memory: deep-promote values escaping arena scopes; gate JIT off inside arena windows (#873)

[InauguralPhysicist]

Closes #873.

promote_if_arena copied only numbers and strings to the heap on store; its container arm was a comment ("Callers should avoid storing arena-allocated complex types"). A list escaping the scope became a dangling reference — reproduced all three severities from pure EigenScript: silent wrong values (the issue's documented-loop repro read iteration 39's data), type confusion (the tag overwritten underneath a binding), and a free(): invalid pointer abort (arena item appended into a heap list, then decref'd through the stale pointer). ASan sees none of it — the arena hands the same region back out.

Design

Deep-promote on store. A loud error would break the documented idiom (tmp is [...] inside the scope is a store); read-side generation checks tax every access. Deep promotion preserves exactly what num/str promotion already promises: unstored intermediates stay arena-cheap and die at reset; anything stored survives by copy. Lists are the only arena-capable container (make_dict/make_fn/buffers/text builders are heap-only constructors), and arena lists are acyclic at promotion time (building a cycle requires mutating through a binding, and binding stores promote), so the recursion terminates.

Every store seam promotes — named binding, OP_SET_LOCAL (module slots are immortal), dict fields (already promoted once lists promote), list_append into a heap list, OP_INDEX_SET (interpreter case and the JIT helper, including the num fast paths, which now heap-force into heap targets while a window is open), iterator-state make_num, set_at 1D/2D, list_insert_at, copy_into. Arg-pack wrappers switch to make_list_heap (they're bound as param slots — heap avoids both the dangle and the new deep-promote cost).

The JIT is gated off while an arena window is open — both fresh-entry sites, the OSR trigger, jit_helper_call's nested-thunk gate (all the same pattern as the existing MT/task-scheduler gates), plus a deep bail when a builtin opens a window mid-thunk. Emitted stores don't arena-promote; arena scopes are explicit scratch windows and run interpreted.

Proof

tests/test_arena_escape.eigs (18 checks, wired after the Arena Ownership section): both issue repros, nested lists, every seam above — each under a stomp loop that overwrites the reclaimed region so a dangling reference reads wrong, not lucky — plus a 12,000-iteration variant proving correctness across OSR thresholds. All 18 were red before the fix (the append seam aborted the process).

Validation

• Release suite 3783/3783 (new section included).
• make asan + ASAN_OPTIONS=detect_leaks=1: 3781/3781, leak tally 0 — the deep-promote's refcount flows are clean.
• Poison build (0xAA + MALLOC_PERTURB_=170): arena tests clean, JIT on and off.
• make jit-smoke green; README documents the now-guaranteed escape semantics.

Closes #873.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a critical arena-allocation escape bug (#873) in the EigenScript runtime by ensuring values that are stored out of an arena_mark…arena_reset window are safely copied to the heap, eliminating dangling references that previously caused silent wrong values, type confusion, and allocator aborts.

Changes:

• Implement deep promotion for arena-backed lists in promote_if_arena, and promote arena values when storing into heap-owned containers (append/indexed store/local/env/builtin seams).
• Gate JIT execution/OSR entry while an arena window is open, including a “deep bail” when a builtin opens an arena window mid-thunk.
• Add a dedicated regression test suite covering the escape scenarios and wire it into the test runner; document the now-guaranteed semantics.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_arena_escape.eigs	New regression suite for #873 covering escape/store seams and OSR/JIT-threshold behavior.
tests/run_all_tests.sh	Adds the new arena escape containment suite to the main test runner.
src/vm.c	Promotes/heap-forces arena values at additional VM/JIT store seams and gates JIT/OSR while an arena window is open.
src/eigenscript.h	Exposes make_num_permanent for heap-only numeric allocation used by store/promotion paths.
src/eigenscript.c	Deep-promotes arena lists in promote_if_arena and promotes arena items appended into heap lists.
src/builtins.c	Promotes arena values written into heap containers in copy_into, set_at, and list_insert_at.
README.md	Documents the new guarantee: stored escaping values are safe via heap promotion.
CHANGELOG.md	Records the fix and its behavioral guarantee, plus the new regression coverage.

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