[Tracking] Migrate dedx_web wasm/dedx_extra.c helpers upstream into libdedx #118

Summary

The web frontend (APTG/dedx_web) carries ~810 LOC of C in wasm/dedx_extra.c that sits on top of libdedx because the upstream public API does not yet expose what a GUI needs. This tracking issue coordinates moving that proven code upstream so libdedx gains a GUI-friendly API, downstream duplication is removed, and the WASM build links a clean vendored libdedx with no local C patches.

Full design: docs/12-libdedx-migration-plan.md in dedx_web (per-symbol inventory + phased plan).

Why this matters

• Duplication / drift — the material display-name table exists twice (C dedx_get_material_friendly_name and TS src/lib/config/material-names.ts, 151 entries each).
• A bug fix stranded downstream — dedx_extra.c contains a corrected inverse-stopping-power branch selection that works around a real bug in upstream dedx_get_inverse_stp(); every other consumer (CLI, Python, openshieldhit) still hits the original bug.
• Re-exported internals — four accessors just publish dedx_internal_* functions that already exist in libdedx but lack a public header entry.

Relationship to existing issues

This is the C-API-surface counterpart to the ecosystem work in the health review #108 (which calls for the Python binding to expose inverse/custom-compound functionality, and lists the GUI query API). It does not duplicate:

• Add query API for valid (program, ion, material) combinations to support GUI/frontend development #79 — query API for valid (program, ion, material) combinations → that is "Phase F" of the plan; tracked there, not re-filed here.
• simple override of elemental I-values #6 — per-element I-value override → a decision point for Phase E below.
• Check mass stopping power units #48 — units documentation → new docstrings added here will use MeV cm²/g / MeV/nucl / g/cm² consistently.

Phases (each a self-contained, independently releasable PR)

• Phase A — Expose nucleon number, atom mass, density and is-gas in the public header #119 — Expose existing internal accessors (nucleon number, atom mass, density, is-gas) in the public header
• Phase B — Add public dedx_get_material_display_name() and make C the single source of truth for display names #120 — Public dedx_get_material_display_name() + make C the single source of truth for display names
• Phase C — Fix dedx_get_inverse_stp() branch selection for monotone STP curves; add Bragg-peak STP tool #121 — Fix dedx_get_inverse_stp() branch selection for monotone curves + add a Bragg-peak STP tool (bug)
• Phase D — Add flat inverse / Bragg-peak convenience wrappers to dedx_wrappers.h #122 — Add flat inverse / Bragg-peak convenience wrappers to dedx_wrappers.h
• Phase E — Public custom-compound config builder + flat forward/inverse/peak wrappers #123 — Public custom-compound config builder + flat forward/inverse/peak wrappers
• Phase F — Add query API for valid (program, ion, material) combinations to support GUI/frontend development #79 — Query API for valid combinations (no separate issue)

Suggested order: A (#119) and F (#79) first (smallest, unblock the GUI), then C (#121, highest physics value), then B (#120), then D (#122) → E (#123).

Filed via Claude Code as part of the dedx_extra.c → libdedx migration plan.