fix(ocr-service): fix ketos 7 segtrain compatibility and prevent OOM

Three issues fixed:

1. --resize both was removed in ketos 7; replaced with --resize union
   which extends the model's class mapping to include training data classes.

2. ketos ignores -s when -i is present, so the 1800px blla model caused
   7+ GB peak RAM and OOM-killed the host (no swap, 5 GB free).
   Now checks the loaded model's input height: only uses the base model
   when it was already fine-tuned at 800px; otherwise trains from scratch
   at 800px (~200 MB peak). After the first run the trained 800px model
   becomes the base for all subsequent fine-tuning runs.

3. segtrain now computes and returns cer = 1 - accuracy, matching the
   recognition training path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ocr-service/main.py

@@ -472,16 +472,35 @@ async def segtrain_model(
                 "-q", "fixed",
                 "-N", "10",
             ]
+            # Train at 800px height. The default blla model uses 1800px, which peaks at
+            # ~7+ GB on CPU and kills the host (ketos ignores -s when -i is present, so
+            # we cannot override the height of an existing model).
+            # Strategy: only use the base model if it is already at 800px (i.e. was
+            # produced by a previous fine-tuning run here). Otherwise train from scratch —
+            # the first run bootstraps a 800px model; all subsequent runs fine-tune it.
+            seg_spec = (
+                "[1,800,0,3 Cr7,7,64,2,2 Gn32 Cr3,3,128,2,2 Gn32 Cr3,3,128 Gn32 "
+                "Cr3,3,256 Gn32 Cr3,3,256 Gn32 Lbx32 Lby32 Cr1,1,32 Gn32 Lby32 Lbx32]"
+            )
+            use_base_model = False
             if os.path.exists(blla_model_path):
-                cmd += ["-i", blla_model_path, "--resize", "both"]
+                try:
+                    from kraken.lib import vgsl as _vgsl
+                    _m = _vgsl.TorchVGSLModel.load_model(blla_model_path)
+                    use_base_model = _m.input[2] == 800  # input is (batch, channels, H, W)
+                    if not use_base_model:
+                        log.info(
+                            "Base model height is %dpx — skipping -i to avoid OOM; "
+                            "will train from scratch at 800px",
+                            _m.input[2],
+                        )
+                except Exception:
+                    pass
+
+            if use_base_model:
+                cmd += ["-i", blla_model_path, "--resize", "union", "-s", seg_spec]
             else:
-                # No pretrained model — train from scratch with reduced height (800px)
+                cmd += ["-s", seg_spec]
-                # to keep peak RAM under ~200 MB on CPU (default 1800px uses ~500 MB+)
-                cmd += [
-                    "-s",
-                    "[1,800,0,3 Cr7,7,64,2,2 Gn32 Cr3,3,128,2,2 Gn32 Cr3,3,128 Gn32 "
-                    "Cr3,3,256 Gn32 Cr3,3,256 Gn32 Lbx32 Lby32 Cr1,1,32 Gn32 Lby32 Lbx32]",
-                ]
             cmd += xml_files
 
             log.info("Running: %s", " ".join(cmd[:5]) + " ...")
@@ -493,7 +512,8 @@ async def segtrain_model(
                 raise RuntimeError(f"ketos segtrain failed (exit {proc.returncode}): {proc.stderr[-500:]}")
 
             accuracy, epochs = _parse_best_checkpoint(checkpoint_dir)
-            log.info("Segmentation training complete — epochs=%s accuracy=%s", epochs, accuracy)
+            cer = round(1.0 - accuracy, 4) if accuracy is not None else None
+            log.info("Segmentation training complete — epochs=%s accuracy=%s cer=%s", epochs, accuracy, cer)
 
             best_model = _find_best_model(checkpoint_dir)
             if best_model is None:
@@ -508,7 +528,7 @@ async def segtrain_model(
             shutil.copy2(best_model, blla_model_path)
             log.info("Replaced blla model at %s", blla_model_path)
 
-            return {"loss": None, "accuracy": accuracy, "cer": None, "epochs": epochs}
+            return {"loss": None, "accuracy": accuracy, "cer": cer, "epochs": epochs}
 
     result = await asyncio.to_thread(_run_segtrain)
     return result