Chapter 29: Tech Debt Cleanuplinear-chapter29linear

Co-authored-by: Hsiang-Ying Fu <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: fuhsnn <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: Symious <14933944+symious@users.noreply.github.com>
Co-authored-by: Jun Kawasaki <jun784@gmail.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

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+# Chapter 29: Tech Debt Cleanup
+
+English | [日本語](README.ja.md)
+
+[Previous: Chapter 28b — Separate Compilation](../chapter28b/README.md)
+
+This chapter makes the compiler easier to read and change while preserving
+Chapter 28b's language and separate-compilation behavior. It starts by breaking
+the parser into grammar-sized pieces. Further cleanup belongs here; earlier
+chapters retain their teaching snapshots.
+
+## Following the grammar
+
+The old `Parser.java` had grown beyond 3,000 lines, mixing recursive descent,
+name resolution, scope management, and IR construction. The
+[`parser/` package](../../src/main/java/com/seaofnodes/simple/parser/README.md) separates
+those responsibilities without introducing an AST: parsing still builds
+Sea-of-Nodes IR directly.
+
+`Parser` owns the source cursor, active scope, type registry, and common token
+and IR helpers. Each component shares that state through `Parser P`.
+`Statements`, `Expressions`, `Declarations`, `Types`, `Functions`, and `Structs`
+follow the corresponding grammar productions. `References` handles name and
+field resolution; `Allocations`, `Conversions`, and `ControlFlow` hold shared
+graph-building operations. `Lexer` owns tokenization and source locations, and
+`Var` records lexical bindings.
+
+The [grammar and code map](29-grammar.md) connects productions to methods.
+Start with `Statements.parseStatement` or `Expressions.parseAssignment` and
+follow the calls alongside it. Deferred parsing remains explicit: `for` updates
+are parsed after their bodies, and declared constructors after field discovery.
+
+The [source layout](../../src/main/java/com/seaofnodes/simple/README.md) describes the
+other packages. `IterPeeps` now lives in `codegen/` beside the compilation passes.
+
+## Cleanup still to do
+
+Constructor completion is a useful next target. `addReturn` already merges field
+values across exit paths, but `_ctorExits` saves those types until all fields
+are known. Checking the final `Return` alone is insufficient today: field
+conversions can erase uninitialized state, and the declaration initializer is
+separate from the user constructor. Simplify that bookkeeping without weakening
+the initialization checks.
+
+Source privacy is deferred. Leading underscores retain the existing export
+filtering behavior; this chapter does not yet enforce access restrictions on
+source uses. The [roadmap](../roadmap.md) retains that proposal and the other
+language candidates.
+
+## Build and test
+
+From the repository root:
+
+```sh
+make lib tests release CHAPTERS=chapter29 CTAGS=
+```
+
+The suite includes the inherited compiler, evaluator, native execution,
+serialization, and separate-compilation tests, plus parser regression tests for
+deferred fragments. Historical test class names retain their original identities.
+The [Chapter 28b library/client example](../chapter28b/README.md) also runs from
+this chapter directory.
+
+IntelliJ has a `chapter29` module and a **chapter29 tests** run configuration.
+Build the native runtime and `sys` library with Make before debugging tests
+that need them; see [the IntelliJ setup](../intellij.md).