npm remote plan: add the S15 spec to Step 15's Files list and fix the two-step claim

The npm remote plan carries a sentence about which steps may edit the S15 spec, and Step 15 part 2 makes it false.

The sentence

docs/plans/2026-07-15-npm-remote.md:1756:

Step 11 and Step 14 are the only steps whose Files list docs/specs/S15-npm-remote.md

Why it goes false

!1879 (merged) is Step 15 part 2, and it edits docs/specs/S15-npm-remote.md: the wide-event field list names http_status, which is in LabKit's deprecated field map and is what the go-logging-field-validator CI job rejects, so the table is corrected to status (fields.HTTPStatusCode). That edit is right on its own terms and the MR description flags it twice.

What is owed is the plan side. While !1879 (merged) is open the sentence is still true and Step 15's Files list still omits the spec. Once !1879 (merged) merges, the sentence names two steps where three have edited the file, and Step 15's Files list is missing an entry a reader cross-referencing the two documents will look for.

What closes this

A docs(plans) MR on its own branch that:

  1. Adds docs/specs/S15-npm-remote.md to Step 15's Files list.
  2. Rewrites the :1756 sentence to admit Step 15, or restates it in a form that does not enumerate the steps.

A step MR cannot carry either edit: AGENTS.md Guardrails reserve the plan file, the Status table included, for a single writer, because parallel step MRs editing adjacent rows collide.

Provenance

Raised in review on !1879 (merged) as item 8 of a ten-item note, and categorised there as cheaper to do as a follow-up than inside the step MR. Searched S15-npm-remote Files and found no existing issue.