feat(registry): declare the capture cadence, the drift basis, and the parity ledger

[JSONbored]

Closes #11146.

The epic measured three mechanisms that each silently broke "every subnet's API, exactly like using it directly". Phase 3 (the surface method dimension) landed in #11210 and the first declared mutation in #11212; this completes the rest in one change.

1. Freshness is measurable

The capture lane's cadence is declared once (SCHEMA_CAPTURE_CADENCE_HOURS = 48) and published on the schema index as capture_cadence_hours. The lane stays manual by ADR 0006 — declaring the cadence does not run it, it makes its silence measurable, which is the difference between an unpublished gap and a published one.

No age is baked into the artifact, deliberately. The index is served for hours after it is built, so a build-stamped age is wrong on arrival; it is also not reproducible across two builds; and because buildTimestamp() returns the 1970 epoch placeholder in every local build, an earlier revision of this branch published a twelve-day-old capture as fresh — caught in a built artifact, and the reason the design changed. Every entry already carries observed_at, so the subtraction belongs to the reader, whose clock is the only one that says now.

2. Drift says what it measures

Captured entries carry drift_basis: "previous-capture". drift_status compares our snapshot to our previous snapshot, never upstream — which is why 23 of 24 measurably-drifted subnets reported unchanged. The payload now says so rather than implying the opposite.

3. The parity ledger

Each gaps row gains schema_parity: captured paths and declared mutations against registered route surfaces and registered mutations, flagged when the catalogue registers fewer routes than the subnet declares.

Derived from schema index entries only — captured documents exist solely in credentialed builds, so a rollup reading them would not be reproducible — with the capture lane now stamping non_get_operation_count so both sides of the mutation ledger are measured. Counts absent on pre-stamp entries report null, never zero.

First measurement: 53 subnets measured, 27 flagged — sn-3 registers 8 routes against 208 declared paths; sn-105 registers 29 (including the POST surface from #11212, which the ledger counts as its 1 registered mutation) against 53.

Validation

• typecheck, lint, format:check
• validate (129 subnets / 3,330 surfaces), validate:api (215 routes), validate:openapi, validate:contract-drift, validate:published-names, validate:unreferenced-exports (731 — at the ceiling, not raised; the earlier revision's new type exports were removed rather than ratcheted), validate:schema-enums, validate:schema-vocabularies, validate:mcp (240 tools), validate:schemas, validate:no-hand-written-mjs
• Full suite green, including artifacts-build-determinism and the schema-index-preservation suite — both re-run against a pristine committed baseline, which is how the build-clock defect above was found
• Two consecutive builds from a pristine baseline: byte-identical

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[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[JSONbored]

Closing on red CI rather than pushing over it. The schema index turned out to be un-annotatable by a PR: its committed copy is a deploy-owned capture cache, and artifacts-build-schema-index asserts a rebuild reproduces it exactly, so any added field breaks the gate that protects 58 captured schemas.

Reworked so that artifact is untouched — the cadence moves to the schema_parity block (a normal built artifact, proven deterministic), and the drift-basis honesty becomes the published drift_status description at the point of consumption. Reopening green.