Fix main-red floor content layer: absent declared roots skip loudly + gate-universe spans the job split + disposition-marker pin matches emission

[gunbai-bot]

The timeout mask (#6488/#6495) and the batch-2 panic mask (#6493) are gone, which exposed the content layer behind them: three reds that every completed floor now hits, all reproduced on clean main before fixing.

1. anchor_source_root panic on dag/compiler (surfaced on Runner offers modeled (ubicloud + GitHub-hosted, cited) + one selection authority; CI routed to ubicloud through the model #6497's run) — a declared medium-structure root that doesn't exist yet (modeled-before-implemented). The walk's own is_dir guard shows absence is a legitimate skip state, but the anchorer panicked first. New non-panicking try_anchor_source_root for declared-root walks: absence skips with a counted [layer-import] line — loud, never silent; CLI args keep the strict refusal.
2. Gate universe vs job split — the universe witness compared all 10 Gate arms against the ci job's 7-gate slice (stale since CI serial job split: bounded build / floor / emit-determinism jobs (operator ruling 2026-07-11) #6472). Now unions floor+regen+emit_determinism (probe receipt: the slices partition the 10 arms exactly), matching its sibling witness's existing idiom.
3. Disposition-marker adjacency pin (landed today, red from first run) — pinned the stamp with no blank line before the docs-only branch; the emitted script has one. Pin now matches emission and still proves the ordering.

Receipts in the commit: ci_spec_witnesses, all 4 universe witnesses, layering clean-tree — green by execution. Remaining pre-existing main reds tracked separately: s1_closure_parses_holds (#6459 wrapper-retained diagnostic arm), ci_deploy_witnesses.

🤖 Generated with Claude Code

[gunbai-bot]

Agreed the finding is real: a zero-fact projection from a skipped absent root is indistinguishable on the fact stream from a genuinely empty root, and the skip is only observable on stderr. Why I'm leaving it as the interim shape rather than typing it into the seed now:

• The whole helper family this lives in is a declared dissolution target (cli_run_runtime_workspace_root_plumbing scaffold marker — anchor_source_root, repo_relative_path*, and call-site plumbing, ~130 LOC, DELETE WHEN Migrate orchestration emission to agnostic registry dispatch (de-bash the compiler stage) #6106 realizes claim-bin path resolution from .dag). Growing its Rust API (a typed skip variant threaded through layer_import_facts's return type and the builtin bridge) adds seed surface to code whose end state is deletion — the typed home for "declared root not yet realized" is the .dag-side layer model when that dissolution lands, where it can be a counted refusal row like every other lens diagnostic.
• The stderr line is deliberately grep-stable ([layer-import] declared root ... absent) so it is countable per-run today, the same interim observability class as the existing [measurement]/[calibration] lines.

So: acknowledged as scaffold debt with a named home, not silently absorbed — the follow-up belongs to the #6106 dissolution, not a second Rust representation. Happy to type it now instead if you think the interim window will be long.

— sent from eager-gull-872