fix: fall back to Sharp when CLI decoders are unavailable

DNG and FITS previews showed "Preview not available" because their CLI
decoders (ExifTool/ImageMagick) were not installed. Sharp can read both
formats natively (DNG is TIFF-based, FITS via libvips fitsload).

Added Sharp fallback to the preview endpoint, batch processing, and
tool factory: when decodeToSharpCompat throws, try sharp(buffer).metadata()
before returning 422. If Sharp can read the buffer, processing continues
without the CLI decoder.

apps/api/src/routes/batch.ts

@@ -13,6 +13,7 @@ import { getBundleForTool, TOOL_BUNDLE_MAP } from "@snapotter/shared";
 import archiver from "archiver";
 import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
 import PQueue from "p-queue";
+import sharp from "sharp";
 import { env } from "../config.js";
 import { autoOrient } from "../lib/auto-orient.js";
 import { resolveConcurrency } from "../lib/env.js";
@@ -169,7 +170,11 @@ export async function registerBatchRoutes(app: FastifyInstance): Promise<void> {
                 if (ext) processFilename = `${processFilename.slice(0, -ext.length)}.png`;
               }
               if (!skipPreprocess && needsCliDecode(validation.format)) {
-                processBuffer = await decodeToSharpCompat(processBuffer, validation.format);
+                try {
+                  processBuffer = await decodeToSharpCompat(processBuffer, validation.format);
+                } catch {
+                  await sharp(processBuffer).metadata();
+                }
                 const ext = processFilename.match(/\.[^.]+$/)?.[0];
                 if (ext) processFilename = `${processFilename.slice(0, -ext.length)}.png`;
               }

apps/api/src/routes/files.ts

@@ -156,17 +156,28 @@ export async function fileRoutes(app: FastifyInstance): Promise<void> {
       try {
         buffer = await decodeToSharpCompat(buffer, validation.format);
       } catch {
-        return reply.status(422).send({
-          error: `Failed to decode ${validation.format.toUpperCase()} file`,
-        });
+        // CLI decoder unavailable -- try Sharp directly as fallback for preview
+        try {
+          await sharp(buffer).metadata();
+        } catch {
+          return reply.status(422).send({
+            error: `Failed to decode ${validation.format.toUpperCase()} file`,
+          });
+        }
       }
     }
 
-    const webp = await sharp(buffer)
-      .resize(1200, 1200, { fit: "inside", withoutEnlargement: true })
-      .webp({ quality: 80 })
-      .toBuffer();
-    return reply.header("Content-Type", "image/webp").send(webp);
+    try {
+      const webp = await sharp(buffer)
+        .resize(1200, 1200, { fit: "inside", withoutEnlargement: true })
+        .webp({ quality: 80 })
+        .toBuffer();
+      return reply.header("Content-Type", "image/webp").send(webp);
+    } catch {
+      return reply.status(422).send({
+        error: `Failed to generate preview for ${validation.format.toUpperCase()} file`,
+      });
+    }
   });
 }
 

apps/api/src/routes/tool-factory.ts

@@ -198,14 +198,18 @@ export function createToolRoute<T>(app: FastifyInstance, config: ToolRouteConfig
         try {
           const fileExt = filename.split(".").pop()?.toLowerCase();
           fileBuffer = await decodeToSharpCompat(fileBuffer, validation.format, fileExt);
-          const ext = filename.match(/\.[^.]+$/)?.[0];
-          if (ext) filename = `${filename.slice(0, -ext.length)}.png`;
-        } catch (err) {
-          return reply.status(422).send({
-            error: `Failed to decode ${validation.format.toUpperCase()} file`,
-            details: err instanceof Error ? err.message : String(err),
-          });
+        } catch {
+          try {
+            await sharp(fileBuffer).metadata();
+          } catch (err) {
+            return reply.status(422).send({
+              error: `Failed to decode ${validation.format.toUpperCase()} file`,
+              details: err instanceof Error ? err.message : String(err),
+            });
+          }
         }
+        const ext = filename.match(/\.[^.]+$/)?.[0];
+        if (ext) filename = `${filename.slice(0, -ext.length)}.png`;
       }
 
       // Sanitize SVG input to prevent XXE, SSRF, and script injection