docs(devx): SELF_TEST_MODES argues the worklist-reading family into gated (#15766)

The `SELF_TEST_MODES` doc block carried a dedicated section for each family that
joined `gated` after the original three -- the `DETERMINED` register (#13886) and
the copied gate vocabulary (#15459) -- but never one for `WORKLIST_READING_CONTROLS`
(#15503), which the self-test body points at this block for by name:

    // ... and SELF_TEST_MODES for why
    // this family is gated: it compares a producer against a declared population

A reader following that pointer landed in a block that discussed the other two by
name and never mentioned the family they were asking about.

The argument is CARRIED, not invented: it restates what `WORKLIST_READING_CONTROLS`
already argues at its own declaration ("No — the empty worklist it pins is the state
the repair programme is trying to reach") and the mechanical half the self-test body
already states. The block now also states the pattern once: a family that joins
`gated` owes a section here.

Comments only -- the non-comment diff is empty; no behaviour change, no counts
restated as integers (the named-list header from PR #15764 is the authority).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

Author: claude

scripts/measure-durability-swallow-family.mjs

@@ -1029,6 +1029,26 @@ function staleLines(stale) {
  * PR #15458 grew the gate's map from 18 names to 20 and this file went stale in
  * four places the same afternoon (#15459, #15473), under a green farm the whole
  * time, which is the cost of an uncross-checked copy stated as a measurement.
+ *
+ * ## The WORKLIST READINGS (#15503) are in both modes, for the same reason
+ *
+ * `WORKLIST_READING_CONTROLS` pins what the tier-1 worklist PRINTS, and the
+ * `--self-test` exercises those readings against a DECLARED population rather
+ * than against this tree: neither `(none …)` line has ever been printed by a run
+ * of this instrument, and an unreachable reading is a reading nobody proofreads.
+ * That does not weaken its claim to `gated`, it is the claim. The family passes
+ * the test the two sections above apply, and its own declaration states the
+ * answer in those words: can a successful repair destroy it? "No — the empty
+ * worklist it pins is the state the repair programme is trying to reach", so the
+ * day this family matters most is the day the programme succeeds. The self-test
+ * body says the mechanical half: it "compares a producer against a declared
+ * population and never touches membership", so no repair can destroy it.
+ *
+ * ⛔ That is the pattern and not a courtesy: A FAMILY THAT JOINS `gated` OWES A
+ * SECTION HERE, arguing on those terms why a successful repair cannot destroy
+ * it. This block is where the self-test body sends a reader asking that
+ * question, and a pointer landing on a block that names every family but the one
+ * asked about is how the next author learns the obligation is optional.
  */
 const SELF_TEST_MODES = new Set(['all', 'gated']);