## Summary

Implements Phase 1 of the module tags design ([#9017](#9017)):

- **`$initial` tag** — automatically computed during the entry BFS. Modules statically imported by user-defined entries (or in their dependency chain) are tagged `$initial`.
- **`tags` filter** — manual code splitting groups can filter by tags with AND semantics. Only modules with all specified tags are captured.

## Implementation

- `ModuleTagBitSet` — `u64`-based bitset (`Copy`, single AND+CMP for `contains_all`). Supports up to 64 tags.
- `ModuleTagRegistry` — sealed registry mapping tag names (`$initial`, future `$lazy`) to bit indices. All registration happens in `new()`.
- `$initial` tag is computed inside `determine_reachable_modules_for_entry` BFS — no separate pass needed.
- Built-in tags use `$` prefix to distinguish from user-defined tags.

## Test plan

- [x] Integration test `tags_initial` — entry with static + dynamic imports, verifies `tags: ['$initial']` captures only statically reachable modules
- [x] `cargo check` compiles
- [x] `just lint-rust` passes
- [x] `just build-rolldown` regenerates bindings
- [x] TypeScript types check

🤖 Generated with [Claude Code](https://claude.com/claude-code)

## [1.0.0-rc.16] - 2026-04-16

### 🚀 Features

- const enum cross-module inlining support (#8796) by @Dunqing
- implement module tagging system for code splitting (#9045) by @hyf0

### 🐛 Bug Fixes

- rolldown_plugin_vite_manifest: handle duplicate chunk names for CSS entries (#9059) by @sapphi-red
- improve error message for invalid return values in function options (#9125) by @shulaoda
- await async export-star init wrappers (#9101) by @thezzisu
- never panic during diagnostic emission (#9091) by @IWANABETHATGUY
- include array rest pattern in binding_identifiers (#9112) by @IWANABETHATGUY
- rolldown: set worker thread count with ROLLDOWN_WORKER_THREADS (#9086) by @fpotter
- rolldown_plugin_lazy_compilation: escape request ID in proxy modules (#9102) by @h-a-n-a
- treat namespace member access as side-effect-free (#9099) by @IWANABETHATGUY
- relax overly conservative side-effect leak check in chunk optimizer (#9085) by @IWANABETHATGUY
- runtime: release `cb` reference after `__commonJS` factory initialization (#9067) by @hyf0-agent
- `@__NO_SIDE_EFFECTS__` wrapper should not remove dynamic imports (#9075) by @IWANABETHATGUY
- rolldown_plugin_vite_import_glob: use POSIX path join/normalize for glob resolution (#9077) by @shulaoda
- emit REQUIRE_TLA error when require() loads a module with top-level await (#9071) by @jaehafe
- emit namespace declaration for empty modules in manual chunks (#8993) by @privatenumber
- rolldown_plugin_vite_import_glob: keep common base on path segment boundary (#9070) by @shulaoda
- prevent circular runtime helper imports during facade elimination (#8989) (#9057) by @IWANABETHATGUY
- correct circular dependency check in facade elimination (#9047) by @h-a-n-a
- docs: correct dead link in CodeSplittingGroup.tags JSDoc (#9051) by @hyf0
- emit DUPLICATE_SHEBANG warning when banner contains shebang (#9026) by @IWANABETHATGUY

### 🚜 Refactor

- use semantic reference flags for member write detection (#9060) by @Dunqing
- extract UsedSymbolRefs newtype wrapper (#9130) by @IWANABETHATGUY
- dedupe await wrapping in export-star init emit (#9119) by @IWANABETHATGUY
- calculate side-effect-free function symbols on demand (#9120) by @IWANABETHATGUY
- extract duplicated top-level await handling into shared helper (#9087) by @IWANABETHATGUY
- rolldown_plugin_vite_import_glob: use split_first for get_common_base (#9069) by @shulaoda
- simplify ESM init deduplication with idiomatic insert check (#9044) by @IWANABETHATGUY

### 📚 Documentation

- document runtime module placement strategy in code-splitting design (#9062) by @IWANABETHATGUY
- clarify `options` hook behavior difference with Rollup in watch mode (#9053) by @sapphi-red
- meta/design: introduce module tags (#9017) by @hyf0

### ⚡ Performance

- convert `generate_transitive_esm_init` to iterative (#9046) by @IWANABETHATGUY

### 🧪 Testing

- merge strict/non_strict test variants using configVariants (#9089) by @IWANABETHATGUY

### ⚙️ Miscellaneous Tasks

- disable Renovate auto-updates for oxc packages (#9129) by @IWANABETHATGUY
- upgrade oxc@0.126.0 (#9127) by @Dunqing
- deps: update napi to v3.8.5 (#9126) by @renovate[bot]
- deps: update dependency @napi-rs/cli to v3.6.2 (#9123) by @renovate[bot]
- move lazy-compilation design doc (#9117) by @h-a-n-a
- deps: update dependency vite-plus to v0.1.18 (#9118) by @renovate[bot]
- deps: update dependency vite-plus to v0.1.17 (#9113) by @renovate[bot]
- deps: update oxc to v0.125.0 (#9094) by @renovate[bot]
- deps: update dependency follow-redirects to v1.16.0 [security] (#9103) by @renovate[bot]
- deps: update test262 submodule for tests (#9097) by @sapphi-red
- deps: update crate-ci/typos action to v1.45.1 (#9096) by @renovate[bot]
- deps: update rust crates (#9081) by @renovate[bot]
- deps: update npm packages (#9080) by @renovate[bot]
- remove outdated TODO in determine_module_exports_kind (#9072) by @jaehafe
- rust/test: support `extendedTests: false` shorthand in test config (#9050) by @hyf0
- ci: extract shared infra-changes anchor in path filters (#9054) by @hyf0
- add docs build check to catch dead links in PRs (#9052) by @hyf0

### ❤️ New Contributors

* @thezzisu made their first contribution in [#9101](#9101)
* @fpotter made their first contribution in [#9086](#9086)
* @jaehafe made their first contribution in [#9071](#9071)
* @privatenumber made their first contribution in [#8993](#8993)

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>