feat: harden pipeline UX — preprocess, rembg alpha, remix/lightbox

Downscale to 2000px JPEG before rembg, random blend opacity, timeout
retries, per-variant remix prefill, lightbox, and longer SFTP idle.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/main.py

@@ -8,7 +8,7 @@ from pathlib import Path
 from typing import Any
 from urllib.parse import quote
 
-from fastapi import FastAPI, Form, HTTPException, Request
+from fastapi import FastAPI, Form, HTTPException, Query, Request
 from fastapi.responses import FileResponse, HTMLResponse, RedirectResponse
 from fastapi.staticfiles import StaticFiles
 from fastapi.templating import Jinja2Templates
@@ -119,13 +119,49 @@ def job_file(job_id: str, rel_path: str) -> FileResponse:
 
 
 @app.get("/jobs/{job_id}/remix", response_class=HTMLResponse)
-def remix_form(request: Request, job_id: str, error: str | None = None) -> HTMLResponse:
+def remix_form(
+    request: Request,
+    job_id: str,
+    error: str | None = None,
+    from_variant: str | None = Query(None, alias="from"),
+) -> HTMLResponse:
     job_root = _job_root(job_id)
     if not (job_root / "rembg.png").exists():
         raise HTTPException(status_code=409, detail="Job hat noch kein Rembg-Ergebnis, Remix noch nicht moeglich.")
 
     assets = pipeline.load_assets()
     options = remix.build_remix_options(assets)
+    prefill: dict[str, str] = {
+        "bg_filter": "",
+        "bg_blend": "",
+        "fg_filter": "",
+        "fg_blend": "",
+        "opacity": config.BLEND_OPACITY if config.BLEND_OPACITY in config.OPACITY_CHOICES else "30%",
+    }
+    if from_variant:
+        manifest = pipeline.read_manifest(job_id) or {}
+        match = next((v for v in manifest.get("variants", []) if v.get("id") == from_variant), None)
+        if match:
+            opacity = match.get("blend_opacity") or prefill["opacity"]
+            if opacity not in config.OPACITY_CHOICES:
+                # Snap odd random values (e.g. 37%) to nearest offered choice.
+                try:
+                    pct = int(str(opacity).rstrip("%"))
+                    nearest = min(
+                        config.OPACITY_CHOICES,
+                        key=lambda c: abs(int(c.rstrip("%")) - pct),
+                    )
+                    opacity = nearest
+                except ValueError:
+                    opacity = prefill["opacity"]
+            prefill = {
+                "bg_filter": match.get("background_filter") or "",
+                "bg_blend": match.get("background_blend") or "",
+                "fg_filter": match.get("foreground_filter") or "",
+                "fg_blend": match.get("foreground_blend") or "",
+                "opacity": opacity,
+            }
+
     return templates.TemplateResponse(
         "remix.html",
         {
@@ -134,6 +170,8 @@ def remix_form(request: Request, job_id: str, error: str | None = None) -> HTMLR
             "job_id": job_id,
             "options": options,
             "opacity_choices": config.OPACITY_CHOICES,
+            "prefill": prefill,
+            "from_variant": from_variant,
             "error": error,
         },
     )