[kumagi]

PR2874 establishes retained packet backing at prefix-return cuts and leaves the rest of the loop open. This package proves the exact named-array maximum across the unchanged PR2697 packet loop, including completed output copies and factory temporaries, and supplies a phase-correct interface for action-private backing.

For N prefixes of F payload symbols, borrowed backing K, directory D and fresh prefix backing Q, the maximum is M = K + (2N+1)F + 4 + D + 2Q + max(Q,F). For example N=2,F=9,Q=4,K=19,D=7 gives prefix peak 87 but copy peak 92. This extends the predecessor's explicitly restricted claim. With action-private backing at most A, including its pending result and excluding caller arrays, the combined bound is max(M, K + 2NF + 3 + D + 2Q + A). A literal counterexample shows why borrowed backing must stay fixed throughout an action, rather than only be restored at return.

Evidence:

• Registered CPython 3.12.13 replay passed: 99 source-execution fixtures, 693 prefix-return and 693 copy-completion cuts, and 10 meaningful accounting/domain/integrity controls.
• Separate integer-identity model: 5,040 parameter cases, 10,080 schedules, 2,278,920 modeled cuts; distinguishes aligned from early-only private-storage peaks.
• Relocated Git-free, read-only-file CPython 3.14.4 optimized replay passed all three commands with unchanged bytes. All 23 exported source entries match their original Git blobs; final committed-byte and metadata checks passed after rebase.

Reproduce: python3.12 -B scripts/research_package.py --package research/selected-packet-backing-envelope. Start review with the package's README.md and PROOF.md; most added files are byte-identical portable source exports and the generated receipt.

Scope: this is a named backing-array component, not total caller memory, physical reuse, native private-scratch certification, a full selected GL64 replay, supplier admission or new kappa. The native sign fixtures certify caller storage and output only; synthetic actions instantiate the private-storage interface. Remaining tasks are an actual native A bound and the same-cut join of other owners plus physical erasure/placement/reuse.

Task selected-stock-envelope, adversarial-audit draw 12518fd3a0ea1f372fc913d00fb7f694, priority revision 5; refined to the released PR2874 handoff. Started at canonical main c7df0bb890cae0cc393cdd32dad19c3facc80992, rebased onto refreshed main a7fc79c0cd63d6aa48df753069fc49eabda79dc3; relevant guidance, selected record and replay tools are unchanged. Exact source heads: Jose Manuel/jmbarrancoml PR2697 a53fdf4bcbe33c6732f0bec1badc8c023380f9d1; Ross Richardson PR2874 08dd02bd8d8b1fadc5fe8589c2d2875d21fe5fce. Credit also starship-s PR2731 and Nick Petalas PR2743 for distinct nonblank-content results. Original licenses/notices retained. Substantial OpenAI Codex assistance, including two separate AI derivations and reviewer controls; no independent human or formal-kernel review claimed.

Canonical claim/handoff: #2319 (comment)

Submission overlap: 491 open PRs, 2,088 closed/merged PRs and 1,526 Discussion records with complete metadata pagination and no warnings, plus a direct latest scoped-thread read. Separate snapshots are not atomic; arbitrary diffs and unpublished work are excluded. Fresh predecessor heads are unchanged. The selected frontier remains untouched.