Add codebase wiki

[shaobohou]

Summary

• Adds a wiki/ directory: an LLM-maintained knowledge base following the Karpathy wiki pattern — persistent, interlinked markdown files that compile codebase knowledge once rather than re-deriving it on every question
• 23 pages across overview, concepts, entities, and design sections
• Covers architecture, core mechanisms, all key classes, and design proposals from a deep review session

Contents

Concepts — core mechanisms and patterns:

• Conversion phases (build time vs run time, the 12 captured closure variables)
• Op registry (two-level factory pattern, register_operation)
• Graph evaluation (toposort, _EvaluationCache reference counting, named-arg protocol)
• Variable semantics (TF variables → functional JAX params)
• Custom gradients (IdentityN detection, subgraph extraction pipeline)
• Library functions (_CachedBuilder lazy compilation, FunctionDefLibrary)
• NumPy compat (dual np/jnp dispatch, polymorphic shapes)
• jax2tf round-trip (what jax2tf does to graphs and how tf2jax handles it)

Entities — specific classes and functions:

• Public API (convert, convert_functional, convert_from_restored)
• _OpNode, _Subgraph, _TensorEdge, _LibraryFunction, _HigherOrderFunction, Variable
• _GraphDef/_NodeDef synthetic types and the dual graph representation
• jax2tf heuristics (_infer_relu_from_jax2tf, cumulative reduction inference)

Design — proposals and trade-off records:

• 7 structural refactoring recommendations (with priority table)
• Full design for lazy custom gradient evaluation using jax.custom_vjp

Test plan

• Wiki is readable and links resolve correctly
• No source files modified

🤖 Generated with Claude Code

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