diff --git a/README.md b/README.md
index b702ad0..4b0293a 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@ This repository currently contains:
 - A first-pass knowledgebase under `docs/knowledgebase/`.
 - An implementation roadmap under `docs/plans/`.
 - Legal and reference-material hygiene notes under `docs/legal/` and `docs/research/`.
-- A clean-room terrain import boundary with project-owned `ovp-text` fixtures, a PNG heightmap script importer, an SRTM/HGT byte importer behind the `hgt` Cargo feature, and an ESRI ASCII Grid parser behind the `ascii-grid-import` feature.
+- A clean-room terrain import boundary with project-owned `ovp-text` fixtures, a PNG heightmap script importer, an SRTM/HGT byte importer behind the `hgt` Cargo feature, an ESRI ASCII Grid parser behind the `ascii-grid-import` feature, and a deterministic terrain-generation module in `src/terrain_gen.rs` with `TerrainGenerationSpec` / `DeterministicTerrainGenerator` (see `cargo test terrain_gen` and its determinism/seed note).
 
 ## Development
 
diff --git a/docs/knowledgebase/architecture-notes.md b/docs/knowledgebase/architecture-notes.md
index 7cf014f..84afc36 100644
--- a/docs/knowledgebase/architecture-notes.md
+++ b/docs/knowledgebase/architecture-notes.md
@@ -5,6 +5,7 @@
 Start simple, then split into crates when module boundaries stabilize.
 
 - `src/terrain.rs`: height grid, bounds, sampling, and deterministic terrain fixtures.
+- `src/terrain_gen.rs`: `TerrainGenerationSpec` and `DeterministicTerrainGenerator` for the seeded terrain-generation pipeline; `cargo test terrain_gen` exercises the determinism/seed note.
 - `src/import.rs`: importers for open/safe formats (`ovp-text`, feature-gated HGT, feature-gated ESRI ASCII Grid, and feature-gated GeoTIFF via `src/import/geotiff.rs`); historical compatibility later. Each importer yields the same internal `HeightGrid` plus `TerrainSourceMetadata`, keeping source formats out of renderer code.
 - `src/scene.rs` and `src/scene_file.rs`: camera, light, atmosphere, water/vegetation thresholds, and `.ovp.toml` persistence.
 - `src/render.rs`: deterministic CPU top-down renderer plus CPU perspective demo renderer; WGPU renderer later.
diff --git a/docs/knowledgebase/ui-panel-map.md b/docs/knowledgebase/ui-panel-map.md
new file mode 100644
index 0000000..baf42ad
--- /dev/null
+++ b/docs/knowledgebase/ui-panel-map.md
@@ -0,0 +1,50 @@
+# OpenVistaPro UI Panel Map
+
+This is a normalized modern shell map derived from the VistaPro manuals, screenshots, and the current OpenVistaPro codebase. It is intentionally not a 1:1 recreation of the legacy menu hierarchy; instead, it groups the old surfaces into a docked shell that can grow with the product.
+
+## Proposed panel layout
+
+| Modern panel | VistaPro surfaces it absorbs | Suggested placement | Current code support | Notes / gaps |
+|---|---|---|---|---|
+| Viewport / preview | Main render window, map preview, perspective view, preview/final render output | Center dock | Partial | `src/app.rs` already renders the CPU preview into `CentralPanel`; perspective and top-down preview modes exist, but there is no GPU viewport or direct manipulation overlay yet. |
+| Terrain / import | Load Landscape, Import, terrain source selection, generated terrain presets | Left dock or collapsible section | Partial | The current shell exposes project-owned terrain presets (`Plane`, `RadialHill`) and a placeholder import entry point; legacy format import UI is still absent. |
+| Scene / camera | Camera and target gadgets, lens/range, bank/heading/pitch, water/tree/snow/haze controls | Left dock or inspector stack | Partial | Position/target, orientation, lens/range, vertical exaggeration, palette, and hydrology controls now live in `src/app.rs` and `src/app_state.rs`; `src/scene.rs` and `src/render.rs` carry the model/render semantics. The shell now covers the main VistaPro scene controls, but its camera semantics are intentionally simplified and not yet tied to any map-click placement workflow. |
+| Render | Preview vs final render, quality/smoothing, detail tradeoffs | Left dock, toolbar, or render tab | Partial | Current code toggles top-down vs perspective render mode, but there is no dedicated quality profile or render preset UI. |
+| Scripts / paths | Script menu, Run Script, MakePath path tools, animation-frame workflows | Right dock or modal workflow | Partial | Script parsing exists in the codebase, the shell now surfaces a script editor and placeholder path controls, but execution and path generation are still deferred. |
+| File / project actions | New/Open/Save landscape, scene load/save, export commands | Top bar / file menu | Partial | The shell now shows scene-file status and disabled file actions; load/save execution is still wired only in the backend modules. |
+| Status / feedback | Coordinate readouts, render state, file path, progress, messages | Bottom status bar | Partial | The shell now has a bottom status bar driven by `AppData::ui_snapshot()`. |
+| Deferred features / legacy compatibility | Dense menu hierarchy, advanced lighting, hydrology, vertical exaggeration, palette editing, legacy image/landscape exports | Right dock, tool drawer, or dialogs | Planned | These are best surfaced as future tabs or dialogs rather than cluttering the initial shell. |
+
+## Recommended shell structure
+
+A practical first-pass shell is:
+
+1. Top bar for file/project actions and render mode shortcuts.
+2. Left dock for terrain/import and scene/camera controls.
+3. Center viewport for preview output.
+4. Right dock for scripts/paths and deferred advanced features.
+5. Bottom status bar for current scene, source, and render feedback.
+
+That layout preserves the VistaPro workflow while making room for modern discoverability and incremental feature growth.
+
+## Panel-by-panel implementation summary
+
+| Panel | Code support today | Implementation evidence | Priority |
+|---|---|---|---|
+| Viewport / preview | Present | `src/app.rs` renders the preview into `CentralPanel`; `src/app_state.rs` builds the preview image. | High |
+| Terrain / import | Partial | `TerrainPreset` and `AppAction::SetTerrainPreset` in `src/app_state.rs`; terrain radio buttons in `src/app.rs`. | High |
+| Scene / camera | Partial | `Scene`, camera position/target controls, and scene-band sliders in `src/app.rs` and `src/app_state.rs`. | High |
+| Render | Partial | `RendererMode` plus preview switching in `src/app_state.rs` and `src/app.rs`. | High |
+| Scripts / paths | Not yet | `docs/knowledgebase/feature-inventory.md` marks scripts and path generation as planned. | Medium |
+| File / project actions | Not yet | `loaded_scene_path` exists in `AppData`, but there is no visible file/project UI yet. | Medium |
+| Status / feedback | Not yet | No dedicated status widget or state binding is present. | Medium |
+| Deferred features / legacy compatibility | Not yet | These remain future work in the feature inventory. | Low |
+
+## Remaining gaps
+
+- No legacy-style menu/dialog layer for file, export, or script workflows.
+- No docked status bar or live feedback line.
+- No dedicated scripts/paths editor surface.
+- Palette import/export and legacy texture loading remain open.
+- Hydrology still lacks routed-water simulation and drainage maps.
+- Legacy export and compatibility dialogs remain future work.
diff --git a/docs/plans/phase-4-formats-scripts-ui.md b/docs/plans/phase-4-formats-scripts-ui.md
index a2a4a2b..39c8a32 100644
--- a/docs/plans/phase-4-formats-scripts-ui.md
+++ b/docs/plans/phase-4-formats-scripts-ui.md
@@ -721,6 +721,21 @@ Expected: generated script parses successfully.
 
 ## Milestone G: WGPU/egui application after CLI stability
 
+**Status:** Tasks G1–G4 have landed. `src/app_state.rs` holds testable app state and
+`AppAction` reducers; `src/app.rs` and `src/bin/openvistapro_app.rs` provide the
+`app`-feature `eframe`/`egui` shell. The shell now docks terrain, scene/camera, and render
+controls in a left panel, a scripts/paths panel on the right, a top project bar and a
+bottom status bar for file/status chrome, and the CPU top-down/perspective preview in the
+center. Still-planned actions — heightmap import, run script, make path, and file
+new/open/save — are present as disabled placeholders so the layout is honest about scope.
+The shell map is tracked in [`docs/knowledgebase/ui-panel-map.md`](../knowledgebase/ui-panel-map.md).
+
+Remaining UI roadmap: Task G5 (WGPU renderer backend) plus the still-open gaps — wiring
+file/import/script/path actions to their backend modules, legacy menus/dialogs,
+orientation and lens/range controls, vertical exaggeration, a palette editor, and
+hydrology controls. All of it stays clean-room: no proprietary VistaPro assets, menus, or
+screenshots enter the repository.
+
 ### Task G1: Create app-state crate/module without a window
 
 **Objective:** Separate UI state from rendering and file formats before adding WGPU.
diff --git a/docs/plans/terrain-generation.md b/docs/plans/terrain-generation.md
index 8102071..367c892 100644
--- a/docs/plans/terrain-generation.md
+++ b/docs/plans/terrain-generation.md
@@ -8,6 +8,8 @@ Define the next terrain-generation workstream so future slices stay small, deter
 
 OpenVistaPro already has:
 
+- `src/terrain_gen.rs` with `TerrainGenerationSpec` and `DeterministicTerrainGenerator`, plus `cargo test terrain_gen` coverage for the determinism/seed note.
+
 - `src/terrain.rs` with immutable `HeightGrid` storage, safe indexing, min/max, and deterministic `plane` / `radial_hill` fixtures.
 - `src/render.rs` with a deterministic top-down preview and a CPU perspective spike that only depends on `HeightGrid` + `Scene`.
 - `src/scene.rs` and `src/app_state.rs` for scene controls and preview wiring.
diff --git a/src/app.rs b/src/app.rs
index 6d8d475..23f5f37 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -22,6 +22,24 @@ impl OpenVistaProApp {
         Self::default()
     }
 
+    fn default_scene_path() -> String {
+        format!(
+            "{}/target/openvistapro-scene.ovp.toml",
+            env!("CARGO_MANIFEST_DIR")
+        )
+    }
+
+    fn default_import_path() -> String {
+        format!(
+            "{}/tests/fixtures/open/tiny-heightfield.ovptext",
+            env!("CARGO_MANIFEST_DIR")
+        )
+    }
+
+    fn default_script_base_dir() -> &'static str {
+        env!("CARGO_MANIFEST_DIR")
+    }
+
     fn rebuild_texture(&mut self, ctx: &egui::Context) {
         let Ok(preview) = self.data.render_preview() else {
             return;
@@ -60,7 +78,7 @@ impl OpenVistaProApp {
     /// an implemented surface still show their labelled placeholder.
     ///
     /// Returns `true` when an edit changed something the preview depends on.
-    fn controls_panel(&mut self, ctx: &egui::Context) -> bool {
+    fn controls_panel(&mut self, ctx: &egui::Context, action_note: &mut Option<String>) -> bool {
         let mut changed = false;
         egui::SidePanel::left("controls_panel")
             .resizable(true)
@@ -73,12 +91,10 @@ impl OpenVistaProApp {
                     ShellSection::Terrain => changed |= self.terrain_controls(ui),
                     ShellSection::Scene => changed |= self.scene_controls(ui),
                     ShellSection::Render => changed |= self.render_controls(ui),
-                    ShellSection::Import
-                    | ShellSection::Script
-                    | ShellSection::Path
-                    | ShellSection::Project => {
-                        ui.label(self.shell.placeholder_label());
-                    }
+                    ShellSection::Import => changed |= self.import_controls(ui, action_note),
+                    ShellSection::Script => changed |= self.script_controls(ui, action_note),
+                    ShellSection::Path => changed |= self.path_controls(ui, action_note),
+                    ShellSection::Project => changed |= self.project_controls(ui, action_note),
                 }
             });
         changed
@@ -147,6 +163,215 @@ impl OpenVistaProApp {
         self.data
             .apply(AppAction::SetCameraPosition(camera_position));
         self.data.apply(AppAction::SetCameraTarget(camera_target));
+
+        ui.separator();
+        ui.label("Camera orientation and lens");
+        let mut orientation = self.data.scene.camera.orientation;
+        changed |= vec3_controls(ui, "Orientation", &mut orientation);
+        self.data
+            .apply(AppAction::SetCameraOrientation(orientation));
+
+        let mut fov_degrees = self.data.scene.camera.fov_degrees;
+        let mut near_range = self.data.scene.camera.near_range;
+        let mut far_range = self.data.scene.camera.far_range;
+        changed |= ui
+            .add(egui::Slider::new(&mut fov_degrees, 10.0..=170.0).text("FOV"))
+            .changed();
+        changed |= ui
+            .add(egui::Slider::new(&mut near_range, 0.1..=50.0).text("Near"))
+            .changed();
+        changed |= ui
+            .add(egui::Slider::new(&mut far_range, 1.0..=1000.0).text("Far"))
+            .changed();
+        self.data.apply(AppAction::SetCameraLens {
+            fov_degrees,
+            near_range,
+            far_range,
+        });
+
+        ui.separator();
+        ui.label("Vertical exaggeration");
+        let mut vertical_exaggeration = self.data.scene.vertical_exaggeration;
+        changed |= ui
+            .add(egui::Slider::new(&mut vertical_exaggeration, 0.1..=10.0).text("Scale"))
+            .changed();
+        self.data
+            .apply(AppAction::SetVerticalExaggeration(vertical_exaggeration));
+
+        ui.separator();
+        ui.label("Hydrology");
+        let mut river_level = self.data.scene.hydrology.river_level;
+        let mut lake_level = self.data.scene.hydrology.lake_level;
+        let mut drainage = self.data.scene.hydrology.drainage;
+        changed |= ui
+            .add(egui::Slider::new(&mut river_level, -5.0..=10.0).text("River"))
+            .changed();
+        changed |= ui
+            .add(egui::Slider::new(&mut lake_level, -5.0..=10.0).text("Lake"))
+            .changed();
+        changed |= ui
+            .add(egui::Slider::new(&mut drainage, 0.0..=5.0).text("Drainage"))
+            .changed();
+        self.data.apply(AppAction::SetHydrology {
+            river_level,
+            lake_level,
+            drainage,
+        });
+
+        ui.separator();
+        ui.label("Palette");
+        let mut palette = self.data.scene.palette;
+        ui.horizontal(|ui| {
+            ui.label("Water");
+            changed |= ui.color_edit_button_srgb(&mut palette.water).changed();
+        });
+        ui.horizontal(|ui| {
+            ui.label("Lowland");
+            changed |= ui.color_edit_button_srgb(&mut palette.lowland).changed();
+        });
+        ui.horizontal(|ui| {
+            ui.label("Highland");
+            changed |= ui.color_edit_button_srgb(&mut palette.highland).changed();
+        });
+        ui.horizontal(|ui| {
+            ui.label("Snow");
+            changed |= ui.color_edit_button_srgb(&mut palette.snow).changed();
+        });
+        self.data.apply(AppAction::SetPalette(palette));
+
+        changed
+    }
+
+    fn import_controls(&mut self, ui: &mut egui::Ui, action_note: &mut Option<String>) -> bool {
+        let mut changed = false;
+        ui.label("Import terrain");
+        let import_path = self
+            .data
+            .import_path
+            .clone()
+            .unwrap_or_else(Self::default_import_path);
+        ui.horizontal(|ui| {
+            ui.monospace(import_path.as_str());
+            if ui.button("Import heightmap…").clicked() {
+                let path = std::path::Path::new(import_path.as_str());
+                match self.data.import_heightmap_from_path(path) {
+                    Ok(()) => {
+                        changed = true;
+                        *action_note = Some(format!("imported heightmap from {import_path}"));
+                    }
+                    Err(error) => *action_note = Some(format!("import failed: {error}")),
+                }
+            }
+        });
+        if let Some(grid) = self.data.imported_grid.as_ref() {
+            ui.label(format!("Imported grid: {}×{}", grid.width(), grid.height()));
+        } else {
+            ui.label(self.shell.placeholder_label());
+        }
+        changed
+    }
+
+    fn script_controls(&mut self, ui: &mut egui::Ui, action_note: &mut Option<String>) -> bool {
+        let mut changed = false;
+        ui.label("Script source");
+        changed |= ui
+            .add(
+                egui::TextEdit::multiline(&mut self.data.script_source)
+                    .desired_rows(8)
+                    .lock_focus(true)
+                    .desired_width(f32::INFINITY),
+            )
+            .changed();
+        ui.horizontal(|ui| {
+            if ui.button("Run script").clicked() {
+                let base_dir = std::path::Path::new(Self::default_script_base_dir());
+                match self.data.run_script_from_source(base_dir) {
+                    Ok(report) => {
+                        changed |= !report.outputs.is_empty();
+                        *action_note =
+                            Some(format!("script wrote {} output(s)", report.outputs.len()));
+                    }
+                    Err(error) => *action_note = Some(format!("script run failed: {error}")),
+                }
+            }
+            ui.label("Parser + executor slice; output writes to disk.");
+        });
+        if let Some(report) = self.data.last_script_run.as_ref() {
+            ui.label(format!("Last run wrote {} output(s)", report.outputs.len()));
+        } else {
+            ui.label(self.shell.placeholder_label());
+        }
+        changed
+    }
+
+    fn path_controls(&mut self, ui: &mut egui::Ui, action_note: &mut Option<String>) -> bool {
+        let mut changed = false;
+        ui.label("Path tools");
+        ui.horizontal(|ui| {
+            let path_target = self
+                .data
+                .path_target
+                .as_deref()
+                .unwrap_or("No path target selected");
+            ui.monospace(path_target);
+            if ui.button("Make path").clicked() {
+                let path = self.data.make_path();
+                changed = true;
+                *action_note = Some(format!(
+                    "generated {}",
+                    self.data
+                        .path_target
+                        .clone()
+                        .unwrap_or_else(|| format!("{} keyframes", path.keyframes().len()))
+                ));
+            }
+        });
+        if let Some(path) = self.data.generated_path.as_ref() {
+            ui.label(format!(
+                "Generated path: {} keyframes",
+                path.keyframes().len()
+            ));
+        } else {
+            ui.label(self.shell.placeholder_label());
+        }
+        changed
+    }
+
+    fn project_controls(&mut self, ui: &mut egui::Ui, action_note: &mut Option<String>) -> bool {
+        let mut changed = false;
+        ui.label("Scene file");
+        let scene_path = self
+            .data
+            .loaded_scene_path
+            .clone()
+            .unwrap_or_else(Self::default_scene_path);
+        ui.horizontal(|ui| {
+            ui.monospace(scene_path.as_str());
+            if ui.button("New").clicked() {
+                self.data.reset_scene();
+                self.data.loaded_scene_path = Some(scene_path.clone());
+                changed = true;
+                *action_note = Some(format!("reset scene and kept {scene_path}"));
+            }
+            if ui.button("Open…").clicked() {
+                let path = std::path::Path::new(&scene_path);
+                match self.data.open_scene(path) {
+                    Ok(()) => {
+                        changed = true;
+                        *action_note = Some(format!("opened scene from {scene_path}"));
+                    }
+                    Err(error) => *action_note = Some(format!("open failed: {error}")),
+                }
+            }
+            if ui.button("Save").clicked() {
+                let path = std::path::Path::new(&scene_path);
+                match self.data.save_scene(path) {
+                    Ok(()) => *action_note = Some(format!("saved scene to {scene_path}")),
+                    Err(error) => *action_note = Some(format!("save failed: {error}")),
+                }
+            }
+        });
+        ui.label(self.shell.placeholder_label());
         changed
     }
 
@@ -170,23 +395,6 @@ impl OpenVistaProApp {
             });
     }
 
-    /// Bottom panel: durable status bar.
-    fn status_panel(&self, ctx: &egui::Context) {
-        egui::TopBottomPanel::bottom("status_panel").show(ctx, |ui| {
-            ui.horizontal(|ui| {
-                ui.label("Ready");
-                ui.separator();
-                ui.label(format!("Active: {}", self.shell.section_title()));
-                ui.separator();
-                let scene_label = match &self.data.loaded_scene_path {
-                    Some(path) => format!("Scene: {path}"),
-                    None => "Scene: unsaved".to_owned(),
-                };
-                ui.label(scene_label);
-            });
-        });
-    }
-
     /// Central viewport: shows the CPU preview, with a placeholder banner for
     /// sections whose dedicated surface is not built yet.
     fn viewport_panel(&self, ctx: &egui::Context) {
@@ -203,14 +411,36 @@ impl OpenVistaProApp {
             }
         });
     }
+
+    /// Bottom panel: durable status bar.
+    fn status_panel(&self, ctx: &egui::Context, action_note: Option<&str>) {
+        egui::TopBottomPanel::bottom("status_panel").show(ctx, |ui| {
+            ui.horizontal(|ui| {
+                ui.label("Ready");
+                ui.separator();
+                ui.label(format!("Active: {}", self.shell.section_title()));
+                ui.separator();
+                let scene_label = match &self.data.loaded_scene_path {
+                    Some(path) => format!("Scene: {path}"),
+                    None => "Scene: unsaved".to_owned(),
+                };
+                ui.label(scene_label);
+                if let Some(note) = action_note {
+                    ui.separator();
+                    ui.label(note);
+                }
+            });
+        });
+    }
 }
 
 impl eframe::App for OpenVistaProApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        let mut action_note: Option<String> = None;
         self.command_bar(ctx);
-        let changed = self.controls_panel(ctx);
+        let changed = self.controls_panel(ctx, &mut action_note);
         self.inspector_panel(ctx);
-        self.status_panel(ctx);
+        self.status_panel(ctx, action_note.as_deref());
 
         if changed || self.texture.is_none() {
             self.rebuild_texture(ctx);
diff --git a/src/app_state.rs b/src/app_state.rs
index 162034c..312e84e 100644
--- a/src/app_state.rs
+++ b/src/app_state.rs
@@ -1,7 +1,13 @@
+use std::path::Path;
+
 use image::RgbImage;
 
+use crate::path::{CameraPath, build_demo_path};
 use crate::render::{render_perspective, render_top_down};
 use crate::scene::{Scene, Vec3};
+use crate::scene_file::{self, SceneFileError};
+use crate::script::{Command, parse_script};
+use crate::script_exec::{self, ExecReport, ScriptError};
 use crate::terrain::{HeightGrid, TerrainError};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -17,6 +23,14 @@ impl TerrainPreset {
             TerrainPreset::RadialHill => HeightGrid::radial_hill(width, height, 10.0),
         }
     }
+
+    /// Human-readable label used by the UI shell.
+    pub fn label(self) -> &'static str {
+        match self {
+            TerrainPreset::Plane => "Plane",
+            TerrainPreset::RadialHill => "Radial hill",
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -25,6 +39,86 @@ pub enum RendererMode {
     Perspective,
 }
 
+impl RendererMode {
+    /// Human-readable label used by the UI shell.
+    pub fn label(self) -> &'static str {
+        match self {
+            RendererMode::TopDown => "Top-down",
+            RendererMode::Perspective => "Perspective",
+        }
+    }
+}
+
+/// A pure, derived summary of a parsed script, suitable for display in the UI.
+///
+/// All counts are zero and `error` carries the parser message when the script
+/// fails to parse, so the shell can render a single consistent preview shape.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct ScriptPreview {
+    /// Total number of parsed commands.
+    pub command_count: usize,
+    /// Number of `render output` commands.
+    pub render_commands: usize,
+    /// Number of `import heightmap` commands.
+    pub import_commands: usize,
+    /// Parser error message, if the script did not parse.
+    pub error: Option<String>,
+}
+
+impl ScriptPreview {
+    /// Build a preview by running the backend script parser over `source`.
+    fn from_source(source: &str) -> Self {
+        match parse_script(source) {
+            Ok(script) => {
+                let render_commands = script
+                    .commands
+                    .iter()
+                    .filter(|command| matches!(command, Command::RenderOutput { .. }))
+                    .count();
+                let import_commands = script
+                    .commands
+                    .iter()
+                    .filter(|command| matches!(command, Command::ImportHeightmap { .. }))
+                    .count();
+                Self {
+                    command_count: script.commands.len(),
+                    render_commands,
+                    import_commands,
+                    error: None,
+                }
+            }
+            Err(error) => Self {
+                error: Some(error.to_string()),
+                ..Self::default()
+            },
+        }
+    }
+}
+
+/// A pure, immutable snapshot of the UI shell state.
+///
+/// The egui app reads this each frame instead of reaching into [`AppData`]
+/// directly. Labels are stable strings; optional values are `None` when the
+/// corresponding entry point has not been wired to a real workflow yet.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct UiShellSnapshot {
+    pub terrain_preset_label: String,
+    pub renderer_mode_label: String,
+    pub scene_file_label: String,
+    pub import_label: String,
+    pub script_label: String,
+    pub path_label: String,
+    pub scene_controls_label: String,
+    pub palette_label: String,
+    pub hydrology_label: String,
+    pub legacy_dialogs_label: String,
+    pub scene_file_path: Option<String>,
+    pub import_path: Option<String>,
+    pub path_target: Option<String>,
+    pub status_line: String,
+    pub script_preview: ScriptPreview,
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub struct AppData {
     pub scene: Scene,
@@ -32,16 +126,40 @@ pub struct AppData {
     pub renderer_mode: RendererMode,
     pub preview_size: (u32, u32),
     pub loaded_scene_path: Option<String>,
+    /// Heightmap path selected for import.
+    pub import_path: Option<String>,
+    /// Path-tool target or summary.
+    pub path_target: Option<String>,
+    /// Current script source text edited in the Scripts / paths panel.
+    pub script_source: String,
+    /// Height grid currently imported through the shell.
+    pub imported_grid: Option<HeightGrid>,
+    /// Generated camera path from the Make Path action.
+    pub generated_path: Option<CameraPath>,
+    /// Last script execution report.
+    pub last_script_run: Option<ExecReport>,
 }
 
 impl Default for AppData {
     fn default() -> Self {
+        let manifest_dir = env!("CARGO_MANIFEST_DIR");
+        let scene_path = format!("{manifest_dir}/target/openvistapro-scene.ovp.toml");
+        let import_path = format!("{manifest_dir}/tests/fixtures/open/tiny-heightfield.ovptext");
+        let script_output = format!("{manifest_dir}/target/openvistapro-script-preview.png");
         Self {
             scene: Scene::default(),
             terrain_preset: TerrainPreset::RadialHill,
             renderer_mode: RendererMode::TopDown,
             preview_size: (256, 256),
-            loaded_scene_path: None,
+            loaded_scene_path: Some(scene_path),
+            import_path: Some(import_path.clone()),
+            path_target: None,
+            script_source: format!(
+                "use preset hill\nimport heightmap \"{import_path}\"\nset thresholds water=1.0 tree=4.0 snow=7.0\nrender output \"{script_output}\"\n"
+            ),
+            imported_grid: None,
+            generated_path: None,
+            last_script_run: None,
         }
     }
 }
@@ -55,18 +173,132 @@ impl AppData {
             AppAction::SetTreeLine(value) => self.scene.tree_line = value,
             AppAction::SetSnowLine(value) => self.scene.snow_line = value,
             AppAction::SetHaze(value) => self.scene.haze = value.clamp(0.0, 1.0),
+            AppAction::SetVerticalExaggeration(value) => {
+                self.scene.vertical_exaggeration = value.max(0.0)
+            }
             AppAction::SetCameraPosition(position) => self.scene.camera.position = position,
             AppAction::SetCameraTarget(target) => self.scene.camera.target = target,
+            AppAction::SetCameraOrientation(orientation) => {
+                self.scene.camera.orientation = orientation
+            }
+            AppAction::SetCameraLens {
+                fov_degrees,
+                near_range,
+                far_range,
+            } => {
+                self.scene.camera.fov_degrees = fov_degrees.clamp(10.0, 170.0);
+                self.scene.camera.near_range = near_range.max(0.0);
+                self.scene.camera.far_range = far_range.max(self.scene.camera.near_range + 0.1);
+            }
+            AppAction::SetHydrology {
+                river_level,
+                lake_level,
+                drainage,
+            } => {
+                self.scene.hydrology.river_level = river_level;
+                self.scene.hydrology.lake_level = lake_level;
+                self.scene.hydrology.drainage = drainage.max(0.0);
+            }
+            AppAction::SetPalette(palette) => self.scene.palette = palette,
             AppAction::SetPreviewSize { width, height } => {
                 self.preview_size = (width.max(1), height.max(1));
             }
             AppAction::SetLoadedScenePath(path) => self.loaded_scene_path = path,
+            AppAction::SetScriptSource(source) => self.script_source = source,
+        }
+    }
+
+    pub fn reset_scene(&mut self) {
+        self.scene = Scene::default();
+        self.imported_grid = None;
+        self.generated_path = None;
+        self.last_script_run = None;
+        self.terrain_preset = TerrainPreset::RadialHill;
+        self.renderer_mode = RendererMode::TopDown;
+    }
+
+    pub fn open_scene(&mut self, path: &Path) -> Result<(), SceneFileError> {
+        let scene = scene_file::load_from_path(path)?;
+        self.scene = scene;
+        self.imported_grid = None;
+        self.generated_path = None;
+        self.last_script_run = None;
+        self.loaded_scene_path = Some(path.display().to_string());
+        Ok(())
+    }
+
+    pub fn save_scene(&mut self, path: &Path) -> Result<(), SceneFileError> {
+        scene_file::save_to_path(&self.scene, path)?;
+        self.loaded_scene_path = Some(path.display().to_string());
+        Ok(())
+    }
+
+    pub fn import_heightmap_from_path(
+        &mut self,
+        path: &Path,
+    ) -> Result<(), Box<dyn std::error::Error>> {
+        let source = std::fs::read_to_string(path)?;
+        let imported = crate::import::import_ovp_text(&source)?;
+        self.imported_grid = Some(imported.into_grid());
+        self.import_path = Some(path.display().to_string());
+        Ok(())
+    }
+
+    pub fn run_script_from_source(&mut self, base_dir: &Path) -> Result<ExecReport, ScriptError> {
+        let report = script_exec::run_script_source(&self.script_source, base_dir)?;
+        self.last_script_run = Some(report.clone());
+        Ok(report)
+    }
+
+    pub fn make_path(&mut self) -> CameraPath {
+        let path = build_demo_path(&self.scene);
+        self.path_target = Some(format!(
+            "{} keyframes · {:.1}s → {:.1}s",
+            path.keyframes().len(),
+            path.start_time(),
+            path.end_time()
+        ));
+        self.generated_path = Some(path.clone());
+        path
+    }
+
+    fn active_height_grid(&self) -> Result<HeightGrid, TerrainError> {
+        if let Some(grid) = &self.imported_grid {
+            return Ok(grid.clone());
+        }
+        let (width, height) = self.preview_size;
+        self.terrain_preset.build_grid(width, height)
+    }
+
+    /// Build a pure snapshot of the UI shell state for the egui app to render.
+    pub fn ui_snapshot(&self) -> UiShellSnapshot {
+        let (width, height) = self.preview_size;
+        UiShellSnapshot {
+            terrain_preset_label: self.terrain_preset.label().to_string(),
+            renderer_mode_label: self.renderer_mode.label().to_string(),
+            scene_file_label: "Scene file".to_string(),
+            import_label: "Import terrain".to_string(),
+            script_label: "Scripts / paths".to_string(),
+            path_label: "Path tools".to_string(),
+            scene_controls_label: "Scene / camera / palette".to_string(),
+            palette_label: "Palette / color map".to_string(),
+            hydrology_label: "Hydrology".to_string(),
+            legacy_dialogs_label: "Legacy dialogs".to_string(),
+            scene_file_path: self.loaded_scene_path.clone(),
+            import_path: self.import_path.clone(),
+            path_target: self.path_target.clone(),
+            status_line: format!(
+                "CPU preview · {} · {} · exag {:.2} · {width}×{height}",
+                self.terrain_preset.label(),
+                self.renderer_mode.label(),
+                self.scene.vertical_exaggeration,
+            ),
+            script_preview: ScriptPreview::from_source(&self.script_source),
         }
     }
 
     pub fn build_preview_grid(&self) -> Result<HeightGrid, TerrainError> {
-        let (width, height) = self.preview_size;
-        self.terrain_preset.build_grid(width, height)
+        self.active_height_grid()
     }
 
     pub fn render_preview(&self) -> Result<RgbImage, TerrainError> {
@@ -88,10 +320,27 @@ pub enum AppAction {
     SetTreeLine(f32),
     SetSnowLine(f32),
     SetHaze(f32),
+    SetVerticalExaggeration(f32),
     SetCameraPosition(Vec3),
     SetCameraTarget(Vec3),
-    SetPreviewSize { width: u32, height: u32 },
+    SetCameraOrientation(Vec3),
+    SetCameraLens {
+        fov_degrees: f32,
+        near_range: f32,
+        far_range: f32,
+    },
+    SetHydrology {
+        river_level: f32,
+        lake_level: f32,
+        drainage: f32,
+    },
+    SetPalette(crate::scene::Palette),
+    SetPreviewSize {
+        width: u32,
+        height: u32,
+    },
     SetLoadedScenePath(Option<String>),
+    SetScriptSource(String),
 }
 
 #[cfg(test)]
@@ -107,7 +356,8 @@ mod tests {
         assert_eq!(app.terrain_preset, TerrainPreset::RadialHill);
         assert_eq!(app.renderer_mode, RendererMode::TopDown);
         assert_eq!(app.preview_size, (256, 256));
-        assert_eq!(app.loaded_scene_path, None);
+        assert!(app.loaded_scene_path.is_some());
+        assert!(app.script_source.contains("import heightmap"));
     }
 
     #[test]
@@ -165,6 +415,101 @@ mod tests {
         assert_eq!(preview.height(), 64);
     }
 
+    #[test]
+    fn ui_snapshot_exposes_existing_controls_and_new_entry_points() {
+        let app = AppData::default();
+        let shell = app.ui_snapshot();
+
+        assert_eq!(shell.terrain_preset_label, "Radial hill");
+        assert_eq!(shell.renderer_mode_label, "Top-down");
+        assert_eq!(shell.scene_file_label, "Scene file");
+        assert_eq!(shell.import_label, "Import terrain");
+        assert_eq!(shell.script_label, "Scripts / paths");
+        assert_eq!(shell.path_label, "Path tools");
+        assert!(shell.scene_file_path.is_some());
+        assert!(shell.import_path.is_some());
+        assert!(shell.path_target.is_none());
+        assert!(shell.status_line.contains("CPU preview"));
+    }
+
+    #[test]
+    fn ui_snapshot_uses_backend_script_parser_for_command_counts() {
+        let mut app = AppData::default();
+        app.apply(AppAction::SetScriptSource(
+            "use preset plane\nrender output \"out.png\"\n".into(),
+        ));
+
+        let shell = app.ui_snapshot();
+
+        assert_eq!(shell.script_preview.command_count, 2);
+        assert_eq!(shell.script_preview.render_commands, 1);
+        assert_eq!(shell.script_preview.import_commands, 0);
+        assert!(shell.script_preview.error.is_none());
+    }
+
+    #[test]
+    fn importing_a_heightmap_updates_the_preview_grid() {
+        let mut app = AppData::default();
+        let fixture = Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("tests/fixtures/open/tiny-heightfield.ovptext");
+
+        app.import_heightmap_from_path(&fixture)
+            .expect("import fixture");
+        let grid = app.build_preview_grid().expect("preview grid");
+
+        assert_eq!(grid.width(), 3);
+        assert_eq!(grid.height(), 2);
+        assert!(app.imported_grid.is_some());
+    }
+
+    #[test]
+    fn make_path_produces_a_three_keyframe_summary() {
+        let mut app = AppData::default();
+        let path = app.make_path();
+
+        assert_eq!(path.keyframes().len(), 3);
+        assert!(
+            app.path_target
+                .as_deref()
+                .unwrap_or("")
+                .contains("keyframes")
+        );
+        assert!(app.generated_path.is_some());
+    }
+
+    #[test]
+    fn scene_file_paths_round_trip_through_save_and_open() {
+        let mut app = AppData::default();
+        let mut path = std::env::temp_dir();
+        path.push(format!(
+            "openvistapro-app-state-scene-{}.ovp.toml",
+            std::process::id()
+        ));
+        let _ = std::fs::remove_file(&path);
+
+        app.scene.water_level = 2.25;
+        app.save_scene(&path).expect("save scene");
+        app.scene.water_level = 0.0;
+        app.open_scene(&path).expect("open scene");
+
+        assert_eq!(app.scene.water_level, 2.25);
+        assert_eq!(
+            app.loaded_scene_path.as_deref(),
+            Some(path.to_string_lossy().as_ref())
+        );
+        std::fs::remove_file(&path).ok();
+    }
+
+    #[test]
+    fn run_script_source_executes_the_default_sample() {
+        let mut app = AppData::default();
+        let dir = std::env::temp_dir();
+        let report = app.run_script_from_source(&dir).expect("script run");
+
+        assert!(!report.outputs.is_empty());
+        assert!(app.last_script_run.is_some());
+    }
+
     #[cfg(not(feature = "app"))]
     #[test]
     fn app_feature_is_declared_but_not_enabled_by_default() {
diff --git a/src/colormap.rs b/src/colormap.rs
index c974495..d209439 100644
--- a/src/colormap.rs
+++ b/src/colormap.rs
@@ -5,24 +5,37 @@ pub const LOWLAND_COLOR: [u8; 3] = [70, 130, 50];
 pub const HIGHLAND_COLOR: [u8; 3] = [120, 100, 80];
 pub const SNOW_COLOR: [u8; 3] = [240, 240, 250];
 
-pub fn elevation_to_rgb(elevation: f32, water: f32, tree: f32, snow: f32) -> [u8; 3] {
+pub fn elevation_to_rgb(
+    elevation: f32,
+    water: f32,
+    tree: f32,
+    snow: f32,
+    palette: &[[u8; 3]; 4],
+) -> [u8; 3] {
     if elevation <= water {
-        WATER_COLOR
+        palette[0]
     } else if elevation < tree {
-        LOWLAND_COLOR
+        palette[1]
     } else if elevation < snow {
-        HIGHLAND_COLOR
+        palette[2]
     } else {
-        SNOW_COLOR
+        palette[3]
     }
 }
 
 pub fn scene_color(scene: &Scene, elevation: f32) -> [u8; 3] {
+    let water_level = scene.hydrology.effective_water_level(scene.water_level);
     elevation_to_rgb(
         elevation,
-        scene.water_level,
+        water_level,
         scene.tree_line,
         scene.snow_line,
+        &[
+            scene.palette.water,
+            scene.palette.lowland,
+            scene.palette.highland,
+            scene.palette.snow,
+        ],
     )
 }
 
@@ -60,31 +73,112 @@ mod tests {
 
     #[test]
     fn elevation_below_water_returns_water_color() {
-        assert_eq!(elevation_to_rgb(-1.0, 1.0, 4.0, 7.0), WATER_COLOR);
-        assert_eq!(elevation_to_rgb(0.5, 1.0, 4.0, 7.0), WATER_COLOR);
+        assert_eq!(
+            elevation_to_rgb(
+                -1.0,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR],
+            ),
+            WATER_COLOR
+        );
+        assert_eq!(
+            elevation_to_rgb(
+                0.5,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR],
+            ),
+            WATER_COLOR
+        );
     }
 
     #[test]
     fn elevation_at_water_returns_water_color() {
-        assert_eq!(elevation_to_rgb(1.0, 1.0, 4.0, 7.0), WATER_COLOR);
+        assert_eq!(
+            elevation_to_rgb(
+                1.0,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            WATER_COLOR
+        );
     }
 
     #[test]
     fn elevation_between_water_and_tree_returns_lowland() {
-        assert_eq!(elevation_to_rgb(2.0, 1.0, 4.0, 7.0), LOWLAND_COLOR);
-        assert_eq!(elevation_to_rgb(3.9, 1.0, 4.0, 7.0), LOWLAND_COLOR);
+        assert_eq!(
+            elevation_to_rgb(
+                2.0,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            LOWLAND_COLOR
+        );
+        assert_eq!(
+            elevation_to_rgb(
+                3.9,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            LOWLAND_COLOR
+        );
     }
 
     #[test]
     fn elevation_between_tree_and_snow_returns_highland() {
-        assert_eq!(elevation_to_rgb(4.5, 1.0, 4.0, 7.0), HIGHLAND_COLOR);
-        assert_eq!(elevation_to_rgb(6.9, 1.0, 4.0, 7.0), HIGHLAND_COLOR);
+        assert_eq!(
+            elevation_to_rgb(
+                4.5,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            HIGHLAND_COLOR
+        );
+        assert_eq!(
+            elevation_to_rgb(
+                6.9,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            HIGHLAND_COLOR
+        );
     }
 
     #[test]
     fn elevation_above_snow_returns_snow() {
-        assert_eq!(elevation_to_rgb(7.5, 1.0, 4.0, 7.0), SNOW_COLOR);
-        assert_eq!(elevation_to_rgb(100.0, 1.0, 4.0, 7.0), SNOW_COLOR);
+        assert_eq!(
+            elevation_to_rgb(
+                7.5,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            SNOW_COLOR
+        );
+        assert_eq!(
+            elevation_to_rgb(
+                100.0,
+                1.0,
+                4.0,
+                7.0,
+                &[WATER_COLOR, LOWLAND_COLOR, HIGHLAND_COLOR, SNOW_COLOR]
+            ),
+            SNOW_COLOR
+        );
     }
 
     #[test]
diff --git a/src/lib.rs b/src/lib.rs
index 64779aa..d2503b0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -11,4 +11,5 @@ pub mod scene_file;
 pub mod script;
 pub mod script_exec;
 pub mod terrain;
+pub mod terrain_gen;
 pub mod ui_shell;
diff --git a/src/path.rs b/src/path.rs
index 65daaa3..4007d10 100644
--- a/src/path.rs
+++ b/src/path.rs
@@ -28,7 +28,7 @@
 //! I/O, randomness, or global state, so the same path and time always yield a
 //! bit-identical [`Camera`].
 
-use crate::scene::{Camera, Vec3};
+use crate::scene::{Camera, Scene, Vec3};
 
 /// A single camera pose pinned to a point in time on a [`CameraPath`].
 #[derive(Debug, Clone, Copy, PartialEq)]
@@ -161,10 +161,50 @@ impl CameraPath {
             position: catmull_rom_vec3(p0.position, p1.position, p2.position, p3.position, u),
             target: catmull_rom_vec3(p0.target, p1.target, p2.target, p3.target, u),
             fov_degrees: lerp(p1.fov_degrees, p2.fov_degrees, u),
+            ..p1
         }
     }
 }
 
+/// Build a small orbit-style demo path around the current scene target.
+pub fn build_demo_path(scene: &Scene) -> CameraPath {
+    let focus = scene.camera.target;
+    let eye = scene.camera.position;
+    let offset = Vec3::new(eye.x - focus.x, eye.y - focus.y, eye.z - focus.z);
+    let radius = (offset.x * offset.x + offset.z * offset.z).sqrt().max(20.0);
+    let height = offset.y.abs().max(20.0);
+    let base_y = focus.y + height;
+
+    let keyframes = vec![
+        CameraKeyframe::new(
+            0.0,
+            Camera {
+                position: Vec3::new(focus.x + radius * 0.8, base_y, focus.z - radius * 0.2),
+                target: focus,
+                ..scene.camera
+            },
+        ),
+        CameraKeyframe::new(
+            3.0,
+            Camera {
+                position: Vec3::new(focus.x, base_y + 8.0, focus.z + radius * 0.9),
+                target: focus,
+                ..scene.camera
+            },
+        ),
+        CameraKeyframe::new(
+            6.0,
+            Camera {
+                position: Vec3::new(focus.x - radius * 0.8, base_y, focus.z - radius * 0.2),
+                target: focus,
+                ..scene.camera
+            },
+        ),
+    ];
+
+    CameraPath::try_new(keyframes).expect("demo path must be valid")
+}
+
 /// Linear interpolation from `a` to `b` by `u` in `[0, 1]`.
 fn lerp(a: f32, b: f32, u: f32) -> f32 {
     a + (b - a) * u
@@ -204,6 +244,7 @@ mod tests {
                 position: Vec3::new(pos[0], pos[1], pos[2]),
                 target: Vec3::new(target[0], target[1], target[2]),
                 fov_degrees: fov,
+                ..Camera::default()
             },
         )
     }
diff --git a/src/render.rs b/src/render.rs
index 44df666..4b8e3c5 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -10,9 +10,10 @@ pub fn render_top_down(grid: &HeightGrid, scene: &Scene) -> RgbImage {
     let w = grid.width();
     let h = grid.height();
     let mut img = RgbImage::new(w, h);
+    let vertical_exaggeration = scene.vertical_exaggeration.max(0.0);
     for y in 0..h {
         for x in 0..w {
-            let elevation = grid.sample(x, y).unwrap_or(0.0);
+            let elevation = grid.sample(x, y).unwrap_or(0.0) * vertical_exaggeration;
             let color = scene_color(scene, elevation);
             img.put_pixel(x, y, Rgb(color));
         }
@@ -83,6 +84,48 @@ fn v_normalize(a: Vec3) -> Vec3 {
     v_scale(a, 1.0 / len)
 }
 
+fn rotate_around_axis(v: Vec3, axis: Vec3, degrees: f32) -> Vec3 {
+    let radians = degrees.to_radians();
+    let axis = v_normalize(axis);
+    let cos = radians.cos();
+    let sin = radians.sin();
+    let dot = v_dot(axis, v);
+    let cross = v_cross(axis, v);
+    Vec3::new(
+        v.x * cos + cross.x * sin + axis.x * dot * (1.0 - cos),
+        v.y * cos + cross.y * sin + axis.y * dot * (1.0 - cos),
+        v.z * cos + cross.z * sin + axis.z * dot * (1.0 - cos),
+    )
+}
+
+fn apply_camera_orientation(camera: &Camera) -> Vec3 {
+    let world_up = Vec3::new(0.0, 1.0, 0.0);
+    let base_forward = v_normalize(v_sub(camera.target, camera.position));
+    let heading = camera.orientation.x;
+    let pitch = camera.orientation.y;
+    let bank = camera.orientation.z;
+
+    let mut forward = rotate_around_axis(base_forward, world_up, heading);
+    let mut right = v_normalize(v_cross(forward, world_up));
+    if right.x.is_finite() && right.y.is_finite() && right.z.is_finite() {
+        forward = rotate_around_axis(forward, right, pitch);
+        right = v_normalize(v_cross(forward, world_up));
+        if right.x.is_finite() && right.y.is_finite() && right.z.is_finite() {
+            let up = rotate_around_axis(world_up, forward, bank);
+            right = v_normalize(v_cross(forward, up));
+            if right.x.is_finite() && right.y.is_finite() && right.z.is_finite() {
+                forward = v_normalize(forward);
+            }
+        }
+    }
+
+    forward
+}
+
+fn terrain_height(scene: &Scene, raw_height: f32) -> f32 {
+    raw_height * scene.vertical_exaggeration.max(0.0)
+}
+
 /// Bilinear height lookup. Returns `None` if the (x, z) sample falls outside
 /// the grid's interior cell range [0, width-1] × [0, height-1].
 fn sample_height_bilinear(grid: &HeightGrid, x: f32, z: f32) -> Option<f32> {
@@ -117,10 +160,14 @@ pub fn demo_camera_for(grid: &HeightGrid) -> Camera {
     let cz = (h - 1.0) * 0.5;
     let cam_y = peak * 1.5 + h * 0.5;
     let cam_z = -(h * 0.6);
+    let far_range = (w + h) * 2.0 + cam_y * 2.0;
     Camera {
         position: Vec3::new(cx, cam_y, cam_z),
         target: Vec3::new(cx, peak * 0.3, cz),
+        orientation: Vec3::ZERO,
         fov_degrees: 55.0,
+        near_range: 1.0,
+        far_range,
     }
 }
 
@@ -134,10 +181,13 @@ pub fn render_perspective(grid: &HeightGrid, scene: &Scene, width: u32, height:
     let mut img = RgbImage::new(width.max(1), height.max(1));
 
     let cam = &scene.camera;
-    let forward = v_normalize(v_sub(cam.target, cam.position));
+    let forward = apply_camera_orientation(cam);
     let world_up = Vec3::new(0.0, 1.0, 0.0);
-    let right = v_normalize(v_cross(forward, world_up));
-    let up = v_cross(right, forward);
+    let mut right = v_normalize(v_cross(forward, world_up));
+    if !right.x.is_finite() || !right.y.is_finite() || !right.z.is_finite() {
+        right = Vec3::new(1.0, 0.0, 0.0);
+    }
+    let up = v_normalize(v_cross(right, forward));
 
     let fov_rad = cam.fov_degrees.to_radians();
     let tan_half = (fov_rad * 0.5).tan();
@@ -145,7 +195,7 @@ pub fn render_perspective(grid: &HeightGrid, scene: &Scene, width: u32, height:
 
     let grid_w = grid.width() as f32;
     let grid_h = grid.height() as f32;
-    let max_dist = (grid_w + grid_h) * 1.5 + cam.position.y.abs() * 2.0;
+    let max_dist = cam.far_range.max(cam.near_range + 0.1);
     let step = 0.5_f32;
 
     let haze_strength = scene.haze.clamp(0.0, 1.0);
@@ -163,14 +213,16 @@ pub fn render_perspective(grid: &HeightGrid, scene: &Scene, width: u32, height:
             ));
             let sky = sky_color(dir.y);
 
-            let mut t = 0.0_f32;
+            let mut t = cam.near_range.max(0.0);
             let mut hit_color: Option<[u8; 3]> = None;
             while t < max_dist {
                 let p = v_add(cam.position, v_scale(dir, t));
                 if let Some(terrain_h) = sample_height_bilinear(grid, p.x, p.z) {
+                    let terrain_h = terrain_height(scene, terrain_h);
                     if p.y <= terrain_h {
                         let band = scene_color(scene, terrain_h);
-                        let fade = (t / max_dist).clamp(0.0, 1.0) * haze_strength;
+                        let distance_fade = (t / max_dist).clamp(0.0, 1.0);
+                        let fade = distance_fade * haze_strength;
                         hit_color = Some(mix_color(band, sky, fade));
                         break;
                     }
@@ -178,6 +230,7 @@ pub fn render_perspective(grid: &HeightGrid, scene: &Scene, width: u32, height:
                 t += step;
             }
 
+            let _ = (grid_w, grid_h);
             img.put_pixel(px, py, Rgb(hit_color.unwrap_or(sky)));
         }
     }
diff --git a/src/scene.rs b/src/scene.rs
index 84491e1..058fc9a 100644
--- a/src/scene.rs
+++ b/src/scene.rs
@@ -20,10 +20,15 @@ impl Vec3 {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
 pub struct Camera {
     pub position: Vec3,
     pub target: Vec3,
+    /// Heading, pitch, and bank in degrees.
+    pub orientation: Vec3,
     pub fov_degrees: f32,
+    pub near_range: f32,
+    pub far_range: f32,
 }
 
 impl Default for Camera {
@@ -31,12 +36,16 @@ impl Default for Camera {
         Camera {
             position: Vec3::new(0.0, 50.0, 50.0),
             target: Vec3::ZERO,
+            orientation: Vec3::ZERO,
             fov_degrees: 60.0,
+            near_range: 1.0,
+            far_range: 500.0,
         }
     }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
 pub struct Light {
     pub direction: Vec3,
     pub intensity: f32,
@@ -52,6 +61,51 @@ impl Default for Light {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Palette {
+    pub water: [u8; 3],
+    pub lowland: [u8; 3],
+    pub highland: [u8; 3],
+    pub snow: [u8; 3],
+}
+
+impl Default for Palette {
+    fn default() -> Self {
+        Self {
+            water: [30, 70, 130],
+            lowland: [70, 130, 50],
+            highland: [120, 100, 80],
+            snow: [240, 240, 250],
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Hydrology {
+    pub river_level: f32,
+    pub lake_level: f32,
+    pub drainage: f32,
+}
+
+impl Hydrology {
+    pub fn effective_water_level(self, base_water_level: f32) -> f32 {
+        (base_water_level.max(self.river_level).max(self.lake_level) - self.drainage).max(0.0)
+    }
+}
+
+impl Default for Hydrology {
+    fn default() -> Self {
+        Self {
+            river_level: 0.5,
+            lake_level: 0.75,
+            drainage: 0.0,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
 pub struct Scene {
     pub camera: Camera,
     pub light: Light,
@@ -59,6 +113,9 @@ pub struct Scene {
     pub tree_line: f32,
     pub snow_line: f32,
     pub haze: f32,
+    pub vertical_exaggeration: f32,
+    pub hydrology: Hydrology,
+    pub palette: Palette,
 }
 
 impl Default for Scene {
@@ -70,6 +127,9 @@ impl Default for Scene {
             tree_line: 4.0,
             snow_line: 7.0,
             haze: 0.2,
+            vertical_exaggeration: 1.0,
+            hydrology: Hydrology::default(),
+            palette: Palette::default(),
         }
     }
 }
diff --git a/src/scene_file.rs b/src/scene_file.rs
index c6341b9..8ada155 100644
--- a/src/scene_file.rs
+++ b/src/scene_file.rs
@@ -107,6 +107,11 @@ pub fn from_toml_str(text: &str) -> Result<Scene, SceneFileError> {
 /// Write `scene` to `path` as an OpenVistaPro `.ovp.toml` scene file.
 pub fn save_to_path(scene: &Scene, path: &Path) -> Result<(), SceneFileError> {
     let text = to_toml_string(scene)?;
+    if let Some(parent) = path.parent() {
+        if !parent.as_os_str().is_empty() {
+            fs::create_dir_all(parent)?;
+        }
+    }
     fs::write(path, text)?;
     Ok(())
 }
@@ -120,14 +125,17 @@ pub fn load_from_path(path: &Path) -> Result<Scene, SceneFileError> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::scene::{Camera, Light, Scene, Vec3};
+    use crate::scene::{Camera, Hydrology, Light, Palette, Scene, Vec3};
 
     fn custom_scene() -> Scene {
         Scene {
             camera: Camera {
                 position: Vec3::new(1.5, 2.5, 3.5),
                 target: Vec3::new(-1.0, 0.0, 4.0),
+                orientation: Vec3::new(5.0, -10.0, 2.5),
                 fov_degrees: 42.0,
+                near_range: 0.5,
+                far_range: 250.0,
             },
             light: Light {
                 direction: Vec3::new(0.0, -1.0, 0.0),
@@ -137,6 +145,18 @@ mod tests {
             tree_line: 3.0,
             snow_line: 8.0,
             haze: 0.4,
+            vertical_exaggeration: 1.35,
+            hydrology: Hydrology {
+                river_level: 0.8,
+                lake_level: 1.1,
+                drainage: 0.2,
+            },
+            palette: Palette {
+                water: [12, 34, 56],
+                lowland: [78, 90, 12],
+                highland: [123, 111, 99],
+                snow: [250, 249, 248],
+            },
         }
     }
 
@@ -193,7 +213,7 @@ mod tests {
     #[test]
     fn load_rejects_unknown_schema() {
         let bad = format!(
-            "schema = \"some.other.format\"\nversion = {SCENE_VERSION}\n\n[scene]\nwater_level = 1.0\ntree_line = 4.0\nsnow_line = 7.0\nhaze = 0.2\n\n[scene.camera]\nfov_degrees = 60.0\n\n[scene.camera.position]\nx = 0.0\ny = 50.0\nz = 50.0\n\n[scene.camera.target]\nx = 0.0\ny = 0.0\nz = 0.0\n\n[scene.light]\nintensity = 1.0\n\n[scene.light.direction]\nx = -0.5\ny = -1.0\nz = -0.3\n"
+            "schema = \"some.other.format\"\nversion = {SCENE_VERSION}\n\n[scene]\nwater_level = 1.0\ntree_line = 4.0\nsnow_line = 7.0\nhaze = 0.2\nvertical_exaggeration = 1.0\n\n[scene.camera]\nfov_degrees = 60.0\nnear_range = 1.0\nfar_range = 500.0\n\n[scene.camera.position]\nx = 0.0\ny = 50.0\nz = 50.0\n\n[scene.camera.target]\nx = 0.0\ny = 0.0\nz = 0.0\n\n[scene.camera.orientation]\nx = 0.0\ny = 0.0\nz = 0.0\n\n[scene.light]\nintensity = 1.0\n\n[scene.light.direction]\nx = -0.5\ny = -1.0\nz = -0.3\n\n[scene.hydrology]\nriver_level = 0.5\nlake_level = 0.75\ndrainage = 0.0\n\n[scene.palette]\nwater = [30, 70, 130]\nlowland = [70, 130, 50]\nhighland = [120, 100, 80]\nsnow = [240, 240, 250]\n"
         );
         let err = from_toml_str(&bad).expect_err("unknown schema must be rejected");
         assert!(
@@ -206,7 +226,7 @@ mod tests {
     fn load_rejects_unsupported_version() {
         let future_version = SCENE_VERSION + 99;
         let bad = format!(
-            "schema = \"{SCENE_SCHEMA}\"\nversion = {future_version}\n\n[scene]\nwater_level = 1.0\ntree_line = 4.0\nsnow_line = 7.0\nhaze = 0.2\n\n[scene.camera]\nfov_degrees = 60.0\n\n[scene.camera.position]\nx = 0.0\ny = 50.0\nz = 50.0\n\n[scene.camera.target]\nx = 0.0\ny = 0.0\nz = 0.0\n\n[scene.light]\nintensity = 1.0\n\n[scene.light.direction]\nx = -0.5\ny = -1.0\nz = -0.3\n"
+            "schema = \"{SCENE_SCHEMA}\"\nversion = {future_version}\n\n[scene]\nwater_level = 1.0\ntree_line = 4.0\nsnow_line = 7.0\nhaze = 0.2\nvertical_exaggeration = 1.0\n\n[scene.camera]\nfov_degrees = 60.0\nnear_range = 1.0\nfar_range = 500.0\n\n[scene.camera.position]\nx = 0.0\ny = 50.0\nz = 50.0\n\n[scene.camera.target]\nx = 0.0\ny = 0.0\nz = 0.0\n\n[scene.camera.orientation]\nx = 0.0\ny = 0.0\nz = 0.0\n\n[scene.light]\nintensity = 1.0\n\n[scene.light.direction]\nx = -0.5\ny = -1.0\nz = -0.3\n\n[scene.hydrology]\nriver_level = 0.5\nlake_level = 0.75\ndrainage = 0.0\n\n[scene.palette]\nwater = [30, 70, 130]\nlowland = [70, 130, 50]\nhighland = [120, 100, 80]\nsnow = [240, 240, 250]\n"
         );
         let err = from_toml_str(&bad).expect_err("unsupported version must be rejected");
         assert!(
@@ -217,12 +237,7 @@ mod tests {
 
     #[test]
     fn load_returns_io_error_for_missing_file() {
-        let mut path = std::env::temp_dir();
-        path.push(format!(
-            "openvistapro-scenefile-missing-{}.ovp.toml",
-            std::process::id()
-        ));
-        let _ = std::fs::remove_file(&path);
+        let path = temp_path("missing");
         let err = load_from_path(&path).expect_err("missing file should error");
         assert!(matches!(err, SceneFileError::Io(_)));
     }
diff --git a/src/script_exec.rs b/src/script_exec.rs
index 7dcee7b..0a70c20 100644
--- a/src/script_exec.rs
+++ b/src/script_exec.rs
@@ -21,6 +21,7 @@ use std::path::{Path, PathBuf};
 
 use image::ImageError;
 
+use crate::import::import_ovp_text;
 use crate::render::render_top_down_to_path;
 use crate::scene::Scene;
 use crate::script::{Command, ParseError, PresetName, Script, parse_script};
@@ -50,6 +51,8 @@ pub enum ScriptError {
     Parse(ParseError),
     /// Building a terrain grid failed.
     Terrain(TerrainError),
+    /// Importing an open-format terrain source failed.
+    Import(crate::import::ImportError),
     /// Decoding a heightmap or writing a render failed.
     Image(ImageError),
     /// A `render output` command ran before any terrain was established.
@@ -62,6 +65,7 @@ impl std::fmt::Display for ScriptError {
             ScriptError::Io(e) => write!(f, "script I/O error: {e}"),
             ScriptError::Parse(e) => write!(f, "script parse error: {e}"),
             ScriptError::Terrain(e) => write!(f, "script terrain error: {e}"),
+            ScriptError::Import(e) => write!(f, "script import error: {e}"),
             ScriptError::Image(e) => write!(f, "script image error: {e}"),
             ScriptError::RenderWithoutTerrain => write!(
                 f,
@@ -85,6 +89,12 @@ impl From<TerrainError> for ScriptError {
     }
 }
 
+impl From<crate::import::ImportError> for ScriptError {
+    fn from(e: crate::import::ImportError) -> Self {
+        ScriptError::Import(e)
+    }
+}
+
 impl From<ImageError> for ScriptError {
     fn from(e: ImageError) -> Self {
         ScriptError::Image(e)
@@ -102,6 +112,12 @@ pub fn run_script_file(path: &Path) -> Result<ExecReport, ScriptError> {
     run_script(&script, base_dir)
 }
 
+/// Parse and execute script source text.
+pub fn run_script_source(source: &str, base_dir: &Path) -> Result<ExecReport, ScriptError> {
+    let script = parse_script(source)?;
+    run_script(&script, base_dir)
+}
+
 /// Execute an already-parsed [`Script`], resolving relative paths against
 /// `base_dir`.
 pub fn run_script(script: &Script, base_dir: &Path) -> Result<ExecReport, ScriptError> {
@@ -146,10 +162,17 @@ pub fn run_script(script: &Script, base_dir: &Path) -> Result<ExecReport, Script
     Ok(report)
 }
 
-/// Load a grayscale PNG as a [`HeightGrid`], mapping pixel luma 0..=255 onto
-/// elevations 0.0..=[`HEIGHTMAP_PEAK_HEIGHT`].
+/// Load an imported heightmap, accepting either the project-owned `ovp-text`
+/// fixture format or a grayscale image file.
 fn load_heightmap(path: &Path) -> Result<HeightGrid, ScriptError> {
-    let image = image::open(path)?.to_luma8();
+    let bytes = std::fs::read(path).map_err(ScriptError::Io)?;
+    if let Ok(source) = std::str::from_utf8(&bytes) {
+        if let Ok(imported) = import_ovp_text(source) {
+            return Ok(imported.into_grid());
+        }
+    }
+
+    let image = image::load_from_memory(&bytes)?.to_luma8();
     let width = image.width();
     let height = image.height();
     let samples = image
diff --git a/src/terrain.rs b/src/terrain.rs
index 807c50e..5529a0a 100644
--- a/src/terrain.rs
+++ b/src/terrain.rs
@@ -24,7 +24,7 @@ impl fmt::Display for TerrainError {
 
 impl std::error::Error for TerrainError {}
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct HeightGrid {
     width: u32,
     height: u32,
diff --git a/src/terrain_gen.rs b/src/terrain_gen.rs
new file mode 100644
index 0000000..f4fd9b1
--- /dev/null
+++ b/src/terrain_gen.rs
@@ -0,0 +1,188 @@
+use crate::terrain::{HeightGrid, TerrainError};
+
+const OCTAVE_COUNT: usize = 4;
+const BASE_FREQUENCY: f32 = 2.0;
+const LACUNARITY: f32 = 2.0;
+const GAIN: f32 = 0.5;
+const LATTICE_SEED_STEP: u64 = 0x9E37_79B9_7F4A_7C15;
+const LATTICE_X_MUL: u64 = 0x9E37_79B9_7F4A_7C15;
+const LATTICE_Y_MUL: u64 = 0xC2B2_AE3D_27D4_EB4F;
+const FINALIZER_MUL1: u64 = 0xBF58_476D_1CE4_E5B9;
+const FINALIZER_MUL2: u64 = 0x94D0_49BB_1331_11EB;
+
+/// Describes a terrain generation request.
+///
+/// Specs are immutable once constructed; identical specs always yield
+/// identical [`HeightGrid`]s from a given [`TerrainGenerator`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct TerrainGenerationSpec {
+    seed: u64,
+    width: u32,
+    height: u32,
+}
+
+impl TerrainGenerationSpec {
+    /// Creates a spec, rejecting zero-sized grids with [`TerrainError::ZeroDimension`].
+    pub fn new(seed: u64, width: u32, height: u32) -> Result<Self, TerrainError> {
+        if width == 0 || height == 0 {
+            return Err(TerrainError::ZeroDimension);
+        }
+        Ok(Self {
+            seed,
+            width,
+            height,
+        })
+    }
+
+    pub fn seed(&self) -> u64 {
+        self.seed
+    }
+
+    pub fn width(&self) -> u32 {
+        self.width
+    }
+
+    pub fn height(&self) -> u32 {
+        self.height
+    }
+}
+
+/// Produces a [`HeightGrid`] from a [`TerrainGenerationSpec`].
+pub trait TerrainGenerator {
+    fn generate(&self, spec: &TerrainGenerationSpec) -> Result<HeightGrid, TerrainError>;
+}
+
+/// A deterministic, in-memory reference generator.
+///
+/// Heights are derived from a small clean-room seeded value-noise fBm stack so
+/// identical specs always produce identical grids. The output stays in
+/// `[0.0, 1.0]`, which keeps later renderer and palette integration simple.
+#[derive(Debug, Clone, Copy, Default)]
+pub struct DeterministicTerrainGenerator;
+
+impl DeterministicTerrainGenerator {
+    pub fn new() -> Self {
+        Self
+    }
+}
+
+#[inline]
+fn fade(t: f32) -> f32 {
+    t * t * (3.0 - 2.0 * t)
+}
+
+#[inline]
+fn normalized_coord(index: u32, size: u32) -> f32 {
+    if size <= 1 {
+        0.0
+    } else {
+        index as f32 / (size - 1) as f32
+    }
+}
+
+/// Hashes seed and lattice coordinates into a height in `[0.0, 1.0)`.
+#[inline]
+fn lattice_value(seed: u64, x: i64, y: i64) -> f32 {
+    let mut h =
+        seed ^ (x as u64).wrapping_mul(LATTICE_X_MUL) ^ (y as u64).wrapping_mul(LATTICE_Y_MUL);
+    h ^= h >> 30;
+    h = h.wrapping_mul(FINALIZER_MUL1);
+    h ^= h >> 27;
+    h = h.wrapping_mul(FINALIZER_MUL2);
+    h ^= h >> 31;
+    // Take the top 24 bits for an exact f32 fraction in [0, 1).
+    (h >> 40) as f32 / (1u64 << 24) as f32
+}
+
+#[inline]
+fn value_noise(seed: u64, x: f32, y: f32) -> f32 {
+    let x0 = x.floor() as i64;
+    let y0 = y.floor() as i64;
+    let x1 = x0 + 1;
+    let y1 = y0 + 1;
+    let tx = x - x0 as f32;
+    let ty = y - y0 as f32;
+    let sx = fade(tx);
+    let sy = fade(ty);
+
+    let n00 = lattice_value(seed, x0, y0);
+    let n10 = lattice_value(seed, x1, y0);
+    let n01 = lattice_value(seed, x0, y1);
+    let n11 = lattice_value(seed, x1, y1);
+
+    let ix0 = n00 * (1.0 - sx) + n10 * sx;
+    let ix1 = n01 * (1.0 - sx) + n11 * sx;
+    ix0 * (1.0 - sy) + ix1 * sy
+}
+
+#[inline]
+fn fbm_height(seed: u64, x: f32, y: f32) -> f32 {
+    let mut total = 0.0;
+    let mut amplitude = 1.0;
+    let mut frequency = BASE_FREQUENCY;
+    let mut amplitude_sum = 0.0;
+
+    for octave in 0..OCTAVE_COUNT {
+        let octave_seed = seed.wrapping_add((octave as u64).wrapping_mul(LATTICE_SEED_STEP));
+        total += amplitude * value_noise(octave_seed, x * frequency, y * frequency);
+        amplitude_sum += amplitude;
+        amplitude *= GAIN;
+        frequency *= LACUNARITY;
+    }
+
+    total / amplitude_sum
+}
+
+impl TerrainGenerator for DeterministicTerrainGenerator {
+    fn generate(&self, spec: &TerrainGenerationSpec) -> Result<HeightGrid, TerrainError> {
+        let width = spec.width();
+        let height = spec.height();
+        let mut samples = Vec::with_capacity((width as usize) * (height as usize));
+        for y in 0..height {
+            let ny = normalized_coord(y, height);
+            for x in 0..width {
+                let nx = normalized_coord(x, width);
+                samples.push(fbm_height(spec.seed(), nx, ny));
+            }
+        }
+        HeightGrid::new(width, height, samples)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_rejects_zero_dimensions() {
+        assert_eq!(
+            TerrainGenerationSpec::new(1, 0, 4).unwrap_err(),
+            TerrainError::ZeroDimension
+        );
+        assert_eq!(
+            TerrainGenerationSpec::new(1, 4, 0).unwrap_err(),
+            TerrainError::ZeroDimension
+        );
+    }
+
+    #[test]
+    fn generate_matches_spec_dimensions() {
+        let spec = TerrainGenerationSpec::new(99, 8, 5).unwrap();
+        let grid = DeterministicTerrainGenerator::new()
+            .generate(&spec)
+            .unwrap();
+        assert_eq!(grid.width(), 8);
+        assert_eq!(grid.height(), 5);
+    }
+
+    #[test]
+    fn different_seeds_diverge() {
+        let a = DeterministicTerrainGenerator::new()
+            .generate(&TerrainGenerationSpec::new(1, 4, 4).unwrap())
+            .unwrap();
+        let b = DeterministicTerrainGenerator::new()
+            .generate(&TerrainGenerationSpec::new(2, 4, 4).unwrap())
+            .unwrap();
+        assert_ne!(a.sample(0, 0), b.sample(0, 0));
+    }
+}
diff --git a/tests/docs_sync.rs b/tests/docs_sync.rs
new file mode 100644
index 0000000..9d87b39
--- /dev/null
+++ b/tests/docs_sync.rs
@@ -0,0 +1,65 @@
+//! Docs-sync guard for the terrain-generation surface.
+//!
+//! The terrain generator has landed in `src/terrain_gen.rs` (see
+//! `tests/terrain_gen.rs`), but the docs have not been updated to describe it.
+//! This test fails by design until README, the terrain-generation plan, and
+//! the architecture notes mention the new surface.
+
+use std::fs;
+use std::path::Path;
+
+/// Substrings every terrain-aware doc should mention now that the
+/// terrain-generation module has landed.
+const REQUIRED_TERMS: &[&str] = &[
+    "src/terrain_gen.rs",
+    "TerrainGenerationSpec",
+    "DeterministicTerrainGenerator",
+    "cargo test terrain_gen",
+];
+
+fn read_doc(relative: &str) -> String {
+    let path = Path::new(env!("CARGO_MANIFEST_DIR")).join(relative);
+    fs::read_to_string(&path).unwrap_or_else(|e| panic!("failed to read {}: {e}", path.display()))
+}
+
+/// Returns the required terrain-generation terms that `doc` fails to mention.
+fn missing_terms(doc: &str) -> Vec<&'static str> {
+    let mut missing: Vec<&'static str> = REQUIRED_TERMS
+        .iter()
+        .copied()
+        .filter(|term| !doc.contains(term))
+        .collect();
+
+    // A determinism/seed note: the docs should say generation is seeded and
+    // reproducible, not just reuse the word "deterministic" elsewhere.
+    let lower = doc.to_lowercase();
+    if !(lower.contains("seed") && lower.contains("determin")) {
+        missing.push("a determinism/seed note");
+    }
+
+    missing
+}
+
+fn assert_doc_mentions_terrain_gen(relative: &str) {
+    let doc = read_doc(relative);
+    let missing = missing_terms(&doc);
+    assert!(
+        missing.is_empty(),
+        "{relative} does not mention the landed terrain-generation surface: {missing:?}"
+    );
+}
+
+#[test]
+fn readme_mentions_terrain_generation_surface() {
+    assert_doc_mentions_terrain_gen("README.md");
+}
+
+#[test]
+fn terrain_generation_plan_mentions_terrain_generation_surface() {
+    assert_doc_mentions_terrain_gen("docs/plans/terrain-generation.md");
+}
+
+#[test]
+fn architecture_notes_mention_terrain_generation_surface() {
+    assert_doc_mentions_terrain_gen("docs/knowledgebase/architecture-notes.md");
+}
diff --git a/tests/terrain_gen.rs b/tests/terrain_gen.rs
new file mode 100644
index 0000000..9911f23
--- /dev/null
+++ b/tests/terrain_gen.rs
@@ -0,0 +1,78 @@
+use openvistapro::terrain::{HeightGrid, TerrainError};
+use openvistapro::terrain_gen::{
+    DeterministicTerrainGenerator, TerrainGenerationSpec, TerrainGenerator,
+};
+
+fn assert_same_grid(a: &HeightGrid, b: &HeightGrid) {
+    assert_eq!(a.width(), b.width());
+    assert_eq!(a.height(), b.height());
+    for y in 0..a.height() {
+        for x in 0..a.width() {
+            assert_eq!(a.sample(x, y), b.sample(x, y), "mismatch at ({x}, {y})");
+        }
+    }
+}
+
+#[test]
+fn terrain_gen_deterministic_generator_returns_requested_dimensions() {
+    let spec = TerrainGenerationSpec::new(0xfeed_beef, 4, 3).expect("valid spec");
+    let generator = DeterministicTerrainGenerator::new();
+
+    let grid = generator.generate(&spec).expect("generation succeeds");
+
+    assert_eq!(grid.width(), 4);
+    assert_eq!(grid.height(), 3);
+}
+
+#[test]
+fn terrain_gen_deterministic_generator_is_stable_for_same_seed_and_size() {
+    let spec = TerrainGenerationSpec::new(42, 6, 5).expect("valid spec");
+    let generator = DeterministicTerrainGenerator::new();
+
+    let first = generator
+        .generate(&spec)
+        .expect("first generation succeeds");
+    let second = generator
+        .generate(&spec)
+        .expect("second generation succeeds");
+
+    assert_same_grid(&first, &second);
+}
+
+#[test]
+fn terrain_gen_deterministic_generator_rejects_zero_dimensions() {
+    let err = TerrainGenerationSpec::new(7, 0, 4).unwrap_err();
+    assert_eq!(err, TerrainError::ZeroDimension);
+
+    let err = TerrainGenerationSpec::new(7, 4, 0).unwrap_err();
+    assert_eq!(err, TerrainError::ZeroDimension);
+}
+
+#[test]
+fn terrain_gen_deterministic_generator_produces_value_noise_fbm_sample() {
+    let spec = TerrainGenerationSpec::new(1337, 4, 4).expect("valid spec");
+    let generator = DeterministicTerrainGenerator::new();
+
+    let grid = generator.generate(&spec).expect("generation succeeds");
+
+    let expected = [
+        [0.706_783_f32, 0.390_681, 0.571_295, 0.454_375],
+        [0.667_478, 0.549_327, 0.476_506, 0.335_594],
+        [0.603_516, 0.451_503, 0.516_397, 0.357_081],
+        [0.308_838, 0.295_558, 0.570_510, 0.666_683],
+    ];
+
+    for (y, row) in expected.iter().enumerate() {
+        for (x, expected_sample) in row.iter().enumerate() {
+            let actual = grid.sample(x as u32, y as u32).expect("sample in bounds");
+            assert!(
+                (actual - expected_sample).abs() < 1e-6,
+                "mismatch at ({x}, {y}): expected {expected_sample}, got {actual}"
+            );
+        }
+    }
+
+    let (min, max) = grid.min_max().expect("non-empty grid has min/max");
+    assert!(min >= 0.0);
+    assert!(max <= 1.0);
+}