[feat](trx-frontend-http): serve the vendored APRS symbol sprites

Embed the six sheets alongside the other vendored assets and serve them
under /vendor with the same immutable cache headers.

The browser computes a symbol's cell from a 16x6 grid of 24px cells, so
a re-vendored sheet at any other size would shift every station onto a
neighbouring icon -- wrong on every packet, and invisible unless you
know which glyph to expect.  Pin the geometry by parsing each embedded
PNG's IHDR in a test.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018huL1ELyr86yVqfAabtioA
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/src/api/assets.rs

@@ -279,6 +279,47 @@ pub(crate) async fn leaflet_layers_2x() -> impl Responder {
         .body(status::LEAFLET_LAYERS_2X)
 }
 
+// ---------------------------------------------------------------------------
+// Vendored APRS symbol sprites
+// ---------------------------------------------------------------------------
+
+fn embedded_png(bytes: &'static [u8]) -> HttpResponse {
+    HttpResponse::Ok()
+        .insert_header((header::CONTENT_TYPE, "image/png"))
+        .insert_header((header::CACHE_CONTROL, "public, max-age=604800, immutable"))
+        .body(bytes)
+}
+
+#[get("/vendor/aprs-symbols-24-0.png")]
+pub(crate) async fn aprs_symbols_primary() -> impl Responder {
+    embedded_png(status::APRS_SYMBOLS_PRIMARY)
+}
+
+#[get("/vendor/aprs-symbols-24-0-2x.png")]
+pub(crate) async fn aprs_symbols_primary_2x() -> impl Responder {
+    embedded_png(status::APRS_SYMBOLS_PRIMARY_2X)
+}
+
+#[get("/vendor/aprs-symbols-24-1.png")]
+pub(crate) async fn aprs_symbols_alternate() -> impl Responder {
+    embedded_png(status::APRS_SYMBOLS_ALTERNATE)
+}
+
+#[get("/vendor/aprs-symbols-24-1-2x.png")]
+pub(crate) async fn aprs_symbols_alternate_2x() -> impl Responder {
+    embedded_png(status::APRS_SYMBOLS_ALTERNATE_2X)
+}
+
+#[get("/vendor/aprs-symbols-24-2.png")]
+pub(crate) async fn aprs_symbols_overlay() -> impl Responder {
+    embedded_png(status::APRS_SYMBOLS_OVERLAY)
+}
+
+#[get("/vendor/aprs-symbols-24-2-2x.png")]
+pub(crate) async fn aprs_symbols_overlay_2x() -> impl Responder {
+    embedded_png(status::APRS_SYMBOLS_OVERLAY_2X)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -307,4 +348,33 @@ mod tests {
         );
         assert_eq!(generated_content_type("secret.txt"), None);
     }
+
+    /// Reads the width and height out of a PNG IHDR chunk.
+    fn png_dimensions(bytes: &[u8]) -> (u32, u32) {
+        assert_eq!(&bytes[..8], b"\x89PNG\r\n\x1a\n", "not a PNG");
+        assert_eq!(&bytes[12..16], b"IHDR", "first chunk is not IHDR");
+        let width = u32::from_be_bytes(bytes[16..20].try_into().expect("IHDR width"));
+        let height = u32::from_be_bytes(bytes[20..24].try_into().expect("IHDR height"));
+        (width, height)
+    }
+
+    /// The browser computes sprite cell offsets from a 16x6 grid of 24px cells,
+    /// so a sheet at any other size would silently shift every APRS symbol.
+    #[test]
+    fn aprs_symbol_sheets_match_the_sprite_grid_the_frontend_assumes() {
+        for (name, bytes) in [
+            ("aprs-symbols-24-0", status::APRS_SYMBOLS_PRIMARY),
+            ("aprs-symbols-24-1", status::APRS_SYMBOLS_ALTERNATE),
+            ("aprs-symbols-24-2", status::APRS_SYMBOLS_OVERLAY),
+        ] {
+            assert_eq!(png_dimensions(bytes), (384, 144), "{name} is not a 16x6 grid");
+        }
+        for (name, bytes) in [
+            ("aprs-symbols-24-0-2x", status::APRS_SYMBOLS_PRIMARY_2X),
+            ("aprs-symbols-24-1-2x", status::APRS_SYMBOLS_ALTERNATE_2X),
+            ("aprs-symbols-24-2-2x", status::APRS_SYMBOLS_OVERLAY_2X),
+        ] {
+            assert_eq!(png_dimensions(bytes), (768, 288), "{name} is not a 2x sheet");
+        }
+    }
 }

src/trx-client/trx-frontend/trx-frontend-http/src/api/mod.rs

@@ -658,6 +658,13 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(assets::leaflet_marker_shadow)
         .service(assets::leaflet_layers)
         .service(assets::leaflet_layers_2x)
+        // Vendored APRS symbol sprites
+        .service(assets::aprs_symbols_primary)
+        .service(assets::aprs_symbols_primary_2x)
+        .service(assets::aprs_symbols_alternate)
+        .service(assets::aprs_symbols_alternate_2x)
+        .service(assets::aprs_symbols_overlay)
+        .service(assets::aprs_symbols_overlay_2x)
         .service(assets::generated_asset)
         // Virtual channels
         .service(vchan::list_channels)

src/trx-client/trx-frontend/trx-frontend-http/src/status.rs

@@ -37,6 +37,22 @@ pub const LEAFLET_MARKER_SHADOW: &[u8] = include_bytes!("../assets/web/vendor/ma
 pub const LEAFLET_LAYERS: &[u8] = include_bytes!("../assets/web/vendor/layers.png");
 pub const LEAFLET_LAYERS_2X: &[u8] = include_bytes!("../assets/web/vendor/layers-2x.png");
 
+// Vendored APRS symbol sprites (https://github.com/hessu/aprs-symbols).
+// Each sheet is a 16x6 grid of 24px cells indexed by `symbol code - 0x21`:
+// table 0 is the primary ('/') set, table 1 the alternate ('\') set, and
+// table 2 the overlay characters drawn on top of an alternate symbol.
+pub const APRS_SYMBOLS_PRIMARY: &[u8] = include_bytes!("../assets/web/vendor/aprs-symbols-24-0.png");
+pub const APRS_SYMBOLS_PRIMARY_2X: &[u8] =
+    include_bytes!("../assets/web/vendor/aprs-symbols-24-0-2x.png");
+pub const APRS_SYMBOLS_ALTERNATE: &[u8] =
+    include_bytes!("../assets/web/vendor/aprs-symbols-24-1.png");
+pub const APRS_SYMBOLS_ALTERNATE_2X: &[u8] =
+    include_bytes!("../assets/web/vendor/aprs-symbols-24-1-2x.png");
+pub const APRS_SYMBOLS_OVERLAY: &[u8] =
+    include_bytes!("../assets/web/vendor/aprs-symbols-24-2.png");
+pub const APRS_SYMBOLS_OVERLAY_2X: &[u8] =
+    include_bytes!("../assets/web/vendor/aprs-symbols-24-2-2x.png");
+
 /// Build version tag used for cache-busting asset URLs and ETag headers.
 /// Computed once from `PKG_VERSION` + `CLIENT_BUILD_DATE`.
 pub fn build_version_tag() -> &'static str {