Live chart-prior seeding: prime the predicted surface in the live node to gate false-deep detections (live #89 equivalent)

[rolker]

Summary

Add a live equivalent of import_bag --prior (#89): a parameter that primes the
live CUBE node's predicted surface from a Chart (contour) prior at activate-time,
so live runs reject false-deep detections the same way the offline importer now
does. Today the gating is offline-only — the live node has no chart-prior/seed param,
so live cubing has no predicted surface to gate against and false-deep detections
pass through (corrupting both live bathy and the co-estimated backscatter).

Prerequisite for rolker/unh_echoboats_project11#350 (Gap 3 — live outlier gating
on the boat).

Background

#89 added predicted-only chart-prior seeding to the offline path:
import_bag --prior <store_dir> loads a store's Chart layer and primes the
predicted surface via cube::loadIntoSheet(..., SourceLayer::Chart, sheet, /*seed_settled=*/false) before the soundings, turning on CUBE's
predicted-surface blunder gate (Node::insert is a pass-through when
predicted_depth_ is NaN). The machinery is reusable as-is; only the live node's
wiring is missing.

Proposed change

In cube_bathymetry_node.cpp:

• New param, e.g. prior_store_dir (default "" = off): path to a bathy store
  whose Chart layer seeds the predicted surface.
• On configure/activate, load that store and call
  cube::loadIntoSheet(prior, SourceLayer::Chart, *geo_map_sheet_, /*seed_settled=*/false) — predicted-only, so the coarse contour gates but is
  never settled into the survey/Draft layer (no contamination of bathy or
  co-estimated backscatter; honest holes, query-time overlay fills at read).
• Order it correctly relative to the existing draft warm-start prime
  (seedSettledDepth, settled=true from the node's own draft_dir): the chart prior
  sets the predicted surface (external prior), the draft warm-start sets settled
  hypotheses (own accumulation) — complementary, both should coexist.
• Reuse import_bag: seed CUBE predicted surface from the Chart (contour) prior to reject false-deep detections #89's validation: refuse/​warn loudly on 0 Chart tiles and on
  all-wrong-GGGS-level charts (chart must be at the survey level — level 10 / 1 m
  cells — to coincide with survey nodes and gate). Open design point: a lifecycle
  node should probably warn loudly + continue ungated rather than fail the
  configure transition (don't take down the live perception stack because the prior
  is misconfigured) — but make the un-gated state impossible to miss in the log.

Bonus

The same chart-derived predicted surface is the input the live slope correction
(#15 / producer #59) needs — so this also unblocks live slope-aware incidence
without self-bootstrapping circularity (the external chart prior is preferred over a
self-derived surface).

Acceptance

• prior_store_dir param primes the predicted surface from the Chart layer at activate, predicted-only (no settled fill).
• A false-deep detection that survives without the prior is rejected with it (live-path test, mirroring #89's SeededPredictedSurfaceRejectsDeepBlunder).
• Coexists with the existing draft warm-start prime.
• Loud, unmissable log when the prior is missing / 0-tile / level-mismatched (un-gated state never silent).

Sibling of #89 (offline). Unblocks rolker/unh_echoboats_project11#350 Gap 3.

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Authored-By: Claude Code Agent
Model: Claude Opus 4.8 (1M context)