Surface exiftool write failures so thermal stretch can't silently drop GPS

On a (near-)full disk, exiftool's temp-copy write partially fails, producing
stretched thermal PNGs with most tags but no GPS. The stretch step was
ignoring exiftool's exit code, so this happened silently.

stretch_thermal._embed_exif now verifies GPS landed (spot-checks first/middle/
last frames), retries once on a transient miss, and otherwise raises a clear
"free up disk space and re-run" error (the pixels are written; only metadata
is missing). embed_metadata.embed_session's exit-code error gets the same hint.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -97,6 +97,10 @@ writable in stock exiftool). It uses this geometry — **not** the raw IMU.
   `tools/exiftool.exe`, the OliverBetz user install (`%LOCALAPPDATA%\Programs\ExifTool`),
   else auto-installed via `winget install OliverBetz.ExifTool`. (SourceForge auto-download
   is unreliable — GDPR/consent wall.)
+- **Disk space:** exiftool writes metadata via a temp copy, so a (near-)full disk causes
+  partial/failed writes — symptom is an image with most tags but **no GPS**. The embed and
+  stretch steps now check exiftool's exit code, verify GPS landed, retry once, and raise a
+  clear "full disk" error instead of silently producing GPS-less files.
 - **GPS source:** cam frames use the fused INS `position` block (falls back to raw `gps`);
   thermal has only `gps`. UTC time = GPS week/tow − 18 leap seconds.
 - **Thermal stretch window:** default = pooled 1–99th percentile across the whole session

embed_metadata.py

@@ -280,7 +280,9 @@ def embed_session(session, out_root=None, gps_source="position", exiftool=None,
     proc.wait()
     argfile.unlink(missing_ok=True)
     if proc.returncode != 0:
-        raise RuntimeError(f"exiftool exited with code {proc.returncode}")
+        raise RuntimeError(
+            f"exiftool exited with code {proc.returncode}. The usual cause is a FULL DISK "
+            "(metadata is written via a temp copy) - free up space and re-run.")
 
     progress(1.0, "Done")
     log(f"\nDone. {updated} files tagged.\nOutput: {out_root}")

stretch_thermal.py

@@ -164,7 +164,7 @@ def _embed_exif(pngs, out_dir: Path, exiftool=None, log=None):
     except BaseException as e:  # noqa: BLE001  (ensure_exiftool may sys.exit)
         log(f"  ! skipping EXIF embed - exiftool unavailable ({e})")
         return
-    arg_lines = []
+    arg_lines, dsts = [], []
     for p in pngs:
         sidecar = p.with_suffix(".json")
         if not sidecar.exists():
@@ -174,17 +174,38 @@ def _embed_exif(pngs, out_dir: Path, exiftool=None, log=None):
         except Exception:  # noqa: BLE001
             continue
         dst = out_dir / (p.stem + ".png")
+        dsts.append(dst)
         arg_lines += ["-overwrite_original", *embed.build_tags(data, {}, None, "gps"),
                       str(dst), "-execute"]
     if not arg_lines:
         return
     argfile = out_dir / "_exif_args.txt"
     argfile.write_text("\n".join(arg_lines) + "\n", encoding="utf-8")
+    cmd = [et, "-m", "-charset", "UTF8", "-charset", "filename=UTF8", "-@", str(argfile)]
+    samples = {dsts[0], dsts[len(dsts) // 2], dsts[-1]}   # spot-check first/mid/last
+
+    def gps_written():
+        return all(subprocess.run([et, "-s", "-s", "-s", "-GPSLatitude", str(s)],
+                                  capture_output=True, text=True).stdout.strip() for s in samples)
+
     log("Embedding GPS / orientation EXIF into the stretched frames ...")
-    subprocess.run([et, "-m", "-charset", "UTF8", "-charset", "filename=UTF8",
-                    "-@", str(argfile)], capture_output=True, text=True)
+    proc = subprocess.run(cmd, capture_output=True, text=True)
+    if proc.returncode == 0 and not gps_written():
+        log("  ! GPS not present after first pass - retrying once ...")
+        proc = subprocess.run(cmd, capture_output=True, text=True)
     argfile.unlink(missing_ok=True)
 
+    err = (proc.stderr or "").strip()
+    if err:
+        log(err)
+    if proc.returncode != 0 or not gps_written():
+        raise RuntimeError(
+            "Could not embed GPS/EXIF into the stretched PNGs (exiftool exit "
+            f"{proc.returncode}). The usual cause is a FULL DISK - free up space and re-run. "
+            "The stretched images were written; only the embedded metadata is missing."
+            + (f"\nexiftool: {err}" if err else ""))
+    log(f"EXIF embedded into {len(dsts)} stretched frames.")
+
 
 def stretch_session(session, out_dir=None, colormap="inferno", lo=None, hi=None,
                     embed_exif=True, exiftool=None, progress=None, log=None) -> dict: