Added prompt overrides for testing the BeyondFacts Lab (#1181)

app/MindWork AI Studio/Assistants/BeyondFactsLab/BeyondFactsLabAssistant.razor

@@ -128,6 +128,8 @@
                     <MudGrid Spacing="3">
                         <MudItem xs="12" lg="8">
                             <div @key="@this.activeStep" class="px-6">
+                                @* It checks the test folder anew for every step, as the key of the step recreates it: *@
+                                <BflPromptOverrideNotice Class="mt-2 mb-2"/>
                                 <MudText Typo="Typo.h5" Class="mt-2">@this.activeStep.Title</MudText>
                                 <MudText Typo="Typo.body2" Class="mb-4">@this.activeStep.Description</MudText>
 

app/MindWork AI Studio/Assistants/BeyondFactsLab/BeyondFactsLabStore.cs

@@ -73,6 +73,11 @@ public sealed partial class BeyondFactsLabStore(ILogger<BeyondFactsLabStore> log
         throw new InvalidOperationException("The AI Studio data directory is not initialized."),
         ROOT_DIRECTORY_NAME);
 
+    /// <summary>
+    /// Gets the folder whose files replace the prompts of the lab while the person allows it, see BflPromptOverrides.
+    /// </summary>
+    public string PromptOverridesDirectory => Path.Combine(this.RootDirectory, BflPromptOverrides.DIRECTORY_NAME);
+
     /// <summary>
     /// Writes a text file so that readers see either the old or the new content, never a part of it.
     /// </summary>

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflConversationService.cs

@@ -58,6 +58,12 @@ public sealed class BflConversationService(BeyondFactsLabStore store, SettingsMa
     /// </summary>
     private readonly Lock runningLock = new();
 
+    /// <summary>
+    /// Gets the folder whose files replace the prompts of the lab, or null while the person does not allow it. The
+    /// setting counts anew for every request, so that switching it on or off shows in the next answer.
+    /// </summary>
+    private string? PromptOverridesDirectory => BflPromptOverrides.ActiveDirectory(settingsManager.ConfigurationData.BeyondFactsLab, store.PromptOverridesDirectory);
+
     /// <summary>
     /// Happens whenever a chat changed: a message, a chunk of an answer, or the end of a request.
     /// </summary>
@@ -144,6 +150,12 @@ public sealed class BflConversationService(BeyondFactsLabStore store, SettingsMa
         {
             requestMaterial = await this.ComposeRequestAsync(location, provider);
         }
+        catch (BflPromptOverrideException exception)
+        {
+            logger.LogWarning(exception, "A prompt override of the BeyondFacts Lab has a placeholder which the lab does not fill.");
+            await messageBus.SendError(new(Icons.Material.Filled.ErrorOutline, string.Format(TA("The file '{0}' in the test folder of the BeyondFacts Lab contains the placeholder '{1}', which the lab does not fill in this file. Please correct the file and try again."),exception.FileName, exception.Placeholder)));
+            return;
+        }
         catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or FormatException)
         {
             logger.LogError(exception, "The BeyondFacts Lab could not put together the system prompt of the chat '{Location}'.", location.Key);
@@ -285,6 +297,14 @@ public sealed class BflConversationService(BeyondFactsLabStore store, SettingsMa
     /// <exception cref="FormatException">A prompt has a placeholder without a value.</exception>
     public async Task<string> ComposeSystemPromptAsync(BflThreadLocation location, AIStudio.Settings.Provider provider) => (await this.ComposeRequestAsync(location, provider)).SystemPrompt;
 
+    /// <summary>
+    /// Checks whether files in the test folder replace prompts of the lab right now, so that the lab can tell the
+    /// person.
+    /// </summary>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>True while the setting allows prompt overrides and a file replaces a prompt with another text.</returns>
+    public async Task<bool> UsesPromptOverridesAsync(CancellationToken token = default) => this.PromptOverridesDirectory is { } directory && (await BflPromptOverrides.FindAsync(directory, token)).Count > 0;
+
     /// <summary>
     /// Puts together what a request of a chat carries beside the conversation: the system prompt, and the images of
     /// the material the model may see.
@@ -302,13 +322,13 @@ public sealed class BflConversationService(BeyondFactsLabStore store, SettingsMa
         {
             case BflStepThreadLocation stepLocation:
                 var forms = await store.LoadFormsAsync(stepLocation.ProjectId);
-                var parts = await BflPromptLibrary.LoadPartsAsync(stepLocation.Step, addressForm);
+                var parts = await BflPromptLibrary.LoadPartsAsync(stepLocation.Step, addressForm, this.PromptOverridesDirectory);
                 var shares = await this.ShareMaterialsAsync(stepLocation, parts, forms, language, provider);
                 var materials = await this.ReadMaterialsAsync(stepLocation.ProjectId, shares);
                 return new(BflPromptComposer.Compose(parts, stepLocation.Step, forms, materials, language), this.ImagesOf(stepLocation.ProjectId, shares));
 
             case BflOnboardingThreadLocation:
-                return new(BflPromptComposer.ComposeOnboarding(await BflPromptLibrary.LoadOnboardingPartsAsync(addressForm), language), []);
+                return new(BflPromptComposer.ComposeOnboarding(await BflPromptLibrary.LoadOnboardingPartsAsync(addressForm, this.PromptOverridesDirectory), language), []);
 
             default:
                 throw new ArgumentOutOfRangeException(nameof(location), location, "The lab has no prompt for this chat.");
@@ -406,7 +426,7 @@ public sealed class BflConversationService(BeyondFactsLabStore store, SettingsMa
     {
         var language = (await settingsManager.GetActiveLanguagePlugin()).LangName;
         var forms = await store.LoadFormsAsync(location.ProjectId);
-        var parts = await BflPromptLibrary.LoadPartsAsync(location.Step, Tools.PluginSystem.I18N.I.AddressForm);
+        var parts = await BflPromptLibrary.LoadPartsAsync(location.Step, Tools.PluginSystem.I18N.I.AddressForm, this.PromptOverridesDirectory);
         return await this.ShareMaterialsAsync(location, parts, forms, language, provider);
     }
 

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflOnboarding.razor

@@ -1,4 +1,5 @@
 @inherits MSGComponentBase
 
+<BflPromptOverrideNotice Class="mb-3"/>
 <ProviderSelection @bind-ProviderSettings="@this.providerSettings" ValidateProvider="@this.ValidateProvider"/>
 <BflChat Location="@BflOnboardingThreadLocation.INSTANCE" Provider="@this.providerSettings" ProviderIssue="@this.ValidateProvider(this.providerSettings)" ShowHeading="@false"/>

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflPromptLibrary.cs

@@ -1,3 +1,5 @@
+using System.Collections.Frozen;
+
 using AIStudio.Settings.DataModel;
 
 namespace AIStudio.Assistants.BeyondFactsLab;
@@ -8,6 +10,7 @@ namespace AIStudio.Assistants.BeyondFactsLab;
 /// <remarks>
 /// The files are German Markdown below Assistants/BeyondFactsLab, embedded into the app. A development build reads
 /// them from the disk, so that a changed prompt shows in the next request without building again; see AppResources.
+/// While the person allows it, files in the folder for prompt overrides replace them, see BflPromptOverrides.
 /// </remarks>
 public static class BflPromptLibrary
 {
@@ -42,6 +45,30 @@ public static class BflPromptLibrary
     /// </summary>
     private const string ADDRESS_INFORMAL_PATH = FOLDER + "/Prompts/snippets/address-informal.md";
 
+    /// <summary>
+    /// The placeholders BflPromptComposer fills in the core.
+    /// </summary>
+    private static readonly FrozenSet<string> CORE_PLACEHOLDERS = FrozenSet.Create(StringComparer.Ordinal,
+        BflPromptTemplate.RESPONSE_LANGUAGE,
+        BflPromptTemplate.ADDRESS_FORM,
+        BflPromptTemplate.KNOWLEDGE,
+        BflPromptTemplate.STEP,
+        BflPromptTemplate.MATERIALS,
+        BflPromptTemplate.DETAILS,
+        BflPromptTemplate.MISSING_DETAILS);
+
+    /// <summary>
+    /// The placeholders BflPromptComposer fills in the prompt of the onboarding.
+    /// </summary>
+    private static readonly FrozenSet<string> ONBOARDING_PLACEHOLDERS = FrozenSet.Create(StringComparer.Ordinal,
+        BflPromptTemplate.RESPONSE_LANGUAGE,
+        BflPromptTemplate.ADDRESS_FORM);
+
+    /// <summary>
+    /// The placeholders of every other file: none, because BflPromptComposer inserts these files as values.
+    /// </summary>
+    private static readonly FrozenSet<string> NO_PLACEHOLDERS = FrozenSet<string>.Empty;
+
     /// <summary>
     /// Gets the prompt of a step, named like the folder of the step.
     /// </summary>
@@ -66,39 +93,83 @@ public static class BflPromptLibrary
         ..BflStep.All.Select(StepPath)
     ];
 
+    /// <summary>
+    /// Gets a file of the lab's prompts relative to the folder of the lab, e.g., "Prompts/core.md".
+    /// </summary>
+    /// <param name="path">The file, one of the paths of this class.</param>
+    /// <exception cref="ArgumentException">The file lies outside the folder of the lab.</exception>
+    public static string RelativePath(string path) => path.StartsWith(FOLDER + "/", StringComparison.Ordinal) ? path[(FOLDER.Length + 1)..] : throw new ArgumentException("The file lies outside the folder of the BeyondFacts Lab.", nameof(path));
+
+    /// <summary>
+    /// Gets the placeholders a file of the lab's prompts may contain.
+    /// </summary>
+    /// <remarks>
+    /// BflPromptComposer fills placeholders in the core and in the prompt of the onboarding only. It inserts every
+    /// other file as a value, whose placeholders it leaves as they are, so that they would reach the model as text.
+    /// </remarks>
+    /// <param name="path">The file, one of the paths of this class.</param>
+    public static IReadOnlySet<string> PlaceholdersOf(string path) => path switch
+    {
+        CORE_PATH => CORE_PLACEHOLDERS,
+        ONBOARDING_PATH => ONBOARDING_PLACEHOLDERS,
+        _ => NO_PLACEHOLDERS
+    };
+
     /// <summary>
     /// Reads the texts of the system prompt of a step.
     /// </summary>
     /// <param name="step">The step.</param>
     /// <param name="addressForm">How the model addresses the person.</param>
+    /// <param name="overrideDirectory">The folder whose files replace the prompts, or null while the person does not allow it.</param>
     /// <param name="token">The cancellation token.</param>
     /// <returns>The texts, which BflPromptComposer puts together.</returns>
     /// <exception cref="FileNotFoundException">The app comes without one of the files.</exception>
-    public static async Task<BflPromptParts> LoadPartsAsync(BflStep step, AddressForm addressForm, CancellationToken token = default) => new(
-        await ReadAsync(CORE_PATH, token),
-        await ReadAsync(KNOWLEDGE_PATH, token),
-        await ReadAsync(StepPath(step), token),
-        await ReadAsync(AddressPath(addressForm), token));
+    /// <exception cref="BflPromptOverrideException">A file which replaces a prompt contains a placeholder which the lab does not fill in it.</exception>
+    public static async Task<BflPromptParts> LoadPartsAsync(BflStep step, AddressForm addressForm, string? overrideDirectory = null, CancellationToken token = default) => new(
+        await ReadAsync(CORE_PATH, overrideDirectory, token),
+        await ReadAsync(KNOWLEDGE_PATH, overrideDirectory, token),
+        await ReadAsync(StepPath(step), overrideDirectory, token),
+        await ReadAsync(AddressPath(addressForm), overrideDirectory, token));
 
     /// <summary>
     /// Reads the texts of the system prompt of the conversation about whether the lab fits a task.
     /// </summary>
     /// <param name="addressForm">How the model addresses the person.</param>
+    /// <param name="overrideDirectory">The folder whose files replace the prompts, or null while the person does not allow it.</param>
     /// <param name="token">The cancellation token.</param>
     /// <returns>The texts, which BflPromptComposer puts together.</returns>
     /// <exception cref="FileNotFoundException">The app comes without one of the files.</exception>
-    public static async Task<BflOnboardingPromptParts> LoadOnboardingPartsAsync(AddressForm addressForm, CancellationToken token = default) => new(
-        await ReadAsync(ONBOARDING_PATH, token),
-        await ReadAsync(AddressPath(addressForm), token));
+    /// <exception cref="BflPromptOverrideException">A file which replaces a prompt contains a placeholder which the lab does not fill in it.</exception>
+    public static async Task<BflOnboardingPromptParts> LoadOnboardingPartsAsync(AddressForm addressForm, string? overrideDirectory = null, CancellationToken token = default) => new(
+        await ReadAsync(ONBOARDING_PATH, overrideDirectory, token),
+        await ReadAsync(AddressPath(addressForm), overrideDirectory, token));
 
     /// <summary>
-    /// Reads a file of the lab's prompts.
+    /// Reads a file of the lab's prompts: the file which replaces it, if there is one, or else the file which comes
+    /// with the app.
+    /// </summary>
+    /// <param name="path">The file, one of the paths of this class.</param>
+    /// <param name="overrideDirectory">The folder whose files replace the prompts, or null while the person does not allow it.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The text of the file.</returns>
+    /// <exception cref="FileNotFoundException">The app comes without the file, or the file is empty.</exception>
+    /// <exception cref="BflPromptOverrideException">The file which replaces the prompt contains a placeholder which the lab does not fill in it.</exception>
+    public static async Task<string> ReadAsync(string path, string? overrideDirectory = null, CancellationToken token = default)
+    {
+        if (overrideDirectory is not null && await BflPromptOverrides.TryReadAsync(overrideDirectory, path, token) is { } replacement)
+            return replacement;
+
+        return await ReadBuiltInAsync(path, token);
+    }
+
+    /// <summary>
+    /// Reads a file of the lab's prompts as it comes with the app.
     /// </summary>
     /// <param name="path">The file, one of the paths of this class.</param>
     /// <param name="token">The cancellation token.</param>
     /// <returns>The text of the file.</returns>
     /// <exception cref="FileNotFoundException">The app comes without the file, or the file is empty.</exception>
-    public static async Task<string> ReadAsync(string path, CancellationToken token = default)
+    public static async Task<string> ReadBuiltInAsync(string path, CancellationToken token = default)
     {
         var text = await AppResources.ReadTextAsync(path, token);
         if (string.IsNullOrWhiteSpace(text))

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflPromptOverrideException.cs

@@ -0,0 +1,24 @@
+namespace AIStudio.Assistants.BeyondFactsLab;
+
+/// <summary>
+/// Tells that a file in the folder for prompt overrides contains a placeholder which the lab does not fill in it.
+/// </summary>
+/// <remarks>
+/// The lab fills placeholders in the core and in the prompt of the onboarding only, and only those it knows; in any
+/// other file, a placeholder would reach the model as text. Whoever tests a changed prompt needs to learn which file
+/// and which placeholder it is, so the message names both.
+/// </remarks>
+/// <param name="fileName">The file, relative to the folder for prompt overrides, with forward slashes.</param>
+/// <param name="placeholder">The name of the placeholder, without braces.</param>
+public sealed class BflPromptOverrideException(string fileName, string placeholder) : FormatException($"The file '{fileName}' in the folder for prompt overrides contains the placeholder '{placeholder}', which the lab does not fill in this file.")
+{
+    /// <summary>
+    /// Gets the file, relative to the folder for prompt overrides, with forward slashes.
+    /// </summary>
+    public string FileName { get; } = fileName;
+
+    /// <summary>
+    /// Gets the name of the placeholder, without braces.
+    /// </summary>
+    public string Placeholder { get; } = placeholder;
+}

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflPromptOverrideNotice.razor

@@ -0,0 +1,8 @@
+@inherits MSGComponentBase
+
+@if (this.usesPromptOverrides)
+{
+    <MudAlert Severity="Severity.Warning" Variant="Variant.Outlined" Dense="true" Class="@this.Class">
+        @TA("The lab currently uses experimental instructions from its test folder. You can switch them off in the options of the lab.")
+    </MudAlert>
+}

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflPromptOverrideNotice.razor.cs

@@ -0,0 +1,72 @@
+using AIStudio.Components;
+
+using Microsoft.AspNetCore.Components;
+
+namespace AIStudio.Assistants.BeyondFactsLab;
+
+/// <summary>
+/// Tells the person that files in the test folder replace prompts of the lab, so that nobody mistakes the answers of
+/// experimental prompts for those of the lab.
+/// </summary>
+/// <remarks>
+/// It checks the folder when it appears, e.g., for every step the person opens, and whenever a setting changes. It
+/// shows nothing while the setting does not allow prompt overrides, or while every file in the folder matches the
+/// prompt it replaces.
+/// </remarks>
+public partial class BflPromptOverrideNotice : MSGComponentBase
+{
+    [Inject]
+    private BflConversationService ConversationService { get; init; } = null!;
+
+    [Inject]
+    private ILogger<BflPromptOverrideNotice> Logger { get; init; } = null!;
+
+    /// <summary>
+    /// Gets or sets the CSS classes of the notice, e.g., for its margins.
+    /// </summary>
+    [Parameter]
+    public string Class { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Whether files in the test folder replace prompts of the lab.
+    /// </summary>
+    private bool usesPromptOverrides;
+
+    /// <inheritdoc />
+    protected override async Task OnInitializedAsync()
+    {
+        this.ApplyFilters([], [Event.CONFIGURATION_CHANGED]);
+        await base.OnInitializedAsync();
+        await this.CheckAsync();
+    }
+
+    /// <inheritdoc />
+    protected override async Task ProcessIncomingMessage<T>(ComponentBase? sendingComponent, Event triggeredEvent, T? data) where T : default
+    {
+        if (triggeredEvent is Event.CONFIGURATION_CHANGED)
+        {
+            // The person may switch the prompt overrides on or off in the options of the lab while the page is open:
+            await this.CheckAsync();
+            this.StateHasChanged();
+        }
+
+        await base.ProcessIncomingMessage(sendingComponent, triggeredEvent, data);
+    }
+
+    /// <summary>
+    /// Checks whether files in the test folder replace prompts of the lab.
+    /// </summary>
+    private async Task CheckAsync()
+    {
+        try
+        {
+            this.usesPromptOverrides = await this.ConversationService.UsesPromptOverridesAsync();
+        }
+        catch (Exception exception) when (exception is IOException or UnauthorizedAccessException)
+        {
+            // Sending reports a problem with the prompts; the notice only stays hidden:
+            this.Logger.LogDebug(exception, "Could not check the test folder of the BeyondFacts Lab.");
+            this.usesPromptOverrides = false;
+        }
+    }
+}

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflPromptOverrides.cs

@@ -0,0 +1,157 @@
+using System.Text;
+
+using AIStudio.Settings.DataModel;
+
+namespace AIStudio.Assistants.BeyondFactsLab;
+
+/// <summary>
+/// Reads the files which replace the prompts of the BeyondFacts Lab, so that changed prompts can be tested without a
+/// new version of AI Studio.
+/// </summary>
+/// <remarks>
+/// The folder mirrors the files of the lab below Assistants/BeyondFactsLab, e.g., Prompts/steps/02-knowledge.md, so
+/// that every name stays unique. Only the files of BflPromptLibrary.AllPaths count; the lab leaves any other file in
+/// the folder alone, and an empty file replaces nothing. The files are instructions of the person, who chose to use
+/// them, so they bypass the prompt injection filter like the prompts which come with the app.
+/// </remarks>
+public static class BflPromptOverrides
+{
+    /// <summary>
+    /// The name of the folder below the folder of the lab.
+    /// </summary>
+    public const string DIRECTORY_NAME = "promptOverrides";
+
+    /// <summary>
+    /// Gets the folder whose files replace the prompts of the lab, or null while the setting does not allow them.
+    /// </summary>
+    /// <param name="settings">The settings of the lab, which an organization may lock.</param>
+    /// <param name="directory">The folder for prompt overrides.</param>
+    public static string? ActiveDirectory(DataBeyondFactsLab settings, string directory) => settings.AllowPromptOverrides ? directory : null;
+
+    /// <summary>
+    /// Reads the file which replaces a prompt of the lab, and checks its placeholders.
+    /// </summary>
+    /// <param name="directory">The folder for prompt overrides.</param>
+    /// <param name="path">The prompt, one of BflPromptLibrary.AllPaths.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The text of the file, or null when no file replaces the prompt.</returns>
+    /// <exception cref="BflPromptOverrideException">The file contains a placeholder which the lab does not fill in it.</exception>
+    public static async Task<string?> TryReadAsync(string directory, string path, CancellationToken token = default)
+    {
+        var text = await TryReadFileAsync(directory, path, token);
+        if (text is null)
+            return null;
+
+        var allowed = BflPromptLibrary.PlaceholdersOf(path);
+        foreach (var placeholder in BflPromptTemplate.NamesIn(text))
+        {
+            if (!allowed.Contains(placeholder))
+                throw new BflPromptOverrideException(BflPromptLibrary.RelativePath(path), placeholder);
+        }
+
+        return text;
+    }
+
+    /// <summary>
+    /// Finds the prompts of the lab which a file in the folder replaces with another text.
+    /// </summary>
+    /// <remarks>
+    /// A copy of a prompt which matches the prompt of this version, apart from line breaks and the space around the
+    /// text, changes nothing and does not count. A copy of an older version does.
+    /// </remarks>
+    /// <param name="directory">The folder for prompt overrides.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The prompts, as paths of BflPromptLibrary.AllPaths.</returns>
+    public static async Task<IReadOnlyList<string>> FindAsync(string directory, CancellationToken token = default)
+    {
+        var replaced = new List<string>();
+        foreach (var path in BflPromptLibrary.AllPaths)
+        {
+            string? text;
+            try
+            {
+                text = await TryReadFileAsync(directory, path, token);
+            }
+            catch (Exception exception) when (exception is IOException or UnauthorizedAccessException)
+            {
+                // The lab will try to read the file, too, so it replaces the prompt as far as the person can tell:
+                replaced.Add(path);
+                continue;
+            }
+
+            if (text is not null && Normalize(text) != Normalize(await BflPromptLibrary.ReadBuiltInAsync(path, token)))
+                replaced.Add(path);
+        }
+
+        return replaced;
+    }
+
+    /// <summary>
+    /// Copies the prompts of this version into the folder, so that changes start from them. A file which exists stays
+    /// as it is.
+    /// </summary>
+    /// <param name="directory">The folder for prompt overrides; it is created when it is missing.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>How many files the folder got.</returns>
+    public static async Task<int> CopyBuiltInAsync(string directory, CancellationToken token = default)
+    {
+        var copied = 0;
+        foreach (var path in BflPromptLibrary.AllPaths)
+        {
+            var target = FilePath(directory, path);
+            if (File.Exists(target))
+                continue;
+
+            Directory.CreateDirectory(Path.GetDirectoryName(target)!);
+            var temporary = $"{target}.{Guid.NewGuid():N}.tmp";
+            await File.WriteAllTextAsync(temporary, await BflPromptLibrary.ReadBuiltInAsync(path, token), new UTF8Encoding(false), token);
+            try
+            {
+                // Moving fails when the file appeared meanwhile, so the person's file is never overwritten:
+                File.Move(temporary, target, false);
+                copied++;
+            }
+            catch (IOException) when (File.Exists(target))
+            {
+                File.Delete(temporary);
+            }
+        }
+
+        return copied;
+    }
+
+    /// <summary>
+    /// Gets the file which replaces a prompt of the lab.
+    /// </summary>
+    /// <param name="directory">The folder for prompt overrides.</param>
+    /// <param name="path">The prompt, one of BflPromptLibrary.AllPaths.</param>
+    public static string FilePath(string directory, string path) => Path.Join([directory, ..BflPromptLibrary.RelativePath(path).Split('/')]);
+
+    /// <summary>
+    /// Reads the file which replaces a prompt of the lab, without checking it.
+    /// </summary>
+    /// <param name="directory">The folder for prompt overrides.</param>
+    /// <param name="path">The prompt, one of BflPromptLibrary.AllPaths.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The text of the file, or null when there is no such file or it is empty.</returns>
+    private static async Task<string?> TryReadFileAsync(string directory, string path, CancellationToken token)
+    {
+        string text;
+        try
+        {
+            text = await File.ReadAllTextAsync(FilePath(directory, path), Encoding.UTF8, token);
+        }
+        catch (Exception exception) when (exception is FileNotFoundException or DirectoryNotFoundException)
+        {
+            return null;
+        }
+
+        return string.IsNullOrWhiteSpace(text) ? null : text;
+    }
+
+    /// <summary>
+    /// Brings a prompt into the form in which two copies compare, whatever system wrote them.
+    /// </summary>
+    /// <param name="text">The prompt.</param>
+    private static string Normalize(string text) => text.ReplaceLineEndings("\n").Trim();
+}

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflPromptTemplate.cs

@@ -60,6 +60,13 @@ public static partial class BflPromptTemplate
         return values.TryGetValue(name, out var value) ? value : throw new FormatException($"The prompt has the placeholder '{name}', which has no value.");
     });
 
+    /// <summary>
+    /// Finds the placeholders of a template, as Fill reads them.
+    /// </summary>
+    /// <param name="template">The template.</param>
+    /// <returns>The name of each placeholder, once each, in the order they first appear.</returns>
+    public static IReadOnlyList<string> NamesIn(string template) => [.. PlaceholderPattern().Matches(template).Select(match => match.Groups["name"].Value).Distinct(StringComparer.Ordinal)];
+
     [GeneratedRegex(@"\{\{\s*(?<name>[^{}]*?)\s*\}\}")]
     private static partial Regex PlaceholderPattern();
 }