docs(handoff): cairn#4 MERGED — the flake exists, and a four-round ladder that ended on the attribution gate

[ZacxDev]

Handoff update for cairn-oss-multi-instance.

What changed

Rank 3 read "devrc consumes cairn as a pinned flake input" and had been re-verified twice as not started — which was true and said nothing about why. The reason: ZacxDev/cairn had no flake.nix at all, so there was nothing for devrc to pin and the first move is a PR to the public repo, not to devrc.

• Half 1 — IN FLIGHT: ZacxDev/cairn#4 (0e6c7cb). Client package, server image, checks, dev shell, and a nix CI job that passed on its first-ever run. Suite 1678 passed / 0 failed; leakscan 0 findings across 36 files.
• Half 2 — not started: the devrc side. Rank 3's closing condition is unchanged and not met — flake.nix still has zero cairn references and readlink -f ~/.local/bin/cairn still resolves into the checkout.

Findings recorded

• 🔴 The devrc and OSS cairn clients have FORKED, measured with values (client diff 259 lines; per-module counts; cairn who absent from OSS by decision; subsystem_touch 6,654 lines vs entry_shape 264). ~90% of the lib drift is sanitisation prose, not behaviour — which is the argument that consolidation is realistic. This is the crux of half 2 and is written down so nobody re-derives it.
• 🔴 A cairn create [not-found] does not mean the scope is unseeded. cairn doctor states the ambiguity is deliberate. The discriminator is the pod's token file: 23 scopes, cairn absent. ⚠ The same read refutes an existing devrc/cairn bullet that concluded "the scope simply did not exist" for a different scope. Correction appended to the store (revision 4f3cb4da30f648e4); new rank 11 files the operator action.
• 🔴 leakscan was blind to .nix — closed in feat(espanso): tune prompt snippets from session-usage mining #4 for the immediate case, filed as a new ranked item for the class.

Note on process

The doc is landed from a worktree on a feature branch, not from main — this repo's CLAUDE.md forbids committing to main in either host checkout, and the handoff tool pushes wherever the checkout sits.

⚠ No clawgate-task: field is recorded: clawgate_handoff.sh resolve exited 5 (0 tasks). Its positive control answered 11 links for another session, so the board is reachable — but a wrong session id answers identically, so that 0 is not a clean bill of health. No task was created to fill the blank.