KarpelesLab / goro / 25354974735

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vm: native try/finally via AST delegation + slot refresh

try/finally is delegated to the AST runner via a new
OP_TRY_FINALLY opcode. The AST already orchestrates the
intricate dance of running finally on every exit path
(normal completion, caught exception, uncaught exception,
return/break/continue inside the try body) — replicating
that natively would be a large amount of bytecode for a
niche feature.

The delegation introduces a slot-cache coherence problem:
the AST writes locals through ctx.OffsetSet, which goes to
the FuncContext hashtable and bypasses Frame.locals[]. To
keep subsequent VM reads correct, OP_TRY_FINALLY ends with
Frame.refreshSlots(ctx), which re-reads every local from
the hashtable into the slot cache.

IsSlotSafe also rejects functions whose body contains a
runnableTry with finally — the delegation reads/writes
locals through the hashtable, so the surrounding scope
needs the hashtable mirror live (SlotOnly off).

phpt under GORO_VM=1: 14 regressions (unchanged).
Tests cover: finally after normal completion, finally
after caught exception, finally after return.

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

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