using ClawdDotNet.Core.Files;
using ClawdDotNet.Core.Config;
using ClawdDotNet.Core.Organisation;
using System.Collections.Concurrent;
using System.Text;
using System.Text.Json;
using ClawdDotNet.Core.Storage;
using ClawdDotNet.Core.Tools;
using Microsoft.Extensions.Logging;

namespace ClawdDotNet.Tools.FileRW;

public sealed class FileRWTool : IAgentTool, IToolStateProbe
{
    /// <summary>
    /// Per-Datei Locking: Verhindert Race Conditions wenn mehrere Agenten
    /// gleichzeitig auf dieselbe Datei zugreifen (read/write/append/delete/copy).
    /// Key = normalisierter absoluter Pfad (lowercase), Value = SemaphoreSlim(1,1).
    /// </summary>
    private static readonly ConcurrentDictionary<string, SemaphoreSlim> FileLocks = new();

    private static SemaphoreSlim GetFileLock(string fullPath)
        => FileLocks.GetOrAdd(NormalizePath(fullPath), _ => new SemaphoreSlim(1, 1));

    private static string NormalizePath(string path)
        => Path.GetFullPath(path).ToLowerInvariant();

    public string Name => "FileRW";

    public string Description => "File management in workspaces:\n" +
        "- workspace='personal': Your PRIVATE folder — only you have access.\n" +
        "- workspace='shared': the instance's SHARED folder, if you have access to it.\n" +
        "- workspace='unit': your unit's workspace; other named workspaces you are a member of " +
        "are listed in the Organisation section of your instructions.\n" +
        "Actions: read, read_many, write, append, list, delete, copy, stock_add.\n" +
        "'read_many' reads multiple files in ONE call - either 'paths' (list) or 'path' " +
        "(directory) with 'pattern' (e.g. \"berlin_2026-09-20_*.txt\"). Use this instead of reading " +
        "many files individually: each individual call costs a step.\n" +
        "'list' by default shows the 50 most recently modified entries, newest first; " +
        "'pattern', 'sort', 'order' and 'limit' control this. It is better to query a specific file " +
        "using 'pattern' rather than searching through a long list.\n" +
        "For copy, files can be copied between workspaces.\n" +
        "'stock_add' adds a new data point to the stock knowledge base (shared:stocks/{ticker}/). " +
        "Protected paths (protectedPaths) only allow creating new files — no overwriting or deleting.";

    public JsonElement InputSchema { get; } = JsonDocument.Parse("""
        {
            "type": "object",
            "properties": {
                "action": {
                    "type": "string",
                    "enum": ["read", "read_many", "write", "append", "list", "delete", "copy", "stock_add"],
                    "description": "The action to perform. 'read_many' reads multiple files at once. 'stock_add' adds a structured data point to the stock knowledge base."
                },
                "workspace": {
                    "type": "string",
                    "description": "The workspace in which to execute the action (source workspace for copy): 'personal', 'shared', 'unit' or the name of a workspace you are a member of. Default is 'personal'."
                },
                "path": {
                    "type": "string",
                    "description": "Relative path to the file or directory"
                },
                "content": {
                    "type": "string",
                    "description": "Content for write or append actions"
                },
                "paths": {
                    "type": "array",
                    "items": { "type": "string" },
                    "description": "Only for read_many: files to read. Alternatively 'path' (directory) with 'pattern'."
                },
                "pattern": {
                    "type": "string",
                    "description": "For read_many and list: file pattern within directory 'path', e.g. 'berlin_2026-09-20_*.txt'. Without pattern, the entire directory is used."
                },
                "sort": {
                    "type": "string",
                    "enum": ["modified", "name"],
                    "description": "Only for list: sorting. Default 'modified' (newest first)."
                },
                "order": {
                    "type": "string",
                    "enum": ["desc", "asc"],
                    "description": "Only for list: sort direction. Default descending for 'modified', ascending for 'name'."
                },
                "limit": {
                    "type": "integer",
                    "description": "Only for list: maximum number of entries. Default 50, maximum 500. The response header always mentions total count."
                },
                "destinationWorkspace": {
                    "type": "string",
                    "description": "Destination workspace for copy, named like 'workspace'. Default is the same workspace as 'workspace'."
                },
                "destinationPath": {
                    "type": "string",
                    "description": "Relative destination path for copy. Required for copy."
                },
                "ticker": {
                    "type": "string",
                    "description": "Stock ticker for stock_add (e.g. 'NVDA', 'TSLA'). Automatically converted to uppercase."
                },
                "category": {
                    "type": "string",
                    "enum": ["news", "social", "analysis", "capitol", "price", "earnings", "filing", "sentiment", "other"],
                    "description": "Category of data point for stock_add."
                },
                "source": {
                    "type": "string",
                    "description": "Source of data point for stock_add (e.g. 'reuters', 'x_unusual_whales', 'youtube', 'reddit')."
                },
                "title": {
                    "type": "string",
                    "description": "Short headline/summary of data point for stock_add."
                },
                "data": {
                    "type": "object",
                    "description": "Structured data of data point for stock_add. Can contain arbitrary fields."
                }
            },
            "required": ["action"]
        }
        """).RootElement.Clone();

    public async Task<ToolResult> ExecuteAsync(
        JsonElement input,
        AgentToolContext context,
        CancellationToken ct)
    {
        var action = input.GetProperty("action").GetString()
            ?? throw new ArgumentException("'action' is required");

        // #718: "shared:betrieb/protokoll.md" names the workspace in the path — as in FTP and RocketChat.
        if (WorkspaceFromPath(ref input) is { } prefixProblem)
            return ToolResult.Fail(prefixProblem);

        var requested = input.TryGetProperty("workspace", out var w) && w.ValueKind == JsonValueKind.String ? w.GetString() : null;
        if (ResolveArea(requested, context) is not { } area)
            return ToolResult.Fail(UnknownWorkspace(requested!, context));

        if (string.IsNullOrWhiteSpace(area.Root))
            return ToolResult.Fail($"Configuration error: the folder of workspace '{area.Name}' is not defined.");

        // Sicherstellen, dass rootPath absolut ist
        var rootPath = Path.GetFullPath(area.Root);

        // Zugriffsprüfung
        if (!IsActionAllowed(action, area))
        {
            return ToolResult.Fail($"Access denied: Action '{action}' is not allowed in workspace '{area.Name}' for this agent.");
        }

        // A workspace with a member list comes into being when it is first used.
        if (!area.IsPersonal && area.Name != WorkspaceLayout.Shared)
            Directory.CreateDirectory(rootPath);

        try
        {
            return action switch
            {
                "read" => await HandleReadAsync(input, rootPath, area, context, ct),
                "read_many" => await HandleReadManyAsync(input, rootPath, area, context, ct),
                "write" => await HandleWriteAsync(input, rootPath, area, context, ct),
                "append" => await HandleAppendAsync(input, rootPath, area, context, ct),
                "list" => await HandleListAsync(input, rootPath, area, context, ct),
                "delete" => await HandleDeleteAsync(input, rootPath, area, context, ct),
                "copy" => await HandleCopyAsync(input, rootPath, area, context, ct),
                "stock_add" => await HandleStockAddAsync(input, context, ct),
                _ => ToolResult.Fail($"Unknown action: {action}")
            };
        }
        catch (UnauthorizedAccessException ex)
        {
            // A refused path is the agent's mistake, not the tool's — no stack trace in the error log.
            context.Logger.LogWarning("FileRW {Action} refused: {Reason}", action, ex.Message);
            return ToolResult.Fail(Denied(ex.Message));
        }
        catch (Exception ex)
        {
            context.Logger.LogError(ex, "Error during FileRW action {Action}", action);
            return ToolResult.Fail($"Error: {ex.Message}");
        }
    }

    /// <summary>
    /// #579: Rechte und Pfad pruefen, bevor ein Aufruf in die Freigabeliste kommt. Dieselben
    /// Pruefungen wie in <see cref="ExecuteAsync"/>, ohne etwas anzufassen.
    /// </summary>
    public string? Preflight(JsonElement input, AgentToolContext context)
    {
        if (input.ValueKind != JsonValueKind.Object
            || !input.TryGetProperty("action", out var a) || a.ValueKind != JsonValueKind.String)
            return null;

        var action = a.GetString() ?? "";
        if (WorkspaceFromPath(ref input) is { } prefixProblem)
            return prefixProblem;
        var requested = input.TryGetProperty("workspace", out var w) && w.ValueKind == JsonValueKind.String
            ? w.GetString() : null;

        if (ResolveArea(requested, context) is not { } area)
            return UnknownWorkspace(requested!, context);

        if (!IsActionAllowed(action, area))
            return $"Access denied: Action '{action}' is not allowed in workspace '{area.Name}' for this agent.";

        if (action != "delete" || string.IsNullOrWhiteSpace(area.Root))
            return null;

        try
        {
            var rootPath = Path.GetFullPath(area.Root);
            var path = GetAndValidatePath(input, rootPath, area, false, context);

            if (!CanOverrideProtection(area) && IsPathProtected(path, rootPath, area))
                return $"🛡️ Protected area: '{Path.GetRelativePath(rootPath, path)}' cannot be deleted.";
        }
        catch (Exception ex) when (ex is not OperationCanceledException)
        {
            // Dieselbe Pfadpruefung wirft bei der Ausfuehrung - dort wird daraus ein Fehler.
            return Denied(ex.Message);
        }

        return null;
    }

    private static string Denied(string message)
        => message.StartsWith("Access denied", StringComparison.Ordinal) ? message : $"Access denied: {message}";

    /// <summary>
    /// #718: A path may name its workspace — <c>shared:betrieb/protokoll.md</c>, the form FTP and
    /// RocketChat take. Agents carry it over to FileRW, and every refusal cost them a step. The
    /// prefix becomes the <c>workspace</c> argument; it must agree with one given, and a list of
    /// paths names one workspace. Returns the refusal, or <c>null</c>.
    /// </summary>
    internal static string? WorkspaceFromPath(ref JsonElement input)
    {
        if (input.ValueKind != JsonValueKind.Object)
            return null;

        // The relative path, or null without a prefix; "\0" when it names a second workspace.
        string? named = null;
        string? Strip(string path)
        {
            if (path.IndexOf(':') <= 0)
                return null;
            var (workspace, relative) = NamedWorkspaces.Split(path);
            if (relative.Length == path.Length)
                return null;
            if (named is not null && !Same(named, workspace))
                return "\0";
            named = workspace;
            return relative;
        }

        var node = System.Text.Json.Nodes.JsonNode.Parse(input.GetRawText())!.AsObject();
        var changed = false;

        if (node["path"] is System.Text.Json.Nodes.JsonValue pv && pv.TryGetValue<string>(out var single) && Strip(single) is { } rel)
        {
            node["path"] = rel;
            changed = true;
        }
        if (node["paths"] is System.Text.Json.Nodes.JsonArray list)
        {
            for (var i = 0; i < list.Count; i++)
            {
                if (list[i] is not System.Text.Json.Nodes.JsonValue v || !v.TryGetValue<string>(out var entry))
                    continue;
                var stripped = Strip(entry);
                if (stripped == "\0")
                    return "'paths' names more than one workspace. Read from one workspace per call (parameter 'workspace').";
                if (stripped is not null)
                {
                    list[i] = stripped;
                    changed = true;
                }
            }
        }
        if (!changed || named is null)
            return null;

        if (node["workspace"] is System.Text.Json.Nodes.JsonValue wv && wv.TryGetValue<string>(out var given)
            && !string.IsNullOrWhiteSpace(given) && !Same(given, named))
            return $"The path names the workspace '{named}', but 'workspace' says '{given}'. Give one of them.";

        node["workspace"] = named;
        input = JsonSerializer.SerializeToElement(node);
        return null;
    }

    private static bool Same(string a, string b) => string.Equals(a, b, StringComparison.OrdinalIgnoreCase);

    // ─── Workspaces (#684) ───

    /// <summary>The folder in the shared workspace that holds the task files.</summary>
    private const string TasksFolder = "tasks";

    /// <summary>A workspace as one call sees it: where it lies and what the agent may do there.</summary>
    private sealed record Area(string Name, string? Root, WorkspaceAccess Access, IReadOnlyList<string> ProtectedPaths)
    {
        public bool IsPersonal => Name == WorkspaceLayout.Personal;
    }

    /// <summary>
    /// Resolves the name an agent gave. "personal" and "shared" work as they always did —
    /// "shared" still by the agent's own <c>sharedAccessLevel</c>. "unit" is the own unit's
    /// workspace; any other name must be a workspace the agent is a member of. Everything
    /// else is <c>null</c>: an unknown name and a workspace the agent may not see get the
    /// same answer, so the answer does not reveal that it exists.
    /// </summary>
    private static Area? ResolveArea(string? requested, AgentToolContext context)
    {
        var name = string.IsNullOrWhiteSpace(requested) ? WorkspaceLayout.Personal : requested.Trim();

        if (name.Equals(WorkspaceLayout.Personal, StringComparison.OrdinalIgnoreCase))
            return new Area(WorkspaceLayout.Personal, context.WorkspacePath, WorkspaceAccess.Manage, []);

        if (name.Equals(WorkspaceLayout.Shared, StringComparison.OrdinalIgnoreCase))
            return new Area(WorkspaceLayout.Shared, context.SharedWorkspacePath, SharedAccess(context), GetProtectedPaths(context));

        // #718: the same resolution as FTP and RocketChat.
        return NamedWorkspaces.Resolve(name, context.AgentId, context.Organisation, context.SharedWorkspacePath) is { } named
            ? new Area(named.Workspace.Id, named.Root, named.Access, NormaliseProtectedPaths(named.Workspace.ProtectedPaths))
            : null;
    }

    /// <summary>The answer to a name that is not a workspace this agent may use — with the ones it may.</summary>
    private static string UnknownWorkspace(string requested, AgentToolContext context)
        => NamedWorkspaces.Unknown(requested, context.AgentId, context.Organisation, SharedAccess(context) > WorkspaceAccess.None);

    /// <summary>The one shared folder, by the level the agent carries for it — as before #684.</summary>
    private static WorkspaceAccess SharedAccess(AgentToolContext context)
        => (context.ToolConfig.TryGetValue("sharedAccessLevel", out var lv) ? lv?.ToString() : "Denied") switch
        {
            "Read" => WorkspaceAccess.Read,
            "ReadWrite" => WorkspaceAccess.Write,
            "Admin" => WorkspaceAccess.Manage,
            _ => WorkspaceAccess.None
        };

    private static bool IsActionAllowed(string action, Area area)
    {
        if (area.IsPersonal) return true; // Alles erlaubt

        return action switch
        {
            "read" or "read_many" or "list" or "copy" => area.Access >= WorkspaceAccess.Read,
            "write" or "append" or "stock_add" => area.Access >= WorkspaceAccess.Write,
            "delete" => area.Access >= WorkspaceAccess.Manage,
            _ => false
        };
    }

    /// <summary>Managing a workspace includes changing and deleting protected files — as the old Admin level did.</summary>
    private static bool CanOverrideProtection(Area area) => area.Access >= WorkspaceAccess.Manage;

    /// <summary>
    /// Prüft ob ein Pfad innerhalb eines geschützten Bereichs liegt.
    /// Geschützte Pfade erlauben nur: read, list, append, write (nur neue Dateien), stock_add.
    /// Kein Überschreiben existierender Dateien, kein Löschen.
    /// Wer den Bereich verwaltet, umgeht den Schutz.
    /// </summary>
    private static bool IsPathProtected(string fullPath, string rootPath, Area area)
    {
        if (area.ProtectedPaths.Count == 0) return false;

        var relativePath = Path.GetRelativePath(rootPath, fullPath)
            .Replace('\\', '/').TrimStart('/');

        // Jeder Eintrag endet auf "/", deshalb greift StartsWith hier auf einer echten
        // Verzeichnisgrenze: "stocks/" trifft "stocks/x.json", aber nicht "stocks-alt/x.json".
        return area.ProtectedPaths.Any(pp =>
            relativePath.StartsWith(pp, StringComparison.OrdinalIgnoreCase) ||
            relativePath.Equals(pp.TrimEnd('/'), StringComparison.OrdinalIgnoreCase));
    }

    /// <summary>
    /// #684: With units, the task files in the shared folder are closed to FileRW. Written
    /// directly, a task file would pass every check the task board makes — the board of the
    /// unit, the address book of the assignment. Tasks go through the Taskboard tool. Without
    /// units nothing changes, so running installations keep what they have.
    /// </summary>
    private static bool IsBlocked(string fullPath, Area area, AgentToolContext context)
    {
        if (area.Name != WorkspaceLayout.Shared || context.Organisation?.HasUnits != true || string.IsNullOrWhiteSpace(area.Root))
            return false;

        var relative = Path.GetRelativePath(Path.GetFullPath(area.Root), fullPath).Replace('\\', '/');
        return relative.Equals(TasksFolder, StringComparison.OrdinalIgnoreCase)
               || relative.StartsWith(TasksFolder + "/", StringComparison.OrdinalIgnoreCase);
    }

    // ─── History (#719) ───

    /// <summary>The workspace as the history names it — the personal one with its owner, since every agent has one.</summary>
    private static string HistoryWorkspace(Area area, AgentToolContext context)
        => area.IsPersonal ? $"{WorkspaceLayout.Personal}:{context.AgentId}" : area.Name;

    /// <summary>
    /// Keeps the version before the change. Best effort: a history that cannot be written
    /// must not stop the work — it is logged, and the change happens without its entry.
    /// </summary>
    private static async Task<FileChange?> BeforeChangeAsync(string path, Area area, AgentToolContext context, CancellationToken ct)
    {
        if (context.History is not { } history)
            return null;
        try
        {
            return await history.BeforeAsync(path, HistoryWorkspace(area, context), ct);
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or Microsoft.Data.Sqlite.SqliteException)
        {
            context.Logger.LogWarning(ex, "File history: the version before could not be kept for {Path}", path);
            return null;
        }
    }

    private static async Task AfterChangeAsync(FileChange? change, string action, AgentToolContext context, CancellationToken ct)
    {
        if (change is null || context.History is not { } history)
            return;
        try
        {
            await history.RecordAsync(change, action, context.AgentId, context.RunId, ct);
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or Microsoft.Data.Sqlite.SqliteException)
        {
            context.Logger.LogWarning(ex, "File history: the change could not be recorded for {Path}", change.FullPath);
        }
    }

    // ─── Lost updates (#720) ───

    /// <summary>Only workspaces more than one agent can write to — never the personal one.</summary>
    private static bool Guarded(Area area, AgentToolContext context) => !area.IsPersonal && context.Files is not null;

    private static void NoteRead(string path, Area area, AgentToolContext context)
    {
        if (Guarded(area, context))
            context.Files!.NoteRead(context.AgentId, path, FileLedger.HashOf(path));
    }

    private static void NoteReplace(string path, Area area, AgentToolContext context)
    {
        if (Guarded(area, context))
            context.Files!.NoteReplace(context.AgentId, context.RunId, path, FileLedger.HashOf(path));
    }

    /// <summary>
    /// The refusal when replacing the file would lose a change this agent has not seen —
    /// kept for the analysis, audited as a conflict. <c>null</c>: go ahead. Called under the
    /// file's lock, so nothing can change between the check and the write.
    /// </summary>
    private static async Task<ToolResult?> RefuseLostUpdateAsync(
        string path, string displayPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        if (!Guarded(area, context))
            return null;
        if (context.Files!.CheckReplace(context.AgentId, context.RunId, path, area.Name, FileLedger.HashOf(path)) is not { } conflict)
            return null;

        context.Logger.LogInformation("Write refused, lost update: {Path} by {Agent} ({Kind})", displayPath, context.AgentId, conflict.Kind);
        await context.Files.RecordAsync(conflict, ct);
        return ToolResult.Conflict(conflict.Message(displayPath));
    }

    private static List<string> NormaliseProtectedPaths(IEnumerable<string> paths)
        => paths
            .Select(p => p.Replace('\\', '/').Trim().Trim('/'))
            .Where(p => p.Length > 0)
            .Select(p => p + "/")
            .ToList();

    private static List<string> GetProtectedPaths(AgentToolContext context)
    {
        if (!context.ToolConfig.TryGetValue("protectedPaths", out var pp) || pp is null)
            return [];

        if (pp is JsonElement je && je.ValueKind == JsonValueKind.Array)
            return je.EnumerateArray()
                .Select(e => e.GetString()?.Replace('\\', '/').Trim().TrimEnd('/') + "/")
                .Where(s => !string.IsNullOrEmpty(s))
                .ToList()!;

        if (pp is string s && !string.IsNullOrWhiteSpace(s))
            return s.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
                .Select(p => p.Replace('\\', '/').TrimEnd('/') + "/")
                .ToList();

        return [];
    }

    /// <summary>
    /// Nachschau nach einem Absturz (#555). Sieht nach, was von einem unterbrochenen
    /// Aufruf übrig ist — verändert nichts.
    ///
    /// <para>Wie weit die Auskunft trägt, hängt an der Aktion:</para>
    /// <list type="bullet">
    /// <item><b>write</b> — seit #553 atomar. Entweder die alte oder die neue Fassung,
    /// nie eine halbe. Ein Vergleich mit dem beabsichtigten Inhalt sagt deshalb
    /// zuverlässig, ob der Aufruf durchkam.</item>
    /// <item><b>append</b> — nicht atomar und nicht atomar zu machen. Hier kann wirklich
    /// ein Riss entstehen, und hier lohnt die Nachschau: Steht der beabsichtigte Text
    /// vollständig am Ende, kam der Aufruf durch; steht ein Anfang davon da, riss es
    /// mittendrin.</item>
    /// <item>alles andere — <see cref="ProbeOutcome.Unknown"/>. Lieber schweigen als
    /// raten.</item>
    /// </list>
    /// </summary>
    public async Task<ProbeFinding> ProbeAsync(JsonElement arguments, AgentToolContext context, CancellationToken ct)
    {
        try
        {
            var action = arguments.TryGetProperty("action", out var a) ? a.GetString() : null;

            if (action is not ("write" or "append"))
                return ProbeFinding.Unknown($"Nothing to probe for action '{action ?? "?"}'.");
            if (WorkspaceFromPath(ref arguments) is { } prefixProblem)
                return ProbeFinding.Unknown(prefixProblem);

            var requested = arguments.TryGetProperty("workspace", out var w) && w.ValueKind == JsonValueKind.String ? w.GetString() : null;
            if (ResolveArea(requested, context) is not { Root: { Length: > 0 } root } area)
                return ProbeFinding.Unknown("Workspace path is unknown.");

            var path = GetAndValidatePath(arguments, Path.GetFullPath(root), area, true, context);
            var erwartet = arguments.TryGetProperty("content", out var c) ? c.GetString() ?? "" : "";

            if (!File.Exists(path))
            {
                return new ProbeFinding(ProbeOutcome.NotStarted,
                    "File does not exist — nothing was written.");
            }

            var vorhanden = await File.ReadAllTextAsync(path, ct);

            if (action == "write")
            {
                return vorhanden == erwartet
                    ? new ProbeFinding(ProbeOutcome.Complete,
                        $"Content matches intended content exactly ({erwartet.Length} characters).")
                    : new ProbeFinding(ProbeOutcome.NotStarted,
                        "File still has old content. Writes are atomic — partial versions cannot exist.");
            }

            // append
            if (vorhanden.EndsWith(erwartet, StringComparison.Ordinal))
            {
                return new ProbeFinding(ProbeOutcome.Complete,
                    $"Intended text is completely at the end ({erwartet.Length} characters).");
            }

            // Wie viel vom Erwarteten steht am Ende? Das ist die Rissstelle.
            for (var laenge = Math.Min(erwartet.Length - 1, vorhanden.Length); laenge > 0; laenge--)
            {
                if (vorhanden.EndsWith(erwartet[..laenge], StringComparison.Ordinal))
                {
                    return new ProbeFinding(ProbeOutcome.Partial,
                        $"Appended {laenge} of {erwartet.Length} characters — call was interrupted.");
                }
            }

            return new ProbeFinding(ProbeOutcome.NotStarted,
                "None of the intended text is at the end of the file.");
        }
        catch (Exception ex)
        {
            // Nie werfen: Eine gescheiterte Nachschau ist keine Aussage über die Welt,
            // sondern eine über die Nachschau.
            return ProbeFinding.Unknown($"Probe not possible: {ex.Message}");
        }
    }

    private string GetAndValidatePath(JsonElement input, string rootPath, Area area, bool checkExtension, AgentToolContext context)
    {
        var relativePath = input.TryGetProperty("path", out var p) ? p.GetString() : "";

        // Prüft Ausbruch aus dem Workspace, absolute Pfade und Alternate Data Streams.
        var fullPath = WorkspacePath.Resolve(rootPath, relativePath, area.Name);

        if (IsBlocked(fullPath, area, context))
            throw new UnauthorizedAccessException(
                "Tasks are kept on the task board — use the Taskboard tool (task_list, task_find, task_create, task_update), not their files.");

        // Extension Check
        if (checkExtension && !Directory.Exists(fullPath))
        {
            var extension = Path.GetExtension(fullPath).ToLowerInvariant();
            
            var configKey = area.IsPersonal ? "personalAllowedExtensions" : "sharedAllowedExtensions";
            
            var allowedExtensions = context.ToolConfig.TryGetValue(configKey, out var ae) && ae is JsonElement je
                ? je.EnumerateArray().Select(x => x.GetString()?.ToLowerInvariant()).ToList()
                : new List<string?> { ".txt", ".json", ".md", ".html", ".js", ".css" }; // Default

            if (!allowedExtensions.Contains(extension))
            {
                throw new UnauthorizedAccessException($"File extension '{extension}' is not allowed in workspace '{area.Name}'.");
            }
        }

        return fullPath;
    }

    /// <summary>
    /// #662: Gibt es den Pfad in einem anderen Workspace, sagt die Fehlermeldung das.
    ///
    /// <para>Anlass aus dem Testbetrieb: Ein guenstiges Modell vergisst regelmaessig
    /// <c>workspace: "shared"</c> und bekommt nur "nicht gefunden" zurueck. Es rät dann
    /// weiter, und jeder Versuch kostet einen Schritt. Der Hinweis nennt nur Workspaces,
    /// die der Agent fuer diese Aktion auch benutzen darf - sonst waere er eine Einladung
    /// zu etwas, das ohnehin abgewiesen wird, und verriete obendrein, dass es sie gibt.</para>
    ///
    /// <para>Seit #684 gibt es mehr als zwei: gesucht wird in allen, die der Agent kennt.</para>
    /// </summary>
    private string AndererWorkspaceHinweis(
        string action, Area area, string? relativePath, AgentToolContext context, bool verzeichnis, string? muster = null)
    {
        // The root of a workspace exists everywhere — pointing there would send the agent in circles.
        if (string.IsNullOrWhiteSpace(relativePath) && string.IsNullOrWhiteSpace(muster))
            return "";

        var candidates = new List<string> { WorkspaceLayout.Personal, WorkspaceLayout.Shared };
        if (context.Organisation is { } org)
            candidates.AddRange(org.WorkspacesFor(context.AgentId).Select(g => g.Workspace.Id));

        foreach (var name in candidates.Where(n => !string.Equals(n, area.Name, StringComparison.OrdinalIgnoreCase)))
        {
            if (ResolveArea(name, context) is not { Root: { Length: > 0 } root } other || !IsActionAllowed(action, other))
                continue;

            try
            {
                var pfad = WorkspacePath.Resolve(Path.GetFullPath(root), relativePath, other.Name);
                if (IsBlocked(pfad, other, context))
                    continue;
                var dort = verzeichnis
                    ? Directory.Exists(pfad) && (string.IsNullOrWhiteSpace(muster) || Directory.EnumerateFiles(pfad, muster).Any())
                    : File.Exists(pfad);
                if (dort)
                    return string.IsNullOrWhiteSpace(muster)
                        ? $" The path exists in the {other.Name} workspace — call with workspace: \"{other.Name}\"."
                        : $" Matching files exist in the {other.Name} workspace — call with workspace: \"{other.Name}\".";
            }
            catch
            {
                // Ein Pfad, der dort gar nicht auflösbar ist, hilft niemandem.
            }
        }
        return "";
    }

    private static string? RelativerPfad(JsonElement input)
        => input.ValueKind == JsonValueKind.Object && input.TryGetProperty("path", out var p) && p.ValueKind == JsonValueKind.String
            ? p.GetString()
            : null;

    private async Task<ToolResult> HandleReadAsync(JsonElement input, string rootPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        var path = GetAndValidatePath(input, rootPath, area, true, context);
        if (!File.Exists(path))
        {
            return ToolResult.Fail(
                $"File not found in {area.Name} workspace: {Path.GetRelativePath(rootPath, path)}."
                + AndererWorkspaceHinweis("read", area, RelativerPfad(input), context, verzeichnis: false));
        }

        var fileLock = GetFileLock(path);
        await fileLock.WaitAsync(ct);
        try
        {
            var content = await File.ReadAllTextAsync(path, ct);
            NoteRead(path, area, context);
            var relativePath = Path.GetRelativePath(rootPath, path);
            return ToolResult.Ok($"[{area.Name}:/{relativePath}]\n{content}");
        }
        finally
        {
            fileLock.Release();
        }
    }

    /// <summary>Hoechstzahl Dateien je <c>read_many</c>.</summary>
    public const int MaxDateienJeAufruf = 50;

    /// <summary>Hoechstzahl Zeichen je <c>read_many</c> - danach werden nur noch Namen genannt.</summary>
    public const int MaxZeichenJeAufruf = 200_000;

    /// <summary>
    /// #663: Mehrere Dateien in einem Aufruf lesen.
    ///
    /// <para>Anlass: Der Tagesabschluss im Testbetrieb muss 24 Stundendateien zu einem
    /// Tagesarchiv zusammenfassen. Einzeln gelesen sind das 24 Schritte, und der Lauf
    /// stirbt an der Schrittgrenze, bevor er fertig ist. Die Grenze soll Endlosschleifen
    /// abfangen, nicht ehrliche Arbeit - also liest das Werkzeug jetzt auf einmal.</para>
    ///
    /// <para>Entweder <c>paths</c> (ausdrueckliche Liste) oder <c>path</c> als Verzeichnis
    /// mit optionalem <c>pattern</c>. Gedeckelt auf <see cref="MaxDateienJeAufruf"/> Dateien
    /// und <see cref="MaxZeichenJeAufruf"/> Zeichen; was nicht mehr hineinpasst, wird am
    /// Ende namentlich genannt, damit der Agent den Rest gezielt nachholen kann.</para>
    /// </summary>
    private async Task<ToolResult> HandleReadManyAsync(JsonElement input, string rootPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        var (dateien, fehler) = SammleDateien(input, rootPath, area, context);
        if (fehler is not null)
            return ToolResult.Fail(fehler);

        if (dateien.Count == 0)
        {
            return ToolResult.Fail(
                $"No matching file found in {area.Name} workspace."
                + AndererWorkspaceHinweis("read_many", area, RelativerPfad(input), context, verzeichnis: true,
                    muster: input.TryGetProperty("pattern", out var m) && m.ValueKind == JsonValueKind.String ? m.GetString() : null));
        }

        var uebersprungen = new List<string>();
        var fehlend = new List<string>();
        var text = new StringBuilder();
        var gelesen = 0;

        foreach (var pfad in dateien.Take(MaxDateienJeAufruf))
        {
            ct.ThrowIfCancellationRequested();
            var relativ = Path.GetRelativePath(rootPath, pfad).Replace('\\', '/');

            if (!File.Exists(pfad)) { fehlend.Add(relativ); continue; }
            if (text.Length >= MaxZeichenJeAufruf) { uebersprungen.Add(relativ); continue; }

            var sperre = GetFileLock(pfad);
            await sperre.WaitAsync(ct);
            string inhalt;
            try
            {
                inhalt = await File.ReadAllTextAsync(pfad, ct);
                NoteRead(pfad, area, context);
            }
            finally { sperre.Release(); }

            text.Append($"\n--- {area.Name}:/{relativ} ---\n").Append(inhalt.TrimEnd()).Append('\n');
            gelesen++;
        }

        uebersprungen.AddRange(dateien.Skip(MaxDateienJeAufruf).Select(d => Path.GetRelativePath(rootPath, d).Replace('\\', '/')));

        var kopf = new StringBuilder($"[{area.Name} Workspace] {gelesen} of {dateien.Count} file(s) read.");
        if (fehlend.Count > 0)
            kopf.Append($"\nNot found: {string.Join(", ", fehlend.Take(10))}{(fehlend.Count > 10 ? " …" : "")}");
        if (uebersprungen.Count > 0)
            kopf.Append($"\nSkipped reading (limit {MaxDateienJeAufruf} files / {MaxZeichenJeAufruf} chars), "
                + $"fetch with an additional call: {string.Join(", ", uebersprungen.Take(10))}{(uebersprungen.Count > 10 ? " …" : "")}");

        return ToolResult.Ok(kopf.Append('\n').Append(text).ToString());
    }

    /// <summary>
    /// Die zu lesenden Dateien: entweder aus <c>paths</c> oder aus Verzeichnis und Muster.
    /// Jeder Pfad geht durch dieselbe Pruefung wie ein einzelnes <c>read</c>.
    /// </summary>
    private (List<string> Dateien, string? Fehler) SammleDateien(
        JsonElement input, string rootPath, Area area, AgentToolContext context)
    {
        try
        {
            if (input.TryGetProperty("paths", out var liste) && liste.ValueKind == JsonValueKind.Array)
            {
                var dateien = new List<string>();
                foreach (var eintrag in liste.EnumerateArray())
                {
                    if (eintrag.ValueKind != JsonValueKind.String) continue;
                    var relativ = eintrag.GetString();
                    if (string.IsNullOrWhiteSpace(relativ)) continue;
                    dateien.Add(PruefeLesepfad(relativ, rootPath, area, context));
                }
                return (dateien, dateien.Count == 0 ? "'paths' contains no valid path." : null);
            }

            var verzeichnis = WorkspacePath.Resolve(rootPath, RelativerPfad(input), area.Name);
            if (!Directory.Exists(verzeichnis))
                return ([], null); // Die Meldung samt Workspace-Hinweis macht der Aufrufer.

            var muster = input.TryGetProperty("pattern", out var m) && m.ValueKind == JsonValueKind.String
                ? m.GetString()
                : null;
            if (MusterFehler(muster) is { } musterFehler)
                return ([], musterFehler);

            var gefunden = Directory.GetFiles(verzeichnis, string.IsNullOrWhiteSpace(muster) ? "*" : muster)
                .OrderBy(f => f, StringComparer.Ordinal)
                .ToList();

            // Dieselbe Endungspruefung wie beim einzelnen Lesen - was dort verboten ist,
            // kommt auch hier nicht durch, nur ohne den Lauf abzubrechen.
            return (gefunden.Where(f => IstLesbar(f, area, context)).ToList(), null);
        }
        catch (UnauthorizedAccessException ex)
        {
            return ([], Denied(ex.Message));
        }
    }

    private string PruefeLesepfad(string relativePath, string rootPath, Area area, AgentToolContext context)
    {
        var json = JsonSerializer.SerializeToElement(new { action = "read", path = relativePath });
        return GetAndValidatePath(json, rootPath, area, true, context);
    }

    private bool IstLesbar(string vollerPfad, Area area, AgentToolContext context)
    {
        try
        {
            var json = JsonSerializer.SerializeToElement(new { action = "read", path = Path.GetFileName(vollerPfad) });
            GetAndValidatePath(json, Path.GetDirectoryName(vollerPfad)!, area, true, context);
            return true;
        }
        catch (UnauthorizedAccessException)
        {
            return false;
        }
    }

    private async Task<ToolResult> HandleWriteAsync(JsonElement input, string rootPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        var path = GetAndValidatePath(input, rootPath, area, true, context);
        var content = input.TryGetProperty("content", out var c) ? c.GetString() ?? "" : "";

        var fileLock = GetFileLock(path);
        await fileLock.WaitAsync(ct);
        try
        {
            // Schutz: In geschützten Bereichen darf nur geschrieben werden wenn die Datei NICHT existiert
            if (!CanOverrideProtection(area) && File.Exists(path) && IsPathProtected(path, rootPath, area))
            {
                var relPath = Path.GetRelativePath(rootPath, path);
                return ToolResult.Fail(
                    $"🛡️ Protected area: File '{relPath}' already exists and cannot be overwritten. " +
                    $"Use 'append' to add data, or create a new file with a different name. " +
                    $"Tip: Use 'stock_add' for structured data points.");
            }

            // #720: not over a change this agent has not seen.
            if (await RefuseLostUpdateAsync(path, $"{area.Name}:/{Path.GetRelativePath(rootPath, path).Replace('\\', '/')}", area, context, ct) is { } conflict)
                return conflict;

            var dir = Path.GetDirectoryName(path);
            if (dir != null && !Directory.Exists(dir)) Directory.CreateDirectory(dir);
            var change = await BeforeChangeAsync(path, area, context, ct);

            // Atomar schreiben (#553): erst in eine Nebendatei, dann ersetzen. Ein Absturz
            // mitten im Vorgang hinterlässt damit entweder die alte oder die neue Fassung,
            // nie eine halbe. Zuvor stand hier File.WriteAllTextAsync — die Anwendung
            // schützte also ihre eigenen Konfigurationsdateien, die Arbeitsergebnisse der
            // Agenten aber nicht.
            await AtomicFile.WriteAllTextAsync(path, content, new UTF8Encoding(false), ct);
            NoteReplace(path, area, context);
            await AfterChangeAsync(change, FileAction.Replace, context, ct);
            return ToolResult.Ok($"[{area.Name} Workspace] File successfully written: {area.Name}:/{Path.GetRelativePath(rootPath, path)}");
        }
        finally
        {
            fileLock.Release();
        }
    }

    private async Task<ToolResult> HandleAppendAsync(JsonElement input, string rootPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        var path = GetAndValidatePath(input, rootPath, area, true, context);
        var content = input.TryGetProperty("content", out var c) ? c.GetString() ?? "" : "";

        var fileLock = GetFileLock(path);
        await fileLock.WaitAsync(ct);
        try
        {
            // Bewusst NICHT atomar (#553): Anhängen ließe sich nur atomar machen, indem
            // die ganze Datei neu geschrieben wird — bei einer großen Protokolldatei wäre
            // das der falsche Handel. Hier bleibt ein Riss möglich; genau dafür gibt es
            // die Zustandsprüfung in #555.
            // #720: appending loses nothing and is not checked — but noted, so whoever read
            // the file before does not replace it without the appended part.
            var before = Guarded(area, context) ? FileLedger.HashOf(path) : null;
            var change = await BeforeChangeAsync(path, area, context, ct);

            // #575: Neu entstehende Dateien gehoeren nur dem Besitzer (0600).
            await using (var stream = ClawdDotNet.Core.Storage.OwnerOnlyFile.OpenAppend(path))
            await using (var writer = new StreamWriter(stream, new UTF8Encoding(false)))
                await writer.WriteAsync(content.AsMemory(), ct);

            if (Guarded(area, context))
                context.Files!.NoteAppend(context.AgentId, context.RunId, path, before, FileLedger.HashOf(path));
            await AfterChangeAsync(change, FileAction.Append, context, ct);
            return ToolResult.Ok($"[{area.Name} Workspace] Content successfully appended to: {area.Name}:/{Path.GetRelativePath(rootPath, path)}");
        }
        finally
        {
            fileLock.Release();
        }
    }

    /// <summary>Wie viele Eintraege ein <c>list</c> ohne ausdrueckliches <c>limit</c> zeigt.</summary>
    public const int StandardEintraege = 50;

    /// <summary>Obergrenze fuer <c>limit</c> - darueber wird die Antwort zur Heuhaufensuche.</summary>
    public const int MaxEintraege = 500;

    /// <summary>
    /// #673: Verzeichnis auflisten - sortiert, gedeckelt, kompakt.
    ///
    /// <para>Anlass: Die Betriebskontrolle im Testbetrieb meldete Stundendateien als fehlend,
    /// die es gab. Das Verzeichnis lieferte 105 Eintraege in der Reihenfolge des Dateisystems,
    /// vierzeilig als eingeruecktes JSON. Darin zwei bestimmte Namen zu finden ist Sucharbeit,
    /// und ein guenstiges Modell erledigt sie falsch.</para>
    ///
    /// <para>Also: neueste zuerst (umstellbar ueber <c>sort</c> und <c>order</c>), <c>pattern</c>
    /// zum Eingrenzen, eine Zeile je Eintrag - und der Kopf sagt, wie viele Eintraege es
    /// insgesamt gibt. Eine gedeckelte Liste, die ihre Deckelung verschweigt, waere die
    /// schlimmere Falle.</para>
    /// </summary>
    private async Task<ToolResult> HandleListAsync(JsonElement input, string rootPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        var path = GetAndValidatePath(input, rootPath, area, false, context);
        if (!Directory.Exists(path))
        {
            return ToolResult.Fail(
                $"Directory not found in {area.Name} workspace: {Path.GetRelativePath(rootPath, path)}."
                + AndererWorkspaceHinweis("list", area, RelativerPfad(input), context, verzeichnis: true));
        }

        var muster = GetOptionalString(input, "pattern");
        if (MusterFehler(muster) is { } musterFehler)
            return ToolResult.Fail(musterFehler);

        List<string> pfade;
        try
        {
            pfade = Directory.GetFileSystemEntries(path, string.IsNullOrWhiteSpace(muster) ? "*" : muster)
                .Where(e => !IsBlocked(e, area, context))
                .ToList();
        }
        catch (ArgumentException ex)
        {
            return ToolResult.Fail($"Invalid pattern '{muster}': {ex.Message}");
        }

        var eintraege = pfade
            .Select(e => new Verzeichniseintrag(
                Path.GetFileName(e),
                Directory.Exists(e),
                Directory.Exists(e) ? 0 : new FileInfo(e).Length,
                File.GetLastWriteTime(e)))
            .ToList();

        var nachName = string.Equals(GetOptionalString(input, "sort"), "name", StringComparison.OrdinalIgnoreCase);
        var absteigend = GetOptionalString(input, "order") is { } o
            ? string.Equals(o, "desc", StringComparison.OrdinalIgnoreCase)
            : !nachName; // newest first, names ascending

        IEnumerable<Verzeichniseintrag> sortiert = nachName
            ? (absteigend
                ? eintraege.OrderByDescending(e => e.Name, StringComparer.OrdinalIgnoreCase)
                : eintraege.OrderBy(e => e.Name, StringComparer.OrdinalIgnoreCase))
            : (absteigend
                ? eintraege.OrderByDescending(e => e.Geaendert)
                : eintraege.OrderBy(e => e.Geaendert));

        var grenze = Math.Clamp(GetInt(input, "limit") ?? StandardEintraege, 1, MaxEintraege);
        var gezeigt = sortiert.Take(grenze).ToList();

        var relativeDirPath = Path.GetRelativePath(rootPath, path);
        var ordnung = nachName
            ? (absteigend ? "name descending" : "name ascending")
            : (absteigend ? "newest first" : "oldest first");

        var text = new StringBuilder();
        text.Append($"[{area.Name} Workspace] Directory: {area.Name}:/{(relativeDirPath == "." ? "" : relativeDirPath)}");
        text.Append($" - {gezeigt.Count} of {eintraege.Count} entries, {ordnung}.");
        if (!string.IsNullOrWhiteSpace(muster))
            text.Append($" Pattern: {muster}.");
        if (eintraege.Count > gezeigt.Count)
            text.Append($"\n{eintraege.Count - gezeigt.Count} more not shown - narrow down with 'pattern' or set 'limit' (max {MaxEintraege}).");
        text.Append("\nModified           Size  Name\n");

        foreach (var e in gezeigt)
        {
            var groesse = e.IstVerzeichnis ? "<DIR>" : e.Groesse.ToString();
            text.Append($"{e.Geaendert:yyyy-MM-dd HH:mm}  {groesse,9}  {e.Name}{(e.IstVerzeichnis ? "/" : "")}\n");
        }

        return await Task.FromResult(ToolResult.Ok(text.ToString().TrimEnd()));
    }

    private readonly record struct Verzeichniseintrag(string Name, bool IstVerzeichnis, long Groesse, DateTime Geaendert);

    /// <summary>
    /// Ein Muster ist ein Dateiname mit Platzhaltern, kein Pfad. <c>Directory.GetFiles</c>
    /// wertet Trennzeichen im Muster aus — <c>pattern: "../*"</c> listet damit das
    /// Elternverzeichnis, an der Pfadpruefung vorbei. Deshalb hier und nicht erst dort.
    /// </summary>
    private static string? MusterFehler(string? muster)
    {
        if (string.IsNullOrWhiteSpace(muster)) return null;

        if (muster.Contains('/') || muster.Contains('\\') || muster.Contains(".."))
            return $"Invalid pattern '{muster}': a pattern is a file name with wildcards "
                 + "(e.g. 'berlin_2026-09-21_*.txt'), not a path. The directory belongs in 'path'.";

        return null;
    }

    private static string? GetOptionalString(JsonElement input, string name)
        => input.TryGetProperty(name, out var v) && v.ValueKind == JsonValueKind.String ? v.GetString() : null;

    private static int? GetInt(JsonElement input, string name)
        => input.TryGetProperty(name, out var v) && v.ValueKind == JsonValueKind.Number && v.TryGetInt32(out var i) ? i : null;

    private async Task<ToolResult> HandleDeleteAsync(JsonElement input, string rootPath, Area area, AgentToolContext context, CancellationToken ct)
    {
        var path = GetAndValidatePath(input, rootPath, area, false, context);

        // Schutz: In geschützten Bereichen ist Löschen komplett verboten (außer Admin)
        if (!CanOverrideProtection(area) && IsPathProtected(path, rootPath, area))
        {
            var relPath = Path.GetRelativePath(rootPath, path);
            return ToolResult.Fail(
                $"🛡️ Protected area: '{relPath}' is in a protected directory and cannot be deleted. " +
                $"Data in protected areas is append-only — it can only be added, not removed.");
        }

        var fileLock = GetFileLock(path);
        await fileLock.WaitAsync(ct);
        try
        {
            if (File.Exists(path))
            {
                var change = await BeforeChangeAsync(path, area, context, ct);
                File.Delete(path);
                await AfterChangeAsync(change, FileAction.Delete, context, ct);
                return ToolResult.Ok($"[{area.Name} Workspace] File deleted: {area.Name}:/{Path.GetRelativePath(rootPath, path)}");
            }
            else if (Directory.Exists(path))
            {
                // #719: every file in it is a deletion of its own in the history.
                var changes = new List<FileChange?>();
                foreach (var file in Directory.EnumerateFiles(path, "*", SearchOption.AllDirectories))
                    changes.Add(await BeforeChangeAsync(file, area, context, ct));
                Directory.Delete(path, true);
                foreach (var change in changes)
                    await AfterChangeAsync(change, FileAction.Delete, context, ct);
                return ToolResult.Ok($"[{area.Name} Workspace] Directory deleted: {area.Name}:/{Path.GetRelativePath(rootPath, path)}");
            }

            return ToolResult.Fail($"File or directory not found in {area.Name} workspace.");
        }
        finally
        {
            fileLock.Release();
        }
    }

    private async Task<ToolResult> HandleCopyAsync(JsonElement input, string sourceRootPath, Area sourceArea, AgentToolContext context, CancellationToken ct)
    {
        var sourcePath = GetAndValidatePath(input, sourceRootPath, sourceArea, false, context);

        var requestedDestination = input.TryGetProperty("destinationWorkspace", out var dw) && dw.ValueKind == JsonValueKind.String
            ? dw.GetString()
            : null;
        var destRelPath = input.TryGetProperty("destinationPath", out var dp) ? dp.GetString() : null;

        if (string.IsNullOrWhiteSpace(destRelPath))
            return ToolResult.Fail("'destinationPath' is required for copy action.");

        var destArea = requestedDestination is null ? sourceArea : ResolveArea(requestedDestination, context);
        if (destArea is null)
            return ToolResult.Fail(UnknownWorkspace(requestedDestination!, context));
        if (string.IsNullOrWhiteSpace(destArea.Root))
            return ToolResult.Fail($"Configuration error: the folder of workspace '{destArea.Name}' is not defined.");

        var destRootPath = Path.GetFullPath(destArea.Root);

        if (!IsActionAllowed("write", destArea))
            return ToolResult.Fail($"Access denied: Writing to workspace '{destArea.Name}' is not allowed for this agent.");

        var destInput = JsonDocument.Parse(JsonSerializer.Serialize(new { path = destRelPath })).RootElement;
        var destPath = GetAndValidatePath(destInput, destRootPath, destArea, false, context);

        if (File.Exists(sourcePath))
        {
            // Schutz: Kein Überschreiben in geschützten Bereichen per Copy
            if (!CanOverrideProtection(destArea) && File.Exists(destPath) && IsPathProtected(destPath, destRootPath, destArea))
            {
                var relPath = Path.GetRelativePath(destRootPath, destPath);
                return ToolResult.Fail(
                    $"🛡️ Protected area: Destination file '{relPath}' already exists and cannot be overwritten.");
            }

            // Deadlock-sicheres Locking: Immer in alphabetischer Reihenfolge locken
            var srcNorm = NormalizePath(sourcePath);
            var dstNorm = NormalizePath(destPath);
            var first = string.Compare(srcNorm, dstNorm, StringComparison.Ordinal) <= 0
                ? GetFileLock(sourcePath) : GetFileLock(destPath);
            var second = string.Compare(srcNorm, dstNorm, StringComparison.Ordinal) <= 0
                ? GetFileLock(destPath) : GetFileLock(sourcePath);

            await first.WaitAsync(ct);
            try
            {
                await second.WaitAsync(ct);
                try
                {
                    // #720: copying over a file replaces it — the same check as a write.
                    if (await RefuseLostUpdateAsync(destPath, $"{destArea.Name}:/{Path.GetRelativePath(destRootPath, destPath).Replace('\\', '/')}", destArea, context, ct) is { } conflict)
                        return conflict;

                    var destDir = Path.GetDirectoryName(destPath);
                    if (destDir != null && !Directory.Exists(destDir)) Directory.CreateDirectory(destDir);
                    var change = await BeforeChangeAsync(destPath, destArea, context, ct);

                    await Task.Run(() => File.Copy(sourcePath, destPath, overwrite: !IsPathProtected(destPath, destRootPath, destArea)), ct);
                    NoteReplace(destPath, destArea, context);
                    await AfterChangeAsync(change, FileAction.Copy, context, ct);

                    var srcLabel = $"{sourceArea.Name}:/{Path.GetRelativePath(sourceRootPath, sourcePath)}";
                    var dstLabel = $"{destArea.Name}:/{Path.GetRelativePath(destRootPath, destPath)}";
                    return ToolResult.Ok($"File copied: {srcLabel} → {dstLabel}");
                }
                finally
                {
                    second.Release();
                }
            }
            finally
            {
                first.Release();
            }
        }
        else if (Directory.Exists(sourcePath))
        {
            // #720/#719: each file the copy would replace is checked and recorded like a single copy.
            var targets = Directory.EnumerateFiles(sourcePath, "*", SearchOption.AllDirectories)
                .Select(f => Path.Combine(destPath, Path.GetRelativePath(sourcePath, f)))
                .ToList();
            foreach (var target in targets)
            {
                var shown = $"{destArea.Name}:/{Path.GetRelativePath(destRootPath, target).Replace('\\', '/')}";
                if (await RefuseLostUpdateAsync(target, shown, destArea, context, ct) is { } conflict)
                    return conflict;
            }
            var changes = new List<FileChange?>();
            foreach (var target in targets)
                changes.Add(await BeforeChangeAsync(target, destArea, context, ct));

            await Task.Run(() => CopyDirectory(sourcePath, destPath), ct);

            foreach (var (target, change) in targets.Zip(changes))
            {
                NoteReplace(target, destArea, context);
                await AfterChangeAsync(change, FileAction.Copy, context, ct);
            }

            var srcLabel = $"{sourceArea.Name}:/{Path.GetRelativePath(sourceRootPath, sourcePath)}";
            var dstLabel = $"{destArea.Name}:/{Path.GetRelativePath(destRootPath, destPath)}";
            return ToolResult.Ok($"Directory copied: {srcLabel} → {dstLabel}");
        }

        return ToolResult.Fail("Source file or directory not found.");
    }

    // ═══════════════════════════════════════════════════
    //  STOCK DATABASE (Append-Only Wissensdatenbank)
    // ═══════════════════════════════════════════════════

    private static readonly JsonSerializerOptions StockJsonOpts = new()
    {
        WriteIndented = true,
        PropertyNameCaseInsensitive = true,
        Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping
    };

    private async Task<ToolResult> HandleStockAddAsync(JsonElement input, AgentToolContext context, CancellationToken ct)
    {
        // Pflichtfelder
        var ticker = (input.TryGetProperty("ticker", out var t) ? t.GetString() : null)?.Trim().ToUpperInvariant();
        if (string.IsNullOrWhiteSpace(ticker))
            return ToolResult.Fail("'ticker' is required for stock_add (e.g. 'NVDA', 'TSLA').");

        var category = (input.TryGetProperty("category", out var cat) ? cat.GetString() : null) ?? "other";
        var source = (input.TryGetProperty("source", out var src) ? src.GetString() : null) ?? "unknown";
        var title = (input.TryGetProperty("title", out var ttl) ? ttl.GetString() : null) ?? "";
        var content = input.TryGetProperty("content", out var cnt) ? cnt.GetString() : null;
        var data = input.TryGetProperty("data", out var d) ? d : (JsonElement?)null;

        if (string.IsNullOrWhiteSpace(title) && string.IsNullOrWhiteSpace(content) && data is null)
            return ToolResult.Fail("At least 'title', 'content', or 'data' must be specified.");

        // SharedWorkspace ist Pflicht für stocks
        var sharedRoot = context.SharedWorkspacePath;
        if (string.IsNullOrWhiteSpace(sharedRoot))
            return ToolResult.Fail("SharedWorkspace is not configured.");

        sharedRoot = Path.GetFullPath(sharedRoot);

        // Zugriffsprüfung
        if (ResolveArea(WorkspaceLayout.Shared, context) is not { } shared || !IsActionAllowed("stock_add", shared))
            return ToolResult.Fail("Access denied: Writing to SharedWorkspace is not allowed.");

        // Sanitize Ticker für Verzeichnisname
        var safeTicker = SanitizeFileName(ticker);
        var stockDir = Path.Combine(sharedRoot, "stocks", safeTicker);
        Directory.CreateDirectory(stockDir);

        // Timestamp-basierten Dateinamen generieren
        var now = DateTime.UtcNow;
        var timestamp = now.ToString("yyyyMMdd_HHmmss");
        var safeSource = SanitizeFileName(source);
        var fileName = $"{timestamp}_{category}_{safeSource}.json";
        var filePath = Path.Combine(stockDir, fileName);

        // Kollisionsvermeidung
        var counter = 1;
        while (File.Exists(filePath))
        {
            fileName = $"{timestamp}_{category}_{safeSource}_{counter}.json";
            filePath = Path.Combine(stockDir, fileName);
            counter++;
        }

        // Datenpunkt erstellen
        var entry = new Dictionary<string, object?>
        {
            ["id"] = $"{safeTicker}_{timestamp}_{category}_{safeSource}",
            ["ticker"] = ticker,
            ["category"] = category,
            ["source"] = source,
            ["title"] = title,
            ["timestamp"] = now.ToString("o"),
            ["agent"] = context.AgentId
        };

        if (!string.IsNullOrWhiteSpace(content))
            entry["content"] = content;

        if (data.HasValue)
            entry["data"] = data.Value;

        // Datenpunkt speichern
        var json = JsonSerializer.Serialize(entry, StockJsonOpts);
        var stockArea = new Area(WorkspaceLayout.Shared, sharedRoot, WorkspaceAccess.Write, []);
        var dataChange = await BeforeChangeAsync(filePath, stockArea, context, ct);
        await ClawdDotNet.Core.Storage.AtomicFile.WriteAllTextAsync(filePath, json, new UTF8Encoding(false), ct);
        await AfterChangeAsync(dataChange, FileAction.Create, context, ct);

        // _index.json aktualisieren (thread-safe via per-file SemaphoreSlim, append-only)
        var indexPath = Path.Combine(stockDir, "_index.json");
        var indexEntry = new Dictionary<string, object?>
        {
            ["file"] = fileName,
            ["category"] = category,
            ["source"] = source,
            ["title"] = title,
            ["timestamp"] = now.ToString("o"),
            ["agent"] = context.AgentId
        };

        int indexCount;

        var indexLock = GetFileLock(indexPath);
        await indexLock.WaitAsync(ct);
        try
        {
            List<Dictionary<string, object?>> index;
            if (File.Exists(indexPath))
            {
                try
                {
                    var existing = await File.ReadAllTextAsync(indexPath, ct);
                    index = JsonSerializer.Deserialize<List<Dictionary<string, object?>>>(existing, StockJsonOpts)
                        ?? [];
                }
                catch (JsonException)
                {
                    // Korrupter Index: Backup + Neustart
                    var backup = indexPath + $".bak_{now:yyyyMMdd_HHmmss}";
                    try { File.Copy(indexPath, backup, overwrite: true); } catch { /* best effort */ }
                    index = [];
                }
            }
            else
            {
                index = [];
            }

            index.Add(indexEntry);
            var indexChange = await BeforeChangeAsync(indexPath, stockArea, context, ct);
            // Atomar: Der Index ist die einzige Übersicht über die Datenpunkte —
            // eine halb geschriebene Datei wäre nicht wiederherstellbar.
            await ClawdDotNet.Core.Storage.AtomicFile.WriteAllTextAsync(
                indexPath, JsonSerializer.Serialize(index, StockJsonOpts), ct: ct);
            await AfterChangeAsync(indexChange, FileAction.Append, context, ct);

            // Den Stand hier festhalten, solange die Sperre noch gilt (B9). Vorher
            // wurde die Datei nach dem Freigeben ein zweites Mal gelesen und geparst:
            // ein paralleler stock_add konnte dazwischenschreiben, und die gemeldete
            // Zahl gehörte dann zu einem anderen Aufruf als die gemeldete Datei.
            // Innerhalb der Sperre ist der Zähler ohnehin bekannt.
            indexCount = index.Count;
        }
        finally
        {
            indexLock.Release();
        }

        var relPath = $"shared:/stocks/{safeTicker}/{fileName}";
        return ToolResult.Ok(
            $"✅ Data point added: {relPath}\n" +
            $"Ticker: {ticker} | Category: {category} | Source: {source}\n" +
            $"Title: {title}\n" +
            $"Index: {indexCount} entries for {ticker}");
    }

    private static string SanitizeFileName(string name)
    {
        var sanitized = name.Trim();
        foreach (var c in Path.GetInvalidFileNameChars())
            sanitized = sanitized.Replace(c, '_');
        return sanitized.Replace(' ', '_');
    }

    private static void CopyDirectory(string sourceDir, string destinationDir)
    {
        Directory.CreateDirectory(destinationDir);

        foreach (var file in Directory.GetFiles(sourceDir))
            File.Copy(file, Path.Combine(destinationDir, Path.GetFileName(file)), overwrite: true);

        foreach (var dir in Directory.GetDirectories(sourceDir))
            CopyDirectory(dir, Path.Combine(destinationDir, Path.GetFileName(dir)));
    }
}