Write v17c release notes

[jameshgrn]

Document all changes from v17b to v17c. Blocked by #34.

[jameshgrn]

Tracking note: duplicate issue #93 was closed on 2026-02-21; consolidated work remains here.

[jameshgrn]

v17c Beta Export Changes Log (2026-03-13)

Database changes applied before export

Reviewer fixes

• 24 lakeflag corrections from Streamlit reviewer (GCS JSON sessions)
• 2,503 child nodes updated with propagated lakeflag values

Topology

• OC flow direction: 26 sections flipped based on SWOT slope validation (180 links, 116 reaches). Backup: reach_topology_backup_OC_3811541ae0d6. (OC: 26 sections flow-direction flipped by v17c pipeline (SWOT-validated) #200)
• OC dist_out: Recomputed for flipped sections via iterative boundary propagation (2,881 nodes updated)
• NA topology reverts (from Investigate 31 extreme bad topology links (>5km boundary gap, N007) #189): 4 bad manually-added links removed, n_rch_up/n_rch_down recomputed for 24 affected reaches
• All regions: n_rch_up/n_rch_down recomputed from reach_topology to ensure consistency

v17c attributes

• All regions: Headwater rch_id_up_main and outlet rch_id_dn_main set to -9999 (null semantics fix, ~170 reaches)
• OC: rch_id_up_main/rch_id_dn_main, hydro_dist_out, best_headwater/best_outlet, is_mainstem_edge, main_path_id, subnetwork_id recomputed via pipeline re-run

Facc

• OC: Facc denoising v3 re-run (5,066 corrections applied, F006 junction violations 480→5)

Lint check fixes

• V010 (main_connection_integrity): Excluded -9999 fill values from FK validation (Fix V010 lint check: exclude -9999 fill values from FK validation #201)

Export details

• Script: scripts/export/export_netcdf.py
• Fix applier: scripts/maintenance/apply_reviewer_fixes.py
• Output: data/exports/{region}_sword_v17c.nc + SHA256SUMS.txt

[jameshgrn]

Release notes shipped in v17c-beta.0.0.1: docs/v17c_release_notes.md