py_register_instance_field mutated the shared Tier-2 registry through direct
struct writes that bypass the read_only seal: it overwrote field-type pointers
in place and reassigned the sealed type entry's field arrays to memory owned by
the per-file arena. In the fused parallel resolve path (one sealed registry
shared by all resolve workers) that is a cross-thread data race, and it leaves
the shared registry pointing into arenas that die with their file -- a
cross-file use-after-free. The count-based seal guard could not see it because
type/func counts never change.
Python extraction emits no instance fields, so resolve-time discovery is the
ONLY source of self.x / PEP-526 fields; a plain read_only gate would silently
drop real attribute-chain CALLS edges. Fix instead routes discovery into a
per-file field overlay on PyLSPContext (arena-backed, dies with the file) and
has py_lookup_field_depth consult shared-base + overlay at the exact precedence
point of the direct field scan. Mutable per-file registries keep the original
in-place write, byte-identical.
Reproduce-first, both halves pinned:
- seal_py_shared_registry_readonly_fields: RED on the bug (field count 0->1 on
a sealed registry), GREEN with the overlay.
- pylsp_fused_self_attr_chain_via_overlay: GREEN with the overlay, RED under a
simulated plain gate (self.b.work() CALLS edge lost) -- proven both ways.
Suites: c_lsp 749, py_lsp 63+45 stress/scale/bench, pipeline 216, registry 54,
scope 10, type_rep 19 -- zero failures.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
Martin Vogel
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