diff --git a/Makefile b/Makefile
index 2863eb5..6283308 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,10 @@
 .PHONY: build deploy sign download-model download-pdfjs download-leaflet compress-assets convert-images pdf-thumbs pdfs watch clean dev audit-marks archive-gc archive-wayback archive-check
 
+# deploy's prerequisite order (clean -> build -> sign) is only correct
+# serially; under `make -j` they could interleave. This build has no
+# intra-target parallelism worth preserving, so disable it outright.
+.NOTPARALLEL:
+
 # Source .env for deploy / GitHub config if it exists.
 # .env format: KEY=value (one per line, no `export` prefix, no quotes needed).
 # Only the variables explicitly listed below are exported to recipe
@@ -114,12 +119,16 @@ convert-images:
 # Thumbnails are written as static/papers/foo.thumb.png alongside each PDF.
 # Skipped silently when pdftoppm is not installed or static/papers/ is empty.
 pdf-thumbs:
+	# A failing pdftoppm must at least warn: the `find | while` pipeline's
+	# exit status is the last iteration's, so without the `||` a corrupt
+	# PDF would silently ship without a thumbnail.
 	@if command -v pdftoppm >/dev/null 2>&1; then \
 	  find static/papers -name '*.pdf' 2>/dev/null | while read pdf; do \
 	    thumb="$${pdf%.pdf}.thumb"; \
 	    if [ ! -f "$${thumb}.png" ] || [ "$$pdf" -nt "$${thumb}.png" ]; then \
 	      echo "  pdf-thumb $$pdf"; \
-	      pdftoppm -r 100 -f 1 -l 1 -png -singlefile "$$pdf" "$$thumb"; \
+	      pdftoppm -r 100 -f 1 -l 1 -png -singlefile "$$pdf" "$$thumb" \
+	        || echo "Warning: pdf-thumb failed for $$pdf (page ships without a thumbnail)" >&2; \
 	    fi; \
 	  done; \
 	else \
diff --git a/pyproject.toml b/pyproject.toml
index b82d0d0..8a0b5eb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,7 +24,10 @@ dependencies = [
     "pillow>=10.0,<12",
     "colorthief>=0.2,<1",
     "pyyaml>=6.0,<7",
-    "einops>=0.8.2",
+    # Not imported by this repo: required at runtime by nomic-embed's
+    # remote modeling code (nomic-bert-2048, loaded by embed.py's page
+    # pass under trust_remote_code with a pinned code_revision).
+    "einops>=0.8.2,<1",
 ]
 
 [[tool.uv.index]]
diff --git a/tools/add-popup-source.sh b/tools/add-popup-source.sh
index 36fdcf5..01dd9ab 100755
--- a/tools/add-popup-source.sh
+++ b/tools/add-popup-source.sh
@@ -49,6 +49,10 @@ EOF
 bold "── new popup provider ──"
 NAME=$(prompt  "slug (lowercase, used as class + data-popup-source key, e.g. 'zenodo'):")
 [[ -z "$NAME" ]] && { warn "slug required"; exit 1; }
+# The slug is interpolated into nginx directives (location /proxy/$NAME/,
+# set \$upstream_$NAME) — validate like import-photo.sh does so a space,
+# ';', or '{' can't produce a config that fails to load.
+[[ "$NAME" =~ ^[a-z0-9-]+$ ]] || { warn "slug must match ^[a-z0-9-]+\$"; exit 1; }
 
 LABEL=$(prompt "display label (e.g. 'Zenodo'):")
 [[ -z "$LABEL" ]] && LABEL="$NAME"
@@ -107,14 +111,16 @@ fi
 
 # ── proxy prefix + upstream host derivation ──────────────────────────
 
+# UPSTREAM_HOST is derived unconditionally: the no-proxy (direct CORS
+# fetch) case is exactly when the host must be added to connect-src, so
+# the checklist's CSP reminder below needs it populated either way.
+UPSTREAM_HOST=$(printf '%s' "$API_URL" | awk -F/ '{print $3}')
 if [[ "$NEEDS_PROXY" -eq 1 ]]; then
-    UPSTREAM_HOST=$(printf '%s' "$API_URL" | awk -F/ '{print $3}')
     UPSTREAM_PATH=$(printf '%s' "$API_URL" | awk -F/ 'BEGIN{OFS="/"} {$1=""; $2=""; $3=""; print}' | sed 's|^///||')
     PROXY_PATH="/proxy/$NAME/"
     PROXY_API_URL="$PROXY_PATH${UPSTREAM_PATH%%\?*}"
     [[ "$API_URL" == *"?"* ]] && PROXY_API_URL="$PROXY_API_URL?${API_URL#*\?}"
 else
-    UPSTREAM_HOST=""
     PROXY_API_URL="$API_URL"
 fi
 
@@ -205,8 +211,9 @@ cat <<EOF
 EOF
 
 if [[ "$NEEDS_PROXY" -eq 0 && -n "$UPSTREAM_HOST" ]]; then
-    echo "  5. In static/js/popups.js top-comment: add $UPSTREAM_HOST to the"
-    echo "     connect-src CSP list."
+    echo "  5. Add https://$UPSTREAM_HOST to connect-src in"
+    echo "     nginx/security-headers.conf (direct CORS fetches are blocked"
+    echo "     by CSP otherwise), and mirror it in the popups.js top-comment."
 fi
 
 echo
diff --git a/tools/archive.py b/tools/archive.py
index 603533f..845a9b3 100644
--- a/tools/archive.py
+++ b/tools/archive.py
@@ -105,14 +105,18 @@ def err(msg: str) -> None:
 
 
 def atomic_write_text(path: Path, text: str) -> None:
-    """Write to path.tmp then os.replace. PROVENANCE.json and the
-    generated index/state files are integrity records — an interrupt
-    mid-write must never leave a truncated file that the next run
-    parses (or mistakes for corruption)."""
+    """Write to a PID-unique temp then os.replace. PROVENANCE.json and
+    the generated index/state files are integrity records — an interrupt
+    mid-write must never leave a truncated file that the next run parses
+    (or mistakes for corruption); fsync makes the rename durable and the
+    PID suffix keeps concurrent runs from sharing a temp file."""
     path.parent.mkdir(parents=True, exist_ok=True)
-    tmp = path.with_suffix(path.suffix + ".tmp")
+    tmp = path.with_suffix(path.suffix + f".tmp.{os.getpid()}")
     try:
-        tmp.write_text(text, encoding="utf-8")
+        with tmp.open("w", encoding="utf-8") as f:
+            f.write(text)
+            f.flush()
+            os.fsync(f.fileno())
         os.replace(tmp, path)
     except BaseException:
         tmp.unlink(missing_ok=True)
diff --git a/tools/embed.py b/tools/embed.py
index d368f17..be16f57 100644
--- a/tools/embed.py
+++ b/tools/embed.py
@@ -120,12 +120,21 @@ PORTAL_BODY_ATTR = "data-portal"
 
 
 def atomic_write_bytes(path: Path, data: bytes) -> None:
-    """Write to path.tmp then os.replace, so an interrupt mid-write
-    cannot leave a truncated file that the next build/serve loads."""
+    """Write to a PID-unique temp then os.replace: an interrupt mid-write
+    cannot leave a truncated file at the final path, fsync makes the
+    rename durable across power loss, and the PID suffix keeps two
+    concurrent runs from interleaving writes into one temp file."""
     path.parent.mkdir(parents=True, exist_ok=True)
-    tmp = path.with_suffix(path.suffix + ".tmp")
-    tmp.write_bytes(data)
-    os.replace(tmp, path)
+    tmp = path.with_suffix(path.suffix + f".tmp.{os.getpid()}")
+    try:
+        with tmp.open("wb") as f:
+            f.write(data)
+            f.flush()
+            os.fsync(f.fileno())
+        os.replace(tmp, path)
+    except BaseException:
+        tmp.unlink(missing_ok=True)
+        raise
 
 
 def atomic_write_text(path: Path, text: str) -> None:
@@ -186,7 +195,9 @@ def save_vec_cache(path: Path, model: str, revision: str, dim: int,
     path.parent.mkdir(parents=True, exist_ok=True)
     # Pass an open file handle, not a path: np.savez_compressed appends
     # ".npz" to bare paths, which would mangle our atomic-rename target.
-    tmp = path.with_suffix(path.suffix + ".tmp")
+    # PID-unique temp so concurrent runs can't interleave; fsync so the
+    # rename is durable.
+    tmp = path.with_suffix(path.suffix + f".tmp.{os.getpid()}")
     try:
         with open(tmp, "wb") as f:
             np.savez_compressed(
@@ -197,6 +208,8 @@ def save_vec_cache(path: Path, model: str, revision: str, dim: int,
                 hashes=hashes,
                 vectors=vectors,
             )
+            f.flush()
+            os.fsync(f.fileno())
         os.replace(tmp, path)
     except BaseException:
         tmp.unlink(missing_ok=True)
diff --git a/tools/extract-dimensions.py b/tools/extract-dimensions.py
index 04017a4..ea9b51f 100755
--- a/tools/extract-dimensions.py
+++ b/tools/extract-dimensions.py
@@ -31,6 +31,7 @@ images are logged and the rest of the walk continues.
 
 from __future__ import annotations
 
+import os
 import sys
 from pathlib import Path
 from typing import Any
@@ -62,13 +63,20 @@ def _is_stale(image: Path, sidecar: Path) -> bool:
 
 
 def _atomic_write_yaml(path: Path, data: dict[str, Any]) -> None:
-    tmp = path.with_suffix(path.suffix + ".tmp")
-    with tmp.open("w", encoding="utf-8") as f:
-        # Preserve a stable key order (width before height) so a manual
-        # diff stays easy to read across regenerations.
-        ordered = {k: data[k] for k in ("width", "height") if k in data}
-        yaml.safe_dump(ordered, f, sort_keys=False, allow_unicode=True)
-    tmp.replace(path)
+    # PID-unique temp (concurrent runs can't share it), removed on
+    # failure. No fsync: sidecars are regenerated from the photo on the
+    # next build, so a lost rename costs one re-extraction, not data.
+    tmp = path.with_suffix(path.suffix + f".tmp.{os.getpid()}")
+    try:
+        with tmp.open("w", encoding="utf-8") as f:
+            # Preserve a stable key order (width before height) so a manual
+            # diff stays easy to read across regenerations.
+            ordered = {k: data[k] for k in ("width", "height") if k in data}
+            yaml.safe_dump(ordered, f, sort_keys=False, allow_unicode=True)
+        tmp.replace(path)
+    except BaseException:
+        tmp.unlink(missing_ok=True)
+        raise
 
 
 def _read_dimensions(image: Path) -> dict[str, int]:
diff --git a/tools/extract-exif.py b/tools/extract-exif.py
index 799ec04..bc70d64 100755
--- a/tools/extract-exif.py
+++ b/tools/extract-exif.py
@@ -381,12 +381,19 @@ def _is_stale(image: Path, sidecar: Path) -> bool:
 
 
 def _atomic_write_yaml(path: Path, data: dict[str, Any]) -> None:
-    tmp = path.with_suffix(path.suffix + ".tmp")
-    with tmp.open("w", encoding="utf-8") as f:
-        # Preserve the SIDECAR_KEYS order so a manual diff is easy to read.
-        ordered = {k: data[k] for k in SIDECAR_KEYS if k in data}
-        yaml.safe_dump(ordered, f, sort_keys=False, allow_unicode=True)
-    tmp.replace(path)
+    # PID-unique temp (concurrent runs can't share it), removed on
+    # failure. No fsync: sidecars are regenerated from the photo on the
+    # next build, so a lost rename costs one re-extraction, not data.
+    tmp = path.with_suffix(path.suffix + f".tmp.{os.getpid()}")
+    try:
+        with tmp.open("w", encoding="utf-8") as f:
+            # Preserve the SIDECAR_KEYS order so a manual diff is easy to read.
+            ordered = {k: data[k] for k in SIDECAR_KEYS if k in data}
+            yaml.safe_dump(ordered, f, sort_keys=False, allow_unicode=True)
+        tmp.replace(path)
+    except BaseException:
+        tmp.unlink(missing_ok=True)
+        raise
 
 
 def _read_one(image: Path) -> dict[str, Any]:
diff --git a/tools/extract-palette.py b/tools/extract-palette.py
index 601824a..d50cd13 100755
--- a/tools/extract-palette.py
+++ b/tools/extract-palette.py
@@ -23,6 +23,7 @@ a palette extraction error.
 
 from __future__ import annotations
 
+import os
 import sys
 from pathlib import Path
 from typing import Any
@@ -62,10 +63,17 @@ def _is_stale(image: Path, sidecar: Path) -> bool:
 
 
 def _atomic_write_yaml(path: Path, data: dict[str, Any]) -> None:
-    tmp = path.with_suffix(path.suffix + ".tmp")
-    with tmp.open("w", encoding="utf-8") as f:
-        yaml.safe_dump(data, f, sort_keys=False, allow_unicode=True)
-    tmp.replace(path)
+    # PID-unique temp (concurrent runs can't share it), removed on
+    # failure. No fsync: sidecars are regenerated from the photo on the
+    # next build, so a lost rename costs one re-extraction, not data.
+    tmp = path.with_suffix(path.suffix + f".tmp.{os.getpid()}")
+    try:
+        with tmp.open("w", encoding="utf-8") as f:
+            yaml.safe_dump(data, f, sort_keys=False, allow_unicode=True)
+        tmp.replace(path)
+    except BaseException:
+        tmp.unlink(missing_ok=True)
+        raise
 
 
 def _extract_palette(image: Path) -> list[str]:
diff --git a/tools/refreeze.sh b/tools/refreeze.sh
index 6429c8d..fd8f6c6 100755
--- a/tools/refreeze.sh
+++ b/tools/refreeze.sh
@@ -8,11 +8,29 @@ FREEZE="$REPO_ROOT/cabal.project.freeze"
 
 cd "$REPO_ROOT"
 
+# Back up the current freeze and restore it if resolution fails, so an
+# unsolvable index never leaves the repo with no freeze file at all
+# (recoverable via git, but the script shouldn't depend on that).
+BACKUP=""
+if [ -f "$FREEZE" ]; then
+    BACKUP="$(mktemp "$FREEZE.bak.XXXXXX")"
+    cp "$FREEZE" "$BACKUP"
+fi
+restore_on_failure() {
+    if [ -n "$BACKUP" ]; then
+        echo "==> Refreeze failed — restoring previous freeze file." >&2
+        mv "$BACKUP" "$FREEZE"
+    fi
+}
+trap restore_on_failure ERR
+
 echo "==> Removing stale freeze file..."
 rm -f "$FREEZE"
 
 echo "==> Resolving dependencies and writing new freeze file..."
 cabal freeze
+trap - ERR
+[ -n "$BACKUP" ] && rm -f "$BACKUP"
 
 echo "==> Verifying build..."
 cabal build
diff --git a/uv.lock b/uv.lock
index dad9b9e..2a76ddc 100644
--- a/uv.lock
+++ b/uv.lock
@@ -389,7 +389,7 @@ requires-dist = [
     { name = "altair", specifier = ">=5.4,<6" },
     { name = "beautifulsoup4", specifier = ">=4.12,<5" },
     { name = "colorthief", specifier = ">=0.2,<1" },
-    { name = "einops", specifier = ">=0.8.2" },
+    { name = "einops", specifier = ">=0.8.2,<1" },
     { name = "faiss-cpu", specifier = ">=1.9,<2" },
     { name = "matplotlib", specifier = ">=3.9,<4" },
     { name = "numpy", specifier = ">=2.0,<3" },