[makspll]

Stacked on #647. Second of the script system PRs.

Feature

• system_builder(..):resource_read(R) and world.query():component_read(C) are declared to Bevy as reads, so readers can run in parallel. resource / component stay read + write.
• The guard enforces this with a read-only bitset in AccessByteSet (from_allowed_lists(read_write, read_only)), checked only by component write claims, so read claims pay nothing.

Fixes found on the way (all pre-existing)

• Query components were declared as reads (ref_id) while scripts could write them, so two script systems writing C ran in parallel. Written components now use mut_id. as_query_state takes declare_writes, because world.query() builds an EntityRef query, which can't mix with writes.
• Resources were declared as FilteredAccess::matches_nothing() + write. An access matching nothing is compatible with everything, so two script systems writing the same resource ran in parallel. They now use add_resource_read / add_resource_write, like Res / ResMut.
• get_all_access_ids reported every access as a write: the read and write sets were swapped. The flag was unused until now.
• Claim count overflow: the 64th concurrent claim wrapped the count to 0, letting a write alias live reads. Claims now fail at the max count (63).

Tests

• Rust: readers are compatible with each other, writers are not.
• Rust: read-only map entries reject writes, also after release_all_accesses, and claims stop at the max count.
• Lua: read_only_parameters_cannot_be_written.lua.

Perf

A/B against #647, medians of 6 interleaved rounds: field get 418 → 387 ns, field set 454 → 450 ns, component/access 2514 → 2417 ns, resource/access 2185 → 2145 ns, i.e. no regression. A first version put a write-forbidden bit into AccessBitField, which made field get 8% slower and field set 4% slower, so it was replaced by the bitset.

🤖 Generated with Claude Code

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/bevy_mod_scripting_bindings/src/world_extensions.rs	89% smaller
crates/bevy_mod_scripting_core/src/extractors.rs	74% smaller
crates/bevy_mod_scripting_world/src/archetype_filter.rs	41% smaller
crates/bevy_mod_scripting_core/src/script_system.rs	22% smaller
crates/bevy_mod_scripting_bindings/src/query.rs	21% smaller
crates/bevy_mod_scripting_world/src/access_map.rs	15% smaller
assets/tests/add_system/read_only_parameters_cannot_be_written.lua	0% smaller
crates/bevy_mod_scripting_functions/src/core.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-read-access
Testbed	linux-gha

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