Add dev query reporter and skill

Ecto telemetry reporter that captures executed SQL queries
to a log file with interpolated parameters and source
locations. Activated/deactivated at runtime via Tidewave
for LLM-driven query analysis workflows.

lib/music_library/query_reporter.ex

@@ -0,0 +1,136 @@
+defmodule MusicLibrary.QueryReporter do
+  @moduledoc """
+  Dev-only Ecto query reporter that captures executed SQL queries to a file.
+
+  Attaches to the main Repo's telemetry event and writes each query as
+  executable SQL with interpolated parameters and source location comments.
+  Designed to be activated at runtime via Tidewave's `project_eval`.
+
+  ## Usage
+
+      MusicLibrary.QueryReporter.start("/tmp/queries.sql")
+      # ... trigger actions ...
+      MusicLibrary.QueryReporter.stop()
+      # read /tmp/queries.sql for captured queries
+  """
+
+  alias Ecto.Adapters.SQL
+
+  require Logger
+
+  @handler_id "music-library-query-reporter"
+  @event [:music_library, :repo, :query]
+
+  @doc """
+  Starts capturing queries to the given file path.
+
+  Truncates the file if it exists. Calling `start/1` while already running
+  restarts with a new file.
+  """
+  # sobelow_skip ["Traversal.FileModule"]
+  @spec start(String.t()) :: :ok
+  def start(file_path) when is_binary(file_path) do
+    # Path is provided by the developer at runtime via IEx/Tidewave
+    File.write!(file_path, "-- Query Reporter started at #{DateTime.utc_now()}\n\n")
+
+    :telemetry.detach(@handler_id)
+
+    :ok =
+      :telemetry.attach(
+        @handler_id,
+        @event,
+        &__MODULE__.handle_event/4,
+        file_path
+      )
+  end
+
+  @doc """
+  Stops capturing queries.
+  """
+  @spec stop() :: :ok | {:error, String.t()}
+  def stop do
+    case :telemetry.detach(@handler_id) do
+      :ok -> :ok
+      {:error, :not_found} -> {:error, "Query reporter is not running"}
+    end
+  end
+
+  # sobelow_skip ["Traversal.FileModule"]
+  @doc false
+  def handle_event(@event, _measurements, metadata, file_path) do
+    entry = format_entry(metadata)
+    # Path is provided by the developer at runtime via IEx/Tidewave
+    File.write!(file_path, entry, [:append])
+  rescue
+    error ->
+      Logger.warning("QueryReporter failed to write: #{inspect(error)}")
+  end
+
+  defp format_entry(metadata) do
+    params = metadata.cast_params || metadata.params || []
+    query = interpolate_query(metadata.query, params)
+    location = extract_source_location(metadata.stacktrace)
+
+    IO.iodata_to_binary([
+      if(location, do: [location, "\n"], else: []),
+      String.trim_trailing(query),
+      ";\n\n"
+    ])
+  end
+
+  defp interpolate_query(query, []), do: query
+
+  defp interpolate_query(query, params) do
+    parts = String.split(query, "?")
+
+    parts
+    |> Enum.zip_reduce(params ++ [:done], [], fn
+      part, :done, acc -> [part | acc]
+      part, param, acc -> [format_param(param), part | acc]
+    end)
+    |> Enum.reverse()
+    |> IO.iodata_to_binary()
+  end
+
+  defp format_param(nil), do: "NULL"
+  defp format_param(value) when is_integer(value), do: Integer.to_string(value)
+  defp format_param(value) when is_float(value), do: Float.to_string(value)
+  defp format_param(true), do: "1"
+  defp format_param(false), do: "0"
+
+  defp format_param(value) when is_binary(value) do
+    if String.printable?(value) do
+      "'" <> String.replace(value, "'", "''") <> "'"
+    else
+      "X'" <> Base.encode16(value) <> "'"
+    end
+  end
+
+  defp format_param(value), do: "'" <> String.replace(to_string(value), "'", "''") <> "'"
+
+  defp extract_source_location(nil), do: nil
+  defp extract_source_location([]), do: nil
+
+  defp extract_source_location(stacktrace) do
+    case SQL.first_non_ecto_stacktrace(stacktrace, %{repo: MusicLibrary.Repo}, 1) do
+      [{module, function, arity, info}] ->
+        format_location(module, function, arity, info)
+
+      _ ->
+        nil
+    end
+  end
+
+  defp format_location(module, function, arity, info) do
+    mfa = Exception.format_mfa(module, function, arity)
+
+    case Keyword.fetch(info, :file) do
+      {:ok, file} ->
+        line = Keyword.get(info, :line, "?")
+        "-- #{mfa}, at: #{file}:#{line}"
+
+      :error ->
+        "-- #{mfa}"
+    end
+  end
+end