docs(chapel-ffi): document self-linking build + ignore regenerable outputs

Follow-up to 53ab9b8 — human/machine parity.

- QUICKSTART-DEV.adoc: new section describing the zig build -Dstubs=true
  default and the cargo build --features chapel two-step; plus the
  -Dstubs=false path for linking against real libechidna_chapel.
- chapel_poc/README.md: mark "Add FFI bindings to call from Rust" as
  DONE, pointing to the Chapel → Zig → Rust chain that's now wired.
- .gitignore: add models/e*/, /models_e*/ (per-epoch training
  checkpoints, regenerable) and src/zig_ffi/zig-out/, .zig-cache/
  (regenerated by `zig build`).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.gitignore

@@ -166,6 +166,14 @@ FINAL_CORPUS_COMPLETENESS_REPORT.md
 PROVER_EXPANSION_ROADMAP.md
 models/neural/
 
+# Per-epoch training checkpoints (regenerated; only models/ root kept)
+models/e*/
+/models_e*/
+
+# Zig FFI build output (regenerated by `zig build`)
+src/zig_ffi/zig-out/
+src/zig_ffi/.zig-cache/
+
 # asdf version manager
 .tool-versions
 

QUICKSTART-DEV.adoc

@@ -27,6 +27,26 @@ just tour      # understand the codebase
 just help-me   # see available commands
 ----
 
+== Optional: Chapel Parallel Proof Search
+
+The Rust core exposes an optional parallel-search path that calls into
+Chapel via a Zig FFI bridge. It is feature-gated and off by default.
+
+[source,bash]
+----
+cd src/zig_ffi && zig build    # builds libechidna_chapel_ffi.{a,so}
+                               # default -Dstubs=true bundles chapel_stubs.c
+                               # so Rust links cleanly without Chapel
+cd ../..
+cargo build --features chapel
+cargo test  --features chapel --lib proof_search
+----
+
+With Chapel actually installed and `libechidna_chapel.so` built from
+`chapel_poc/`, pass `-Dstubs=false` to the Zig build and link the
+Chapel library alongside. Stubs return "Chapel unavailable" at runtime
+so `cargo test --features chapel` still passes on hosts without Chapel.
+
 == Before Committing
 
 [source,bash]

chapel_poc/README.md

@@ -103,7 +103,16 @@ Speedup: 1.51x
 
 ## Next Steps
 
-1. **Integration**: Add FFI bindings to call from Rust
+1. ~~**Integration**: Add FFI bindings to call from Rust~~ — **DONE**.
+   Chapel `export` functions in `chapel_ffi_exports.chpl` are wrapped by
+   the Zig bridge at `../src/zig_ffi/chapel_bridge.zig`, which in turn
+   exports the `echidna_*` C ABI consumed by
+   `../src/rust/proof_search.rs` under `#[cfg(feature = "chapel")]`.
+   Build the Zig bridge with `cd ../src/zig_ffi && zig build` (default
+   `-Dstubs=true` bundles `chapel_stubs.c` so Rust links without a
+   Chapel install); then `cargo build --features chapel` from the repo
+   root. Pass `-Dstubs=false` to the Zig build to link against the real
+   `libechidna_chapel.so` produced in this directory.
 2. **Real Provers**: Replace mock with actual prover backends
 3. **Distributed**: Run on multi-node cluster
 4. **ML Integration**: Parallel model training