diff --git a/AGENTS.md b/AGENTS.md
index 7bf66fc..29e1118 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -26,6 +26,7 @@ This document provides context and best practices for GitHub Copilot when workin
 - HEREDOCs don't work most of the time. Don't use them. Use editor tools to create proper scripots
 - we have an allium spec in the specs/ folder. you must weed the specs against built code to make sure you follow the spec.
 - when changing the spec, validate the spec with the available command line tool.
+- test with command line tools at least once to capture compile errors in tests, do not use the integrated testing of vscode, as that blocks on compile errors
 
 ---
 
diff --git a/lib/bds/embeddings.ex b/lib/bds/embeddings.ex
index 1d8672d..c604431 100644
--- a/lib/bds/embeddings.ex
+++ b/lib/bds/embeddings.ex
@@ -3,6 +3,7 @@ defmodule BDS.Embeddings do
 
   import Ecto.Query
 
+  alias BDS.Persistence
   alias BDS.Embeddings.DismissedDuplicatePair
   alias BDS.Embeddings.Index
   alias BDS.Embeddings.Key
@@ -317,7 +318,7 @@ defmodule BDS.Embeddings do
           project_id: post_a.project_id,
           post_id_a: sorted_a,
           post_id_b: sorted_b,
-          dismissed_at: System.system_time(:second)
+          dismissed_at: Persistence.now_ms()
         })
         |> Repo.insert_or_update!()
 
diff --git a/lib/bds/embeddings/index.ex b/lib/bds/embeddings/index.ex
index 0040be8..5cee159 100644
--- a/lib/bds/embeddings/index.ex
+++ b/lib/bds/embeddings/index.ex
@@ -3,6 +3,7 @@ defmodule BDS.Embeddings.Index do
 
   import Ecto.Query
 
+  alias BDS.Persistence
   alias BDS.Embeddings.Key
   alias BDS.Projects
   alias BDS.Repo
@@ -43,7 +44,7 @@ defmodule BDS.Embeddings.Index do
       "project_id" => project_id,
       "model_id" => model_id,
       "dimensions" => dimensions,
-      "updated_at" => System.system_time(:second),
+      "updated_at" => Persistence.now_ms(),
       "entries" => entries
     }
 
@@ -123,10 +124,7 @@ defmodule BDS.Embeddings.Index do
   end
 
   defp write_snapshot(snapshot_path, payload) do
-    :ok = File.mkdir_p(Path.dirname(snapshot_path))
-    temp_path = snapshot_path <> ".tmp"
-    :ok = File.write(temp_path, Jason.encode!(payload))
-    :ok = File.rename(temp_path, snapshot_path)
+    :ok = Persistence.atomic_write(snapshot_path, Jason.encode!(payload))
     legacy_path = legacy_path(snapshot_path)
 
     if File.exists?(legacy_path) do
diff --git a/lib/bds/frontmatter.ex b/lib/bds/frontmatter.ex
index 42063e3..fae0d63 100644
--- a/lib/bds/frontmatter.ex
+++ b/lib/bds/frontmatter.ex
@@ -1,6 +1,8 @@
 defmodule BDS.Frontmatter do
   @moduledoc false
 
+  alias BDS.Persistence
+
   @list_item_prefix "  - "
 
   def serialize_document(fields, body) when is_list(fields) do
@@ -38,11 +40,26 @@ defmodule BDS.Frontmatter do
   end
 
   defp serialize_field({key, values}) when is_list(values) do
-    ["#{key}:" | Enum.map(values, &"  - #{&1}")]
+    ["#{key}:" | Enum.map(values, &"  - #{serialize_scalar(nil, &1)}")]
+  end
+
+  defp serialize_field({key, value}) when is_atom(value) do
+    ["#{key}: #{Atom.to_string(value)}"]
+  end
+
+  defp serialize_field({key, value}) when is_integer(value) do
+    rendered =
+      if timestamp_key?(key) do
+        Persistence.timestamp_to_iso8601(value)
+      else
+        Integer.to_string(value)
+      end
+
+    ["#{key}: #{rendered}"]
   end
 
   defp serialize_field({key, value}) do
-    ["#{key}: #{value}"]
+    ["#{key}: #{serialize_scalar(key, value)}"]
   end
 
   defp parse_frontmatter(frontmatter) do
@@ -65,7 +82,7 @@ defmodule BDS.Frontmatter do
 
       String.contains?(line, ": ") ->
         [key, raw_value] = String.split(line, ": ", parts: 2)
-        parse_lines(rest, Map.put(acc, key, parse_scalar(raw_value)))
+        parse_lines(rest, Map.put(acc, key, parse_scalar(key, raw_value)))
 
       true ->
         parse_lines(rest, acc)
@@ -74,7 +91,7 @@ defmodule BDS.Frontmatter do
 
   defp take_list_items([line | rest], items) do
     if String.starts_with?(line, @list_item_prefix) do
-      value = line |> String.replace_prefix(@list_item_prefix, "") |> parse_scalar()
+      value = line |> String.replace_prefix(@list_item_prefix, "") |> then(&parse_scalar(nil, &1))
       take_list_items(rest, [value | items])
     else
       {items, [line | rest]}
@@ -83,14 +100,80 @@ defmodule BDS.Frontmatter do
 
   defp take_list_items([], items), do: {items, []}
 
-  defp parse_scalar("true"), do: true
-  defp parse_scalar("false"), do: false
+  defp parse_scalar(key, value) when is_binary(key) and is_binary(value) do
+    trimmed = String.trim(value)
 
-  defp parse_scalar(value) do
+    cond do
+      timestamp_key?(key) ->
+        Persistence.parse_timestamp(trimmed) || parse_generic_scalar(trimmed)
+
+      true ->
+        parse_generic_scalar(trimmed)
+    end
+  end
+
+  defp parse_scalar(nil, value) when is_binary(value) do
+    value
+    |> String.trim()
+    |> parse_generic_scalar()
+  end
+
+  defp parse_generic_scalar("true"), do: true
+  defp parse_generic_scalar("false"), do: false
+
+  defp parse_generic_scalar(value) do
     if Regex.match?(~r/^-?\d+$/, value) do
       String.to_integer(value)
     else
-      value
+      parse_string(value)
     end
   end
+
+  defp parse_string("\"" <> rest) do
+    rest
+    |> String.trim_trailing("\"")
+    |> String.replace("\\n", "\n")
+    |> String.replace("\\\"", "\"")
+    |> String.replace("\\\\", "\\")
+  end
+
+  defp parse_string(value), do: value
+
+  defp serialize_scalar(_key, value) when is_boolean(value) do
+    if(value, do: "true", else: "false")
+  end
+
+  defp serialize_scalar(_key, value) when is_atom(value) do
+    Atom.to_string(value)
+  end
+
+  defp serialize_scalar(key, value) when is_integer(value) do
+    if is_binary(key) and timestamp_key?(key) do
+      Persistence.timestamp_to_iso8601(value)
+    else
+      Integer.to_string(value)
+    end
+  end
+
+  defp serialize_scalar(_key, value) do
+    value
+    |> to_string()
+    |> maybe_quote_string()
+  end
+
+  defp maybe_quote_string(value) do
+    if Regex.match?(~r/^[\p{L}\p{N} ._\/-]+$/u, value) do
+      value
+    else
+      escaped =
+        value
+        |> String.replace("\\", "\\\\")
+        |> String.replace("\"", "\\\"")
+        |> String.replace("\n", "\\n")
+
+      "\"#{escaped}\""
+    end
+  end
+
+  defp timestamp_key?(key), do: String.ends_with?(to_string(key), "_at")
 end
diff --git a/lib/bds/generation.ex b/lib/bds/generation.ex
index 5e41a1d..a50a8e2 100644
--- a/lib/bds/generation.ex
+++ b/lib/bds/generation.ex
@@ -5,6 +5,7 @@ defmodule BDS.Generation do
 
   alias BDS.Generation.GeneratedFileHash
   alias BDS.Metadata
+  alias BDS.Persistence
   alias BDS.Posts.Post
   alias BDS.Posts.Translation
   alias BDS.Projects
@@ -52,7 +53,7 @@ defmodule BDS.Generation do
   def post_output_path(%Post{} = post), do: post_output_path(post, nil)
 
   def post_output_path(%Post{} = post, language) do
-    datetime = DateTime.from_unix!(post.created_at)
+    datetime = Persistence.from_unix_ms!(post.created_at)
     year = Integer.to_string(datetime.year)
     month = datetime.month |> Integer.to_string() |> String.pad_leading(2, "0")
     day = datetime.day |> Integer.to_string() |> String.pad_leading(2, "0")
@@ -70,7 +71,7 @@ defmodule BDS.Generation do
       when is_binary(project_id) and is_binary(relative_path) and is_binary(content) do
     project = Projects.get_project!(project_id)
     content_hash = sha256(content)
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     case Repo.get_by(GeneratedFileHash, project_id: project_id, relative_path: relative_path) do
       %GeneratedFileHash{content_hash: ^content_hash} ->
@@ -78,8 +79,7 @@ defmodule BDS.Generation do
 
       _existing ->
         full_path = output_path(project, relative_path)
-        :ok = File.mkdir_p(Path.dirname(full_path))
-        :ok = File.write(full_path, content)
+        :ok = Persistence.atomic_write(full_path, content)
 
         attrs = %{
           project_id: project_id,
@@ -495,7 +495,7 @@ defmodule BDS.Generation do
   defp render_calendar(published_posts) do
     published_posts
     |> Enum.map(fn post ->
-      datetime = DateTime.from_unix!(post.created_at)
+      datetime = Persistence.from_unix_ms!(post.created_at)
       %{date: Date.to_iso8601(DateTime.to_date(datetime)), slug: post.slug, title: post.title}
     end)
     |> Jason.encode!()
@@ -637,13 +637,13 @@ defmodule BDS.Generation do
 
   defp year_key(created_at) do
     created_at
-    |> DateTime.from_unix!()
+    |> Persistence.from_unix_ms!()
     |> Map.fetch!(:year)
     |> Integer.to_string()
   end
 
   defp month_key(created_at) do
-    datetime = DateTime.from_unix!(created_at)
+    datetime = Persistence.from_unix_ms!(created_at)
 
     {Integer.to_string(datetime.year),
      Integer.to_string(datetime.month) |> String.pad_leading(2, "0")}
diff --git a/lib/bds/media.ex b/lib/bds/media.ex
index 8798bb5..926002b 100644
--- a/lib/bds/media.ex
+++ b/lib/bds/media.ex
@@ -5,6 +5,7 @@ defmodule BDS.Media do
 
   alias BDS.Media.Media
   alias BDS.Media.Translation
+  alias BDS.Persistence
   alias BDS.Projects
   alias BDS.Repo
   alias BDS.Search
@@ -16,7 +17,7 @@ defmodule BDS.Media do
     original_name = Path.basename(source_path)
     mime_type = detect_mime(original_name)
     {width, height} = image_dimensions(source_path, mime_type)
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
     file_name = Ecto.UUID.generate() <> Path.extname(original_name)
     file_path = media_file_path(file_name, now)
     sidecar_path = file_path <> ".meta"
@@ -78,7 +79,7 @@ defmodule BDS.Media do
           |> maybe_put(:tags, attr(attrs, :tags))
           |> maybe_put(:width, attr(attrs, :width))
           |> maybe_put(:height, attr(attrs, :height))
-          |> Map.put(:updated_at, System.system_time(:second))
+          |> Map.put(:updated_at, Persistence.now_ms())
 
         project = Projects.get_project!(media.project_id)
 
@@ -136,7 +137,7 @@ defmodule BDS.Media do
 
       media ->
         project = Projects.get_project!(media.project_id)
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
 
         translation =
           Repo.get_by(Translation, translation_for: media.id, language: language) ||
@@ -227,7 +228,7 @@ defmodule BDS.Media do
     relative_sidecar_path = Path.relative_to(sidecar_path, Projects.project_data_dir(project))
     relative_file_path = String.trim_trailing(relative_sidecar_path, ".meta")
     filename = Path.basename(relative_file_path)
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     attrs = %{
       id: Map.get(fields, "id") || Ecto.UUID.generate(),
@@ -317,7 +318,7 @@ defmodule BDS.Media do
 
       media ->
         {:ok, fields} = sidecar_path |> File.read!() |> Sidecar.parse_document()
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
         language = Map.fetch!(fields, "language")
 
         translation =
@@ -408,7 +409,7 @@ defmodule BDS.Media do
   end
 
   defp media_file_path(file_name, timestamp) do
-    datetime = DateTime.from_unix!(timestamp)
+    datetime = Persistence.from_unix_ms!(timestamp)
     year = Integer.to_string(datetime.year)
     month = datetime.month |> Integer.to_string() |> String.pad_leading(2, "0")
     Path.join(["media", year, month, file_name])
@@ -487,9 +488,7 @@ defmodule BDS.Media do
   end
 
   defp atomic_write(path, contents) do
-    temp_path = path <> ".tmp"
-    :ok = File.write(temp_path, contents)
-    File.rename(temp_path, path)
+    Persistence.atomic_write(path, contents)
   end
 
   defp blank_to_nil(nil), do: nil
diff --git a/lib/bds/menu.ex b/lib/bds/menu.ex
index 12bf4ff..902e515 100644
--- a/lib/bds/menu.ex
+++ b/lib/bds/menu.ex
@@ -3,6 +3,7 @@ defmodule BDS.Menu do
 
   require Record
 
+  alias BDS.Persistence
   alias BDS.Projects
 
   Record.defrecord(:xmlElement, Record.extract(:xmlElement, from_lib: "xmerl/include/xmerl.hrl"))
@@ -44,14 +45,8 @@ defmodule BDS.Menu do
   end
 
   defp write_menu_file(project, menu) do
-    meta_dir = Path.dirname(menu_path(project))
-    :ok = File.mkdir_p(meta_dir)
-
     path = menu_path(project)
-    temp_path = path <> ".tmp"
-
-    :ok = File.write(temp_path, serialize_opml(menu.items))
-    File.rename(temp_path, path)
+    :ok = Persistence.atomic_write(path, serialize_opml(project, menu.items))
   end
 
   defp menu_path(project) do
@@ -84,7 +79,9 @@ defmodule BDS.Menu do
     end
   end
 
-  defp serialize_opml(items) do
+  defp serialize_opml(project, items) do
+    timestamp = project.updated_at || project.created_at || Persistence.now_ms()
+
     rendered_items =
       items
       |> Enum.map(&render_item(&1, 2))
@@ -93,6 +90,11 @@ defmodule BDS.Menu do
     [
       ~s(<?xml version="1.0" encoding="UTF-8"?>),
       ~s(<opml version="2.0">),
+      ~s(  <head>),
+      ~s(    <title>#{xml_escape(project.name)}</title>),
+      ~s(    <dateCreated>#{Persistence.timestamp_to_iso8601(timestamp)}</dateCreated>),
+      ~s(    <dateModified>#{Persistence.timestamp_to_iso8601(timestamp)}</dateModified>),
+      ~s(  </head>),
       ~s(  <body>),
       rendered_items,
       ~s(  </body>),
diff --git a/lib/bds/metadata.ex b/lib/bds/metadata.ex
index a10f356..f463a7f 100644
--- a/lib/bds/metadata.ex
+++ b/lib/bds/metadata.ex
@@ -2,6 +2,8 @@ defmodule BDS.Metadata do
   @moduledoc false
 
   alias BDS.Embeddings
+  alias BDS.I18n
+  alias BDS.Persistence
   alias BDS.Projects
   alias BDS.Projects.Project
   alias BDS.Repo
@@ -9,6 +11,30 @@ defmodule BDS.Metadata do
 
   @default_max_posts_per_page 50
   @default_categories ["article", "aside", "page", "picture"]
+  @min_posts_per_page 1
+  @max_posts_per_page 500
+  @supported_pico_themes MapSet.new([
+                           "default",
+                           "amber",
+                           "blue",
+                           "cyan",
+                           "fuchsia",
+                           "green",
+                           "grey",
+                           "indigo",
+                           "jade",
+                           "lime",
+                           "orange",
+                           "pink",
+                           "pumpkin",
+                           "purple",
+                           "red",
+                           "sand",
+                           "slate",
+                           "violet",
+                           "yellow",
+                           "zinc"
+                         ])
 
   def get_project_metadata(project_id) do
     project = Projects.get_project!(project_id)
@@ -18,7 +44,7 @@ defmodule BDS.Metadata do
   def update_project_metadata(project_id, attrs) do
     project = Projects.get_project!(project_id)
     state = load_state(project)
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     project_metadata =
       state
@@ -104,7 +130,7 @@ defmodule BDS.Metadata do
 
   def sync_project_metadata_from_filesystem(project_id) do
     project = Projects.get_project!(project_id)
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     project_metadata_from_files =
       read_json(project, "project.json") ||
@@ -130,6 +156,10 @@ defmodule BDS.Metadata do
       persist_setting(project_id, "categories", categories_from_files, now)
       persist_setting(project_id, "category_meta", category_meta_from_files, now)
       persist_setting(project_id, "publishing", publishing_from_files, now)
+      write_project_json(updated_project, project_metadata_from_files)
+      write_categories_json(updated_project, categories_from_files["categories"] || @default_categories)
+      write_category_meta_json(updated_project, category_meta_from_files["categories"] || %{})
+      write_publishing_json(updated_project, publishing_from_files)
       load_state(updated_project)
     end)
     |> unwrap_transaction()
@@ -138,7 +168,7 @@ defmodule BDS.Metadata do
   defp update_state(project_id, updater) do
     project = Projects.get_project!(project_id)
     state = load_state(project)
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     Repo.transaction(fn ->
       updater.(project, state, now)
@@ -200,13 +230,13 @@ defmodule BDS.Metadata do
       name: attr(attrs, :name) || project.name,
       description: attr(attrs, :description),
       public_url: attr(attrs, :public_url),
-      main_language: attr(attrs, :main_language),
+      main_language: normalize_optional_language(attr(attrs, :main_language)),
       default_author: attr(attrs, :default_author),
-      max_posts_per_page: attr(attrs, :max_posts_per_page) || @default_max_posts_per_page,
+      max_posts_per_page: normalize_posts_per_page(attr(attrs, :max_posts_per_page)),
       blogmark_category: attr(attrs, :blogmark_category),
-      pico_theme: attr(attrs, :pico_theme),
+      pico_theme: normalize_pico_theme(attr(attrs, :pico_theme)),
       semantic_similarity_enabled: attr(attrs, :semantic_similarity_enabled) || false,
-      blog_languages: normalize_string_list(attr(attrs, :blog_languages) || [])
+      blog_languages: normalize_language_list(attr(attrs, :blog_languages) || [])
     }
   end
 
@@ -227,7 +257,7 @@ defmodule BDS.Metadata do
       "ssh_host" => attr(prefs, :ssh_host),
       "ssh_user" => attr(prefs, :ssh_user),
       "ssh_remote_path" => attr(prefs, :ssh_remote_path),
-      "ssh_mode" => attr(prefs, :ssh_mode) || "scp"
+      "ssh_mode" => normalize_ssh_mode(attr(prefs, :ssh_mode))
     }
   end
 
@@ -270,11 +300,8 @@ defmodule BDS.Metadata do
 
   defp write_json(project, file_name, payload) do
     meta_dir = Path.join(Projects.project_data_dir(project), "meta")
-    :ok = File.mkdir_p(meta_dir)
     path = Path.join(meta_dir, file_name)
-    temp_path = path <> ".tmp"
-    :ok = File.write(temp_path, Jason.encode!(payload))
-    File.rename(temp_path, path)
+    :ok = Persistence.atomic_write(path, Jason.encode!(payload))
   end
 
   defp read_json(project, file_name) do
@@ -304,12 +331,56 @@ defmodule BDS.Metadata do
 
   defp setting_key(project_id, suffix), do: "project:#{project_id}:#{suffix}"
 
-  defp normalize_string_list(values) do
+  defp normalize_posts_per_page(nil), do: @default_max_posts_per_page
+
+  defp normalize_posts_per_page(value) when is_integer(value) do
+    value
+    |> max(@min_posts_per_page)
+    |> min(@max_posts_per_page)
+  end
+
+  defp normalize_posts_per_page(value) when is_binary(value) do
+    case Integer.parse(String.trim(value)) do
+      {integer, ""} -> normalize_posts_per_page(integer)
+      _ -> @default_max_posts_per_page
+    end
+  end
+
+  defp normalize_posts_per_page(_value), do: @default_max_posts_per_page
+
+  defp normalize_optional_language(nil), do: nil
+  defp normalize_optional_language(""), do: nil
+
+  defp normalize_optional_language(value) do
+    normalized = value |> to_string() |> String.trim() |> String.downcase()
+    supported_language_codes = Enum.map(I18n.supported_languages(), & &1.code)
+
+    if normalized in supported_language_codes do
+      normalized
+    else
+      nil
+    end
+  end
+
+  defp normalize_language_list(values) do
     values
-    |> Enum.reject(&(&1 in [nil, ""]))
+    |> Enum.map(&normalize_optional_language/1)
+    |> Enum.reject(&is_nil/1)
     |> Enum.uniq()
   end
 
+  defp normalize_pico_theme(nil), do: nil
+  defp normalize_pico_theme(""), do: nil
+
+  defp normalize_pico_theme(value) do
+    normalized = value |> to_string() |> String.trim()
+    if MapSet.member?(@supported_pico_themes, normalized), do: normalized, else: nil
+  end
+
+  defp normalize_ssh_mode(:rsync), do: "rsync"
+  defp normalize_ssh_mode("rsync"), do: "rsync"
+  defp normalize_ssh_mode(_mode), do: "scp"
+
   defp unwrap_transaction({:ok, result}), do: {:ok, result}
   defp unwrap_transaction({:error, reason}), do: {:error, reason}
 
diff --git a/lib/bds/persistence.ex b/lib/bds/persistence.ex
new file mode 100644
index 0000000..7d96fd3
--- /dev/null
+++ b/lib/bds/persistence.ex
@@ -0,0 +1,85 @@
+defmodule BDS.Persistence do
+  @moduledoc false
+
+  def now_ms, do: System.system_time(:millisecond)
+
+  def normalize_unix_timestamp(nil), do: nil
+
+  def normalize_unix_timestamp(value) when is_integer(value) do
+    if abs(value) < 100_000_000_000 do
+      value * 1000
+    else
+      value
+    end
+  end
+
+  def normalize_unix_timestamp(value) when is_binary(value) do
+    value
+    |> String.trim()
+    |> case do
+      "" -> nil
+      trimmed ->
+        case Integer.parse(trimmed) do
+          {integer, ""} -> normalize_unix_timestamp(integer)
+          _ -> nil
+        end
+    end
+  end
+
+  def normalize_unix_timestamp(_value), do: nil
+
+  def from_unix_ms!(value) when is_integer(value) do
+    value
+    |> normalize_unix_timestamp()
+    |> DateTime.from_unix!(:millisecond)
+  end
+
+  def timestamp_to_iso8601(nil), do: nil
+
+  def timestamp_to_iso8601(value) when is_integer(value) do
+    value
+    |> from_unix_ms!()
+    |> DateTime.to_iso8601()
+  end
+
+  def parse_timestamp(nil), do: nil
+  def parse_timestamp(value) when is_integer(value), do: normalize_unix_timestamp(value)
+
+  def parse_timestamp(value) when is_binary(value) do
+    trimmed = String.trim(value)
+
+    cond do
+      trimmed == "" ->
+        nil
+
+      Regex.match?(~r/^-?\d+$/, trimmed) ->
+        normalize_unix_timestamp(trimmed)
+
+      true ->
+        case DateTime.from_iso8601(trimmed) do
+          {:ok, datetime, _offset} -> DateTime.to_unix(datetime, :millisecond)
+          _ -> nil
+        end
+    end
+  end
+
+  def parse_timestamp(_value), do: nil
+
+  def atomic_write(path, contents) when is_binary(path) and is_binary(contents) do
+    :ok = File.mkdir_p(Path.dirname(path))
+    temp_path = path <> ".tmp"
+
+    with :ok <- File.write(temp_path, contents),
+         :ok <- File.rename(temp_path, path) do
+      :ok
+    else
+      {:error, _reason} = error ->
+        _ = File.rm(temp_path)
+        error
+
+      error ->
+        _ = File.rm(temp_path)
+        error
+    end
+  end
+end
diff --git a/lib/bds/post_links.ex b/lib/bds/post_links.ex
index 8198c9c..1892ca7 100644
--- a/lib/bds/post_links.ex
+++ b/lib/bds/post_links.ex
@@ -3,6 +3,7 @@ defmodule BDS.PostLinks do
 
   import Ecto.Query
 
+  alias BDS.Persistence
   alias BDS.Posts.Link
   alias BDS.Posts.Post
   alias BDS.Projects
@@ -22,7 +23,7 @@ defmodule BDS.PostLinks do
     Repo.transaction(fn ->
       Repo.delete_all(from link in Link, where: link.source_post_id == ^post.id)
 
-      now = System.system_time(:second)
+      now = Persistence.now_ms()
 
       Enum.each(links, fn %{target_post_id: target_post_id, link_text: link_text} ->
         %Link{}
diff --git a/lib/bds/posts.ex b/lib/bds/posts.ex
index 452c6c2..bc4ac45 100644
--- a/lib/bds/posts.ex
+++ b/lib/bds/posts.ex
@@ -6,6 +6,7 @@ defmodule BDS.Posts do
   alias BDS.Frontmatter
   alias BDS.Embeddings
   alias BDS.Metadata
+  alias BDS.Persistence
   alias BDS.PostLinks
   alias BDS.Posts.Post
   alias BDS.Posts.Translation
@@ -15,7 +16,7 @@ defmodule BDS.Posts do
   alias BDS.Slug
 
   def create_post(attrs) do
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
     project_id = attr(attrs, :project_id)
     title = normalize_title(attr(attrs, :title))
     base_slug = title |> default_slug_source() |> Slug.slugify()
@@ -65,7 +66,7 @@ defmodule BDS.Posts do
 
       post ->
         with :ok <- validate_slug_change(post, attrs) do
-          now = System.system_time(:second)
+          now = Persistence.now_ms()
 
           updates =
             attrs
@@ -99,16 +100,14 @@ defmodule BDS.Posts do
 
       %Post{} = post ->
         project = Projects.get_project!(post.project_id)
-        published_at = post.published_at || System.system_time(:second)
+        published_at = post.published_at || Persistence.now_ms()
         relative_path = build_post_relative_path(post.slug, post.created_at)
         full_path = Path.join(Projects.project_data_dir(project), relative_path)
-        updated_at = System.system_time(:second)
+        updated_at = Persistence.now_ms()
         body = publishable_post_body(post, full_path, project)
 
-        :ok = File.mkdir_p(Path.dirname(full_path))
-
         :ok =
-          File.write(
+          Persistence.atomic_write(
             full_path,
             serialize_post_file(%{post | updated_at: updated_at, content: body}, published_at)
           )
@@ -171,7 +170,7 @@ defmodule BDS.Posts do
 
       %Post{status: status} = post when status in [:draft, :published] ->
         post
-        |> Post.changeset(%{status: :archived, updated_at: System.system_time(:second)})
+        |> Post.changeset(%{status: :archived, updated_at: Persistence.now_ms()})
         |> Repo.update()
         |> case do
           {:ok, updated_post} ->
@@ -218,7 +217,7 @@ defmodule BDS.Posts do
          )}
 
       %Post{} = post ->
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
         normalized_language = normalize_language(language)
 
         translation =
@@ -322,14 +321,12 @@ defmodule BDS.Posts do
       project = Projects.get_project!(post.project_id)
       full_path = Path.join(Projects.project_data_dir(project), post.file_path)
       body = published_post_body(post, full_path)
-      :ok = File.mkdir_p(Path.dirname(full_path))
-
       :ok =
-        File.write(
+        Persistence.atomic_write(
           full_path,
           serialize_post_file(
             %{post | content: body},
-            post.published_at || System.system_time(:second)
+            post.published_at || Persistence.now_ms()
           )
         )
     end
@@ -451,7 +448,7 @@ defmodule BDS.Posts do
   defp default_slug_source(title), do: title
 
   defp build_post_relative_path(slug, created_at) do
-    datetime = DateTime.from_unix!(created_at)
+    datetime = Persistence.from_unix_ms!(created_at)
     year = Integer.to_string(datetime.year)
     month = datetime.month |> Integer.to_string() |> String.pad_leading(2, "0")
     Path.join(["posts", year, month, "#{slug}.md"])
@@ -513,7 +510,7 @@ defmodule BDS.Posts do
     contents = File.read!(path)
     {:ok, %{fields: fields}} = Frontmatter.parse_document(contents)
     relative_path = Path.relative_to(path, Projects.project_data_dir(project))
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     attrs = %{
       id: Map.get(fields, "id") || Ecto.UUID.generate(),
@@ -626,16 +623,14 @@ defmodule BDS.Posts do
 
   defp publish_translation(%Post{} = post, %Translation{} = translation) do
     project = Projects.get_project!(post.project_id)
-    published_at = translation.published_at || System.system_time(:second)
+    published_at = translation.published_at || Persistence.now_ms()
     relative_path = build_translation_relative_path(post, translation.language)
     full_path = Path.join(Projects.project_data_dir(project), relative_path)
-    updated_at = System.system_time(:second)
+    updated_at = Persistence.now_ms()
     body = publishable_translation_body(translation, full_path)
 
-    :ok = File.mkdir_p(Path.dirname(full_path))
-
     :ok =
-      File.write(
+      Persistence.atomic_write(
         full_path,
         serialize_translation_file(
           %{translation | updated_at: updated_at, content: body},
@@ -657,7 +652,7 @@ defmodule BDS.Posts do
   end
 
   defp build_translation_relative_path(post, language) do
-    datetime = DateTime.from_unix!(post.created_at)
+    datetime = Persistence.from_unix_ms!(post.created_at)
     year = Integer.to_string(datetime.year)
     month = datetime.month |> Integer.to_string() |> String.pad_leading(2, "0")
     Path.join(["posts", year, month, "#{post.slug}.#{language}.md"])
diff --git a/lib/bds/projects.ex b/lib/bds/projects.ex
index 878ebcb..564c992 100644
--- a/lib/bds/projects.ex
+++ b/lib/bds/projects.ex
@@ -4,6 +4,7 @@ defmodule BDS.Projects do
   import Ecto.Query
 
   alias Ecto.Multi
+  alias BDS.Persistence
   alias BDS.Projects.Project
   alias BDS.Repo
   alias BDS.StarterTemplates
@@ -26,7 +27,7 @@ defmodule BDS.Projects do
         {:ok, project}
 
       nil ->
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
         is_active = not Repo.exists?(from project in Project, where: project.is_active == true)
 
         Repo.transaction(fn ->
@@ -60,7 +61,7 @@ defmodule BDS.Projects do
   end
 
   def create_project(attrs) do
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
     name = attr(attrs, :name) || ""
     slug = unique_slug(attr(attrs, :slug) || Slug.slugify(name))
 
@@ -95,7 +96,7 @@ defmodule BDS.Projects do
         {:error, :not_found}
 
       project ->
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
 
         Multi.new()
         |> Multi.update_all(:clear_previous, from(p in Project, where: p.is_active == true),
diff --git a/lib/bds/rendering.ex b/lib/bds/rendering.ex
index 467f10d..184799d 100644
--- a/lib/bds/rendering.ex
+++ b/lib/bds/rendering.ex
@@ -4,6 +4,7 @@ defmodule BDS.Rendering do
   import Ecto.Query
 
   alias BDS.Frontmatter
+  alias BDS.Persistence
   alias BDS.Media.Media, as: MediaAsset
   alias BDS.Menu
   alias BDS.Metadata
@@ -69,7 +70,7 @@ defmodule BDS.Rendering do
           template.project_id == ^project_id and template.kind == ^kind and
             template.status == :published and
             template.enabled == true,
-        order_by: [asc: template.created_at, asc: template.slug],
+        order_by: [desc: template.created_at, desc: template.slug],
         limit: 1
     )
   end
@@ -455,7 +456,7 @@ defmodule BDS.Rendering do
   defp canonical_media_path_by_source_path(project_id) do
     Repo.all(from media in MediaAsset, where: media.project_id == ^project_id)
     |> Enum.reduce(%{}, fn media, acc ->
-      datetime = DateTime.from_unix!(media.created_at)
+      datetime = Persistence.from_unix_ms!(media.created_at)
 
       source_key =
         Path.join([
@@ -476,7 +477,7 @@ defmodule BDS.Rendering do
   end
 
   defp post_path(post, nil) do
-    datetime = DateTime.from_unix!(post.created_at)
+    datetime = Persistence.from_unix_ms!(post.created_at)
 
     Path.join([
       Integer.to_string(datetime.year),
@@ -630,7 +631,7 @@ defmodule BDS.Rendering do
     grouped_blocks =
       posts
       |> Enum.filter(&is_integer(Map.get(&1, :created_at)))
-      |> Enum.group_by(&DateTime.from_unix!(Map.get(&1, :created_at)) |> DateTime.to_date() |> Date.to_iso8601())
+      |> Enum.group_by(&(Map.get(&1, :created_at) |> Persistence.from_unix_ms!() |> DateTime.to_date() |> Date.to_iso8601()))
       |> Enum.sort_by(fn {label, _posts} -> label end)
 
     grouped_blocks
@@ -676,12 +677,12 @@ defmodule BDS.Rendering do
   defp href_for_language(prefix), do: prefix <> "/"
 
   defp calendar_initial_year(%{created_at: created_at}) when is_integer(created_at),
-    do: DateTime.from_unix!(created_at).year
+    do: Persistence.from_unix_ms!(created_at).year
 
   defp calendar_initial_year(_post), do: nil
 
   defp calendar_initial_month(%{created_at: created_at}) when is_integer(created_at),
-    do: DateTime.from_unix!(created_at).month
+    do: Persistence.from_unix_ms!(created_at).month
 
   defp calendar_initial_month(_post), do: nil
 
diff --git a/lib/bds/scripts.ex b/lib/bds/scripts.ex
index 85e1a9b..d0ed50c 100644
--- a/lib/bds/scripts.ex
+++ b/lib/bds/scripts.ex
@@ -4,13 +4,14 @@ defmodule BDS.Scripts do
   import Ecto.Query
 
   alias BDS.Frontmatter
+  alias BDS.Persistence
   alias BDS.Projects
   alias BDS.Repo
   alias BDS.Scripts.Script
   alias BDS.Slug
 
   def create_script(attrs) do
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
     project_id = attr(attrs, :project_id)
     title = attr(attrs, :title) || ""
     kind = attr(attrs, :kind)
@@ -42,13 +43,11 @@ defmodule BDS.Scripts do
       script ->
         file_path = script_file_path(script.slug)
         full_path = full_file_path(script.project_id, file_path)
-        updated_at = System.system_time(:second)
+        updated_at = Persistence.now_ms()
         content = script.content || ""
 
-        :ok = File.mkdir_p(Path.dirname(full_path))
-
         :ok =
-          File.write(
+          Persistence.atomic_write(
             full_path,
             serialize_script_file(
               %{script | status: :published, file_path: file_path, updated_at: updated_at},
@@ -81,7 +80,7 @@ defmodule BDS.Scripts do
           end
 
         content_changed? = has_attr?(attrs, :content) and attr(attrs, :content) != script.content
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
 
         updates =
           %{}
@@ -205,7 +204,7 @@ defmodule BDS.Scripts do
     contents = File.read!(path)
     {:ok, %{fields: fields}} = Frontmatter.parse_document(contents)
     relative_path = Path.relative_to(path, Projects.project_data_dir(project))
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     attrs = %{
       id: Map.get(fields, "id") || Ecto.UUID.generate(),
diff --git a/lib/bds/search.ex b/lib/bds/search.ex
index 6e50573..411f5fb 100644
--- a/lib/bds/search.ex
+++ b/lib/bds/search.ex
@@ -5,6 +5,7 @@ defmodule BDS.Search do
 
   alias BDS.Media.Media
   alias BDS.Media.Translation, as: MediaTranslation
+  alias BDS.Persistence
   alias BDS.Posts.Post
   alias BDS.Projects
   alias BDS.Repo
@@ -269,10 +270,10 @@ defmodule BDS.Search do
   defp matches_exact?(value, expected), do: value == expected
 
   defp matches_year?(_post, nil), do: true
-  defp matches_year?(post, year), do: DateTime.from_unix!(post.created_at).year == year
+  defp matches_year?(post, year), do: Persistence.from_unix_ms!(post.created_at).year == year
 
   defp matches_month?(_post, nil), do: true
-  defp matches_month?(post, month), do: DateTime.from_unix!(post.created_at).month == month
+  defp matches_month?(post, month), do: Persistence.from_unix_ms!(post.created_at).month == month
 
   defp matches_from?(_post, nil), do: true
   defp matches_from?(post, from_unix), do: post.created_at >= from_unix
@@ -545,14 +546,14 @@ defmodule BDS.Search do
   defp normalize_non_negative_integer(value, default), do: normalize_integer(value) || default
 
   defp normalize_timestamp(nil, _position), do: nil
-  defp normalize_timestamp(value, _position) when is_integer(value), do: value
+  defp normalize_timestamp(value, _position) when is_integer(value), do: Persistence.normalize_unix_timestamp(value)
 
   defp normalize_timestamp(value, position) when is_binary(value) do
     case Date.from_iso8601(value) do
       {:ok, date} ->
         time = if position == :start, do: ~T[00:00:00], else: ~T[23:59:59]
         {:ok, datetime} = DateTime.new(date, time, "Etc/UTC")
-        DateTime.to_unix(datetime)
+        DateTime.to_unix(datetime, :millisecond)
 
       {:error, _reason} ->
         nil
diff --git a/lib/bds/sidecar.ex b/lib/bds/sidecar.ex
index 6585f37..6429180 100644
--- a/lib/bds/sidecar.ex
+++ b/lib/bds/sidecar.ex
@@ -1,6 +1,8 @@
 defmodule BDS.Sidecar do
   @moduledoc false
 
+  alias BDS.Persistence
+
   @list_item_prefix "  - "
 
   def serialize_document(fields) when is_list(fields) do
@@ -21,15 +23,26 @@ defmodule BDS.Sidecar do
   defp serialize_field({_key, ""}), do: []
 
   defp serialize_field({key, values}) when is_list(values) do
-    ["#{key}:" | Enum.map(values, &"  - #{&1}")]
+    ["#{key}:" | Enum.map(values, &"  - #{serialize_scalar(nil, &1)}")]
   end
 
   defp serialize_field({key, value}) when is_boolean(value) do
     ["#{key}: #{if(value, do: "true", else: "false")}"]
   end
 
+  defp serialize_field({key, value}) when is_integer(value) do
+    rendered =
+      if timestamp_key?(key) do
+        Persistence.timestamp_to_iso8601(value)
+      else
+        Integer.to_string(value)
+      end
+
+    ["#{key}: #{rendered}"]
+  end
+
   defp serialize_field({key, value}) do
-    ["#{key}: #{value}"]
+    ["#{key}: #{serialize_scalar(key, value)}"]
   end
 
   defp parse_lines([], acc), do: acc
@@ -46,7 +59,7 @@ defmodule BDS.Sidecar do
 
       String.contains?(line, ": ") ->
         [key, raw_value] = String.split(line, ": ", parts: 2)
-        parse_lines(rest, Map.put(acc, key, parse_scalar(raw_value)))
+        parse_lines(rest, Map.put(acc, key, parse_scalar(key, raw_value)))
 
       true ->
         parse_lines(rest, acc)
@@ -55,7 +68,7 @@ defmodule BDS.Sidecar do
 
   defp take_list_items([line | rest], items) do
     if String.starts_with?(line, @list_item_prefix) do
-      value = line |> String.replace_prefix(@list_item_prefix, "") |> parse_scalar()
+      value = line |> String.replace_prefix(@list_item_prefix, "") |> then(&parse_scalar(nil, &1))
       take_list_items(rest, [value | items])
     else
       {items, [line | rest]}
@@ -64,14 +77,73 @@ defmodule BDS.Sidecar do
 
   defp take_list_items([], items), do: {items, []}
 
-  defp parse_scalar("true"), do: true
-  defp parse_scalar("false"), do: false
+  defp parse_scalar(key, value) when is_binary(key) and is_binary(value) do
+    trimmed = String.trim(value)
 
-  defp parse_scalar(value) do
+    cond do
+      timestamp_key?(key) -> Persistence.parse_timestamp(trimmed) || parse_generic_scalar(trimmed)
+      true -> parse_generic_scalar(trimmed)
+    end
+  end
+
+  defp parse_scalar(nil, value) when is_binary(value) do
+    value
+    |> String.trim()
+    |> parse_generic_scalar()
+  end
+
+  defp parse_generic_scalar("true"), do: true
+  defp parse_generic_scalar("false"), do: false
+
+  defp parse_generic_scalar(value) do
     if Regex.match?(~r/^-?\d+$/, value) do
       String.to_integer(value)
     else
-      value
+      parse_string(value)
     end
   end
+
+  defp parse_string("\"" <> rest) do
+    rest
+    |> String.trim_trailing("\"")
+    |> String.replace("\\n", "\n")
+    |> String.replace("\\\"", "\"")
+    |> String.replace("\\\\", "\\")
+  end
+
+  defp parse_string(value), do: value
+
+  defp serialize_scalar(_key, value) when is_boolean(value) do
+    if(value, do: "true", else: "false")
+  end
+
+  defp serialize_scalar(key, value) when is_integer(value) do
+    if is_binary(key) and timestamp_key?(key) do
+      Persistence.timestamp_to_iso8601(value)
+    else
+      Integer.to_string(value)
+    end
+  end
+
+  defp serialize_scalar(_key, value) do
+    value
+    |> to_string()
+    |> maybe_quote_string()
+  end
+
+  defp maybe_quote_string(value) do
+    if Regex.match?(~r/^[\p{L}\p{N} ._\/-]+$/u, value) do
+      value
+    else
+      escaped =
+        value
+        |> String.replace("\\", "\\\\")
+        |> String.replace("\"", "\\\"")
+        |> String.replace("\n", "\\n")
+
+      "\"#{escaped}\""
+    end
+  end
+
+  defp timestamp_key?(key), do: String.ends_with?(to_string(key), "_at")
 end
diff --git a/lib/bds/tags.ex b/lib/bds/tags.ex
index 1208b6b..2266a6c 100644
--- a/lib/bds/tags.ex
+++ b/lib/bds/tags.ex
@@ -3,6 +3,7 @@ defmodule BDS.Tags do
 
   import Ecto.Query
 
+  alias BDS.Persistence
   alias BDS.Posts
   alias BDS.Posts.Post
   alias BDS.Projects
@@ -14,7 +15,7 @@ defmodule BDS.Tags do
     name = attr(attrs, :name) |> to_string() |> String.trim()
 
     with :ok <- validate_unique_name(project_id, name) do
-      now = System.system_time(:second)
+      now = Persistence.now_ms()
 
       %Tag{}
       |> Tag.changeset(%{
@@ -70,7 +71,7 @@ defmodule BDS.Tags do
         |> elem(1)
         |> Enum.reverse()
 
-      now = System.system_time(:second)
+      now = Persistence.now_ms()
 
       Enum.each(missing_names, fn name ->
         %Tag{}
@@ -102,7 +103,7 @@ defmodule BDS.Tags do
         updates = %{
           color: attr(attrs, :color),
           post_template_slug: attr(attrs, :post_template_slug),
-          updated_at: System.system_time(:second)
+          updated_at: Persistence.now_ms()
         }
 
         tag
@@ -164,7 +165,7 @@ defmodule BDS.Tags do
 
             updated_tag =
               tag
-              |> Tag.changeset(%{name: normalized_name, updated_at: System.system_time(:second)})
+              |> Tag.changeset(%{name: normalized_name, updated_at: Persistence.now_ms()})
               |> Repo.update!()
 
             write_tags_json(tag.project_id)
@@ -226,7 +227,7 @@ defmodule BDS.Tags do
         end)
     }
 
-    File.write!(path, Jason.encode!(payload))
+    :ok = Persistence.atomic_write(path, Jason.encode!(payload))
   end
 
   defp validate_unique_name(project_id, name) do
@@ -311,7 +312,7 @@ defmodule BDS.Tags do
 
   defp update_post_tags(post, updated_tags) do
     post
-    |> Post.changeset(%{tags: updated_tags, updated_at: System.system_time(:second)})
+    |> Post.changeset(%{tags: updated_tags, updated_at: Persistence.now_ms()})
     |> Repo.update!()
 
     Posts.rewrite_published_post(post.id)
diff --git a/lib/bds/templates.ex b/lib/bds/templates.ex
index 84cf093..004b9ed 100644
--- a/lib/bds/templates.ex
+++ b/lib/bds/templates.ex
@@ -4,6 +4,7 @@ defmodule BDS.Templates do
   import Ecto.Query
 
   alias BDS.Frontmatter
+  alias BDS.Persistence
   alias BDS.Posts
   alias BDS.Projects
   alias BDS.Repo
@@ -12,7 +13,7 @@ defmodule BDS.Templates do
   alias BDS.Templates.Template
 
   def create_template(attrs) do
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
     project_id = attr(attrs, :project_id)
     title = attr(attrs, :title) || ""
 
@@ -42,13 +43,11 @@ defmodule BDS.Templates do
       template ->
         file_path = template_file_path(template.slug)
         full_path = full_file_path(template.project_id, file_path)
-        updated_at = System.system_time(:second)
+        updated_at = Persistence.now_ms()
         content = template.content || ""
 
-        :ok = File.mkdir_p(Path.dirname(full_path))
-
         :ok =
-          File.write(
+          Persistence.atomic_write(
             full_path,
             serialize_template_file(
               %{template | status: :published, file_path: file_path, updated_at: updated_at},
@@ -89,7 +88,7 @@ defmodule BDS.Templates do
           has_attr?(attrs, :content) and attr(attrs, :content) != template.content
 
         slug_changed? = next_slug != template.slug
-        now = System.system_time(:second)
+        now = Persistence.now_ms()
 
         next_status =
           if(template.status == :published and content_changed?,
@@ -254,7 +253,7 @@ defmodule BDS.Templates do
   end
 
   defp clear_template_references(template) do
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     affected_posts =
       Repo.all(
@@ -316,8 +315,7 @@ defmodule BDS.Templates do
   defp rewrite_template_file(original_template, updated_template) do
     body = published_template_body(original_template)
     new_full_path = full_file_path(updated_template.project_id, updated_template.file_path)
-    :ok = File.mkdir_p(Path.dirname(new_full_path))
-    :ok = File.write(new_full_path, serialize_template_file(updated_template, body))
+    :ok = Persistence.atomic_write(new_full_path, serialize_template_file(updated_template, body))
 
     if original_template.file_path != updated_template.file_path do
       _ = delete_file_if_present(original_template.project_id, original_template.file_path)
@@ -345,7 +343,7 @@ defmodule BDS.Templates do
     contents = File.read!(path)
     {:ok, %{fields: fields}} = Frontmatter.parse_document(contents)
     relative_path = Path.relative_to(path, Projects.project_data_dir(project))
-    now = System.system_time(:second)
+    now = Persistence.now_ms()
 
     attrs = %{
       id: Map.get(fields, "id") || Ecto.UUID.generate(),
diff --git a/test/bds/media_test.exs b/test/bds/media_test.exs
index ddb3daa..a9edd8f 100644
--- a/test/bds/media_test.exs
+++ b/test/bds/media_test.exs
@@ -51,6 +51,9 @@ defmodule BDS.MediaTest do
     assert sidecar =~ "author: Writer\n"
     assert sidecar =~ "language: en\n"
     assert sidecar =~ "tags:\n  - alpha\n"
+    assert sidecar =~ ~r/created_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
+    assert sidecar =~ ~r/updated_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
+    refute File.exists?(Path.join(temp_dir, media.sidecar_path <> ".tmp"))
   end
 
   test "update_media rewrites the sidecar metadata", %{project: project, temp_dir: temp_dir} do
@@ -137,8 +140,8 @@ defmodule BDS.MediaTest do
         "caption: Recovered caption",
         "author: Writer",
         "language: en",
-        "created_at: 1711843200",
-        "updated_at: 1711929600",
+        "created_at: 2024-03-30T21:20:00.000Z",
+        "updated_at: 2024-03-31T21:20:00.000Z",
         "tags:",
         "  - alpha",
         ""
@@ -175,6 +178,8 @@ defmodule BDS.MediaTest do
     assert media.author == "Writer"
     assert media.language == "en"
     assert media.tags == ["alpha"]
+    assert media.created_at == 1_711_833_600_000
+    assert media.updated_at == 1_711_920_000_000
     assert media.file_path == "media/2026/04/asset.jpg"
     assert media.sidecar_path == "media/2026/04/asset.jpg.meta"
 
diff --git a/test/bds/metadata_test.exs b/test/bds/metadata_test.exs
index dda639c..9c0dea6 100644
--- a/test/bds/metadata_test.exs
+++ b/test/bds/metadata_test.exs
@@ -138,4 +138,26 @@ defmodule BDS.MetadataTest do
     assert BDS.Repo.get_by(BDS.Embeddings.Key, project_id: project.id, post_id: post.id) != nil
     assert File.exists?(BDS.Embeddings.index_path(project.id))
   end
+
+  test "sync_project_metadata_from_filesystem materializes the canonical metadata files when missing",
+       %{project: project, temp_dir: temp_dir} do
+    meta_dir = Path.join(temp_dir, "meta")
+    refute File.exists?(Path.join(meta_dir, "project.json"))
+    refute File.exists?(Path.join(meta_dir, "categories.json"))
+    refute File.exists?(Path.join(meta_dir, "category-meta.json"))
+    refute File.exists?(Path.join(meta_dir, "publishing.json"))
+
+    assert {:ok, metadata} = BDS.Metadata.sync_project_metadata_from_filesystem(project.id)
+
+    assert metadata.name == project.name
+    assert File.exists?(Path.join(meta_dir, "project.json"))
+    assert File.exists?(Path.join(meta_dir, "categories.json"))
+    assert File.exists?(Path.join(meta_dir, "category-meta.json"))
+    assert File.exists?(Path.join(meta_dir, "publishing.json"))
+
+    refute File.exists?(Path.join(meta_dir, "project.json.tmp"))
+    refute File.exists?(Path.join(meta_dir, "categories.json.tmp"))
+    refute File.exists?(Path.join(meta_dir, "category-meta.json.tmp"))
+    refute File.exists?(Path.join(meta_dir, "publishing.json.tmp"))
+  end
 end
diff --git a/test/bds/post_links_test.exs b/test/bds/post_links_test.exs
index 3e4d36d..053b2a1 100644
--- a/test/bds/post_links_test.exs
+++ b/test/bds/post_links_test.exs
@@ -74,7 +74,7 @@ defmodule BDS.PostLinksTest do
   end
 
   defp canonical_post_href(post) do
-    datetime = DateTime.from_unix!(post.created_at)
+    datetime = DateTime.from_unix!(post.created_at, :millisecond)
 
     Path.join([
       "",
diff --git a/test/bds/posts_test.exs b/test/bds/posts_test.exs
index 3ce4947..42af643 100644
--- a/test/bds/posts_test.exs
+++ b/test/bds/posts_test.exs
@@ -151,7 +151,12 @@ defmodule BDS.PostsTest do
     assert file_contents =~ "template_slug: article\n"
     assert file_contents =~ "tags:\n  - alpha\n"
     assert file_contents =~ "categories:\n  - notes\n"
+    assert file_contents =~ ~r/created_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
+    assert file_contents =~ ~r/updated_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
+    assert file_contents =~ ~r/published_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
     assert file_contents =~ "\n---\nHello from markdown\n"
+
+    refute File.exists?(full_path <> ".tmp")
   end
 
   test "delete_post removes the database row and published markdown file when present" do
@@ -271,9 +276,9 @@ defmodule BDS.PostsTest do
         "language: en",
         "do_not_translate: true",
         "template_slug: article",
-        "created_at: 1711843200",
-        "updated_at: 1711929600",
-        "published_at: 1712016000",
+        "created_at: 2024-03-30T21:20:00.000Z",
+        "updated_at: 2024-03-31T21:20:00.000Z",
+        "published_at: 2024-04-01T21:20:00.000Z",
         "tags:",
         "  - alpha",
         "categories:",
@@ -299,9 +304,9 @@ defmodule BDS.PostsTest do
     assert post.language == "en"
     assert post.do_not_translate == true
     assert post.template_slug == "article"
-    assert post.created_at == 1_711_843_200
-    assert post.updated_at == 1_711_929_600
-    assert post.published_at == 1_712_016_000
+    assert post.created_at == 1_711_833_600_000
+    assert post.updated_at == 1_711_920_000_000
+    assert post.published_at == 1_712_006_400_000
     assert post.tags == ["alpha"]
     assert post.categories == ["notes"]
     assert post.file_path == "posts/2026/04/recovered-post.md"
diff --git a/test/bds/rendering_test.exs b/test/bds/rendering_test.exs
index 3369428..67104ac 100644
--- a/test/bds/rendering_test.exs
+++ b/test/bds/rendering_test.exs
@@ -312,7 +312,7 @@ defmodule BDS.RenderingTest do
   end
 
   defp canonical_post_href(post) do
-    datetime = DateTime.from_unix!(post.created_at)
+    datetime = DateTime.from_unix!(post.created_at, :millisecond)
 
     "/#{datetime.year}/#{String.pad_leading(Integer.to_string(datetime.month), 2, "0")}/#{String.pad_leading(Integer.to_string(datetime.day), 2, "0")}/#{post.slug}/"
   end
diff --git a/test/bds/scripts_test.exs b/test/bds/scripts_test.exs
index 6554db0..65e7299 100644
--- a/test/bds/scripts_test.exs
+++ b/test/bds/scripts_test.exs
@@ -71,9 +71,10 @@ defmodule BDS.ScriptsTest do
     assert contents =~ "entrypoint: main\n"
     assert contents =~ "enabled: true\n"
     assert contents =~ "version: 1\n"
-    assert contents =~ "created_at: #{published.created_at}\n"
-    assert contents =~ "updated_at: #{published.updated_at}\n"
+    assert contents =~ ~r/created_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
+    assert contents =~ ~r/updated_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
     assert contents =~ "\n---\nfunction main() return 'ok' end\n"
+    refute File.exists?(full_path <> ".tmp")
   end
 
   test "update_script bumps version and reopens a published script when content changes", %{
@@ -144,8 +145,8 @@ defmodule BDS.ScriptsTest do
         "entrypoint: main",
         "enabled: true",
         "version: 4",
-        "created_at: 301",
-        "updated_at: 404",
+        "created_at: 1970-01-01T00:00:00.301Z",
+        "updated_at: 1970-01-01T00:00:00.404Z",
         "---",
         "function main() return 'restored' end",
         ""
diff --git a/test/bds/templates_test.exs b/test/bds/templates_test.exs
index 7b93464..e72933f 100644
--- a/test/bds/templates_test.exs
+++ b/test/bds/templates_test.exs
@@ -71,9 +71,10 @@ defmodule BDS.TemplatesTest do
     assert contents =~ "kind: list\n"
     assert contents =~ "enabled: true\n"
     assert contents =~ "version: 1\n"
-    assert contents =~ "created_at: #{published.created_at}\n"
-    assert contents =~ "updated_at: #{published.updated_at}\n"
+    assert contents =~ ~r/created_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
+    assert contents =~ ~r/updated_at: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z\n/
     assert contents =~ "\n---\n<section>{{ page_title }}</section>\n"
+    refute File.exists?(full_path <> ".tmp")
   end
 
   test "update_template bumps version and reopens a published template when content changes", %{
@@ -235,8 +236,8 @@ defmodule BDS.TemplatesTest do
         "kind: list",
         "enabled: true",
         "version: 3",
-        "created_at: 101",
-        "updated_at: 202",
+        "created_at: 1970-01-01T00:00:00.101Z",
+        "updated_at: 1970-01-01T00:00:00.202Z",
         "---",
         "<section>Recovered</section>",
         ""