Record P104 private descent fanout reuse construction

[1337isnot1337]

Contribution

This PR records an exact P104 construction change based on PR #2152 at 05f7aad0f08992ee48ec2dd93e896d9a4567847d. The predecessor is still open, so this PR carries a source-pinned patch and replay package instead of duplicating its full source tree.

On the original fanout.py word, the existing private copy for pair (4,57) descends through the three nested contact frames for public helper 7, supplies those live-Y contacts, then continues to La to seed the remaining helpers. The helper register stays allocated and untouched. The full 735-input endpoint map passes exact rational replay and native lowering.

Evidence

• Combined transport rank mass decreases from 5,894 to 5,885; private COPY mass remains 56.
• Scalar ADD count decreases from 20,956 to 20,947. Seven entry-compensation ADDs and one each of helper seed and helper restoration disappear; three direct private contacts replace three public contact ADDs.
• The exact selected-threshold moment remains greater than one. The optimistic complex-side cap is 0.00165874758371416805798661, below selected κ = 0.001672660197076918. This is a local cost reduction, not an improved κ or supplier.
• Native replay passes 3,743 transport occurrences, 3,050 distinct recipes, all eight private paths, and 4,096 Gaussian basis columns; the wrong-phase control rejects.
• Five scalar negative controls reject, including omission of one reused contact.

Scope and reproduction

The initial Discussion claim called the target word “coalesced.” The checked experiment applies to PR #2152's original fanout.py word before its separate coalesced.py rechart; the coalesced variant remains untested. This package records that scope correction and pins the exact patch, source hashes, cost inputs, and replay receipts.

See research/p104-private-descent-reuse-seed915fa969/README.md for reproduction commands, exact moment and root intervals, predecessor attribution, and remaining obligations. No selected frontier change, merge, or κ claim is requested.