docs: lead with native S-101 chart support

README.md

@@ -1,10 +1,10 @@
 <h1 align="center">tile57</h1>
 
 <p align="center">
-  <b>⚓ An S-57/S-101 chart engine: vector tiles, S-52 styles, PNG and PDF.</b><br>
-  tile57 turns IHO S-57 ENC cells into vector tiles (MLT or MVT) with a matching MapLibre
-  S-52 style, or renders finished charts directly to PNG and PDF — one Zig library with a
-  C ABI, compiled natively or to WASM.
+  <b>⚓ An S-101 / S-57 chart engine: vector tiles, S-52 styles, PNG and PDF.</b><br>
+  tile57 reads native IHO <b>S-101</b> ENC charts — and legacy <b>S-57</b> cells — and turns
+  them into vector tiles (MLT or MVT) with a matching MapLibre S-52 style, or renders finished
+  charts directly to PNG and PDF — one Zig library with a C ABI, compiled natively or to WASM.
 </p>
 
 <p align="center">
@@ -32,9 +32,9 @@ entirely with AI assistance. A few specific goals shape its design:
   Claude and reviewed by a human. The project tests how far AI can carry the heavy lifting of
   spec interpretation, test coverage, and implementation correctness on a non-trivial domain.
 
-- **Spec adherence first.** The goal is to implement S-57 decoding, S-101 portrayal, and S-52
-  display as faithfully as possible, using the actual IHO spec documents and the official
-  Portrayal Catalogue — not approximations or shortcuts.
+- **Spec adherence first.** The goal is to implement native S-101 and S-57 decoding, S-101
+  portrayal, and S-52 display as faithfully as possible, using the actual IHO spec documents
+  and the official Portrayal Catalogue — not approximations or shortcuts.
 
 - **Cross-platform via Zig.** Zig's build system and cross-compilation support let the same
   core compile to native (Linux, macOS, Windows) and **WASM** without code changes. Go and Zig
@@ -59,14 +59,17 @@ entirely with AI assistance. A few specific goals shape its design:
 
 ---
 
-**tile57** decodes NOAA/IHO **S-57** ENC cells and generates **vector tiles** by
-`(z, x, y)` — MapLibre Tiles (MLT, the default; MapLibre GL JS ≥ 5.12
-decodes them natively) or Mapbox Vector Tiles — running the
-official IHO **S-101 Portrayal Catalogue** in embedded Lua to produce S-52
-nautical portrayal. Alongside the tiles it emits a **MapLibre GL style** and the
-portrayal **assets** it references — colour tables, line styles, and the sprite
-+ area-fill pattern atlases — so a renderer like
-[MapLibre](https://github.com/maplibre/maplibre-native) can draw a chart directly.
+**tile57** reads native IHO **S-101** ENC charts (S-100 Part 10a) *and* legacy
+NOAA/IHO **S-57** ENC cells — the format is detected from the `.000` file itself —
+and generates **vector tiles** by `(z, x, y)`: MapLibre Tiles (MLT, the default;
+MapLibre GL JS ≥ 5.12 decodes them natively) or Mapbox Vector Tiles. A native
+S-101 dataset feeds the portrayal engine directly; an S-57 cell is converted to
+the S-101 model first. Either way, the official IHO **S-101 Portrayal Catalogue**
+runs in embedded Lua to produce S-52 nautical portrayal. Alongside the tiles it
+emits a **MapLibre GL style** and the portrayal **assets** it references — colour
+tables, line styles, and the sprite + area-fill pattern atlases — so a renderer
+like [MapLibre](https://github.com/maplibre/maplibre-native) can draw a chart
+directly.
 
 It holds only its working set:
 
@@ -83,13 +86,18 @@ It holds only its working set:
 
 ## Pipeline
 
+Both source formats converge on the same S-101 feature records — a native S-101
+dataset produces them directly; an S-57 cell is adapted into them:
+
 ```
-S-57 ENC cell (.000)
-   │  ISO 8211 decode                    src/iso8211/
-   ▼
-S-57 feature + geometry model            src/s57/
-   │  adapt S-57 → S-101 features        src/s101/ (adapter)
-   ▼
+S-101 ENC (.000)              S-57 ENC cell (.000)
+   │ ISO 8211 decode             │ ISO 8211 decode          src/iso8211/
+   ▼                             ▼
+S-100 spatial + feature       S-57 feature + geometry       src/s57/  ·  src/s101/
+   records                       model
+   │ assemble to S-101           │ adapt S-57 → S-101        (native.zig / adapter.zig)
+   └──────────────┬──────────────┘
+                  ▼
 S-101 feature records
    │  S-101 portrayal (embedded Lua)     src/portray/ + rules
    ▼
@@ -100,10 +108,14 @@ render Surface ──► MVT / MLT tiles (src/tiles/)  +  MapLibre style.json +
              └───► PNG raster / vector PDF / terminal text (src/render/)
 ```
 
-The stages are separate Zig modules — `iso8211`, `s57`, `s101`, `tiles`,
-`render`, `scene`, `style` — pure Zig with no libc; only the Lua portrayal
-(`portray`) and the sprite rasterizer (`sprite`) pull in C. See
-[the architecture docs](docs/docs/architecture.md).
+A native S-101 chart is read straight into the S-101 model — its in-band code
+tables already carry the S-101 class and attribute names — so no conversion runs;
+its `.001…` update files are applied on load. An S-57 cell is read into the S-57
+model and adapted (a best-effort, S-65-guided step; see
+[limitations](docs/docs/limitations.md)). The stages are separate Zig modules —
+`iso8211`, `s57`, `s101`, `tiles`, `render`, `scene`, `style` — pure Zig with no
+libc; only the Lua portrayal (`portray`) and the sprite rasterizer (`sprite`) pull
+in C. See [the architecture docs](docs/docs/architecture.md).
 
 ## Use it from Zig
 
@@ -151,6 +163,8 @@ and the asset/atlas generators. See [the C API docs](docs/docs/c-api.md).
 
 The offline tool bakes charts and emits portrayal assets:
 
+Any `.000` — native S-101 or S-57 — works everywhere; the format is auto-detected.
+
 ```sh
 zig build                                    # builds zig-out/bin/tile57
 tile57 bake CELL.000 -o out/                 # one cell -> out/tiles/<CELL>.pmtiles + partition.tpart
@@ -159,6 +173,7 @@ tile57 assets   -o assets/                   # colortables + linestyles + sprite
 tile57 png ENC_ROOT --view -76.48,38.974,15 --size 1600x1200 -o chart.png
 tile57 pdf ENC_ROOT --view -76.48,38.974,15 --size 1600x1200 -o chart.pdf
 tile57 ascii CELL.000 --view -76.48,38.974,13 --ansi --tui    # the chart in your terminal
+tile57 s101 CELL.000                         # inspect a native S-101 dataset
 ```
 
 ## Build

docs/docs/getting-started.md

@@ -13,7 +13,9 @@ uses the engine from Zig and C. It assumes you have finished
 ## 1. Bake a chart with the CLI
 
 The `tile57` binary is the offline tool. It bakes ENC charts to PMTiles and emits
-the portrayal assets a renderer needs:
+the portrayal assets a renderer needs. Every `CELL.000` below can be a native S-101
+chart or an S-57 cell — the format is detected from the file, so the same commands
+work on either:
 
 ```sh
 zig build                          # builds zig-out/bin/tile57
@@ -39,6 +41,7 @@ $T pdf CELL.000 --view -76.48,38.974,15 --size 1600x1200 -o chart.pdf
 # Inspect / summarise
 $T inspect out/tiles/US5MD1MC.pmtiles  # zoom range + tile counts for one chart
 $T cell    CELL.000                    # summarise an S-57 chart
+$T s101    CELL.000                    # inspect a native S-101 dataset
 $T version
 ```