. The guard used to grant C on every entity, so world.get_component(e_without_a, C) gave aliased mutable access.

The new ArchetypeFilter (in bevy_mod_scripting_world) restricts each component to the archetypes matched by the queries that declare it. The check happens in reflect_(mut_)unsafe. Its module docs cover why archetypes and not tables, why it is sound for every filter, and why the filter can't go stale.

The new test system_cannot_access_component_outside_query_archetypes.lua fails with the check disabled. Benches (field get/set, component/resource access/get, query/100) stay within noise against main, but they run in exclusive contexts, so the filtered path isn't benched.

Tests

• Rust: replace, removal + slot recycling, deferred changes to running schedules, error messages.
• Lua: replacement and the archetype guard. system_with_parameters.lua now records finished: its assertions only got logged before, and its _1 tuple-field access had never worked.

🤖 Generated with Claude Code

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/bevy_mod_scripting_core/src/pipeline/hooks.rs	90% smaller
crates/bevy_mod_scripting_core/src/pipeline/mod.rs	38% smaller
crates/bevy_mod_scripting_core/src/script_system.rs	11% smaller
assets/tests/add_system/system_with_parameters.lua	4% smaller
crates/testing_crates/script_integration_test_harness/src/test_functions.rs	4% smaller
crates/bevy_mod_scripting_core/src/lib.rs	1% smaller
crates/bevy_mod_scripting_world/src/world.rs	1% smaller
assets/tests/add_system/adding_system_again_replaces_it.lua	0% smaller
assets/tests/add_system/system_cannot_access_component_outside_query_archetypes.lua	0% smaller
crates/bevy_mod_scripting_bindings/src/reference.rs	0% smaller
crates/bevy_mod_scripting_core/src/handler.rs	0% smaller
crates/bevy_mod_scripting_world/src/archetype_filter.rs	0% smaller
crates/bevy_mod_scripting_world/src/lib.rs	0% smaller
crates/bevy_system_reflection/src/lib.rs	0% smaller
docs/src/ReleaseNotes/0.23-to-0.24.md	Unsupported file format
docs/src/ScriptSystems/introduction.md	Unsupported file format

[github-actions]

Bencher Report

Project	Bevy Scripting
Branch	agent/script-systems-stabilise
Testbed	linux-gha

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