docs(gate): re-measure the pinned-set churn over the full commit population

The shipped comment justified this ratchet with "the 269 commits on `main` in
the month to 2026-08-18 ... changed in 7 commits (2.6%) ... zero left". 269 was
the depth of the shallow clone the measuring agent ran in, not the month's
traffic (#9878).

A denominator swap would not have been honest: the numerator was computed over
the same 269 visible commits, so `7/3,110` would have replaced one unverified
number with another inside the comment whose whole job is to justify a
merge-blocking gate. Re-measured instead, over the full population.

Method (stated in the comment so it can be redone): membership is proxied by
`assertEngine…Dispatch(` call sites in test files under the scan roots,
calibrated against this gate's own ledger at HEAD — 0 false negatives on the
file sets, 309 of 310 (file, verb) rows agreeing on the exact count.

Over 3,103 first-parent commits (2026-07-18..2026-08-18):

  delete   changed in 111 commits (3.6%)   162 entered   1 left
  update   changed in 103 commits (3.3%)   160 entered   1 left

The rate is HIGHER than the sample reported, which is the direction swapping
only the denominator would have hidden. The single departure per verb is one
commit, f16e54e, that DELETED a test file and added a replacement carrying
both pins in the same commit — repo-wide coverage never dropped. Zero instances
of the shape this ratchet catches (file present, verb gone), and zero per-file
counts that shrank without reaching zero.

Also corrects "308 entries today" to 310 in the same paragraph, which the
merge's ledger regeneration moved.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XqDQYVU5smx29ts9pAErja

Author: claude

scripts/check-engine-double-contract.mjs

@@ -177,14 +177,43 @@
 //     ratchet itself.
 //
 // The maintenance objection to an enumeration is real but was measured and is
-// small. Over the 269 commits on `main` in the month to 2026-08-18, membership
-// of the pinned set changed in 7 commits (2.6%): 8 files entered per verb, and
-// **zero left**. So the nuisance case an identity ledger is accused of -- a
-// correct change reddened by a legitimate decrease -- fired 0 times in a month,
-// while the additions it does redden on are already in conversation with this
-// gate (they are new fakes that had to write `assert…Dispatch` because PINNED
-// demanded it). 308 entries today against the 135 the DEBT ledger already
-// carries: same file format, same order of magnitude, same reconciliation shape.
+// small. Measured over the FULL population: 3,103 first-parent commits on
+// `main` in the month to 2026-08-18 (`git log --first-parent
+// --since=2026-07-18 --until=2026-08-18 origin/main`). Membership of the pinned
+// set changed in 111 of them for `delete` (3.6%) and 103 for `update` (3.3%);
+// 162 and 160 files ENTERED, and exactly ONE left per verb.
+//
+// ⛔ An earlier revision of this comment read "the 269 commits ... changed in 7
+// commits (2.6%) ... zero left". 269 was the depth of the shallow clone the
+// measuring agent ran in, not the month's traffic, and the 7 and the "zero"
+// were themselves computed over only those 269 commits -- so every number in
+// the sentence, numerator included, described a ~9% sample. It is re-measured
+// here rather than rescaled: the true rate is HIGHER than the sample reported,
+// which is the direction that swapping only the denominator would have hidden.
+//
+// The single departure per verb is the case worth stating precisely, because it
+// is the nuisance an identity ledger is accused of and it did not behave like
+// one: f16e54e1d deleted `protocol-delete-object-package-binding-guard.test.ts`
+// and added a replacement carrying both pins in the SAME commit, so repo-wide
+// coverage never dropped. It lands in the "file gone from disk" world below,
+// whose remedy is mechanical and carries no judgement call. Across the whole
+// month there were ZERO instances of the shape this ratchet exists to catch --
+// file present, verb gone -- and zero per-file counts that shrank without
+// reaching zero.
+//
+// Method, stated so this can be redone rather than trusted: membership is
+// proxied by `assertEngine…Dispatch(` call sites in test files under the scan
+// roots, calibrated against this gate's own ledger at HEAD -- 0 false negatives
+// on the file sets, and 309 of 310 (file, verb) rows agreeing on the exact
+// count. Anyone re-running it must first prove their clone actually covers the
+// window; a shallow one silently answers for its own depth, which is the whole
+// reason this paragraph had to be rewritten.
+//
+// So the additions the ratchet does redden on are already in conversation with
+// this gate (they are new fakes that had to write `assert…Dispatch` because
+// PINNED demanded it). 310 entries today against the 135 the DEBT ledger
+// already carries: same file format, same order of magnitude, same
+// reconciliation shape.
 //
 // ## How a LEGITIMATE decrease is expressed (the anti-nuisance half)
 //