surtgis v0.14.2

Patch release. Closes ROADMAP item H ("TopoToolbox-style channel
network depth") which was marked partially done in the 2026-06-06
survey. Two additive phases land in surtgis-algorithms::fluvial;
no breaking changes; existing API surface preserved.

Added — Phase 1 (PR #22)

• KsnSegment.ksn_ci: (f64, f64) — 95 % CI on ksn_mean from
  a deterministic percentile bootstrap over the segment's per-cell
  ksn values.

• KsnParams.bootstrap_n: usize (default 200) and
  KsnParams.seed: u64 (default 42). Mirrors the
  concavity_index recipe — hash(seed, segment_id, boot_k, cell_k)
  generates resampling indices. bootstrap_n = 0 disables the CI;
  it then equals (ksn_mean, ksn_mean), preserving legacy behaviour.

• fluvial::long_profile — new module. Walks each outlet
  upstream along the largest-area path at every confluence, emits
  per-node (coord, distance_from_outlet_m, elevation, area_m2, chi, ksn). χ and ksn are passed in as optional rasters —
  caller computes them with whatever θ_ref / smoothing-window choices
  they want; the extractor stays agnostic.

  New types: LongProfile, LongProfileNode, LongProfileParams,
  LongProfileError. Re-exported at fluvial::.

Added — Phase 2 (PR #23)

• fluvial::swath_profile — new module. Standard TopoToolbox
  swath: densify a polyline baseline to step_along_m spacing,
  cast perpendiculars at every vertex, sample the raster within
  ±half_width_m at step_cross_m steps, emit per-bin
  min / max / mean / median / p25 / p75 / n_samples.

  Baseline is caller-supplied — works equally for LongProfile
  nodes (.iter().map(|n| n.coord).collect()), fault traces, hand-
  picked transects, etc.

  New types: SwathProfile, SwathStats, SwathParams,
  SwathError. Re-exported at fluvial::.

• fluvial::export — new module. CSV / JSON writers for the
  four data products:

  Product	CSV	JSON
  LongProfile	row per node, profile_id groups outlets	hierarchical, nested nodes array
  SwathProfile	row per bin	row array
  KsnResult segments	row per segment + geometry_wkt LINESTRING	row array with nested coords
  χ raster	row per finite cell	(use the CSV)

  The core types stay free of serde derives — wrapper structs in
  export.rs own the serialisation. Adds serde_json and csv
  to surtgis-algorithms dependencies.

  Free functions: write_long_profiles_csv, write_long_profiles_json,
  write_swath_csv, write_swath_json, write_ksn_segments_csv,
  write_ksn_segments_json, write_chi_csv. All take any
  impl Write so callers can stream to files, buffers, gz wrappers,
  whatever.

Verified

• cargo test --release -p surtgis-algorithms fluvial: 42/42 green
  (was 34 pre-sprint; +8 new tests across Phase 1 and Phase 2).
• cargo build --release --workspace: clean.

Deferred and rule-outs

The 2026-06-06 ROADMAP survey listed several follow-up items under
H. Status now:

• Bootstrap CI on ksn — done (Phase 1).
• Long-profile extractor — done (Phase 1).
• Swath profiles — done (Phase 2).
• CSV/JSON export — done (Phase 2).
• Knickpoint detection — already shipped pre-sprint
  (Neely et al. 2017 KZP variant).
• Divide migration — already shipped pre-sprint
  (Whipple/Forte/Willett 2017).
• Per-tributary profile walker convenience helper —
  deferred. Callers can iterate confluences and call
  long_profile themselves; the convenience wrapper isn't a
  blocker.
• In-Rust figure generators — out of scope. Users will
  re-plot the data in matplotlib / ggplot2 / R for paper-grade
  figures anyway; the CSV / JSON export is what they actually
  need.

After this release ROADMAP item H moves from partially done to
done. See ROADMAP.md for the updated entry.