Adopt the OKF timestamp change and a simpler frontmatter convention

[leoafarias]

Summary

Upstream restated OKF 0.2 so that every timestamp is an ISO 8601 datetime with an explicit UTC offset, covering generated.at, verified[].at, stale_after, sources[].last_modified and usage_window. Wayfinder, the Concepta Profile and the vendored spec copy were pinned to the pre-revision text.

This issue also absorbs #78, closed as a duplicate: the spec pin moves to the canonical repository in the same change.

Correction to the original plan. The revision was first described as knowledge-catalog 62432a0. That commit does not exist in open-knowledge-format, so "pin 62432a0 on open-knowledge-format" was not a reachable instruction. The two upstream copies are byte-identical at 1006 lines, so the canonical pin is open-knowledge-format@ad30107 — the merge of okf-iso-datetimes, 2026-08-21 — with knowledge-catalog@62432a0 recorded as the mirror the okf package names. Pinning the canonical repository therefore costs nothing beyond the revision itself.

Status

Implemented on verify-issue-queue-2026-09-12, pending a pull request and the release. Verified there by melos lint (analyze clean, format clean, 392 tests) and the example gate at Automated gate: PASS with 0 error(s), 0 advisory(ies) from OKF.

• Upgrade okf. ^0.3.0 → ^0.5.0 in wayfinder, wayfinder_cli and wayfinder_embeddings. The pub workspace forces this to be atomic — one package at ^0.5.0 against the others at ^0.3.0 fails version solving.
• Release Concepta Profile 2026.2. Spec pin moved; §5.5 row and §6.4 treat stale_after as an absolute instant compared against now; new §6.5 states the timestamp requirement; §11 binds 2026.2; §15.3 carries the sections, the driver and the migration in words. 2026.1 is preserved byte-identical under profile/versions/, which this created for the first time.
• Re-vendor the specification. references/OKF-0.2.md is byte-identical to ad30107 with its header recording the mirror. The filename keeps 0.2, because OKF is still 0.2.
• Compatibility and coverage evidence. The review gained a timestamp-revision section with four records; the matrix gained two rows splitting §6.5 into its automated MUST NOT and its contextual SHOULDs. The implementation guide binds 2026.2 with its own §9 entry.
• Frontmatter writing convention. §6.5 adds three producer SHOULDs — quoted timestamps, block-style structured values, and verified as a list — with an explicit requirement that readers keep accepting inline YAML, because the spec's own examples use it. Taught in the authoring reference and the seed templates.
• Migrate examples/knowledge. Block-style frontmatter, quoted timestamps, verified as a list, and offsets on the two date-only values. OKF advisories went from two to none.
• Release Wayfinder with the new okf and Profile 2026.2. Both package changelogs carry an Unreleased entry describing the user-visible consequence: a bundle still declaring concepta_profile: "2026.1" now reports an unsupported release rather than a conformance verdict.

Downstream bundle migration stays with each consumer, through okf format --migrate-timestamps or the authoring skill, and is not tracked here.

Two further corrections

• "okf 0.4 already resolves" was wrong. A ^0.3.0 constraint does not admit 0.4 or 0.5, so the pin genuinely blocked the upgrade.
• The upgrade forced an SDK decision. okf 0.4.1 raised its floor from 3.4 to 3.9, and packages/wayfinder declared >=3.6.0. Every package now declares >=3.11.0 <4.0.0, matching conceptadev/mix for organization-wide consistency; the dependency-derived minimums were lower (3.9.0 for wayfinder, 3.10.7 forced by the exactly pinned llamadart). Moving the core package's floor also switched its formatter to tall style and enabled use_null_aware_elements, which account for most of the diff. The matching okf change is not done and belongs to conceptadev/okf.
• SEEDING.md is no longer at the repository root. It lives at skills/adopt-knowledge-bundle/SEEDING.md.

[leoafarias]

Folding the unique remainder of #78 into this issue so #78 can close as a duplicate.

This plan already covers adopting the OKF 0.2 timestamp change (Profile 2026.2, vendored spec, one authoring form, okf upgrade, content migration). #78 still adds two acceptance items that are not yet stated here:

1. Canonical pin. Re-point the OKF 0.2 pin to a SHA on GoogleCloudPlatform/open-knowledge-format, the maintained spec repo. Pinning 62432a0 only as a knowledge-catalog commit is not enough — that is the frozen copy Re-pin OKF 0.2 to the canonical open-knowledge-format repository and review the ISO-datetime change #78 called out. Checked just now: 62432a0 exists on GoogleCloudPlatform/knowledge-catalog (the #323 timestamp change) and does not exist on open-knowledge-format. The same change on the canonical repo is merge ad30107 (okf-iso-datetimes; tip commit 3dc3029). Confirm the equivalent canonical SHA and update pin references to that repository.

2. Compatibility review. AGENTS.md requires a compatibility review for an upstream specification change, even without another Profile convention change. Update docs/compatibility-review.md for the ISO-datetime-with-offset rule.

Closing #78 as a duplicate of this issue.