v0.8.5 — Fail-Fast Training Guard, Refit Telemetry & Canvas Help Guide

📦 Release

• Version sync to 0.8.5 (app + frontend + core): root pyproject.toml,
  frontend/ml-canvas/package.json / package-lock.json, and
  skyulf-core/setup.py bumped to 0.8.5.

🧠 Core — legible tuning failures

• grid/random search no longer discards the original per-fold error when
  every candidate fails: the first trial error is threaded through the
  evaluation chain and appended to the All trials failed exception as
  First trial error: … — mirroring the detail optuna/halving already
  had, so a cryptic "All trials failed" now names the root cause (e.g. a
  non-numeric column reaching sklearn).

🔧 App — fail-fast guard & fold-refit telemetry

• Non-numeric training-frame guard: before tuning starts, the training
  node preflights its frame and raises an actionable ValueError listing any
  leftover object/string/category/datetime columns — instead of dying deep
  inside sklearn with every fold error swallowed. The target column and the
  time-series CV time column are legitimately non-numeric and excluded. The
  message explains the most common cause: after a Split, merged branches
  resolve overlapping columns by pure merge order, so the last connected
  branch may have overwritten an earlier branch's encoding.
• fold_refit_fallback metric: graphs that can't use per-fold refit and
  fall back to pre-transformed scoring now stamp a stable reason code into
  the node metrics (nested_merge, fork_not_splitter,
  learner_before_split, row_changing_branch_step, unsupported_graph,
  payload_reconstruction_failed) — demand telemetry for which unsupported
  shapes users actually hit.
• fold_refit_audit metric: a new AuditedFoldPreprocessor
  (skyulf-core) records the input row count of every per-fold
  fit/transform; isolation_ok proves no preprocessing fit saw more rows
  than the train split, i.e. no held-out row leaked into a fit.

🎨 App — job details, help guide & canvas UX

• Score Advisory amber tile + modal in Job Details: flags runs that fell
  back to pre-transformed scoring (optimistically biased scores) with a
  plain-language explanation mapped from the fold_refit_fallback code; a
  new Fold Refit Audit detail modal shows the per-fold isolation verdict.
  The placeholder Progress tile was removed.
• In-app help guide: the navbar's round book button opens "How pipelines
  work" — ten sections covering linear chains, branches, merge ownership,
  post-split merge order, row alignment, Run Preview vs Run All Experiments,
  where results live, the Leakage Gate and Fold Refit Audit, the Score
  Advisory, and badge/edge-color semantics.
• Canvas UX fixes: Preview Results gained an always-visible X close
  (dismissed until new results or validation issues arrive); Run Preview is
  always visible and explains its blockers on click; the legend button uses
  a tag icon with updated post-split merge-ownership copy and renders above
  the results panel; fixed stacking so canvas buttons no longer float over
  modals or the maximized panel, and the sidebar expand button no longer
  overlays everything; zoom controls lift above an expanded results panel.

📚 Docs

• multi_path_pipelines.md: after a Split, merge ownership is inert —
  overlapping columns resolve by pure merge order (last connected branch
  wins every shared column); keep post-split branches disjoint or fully
  numeric.
• troubleshooting.md: new entry for "All trials failed" /
  non-numeric-column errors after a Split; PropertiesPanel shows a matching
  post-split note under the merge-strategy select; leakage_proof_pandas.md
  cross-links to the guide.

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