Add the dynamic-binding cluster on the Chez RT: a per-thread binding stack
(host/chez/dyn-binding.ss) backing binding / with-bindings* / var-set /
thread-bound? / with-local-vars / with-redefs / bound-fn* /
get-thread-bindings / alter-var-root + the __local-var seam.
Frames are stored innermost-first as identity-keyed alists of mutable
(cell . value) pairs, so var-set updates the current binding in place. The
two var-read paths — var-deref (compiled code) and jolt-var-get (var-get /
deref on a cell) — are chained onto the stack so a `binding` frame is seen
by every read, with a fast path when the stack is empty. var-cells now hash
by ns/name so a var works as a map key (with-redefs builds (hash-map (var f)
v); get-thread-bindings returns a var-keyed map).
Fix a latent bug exposed once with-in-str could bind *in*: seq? didn't
recognize a lazy-seq. predicates.ss's jolt-seq? predates the lazyseq record,
and unlike the native-op dispatchers it's reached via var-deref, so the
patch must re-def-var! the var, not just set! the top-level binding.
Note: with-bindings* over a hash-map literal now returns the correct Clojure
value where the seed returns a stale one — the seed's PHM can't find a var
key (which is why its `binding` uses array-map); on Chez frames look up by
cell identity.
Prelude corpus parity 1972 -> 2000, floor raised. Gate: _dynbind 24/24,
prelude corpus 0 divergences, full jpm test, conformance 355x3.
fc6551f877