LA-59–LA-61: Complete reflective native mutation failure metadata #756

Scope

One local interpreter milestone under Track A #600 and exception owner #124, delivered in a single feature PR.

• LA-59: Frame/code/cell/frame-locals-proxy/property/super attribute mutation failures distinguish missing names from read-only native attributes, retain original receiver/string-subtype key identity where CPython supplies it, and preserve writable cell/property behavior.
• LA-60: Direct scalar native storage descriptors use the same empty AttributeError metadata contract as ordinary mutation, including subtype receivers and receiver validation order.
• LA-61: Composed module/dynamic/generator programs and an installed offline example cover retained owner cycles, original frames, cancellation/restart, and shared resource limits; reconcile inventories and exact remaining boundaries.

Acceptance

Pinned CPython 3.14.7 source/reference cases; focused Python tests during implementation; local Chromium acceptance after meaningful batches; complete local PR CI-equivalent suite before the first push. Squash local work into one feature commit, open one PR, retain successful evidence without redundant reruns, and squash merge after required checks pass.

Tracing/frame jumping, original-instance shared-key deletion, remaining native/import/parser metadata, exception groups/except*, traceback objects/mutation and note export retain #124. Broader formatting, container/iterator/codec APIs and library/package/candidate/release gates retain their existing owners. No release or deployment is included.

Accepted — 2026-11-02

Completed in #758, squash merged as 56e19c1. All 678 shared local PR-check IDs pass, with 2,257 exception unit tests, every final Node/Chromium profile/driver combination and 215 isolated installed-wheel offline checks. The final corpus has 1,828 cases (1,808 supported comparisons, 20 explicit refusals, 267 shared core cases and six separate existing qualifications). The source audit records 140 refusal sites; all eight revision-22 execution resource observations remain stable. Final main smoke passes. The duplicate PR workflow was cancelled after merge to reuse successful local validation. #757 owns the explicitly retained callback-bearing key lookup work; the other stated parent gates remain open.