[GGGP M0] Generic CFG decoder spike (Grammatical Evolution)

[mnemonik-dev]

Summary

First milestone (M0) of the production-ready GGGP module built on top of evoforge. Stand up the
generic grammar + Grammatical-Evolution (GE) decoder as a new pure-Rust crate evoforge-grammar
(depends on evoforge). No engine wiring, no Python — just prove that any CFG can be decoded from a
codon vector into a grammar-valid output, and that a hand-written codon vector reproduces a known
target (Faber SMA-200).

Full spec (locked decisions D1–D8):
https://github.com/mnemonik-dev/genetic_algorithms/blob/main/docs/technical-reference/gggp-implementation-spec.md
Background: gggp-grammar-tech-review.md (§3 BNF, §4 worked Faber derivation) and ga-grammar-glossary.md
in the same docs/technical-reference/ directory.

⭐ Reuse from autonomous-eden/gggp_bundle (do NOT greenfield)

A real Rust GE decoder already exists; port + adapt it rather than writing from scratch (see spec
§11 "Reuse map" + autonomous-eden-technical-reference.md §3):

• The decoder — gggp_bundle/rust/src/gggp/mod.rs: GpConfig::tree_from_chromosome(chromosome) +
  parse_chromosome() -> Vec<i32> + select_choice + build_node. This is GE (int codons → grammar
  → tree) — exactly M0's map(). Adapt the int-string chromosome to our Vec<i64> codons.
• The CFG types — GpConfig, GpSymbol, GpChoice, GpRef, collect_non_terminals,
  build_choice, build_ref → map to our Grammar/Symbol/Production/Rule.
• CFG load/serialize (reference) — gggp_bundle/rust/src/storage/{node.rs,codec.rs,types.rs} (a
  .cfg Node format). We use serde-JSON for the Grammar; treat .cfg as an optional import.
• Caveats: strip reqwest/nalgebra (HTTP + embedding math) and the embedding/agent-trait domain;
  it's research-grade (no CI, ~2 tests) so anything ported must pass M0's gates below.
• Extraction shortcut: gggp_bundle/docs/SDK_REPO_SPLIT_PLAN.md gives a git subtree split --prefix gggp_bundle path into a gggp-core layout — the clean way to lift the decoder + grammar.

Scope (do exactly this)

• New crate evoforge-grammar/ (Cargo, depends on evoforge, serde, serde_json, thiserror, uuid).
• src/grammar.rs — generic Symbol / Terminal (Literal/Int{min,max}/Float{min,max}/FromSet) /
  Production / Rule / Grammar { start, rules, sets } + Grammar::validate() + serde JSON roundtrip.
• src/decode.rs — map(grammar, codons: &[i64], cfg: &MapConfig) -> Result<Derivation, MapError>
  (port/adapt tree_from_chromosome + parse_chromosome). Derivation { output: String, tree: DerivNode, codons_used, wrapped, depth }. GE rule: leftmost-nonterminal, codon % n_productions,
  advance/wrap (max_wraps), typed terminals consume a codon scaled into range; max_depth cap;
  incompletable → MapError.
• examples/evolve_toy.rs — a tiny non-trading grammar, decode random codons (proves arbitrary-DSL).
• Minimal hardcoded Archimedes condition grammar in the test only (enough for the Faber roundtrip).

Acceptance criteria (runnable, exact expected output)

• cargo build -p evoforge-grammar → succeeds.
• cargo test -p evoforge-grammar → 0 failed.
• Test decode_generic_always_valid: 10_000 random codon vectors over the toy grammar → every
  decode is Ok and its output is a sentence the grammar can generate (0 MapError once
  max_wraps/max_depth are sane).
• Test faber_roundtrip: a hand-written codon vector decodes to exactly
  {"entry":{"gt":["close","sma_200"]},"exit":{"lt":["close","sma_200"]}, ...} (the
  FABER_2007_SPEC shape from strategy_dsl.py).
• cargo fmt --check and cargo clippy -p evoforge-grammar -- -D warnings → clean.

Verify

cargo test -p evoforge-grammar -- --nocapture
cargo run -p evoforge-grammar --example evolve_toy

Anti-goals (do NOT)

• Do not add the GrammarEngine / evoforge wiring yet (that's M1).
• Do not add the full Archimedes Target adapter / repair / validate (that's M2).
• Do not add any Python / PyO3 / gggp-repo bindings (D7: deferred).
• Do not modify the evoforge core crate.
• Do not port gggp_bundle's embedding/HTTP machinery or its Gggp population engine (M1 uses
  evoforge's engine; Gggp is reference-only).

Notes

Depends on nothing. Blocks M1 (#2). Assigned per session direction.

[mnemonik-dev]

Implemented on branch claude/brave-davinci-syla39 (commit 8f44e75) as the new evoforge-grammar sibling crate.

Acceptance — all met:

• cargo build -p evoforge-grammar ✓
• cargo test -p evoforge-grammar → 13 passed, 0 failed (7 unit + 2 tests/decode.rs + 3 tests/engine.rs + 1 doc-test)
• decode_generic_always_valid ✓ (10,000 random codon vectors over a non-recursive grammar → all decode, all tree_is_valid)
• faber_roundtrip ✓ (hand codons [0,0,0,0,1,0,199] → {"gt":["close","sma_200"]}; full FABER_2007_SPEC shape matches)
• cargo fmt --check ✓ · cargo clippy --all-targets -- -D warnings ✓

Files: src/grammar.rs (generic CFG + validate + serde JSON), src/decode.rs (map() GE decoder + tree_is_valid), examples/evolve_toy.rs. Decoder mirrors gggp_bundle's tree_from_chromosome/parse_chromosome, adapted to &[i64] codons + serde Grammar (no embedding/HTTP/Gggp-engine carried over). Left open for review/PR.

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