Initialize classes lazily per JVMS 5.5

[dlunch]

Summary

Moves class initialization (<clinit>) from eager (at registration) to the spec-mandated first active use, and fixes two related issues found along the way.

Lazy initialization

• Class gains a shared InitState machine (NotInitialized / InProgress / Initialized / Erroneous). ensure_initialized runs at the four JVMS §5.5 triggers — new, getstatic, putstatic, invokestatic — initializing the superclass chain first; interfaces initialize only on access to their own static fields. InProgress re-entry returns immediately, so a clinit touching its own statics works.
• clinit now runs through execute_method, so it gets a java frame: class resolution inside clinit uses the initializing class's loader context, clinit shows up in stack traces, and objects it allocates are rooted to its frame.
• resolve_class_internal returns the registry's canonical Class (loader wrappers may build a fresh instance around an already-registered definition, which would otherwise double-run clinit — guarded by the DoubleInit fixture).
• Failure handling per spec: non-Error exceptions are wrapped in ExceptionInInitializerError (new runtime class); Errors propagate as-is; the class becomes erroneous and later uses throw NoClassDefFoundError.

ConstantValue (static final compile-time constants)

javac emits compile-time constants as ConstantValue attributes with no clinit code, so they previously read as zero/null. ClassDefinition::prepare now materializes them into static storage during preparation, including String constants.

Class.getName

Returned the internal slash form (java/lang/X); now returns the dotted binary name. Two existing tests had encoded the buggy form and were corrected.

Test plan

• E2E fixtures with expected output generated by running them on a real JVM (OpenJDK 26): LazyClinit (all four triggers, superclass-before-subclass ordering, interface non-initialization on implementor instantiation, clinit re-entrancy), ClinitFailure (ExceptionInInitializerError → NoClassDefFoundError, Error unwrapped), StaticOrder (ldc class literal resolves without initializing — verified to fail on the pre-change commit), DoubleInit (no double clinit through on-demand class loading).
• Rust-side tests where bytecode can't observe the behavior: test_constant_value (javac inlines constants at use sites) and the existing test_putstatic.
• Comparing against real-JVM output caught the Class.getName bug.
• cargo test --workspace green, fmt clean, clippy no new warnings.

Design docs from the forge pipeline (PRD/architecture/review) are kept locally under docs/ and not part of this PR.

[codecov]

Codecov Report

❌ Patch coverage is 87.31707% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.08%. Comparing base (ebd9c03) to head (870a185).

Files with missing lines	Patch %	Lines
...lasses/java/lang/exception_in_initializer_error.rs	43.47%	13 Missing ⚠️
jvm/src/jvm.rs	78.57%	9 Missing ⚠️
jvm/src/array_class_definition.rs	0.00%	2 Missing ⚠️
java_runtime/src/classes/java/lang/throwable.rs	97.95%	1 Missing ⚠️
jvm_rust/src/class_definition.rs	96.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #160      +/-   ##
==========================================
+ Coverage   80.53%   81.08%   +0.55%     
==========================================
  Files         183      184       +1     
  Lines        8018     8199     +181     
==========================================
+ Hits         6457     6648     +191     
+ Misses       1561     1551      -10     

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[Copilot]

Pull request overview

This PR updates the JVM’s class initialization behavior to be spec-aligned (lazy <clinit> on first active use), fixes handling of ConstantValue static finals during preparation, and corrects Class.getName() to return dotted binary names.

Changes:

• Add per-Class initialization state and trigger initialization on new, getstatic, putstatic, and invokestatic entrypoints.
• Materialize ConstantValue attributes into static storage during a new ClassDefinition::prepare phase (including String constants).
• Fix java.lang.Class.getName() (and related tests) to return dotted names; add ExceptionInInitializerError to the runtime.

Reviewed changes

Copilot reviewed 26 out of 46 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/test_constant_value.rs	Adds a Rust-side unit test asserting ConstantValue statics are visible via get_static_field.
test_data/unit/Constants.java	Adds a Java source fixture for constant-value fields.
test_data/StaticOrder.txt	Adds expected output fixture for class-literal vs initialization order behavior.
test_data/StaticOrder.java	Adds Java fixture verifying Helper.class doesn’t initialize Helper until active use.
test_data/LazyClinit.txt	Adds expected output fixture for lazy initialization triggers and ordering.
test_data/LazyClinit.java	Adds Java fixture covering the four init triggers, ordering, and self-reference behavior.
test_data/DoubleInit.txt	Adds expected output fixture ensuring <clinit> runs once.
test_data/DoubleInit.java	Adds Java fixture to catch double-initialization via repeated active use.
test_data/ClinitFailure.txt	Adds expected output fixture for initializer failure behavior.
test_data/ClinitFailure.java	Adds Java fixture covering ExceptionInInitializerError and subsequent NoClassDefFoundError behavior.
jvm/src/jvm.rs	Implements lazy init via ensure_initialized, integrates it into object creation/static field access/static calls, and avoids double init via registry canonicalization.
jvm/src/class_loader.rs	Introduces InitState and stores it on Class instances so init state can be shared.
jvm/src/class_definition.rs	Extends the ClassDefinition trait with a prepare hook.
jvm/src/array_class_definition.rs	Implements a no-op prepare for array class definitions.
jvm_rust/src/class_definition.rs	Parses ConstantValue attributes and implements prepare to materialize constants into static storage.
java_runtime/tests/classes/java/lang/test_throwable.rs	Updates expectations to match dotted getName() output in Throwable::toString / stack trace headers.
java_runtime/src/loader.rs	Registers ExceptionInInitializerError as a runtime-provided class.
java_runtime/src/classes/java/lang/exception_in_initializer_error.rs	Adds a minimal ExceptionInInitializerError runtime class and constructors used by the VM.
java_runtime/src/classes/java/lang/class.rs	Fixes Class.getName() to return dotted binary names.
java_runtime/src/classes/java/lang.rs	Wires the new runtime class module into the java.lang exports.

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