[tvolk131]

Repeated calls rebuild the same helper bodies, making compilation exponential for nested call graphs.

Cache bodies by AST identity within one compilation, shared across child scopes and reused by custom calls, list/array folds, and for_while. Three regression tests cover retained sharing, bytecode and runtime behavior, parameter isolation, and debug identity.

Based directly on master, with changes confined to src/compile/. Applies cleanly alongside #453; the combined library tests pass.

• Before/after CMRs and bytecode match for p2pkh, HTLC, and kitchen-sink fixtures with debug symbols on and off.
• Synthetic 575-byte helper chain: compilation approximately 81.5 ms → 74 µs; best of three release runs with allocation counting on an Apple M4 Pro, excluding setup and output destruction. This demonstrates scaling rather than a general contract speedup.

Draft pending hand-review.

Written with GPT 6.1 Sol on Extra High.