diff --git a/src/ClawdDotNet.App/AppHost.cs b/src/ClawdDotNet.App/AppHost.cs
index 1139ee5..ee6d2c1 100644
--- a/src/ClawdDotNet.App/AppHost.cs
+++ b/src/ClawdDotNet.App/AppHost.cs
@@ -214,6 +214,9 @@ public sealed class AppHost : IAsyncDisposable
     /// <summary>Agenten anlegen, entfernen, Werkzeuge zulassen und einstellen.</summary>
     public AgentAdministration AgentAdmin => _agentAdmin.Value;
 
+    /// <summary>#683: Units, moves, tool ceilings, unit-wide values. Stateless.</summary>
+    public OrgAdministration Organisation => new(this, LoggerFactory.CreateLogger("ClawdDotNet.App.Organisation"));
+
     /// <summary>Dienste der Instanz anlegen, entfernen, umschalten.</summary>
     public ServiceAdministration ServiceAdmin => _serviceAdmin.Value;
 
diff --git a/src/ClawdDotNet.App/Services/AgentAdministration.cs b/src/ClawdDotNet.App/Services/AgentAdministration.cs
index 877457f..905f07e 100644
--- a/src/ClawdDotNet.App/Services/AgentAdministration.cs
+++ b/src/ClawdDotNet.App/Services/AgentAdministration.cs
@@ -1,6 +1,7 @@
 using ClawdDotNet.Core.Config;
 using ClawdDotNet.Core.Instances;
 using ClawdDotNet.Core.Staging;
+using Microsoft.Extensions.Logging;
 
 namespace ClawdDotNet.App.Services;
 
@@ -9,7 +10,8 @@ public sealed record NewAgent(
     string AgentId,
     string DisplayName,
     string Model,
-    string Description = "");
+    string Description = "",
+    string? UnitId = null);
 
 /// <summary>
 /// Agenten anlegen, entfernen, ihre Werkzeuge zulassen und einstellen.
@@ -86,6 +88,10 @@ public sealed class AgentAdministration(AppHost host)
         if (Find(agentId) is not null)
             return AdminResult.Failure($"Ein Agent mit der ID '{agentId}' existiert bereits.");
 
+        var unitId = string.IsNullOrWhiteSpace(request.UnitId) ? null : request.UnitId.Trim();
+        if (unitId is not null && host.Organisation.Current().Unit(unitId) is null)
+            return AdminResult.Failure($"There is no unit '{unitId}'.");
+
         string agentDir;
 
         try
@@ -111,6 +117,14 @@ public sealed class AgentAdministration(AppHost host)
         config.Model = request.Model;
         config.Description = request.Description;
 
+        // #683: Placed into a unit, the agent starts with the unit's defaults.
+        if (unitId is not null)
+        {
+            config.UnitId = unitId;
+            config.UnitSinceUtc = DateTime.UtcNow;
+            host.Organisation.ApplyDefaultsToNewAgent(config);
+        }
+
         host.Directories.SaveAgentSettings(agentDir, config);
 
         host.Instance.Agents.Add(config);
@@ -181,6 +195,10 @@ public sealed class AgentAdministration(AppHost host)
 
         if (enabled)
         {
+            // #683: What the unit may not have, a member cannot be granted.
+            if (!agent.Tools.ContainsKey(toolName) && host.Organisation.CeilingRefusal(agent, toolName) is { } refused)
+                return AdminResult.Failure(refused);
+
             if (!agent.Tools.ContainsKey(toolName))
                 agent.Tools[toolName] = new Dictionary<string, object?>();
         }
@@ -278,6 +296,10 @@ public sealed class AgentAdministration(AppHost host)
         if (Find(agentId) is not { } agent)
             return AdminResult.Failure($"Kein Agent mit der ID '{agentId}'.");
 
+        // #683: Settings for a tool the agent does not have yet grant it — the ceiling applies.
+        if (!agent.Tools.ContainsKey(toolName) && host.Organisation.CeilingRefusal(agent, toolName) is { } refused)
+            return AdminResult.Failure(refused);
+
         // #641: Die Einstellungsmasken kennen die Rechte nicht und schreiben ein frisches
         // Woerterbuch. Ohne diese Uebernahme loeschte jedes Speichern still "erlaubt" und
         // "verboten" - und damit die Rechte des Agenten.
@@ -309,6 +331,22 @@ public sealed class AgentAdministration(AppHost host)
     /// </summary>
     public void Save()
     {
+        // #683: The desktop toggles tools directly on the configuration objects and only
+        // saves here. The ceiling is a rule of writing, so it is enforced here as well: a
+        // tool beyond it does not get saved.
+        var chart = host.Organisation.Current();
+        foreach (var agent in host.Instance.Agents)
+        {
+            if (chart.ToolCeiling(agent.UnitId) is not { } ceiling)
+                continue;
+            foreach (var tool in agent.Tools.Keys.Where(t => !ceiling.Contains(t)).ToList())
+            {
+                agent.Tools.Remove(tool);
+                host.LoggerFactory.CreateLogger("ClawdDotNet.App.Organisation").LogWarning(
+                    "Tool {Tool} removed from {AgentId}: beyond the tool ceiling of its unit", tool, agent.AgentId);
+            }
+        }
+
         foreach (var agent in host.Instance.Agents)
             PersistAgent(agent);
 
@@ -329,7 +367,7 @@ public sealed class AgentAdministration(AppHost host)
     /// werden sie gelesen, und was in <c>AgentSettings.json</c> danebenstünde, überschriebe
     /// der nächste Ladevorgang ohnehin.</para>
     /// </summary>
-    private void PersistAgent(AgentConfig agent)
+    internal void PersistAgent(AgentConfig agent)
     {
         // Ein Agent ohne Verzeichnis ist einer aus einer von Hand gepflegten
         // Instanzdatei. Ihm hier einen Ordner anzulegen waere eine Nebenwirkung des
diff --git a/src/ClawdDotNet.App/Services/OrgAdministration.cs b/src/ClawdDotNet.App/Services/OrgAdministration.cs
new file mode 100644
index 0000000..7dd0f84
--- /dev/null
+++ b/src/ClawdDotNet.App/Services/OrgAdministration.cs
@@ -0,0 +1,598 @@
+using System.Text.Json;
+using ClawdDotNet.Core.Audit;
+using ClawdDotNet.Core.Config;
+using ClawdDotNet.Core.Organisation;
+using Microsoft.Extensions.Logging;
+
+namespace ClawdDotNet.App.Services;
+
+/// <summary>A unit-wide value that can be written into the members (#683).</summary>
+public enum UnitSetting
+{
+    DailyCostUsd,
+    DailyTokens,
+    Model,
+    WhenExhausted
+}
+
+/// <summary>How a unit-wide number is turned into per-agent values.</summary>
+public enum UnitSettingMode
+{
+    /// <summary>Every agent gets the value ("each gets 10 $").</summary>
+    PerAgent,
+
+    /// <summary>The value is a total, split in proportion to the current values ("the unit gets 100 $").</summary>
+    Distribute
+}
+
+/// <summary>One line of a preview: what would change at one agent.</summary>
+public sealed record UnitSettingChange(
+    string AgentId,
+    string DisplayName,
+    string Current,
+    string Proposed,
+    bool Outlier,
+    bool SelectedByDefault);
+
+/// <summary>What a move or a lowered ceiling would do before it is done.</summary>
+public sealed record StructurePreview(
+    IReadOnlyList<string> AffectedAgents,
+    IReadOnlyDictionary<string, IReadOnlyList<string>> ToolsLost,
+    IReadOnlyList<string> Running,
+    IReadOnlyList<string> Problems)
+{
+    public bool CanApply => Running.Count == 0 && Problems.Count == 0;
+}
+
+/// <summary>
+/// #683: Units — create, rename, lead, move, limit — and unit-wide values written into the
+/// members. The rules live here, not in a user interface, so the WebUI and the desktop
+/// apply the same ones (like <see cref="AgentAdministration"/>).
+///
+/// <para><b>Three rules from the concept (section 3):</b></para>
+/// <list type="number">
+/// <item><b>No value overrides another at run time.</b> A unit-wide value is written into
+/// the agents after a preview; the unit keeps it only as the default for agents that join.
+/// Outliers — the specialist with a deliberately large budget — are marked and not
+/// selected by default.</item>
+/// <item><b>The tool ceiling is checked when writing.</b> A tool beyond it cannot be
+/// granted; lowering it removes the tools from the agents, after a preview.</item>
+/// <item><b>A move never happens under a running agent.</b> The concept says "with the
+/// instance stopped", so that no agent gets different rights in the middle of a run. The
+/// administration runs inside the instance and cannot stop it; it refuses while an affected
+/// agent runs, which serves the same purpose more narrowly.</item>
+/// </list>
+///
+/// <para>Every structural change is written to the audit log with its reason — a change of
+/// structure is a change of rights (#205, #641).</para>
+/// </summary>
+public sealed class OrgAdministration(AppHost host, ILogger logger)
+{
+    /// <summary>A value this far from the median of the others is an outlier.</summary>
+    public const decimal OutlierFactor = 3m;
+
+    private OrgChart Chart => OrgChart.From(host.Instance);
+
+    public OrgChart Current() => Chart;
+
+    // ─── units ───
+
+    public AdminResult CreateUnit(string id, string name, string? parentId, string? goal = null, string reason = "")
+    {
+        id = (id ?? "").Trim();
+        if (id.Length == 0 || id.Any(c => !(char.IsLetterOrDigit(c) || c is '-' or '_')))
+            return AdminResult.Failure("A unit id consists of letters, digits, '-' and '_'.");
+        if (string.IsNullOrWhiteSpace(name))
+            return AdminResult.Failure("A unit needs a name.");
+        if (Chart.Unit(id) is not null)
+            return AdminResult.Failure($"There is already a unit '{id}'.");
+        if (!string.IsNullOrWhiteSpace(parentId) && Chart.Unit(parentId) is null)
+            return AdminResult.Failure($"There is no unit '{parentId}' to put it under.");
+
+        host.Instance.Units.Add(new UnitConfig
+        {
+            Id = id,
+            Name = name.Trim(),
+            ParentId = string.IsNullOrWhiteSpace(parentId) ? null : parentId.Trim(),
+            Goal = goal?.Trim() ?? ""
+        });
+
+        Save(null, "unit_create", new { id, name, parentId, goal }, reason);
+        return AdminResult.Success($"Unit '{name.Trim()}' created.");
+    }
+
+    public AdminResult UpdateUnit(string unitId, string? name, string? goal, string reason = "")
+    {
+        if (FindUnit(unitId) is not { } unit)
+            return AdminResult.Failure($"There is no unit '{unitId}'.");
+
+        if (name is not null)
+        {
+            if (string.IsNullOrWhiteSpace(name))
+                return AdminResult.Failure("A unit needs a name.");
+            unit.Name = name.Trim();
+        }
+        if (goal is not null)
+            unit.Goal = goal.Trim();
+
+        Save(null, "unit_update", new { unitId, name, goal }, reason);
+        return AdminResult.Success($"Unit '{unit.Name}' updated.");
+    }
+
+    /// <summary>Only an empty unit can go — members and sub-units have to be moved first.</summary>
+    public AdminResult DeleteUnit(string unitId, string reason = "")
+    {
+        if (FindUnit(unitId) is not { } unit)
+            return AdminResult.Failure($"There is no unit '{unitId}'.");
+        var chart = Chart;
+        if (chart.MembersOf(unit.Id).Count > 0 || chart.Children(unit.Id).Count > 0)
+            return AdminResult.Failure($"Unit '{unit.Name}' still has members or sub-units. Move them first.");
+
+        host.Instance.Units.Remove(unit);
+        Save(null, "unit_delete", new { unitId }, reason);
+        return AdminResult.Success($"Unit '{unit.Name}' deleted.");
+    }
+
+    /// <summary>The lead must be a member of the unit. <c>null</c> leaves it without a lead.</summary>
+    public AdminResult SetLeader(string unitId, string? agentId, string reason = "")
+    {
+        if (FindUnit(unitId) is not { } unit)
+            return AdminResult.Failure($"There is no unit '{unitId}'.");
+
+        if (!string.IsNullOrWhiteSpace(agentId))
+        {
+            if (host.AgentAdmin.Find(agentId) is not { } agent)
+                return AdminResult.Failure($"There is no agent '{agentId}'.");
+            if (!string.Equals(agent.UnitId, unit.Id, StringComparison.OrdinalIgnoreCase))
+                return AdminResult.Failure($"'{agentId}' is not a member of '{unit.Name}'. Move it there first.");
+        }
+
+        unit.LeaderAgentId = string.IsNullOrWhiteSpace(agentId) ? null : agentId.Trim();
+        Save(null, "unit_lead", new { unitId, agentId }, reason);
+        return AdminResult.Success(unit.LeaderAgentId is null
+            ? $"'{unit.Name}' has no lead now; the lead above takes over."
+            : $"'{unit.LeaderAgentId}' leads '{unit.Name}'.");
+    }
+
+    // ─── moves ───
+
+    public StructurePreview PreviewMoveAgent(string agentId, string? targetUnitId)
+    {
+        var chart = Chart;
+        var problems = new List<string>();
+        if (chart.Agent(agentId) is null)
+            problems.Add($"There is no agent '{agentId}'.");
+        if (!string.IsNullOrWhiteSpace(targetUnitId) && chart.Unit(targetUnitId) is null)
+            problems.Add($"There is no unit '{targetUnitId}'.");
+
+        return Preview([agentId], NullIfEmpty(targetUnitId), movingUnit: null, problems);
+    }
+
+    /// <summary>
+    /// Moves an agent. Tools beyond the new unit's ceiling are removed only with
+    /// <paramref name="dropExcessTools"/> — otherwise the move is refused and says which.
+    /// A lead leaving its unit leaves it without a lead.
+    /// </summary>
+    public AdminResult MoveAgent(string agentId, string? targetUnitId, string reason, bool dropExcessTools = false)
+    {
+        targetUnitId = NullIfEmpty(targetUnitId);
+        var preview = PreviewMoveAgent(agentId, targetUnitId);
+        if (Refusal(preview, dropExcessTools) is { } refused)
+            return refused;
+
+        var agent = host.AgentAdmin.Find(agentId)!;
+        if (string.Equals(agent.UnitId, targetUnitId, StringComparison.OrdinalIgnoreCase))
+            return AdminResult.Success($"'{agentId}' is already there.");
+
+        var from = agent.UnitId;
+        if (FindUnit(from) is { } oldUnit
+            && string.Equals(oldUnit.LeaderAgentId, agentId, StringComparison.OrdinalIgnoreCase))
+            oldUnit.LeaderAgentId = null;
+
+        DropTools(preview);
+        agent.PreviousUnitId = from;
+        agent.UnitId = targetUnitId;
+        agent.UnitSinceUtc = DateTime.UtcNow;
+        host.AgentAdmin.PersistAgent(agent);
+
+        Save(agentId, "agent_move", new { agentId, from, to = targetUnitId, toolsLost = preview.ToolsLost }, reason);
+        return AdminResult.Success($"'{agentId}' moved to {Describe(targetUnitId)}.");
+    }
+
+    public StructurePreview PreviewMoveUnit(string unitId, string? newParentId)
+    {
+        var chart = Chart;
+        var problems = new List<string>();
+        newParentId = NullIfEmpty(newParentId);
+
+        if (chart.Unit(unitId) is null)
+            problems.Add($"There is no unit '{unitId}'.");
+        else if (newParentId is not null)
+        {
+            if (chart.Unit(newParentId) is null)
+                problems.Add($"There is no unit '{newParentId}'.");
+            else if (string.Equals(newParentId, unitId, StringComparison.OrdinalIgnoreCase)
+                     || chart.Ancestors(newParentId).Any(u => string.Equals(u.Id, unitId, StringComparison.OrdinalIgnoreCase)))
+                problems.Add("A unit cannot be moved under itself or one of its own sub-units.");
+        }
+
+        var agents = Subtree(chart, unitId).SelectMany(u => chart.MembersOf(u.Id)).Select(a => a.AgentId).ToList();
+        return Preview(agents, targetUnitId: null, movingUnit: (unitId, newParentId), problems);
+    }
+
+    /// <summary>
+    /// Moves a unit with everything in it. Its members keep their unit; what changes is
+    /// what lies above — leads, reach and possibly the tool ceiling.
+    /// </summary>
+    public AdminResult MoveUnit(string unitId, string? newParentId, string reason, bool dropExcessTools = false)
+    {
+        newParentId = NullIfEmpty(newParentId);
+        var preview = PreviewMoveUnit(unitId, newParentId);
+        if (Refusal(preview, dropExcessTools) is { } refused)
+            return refused;
+
+        var unit = FindUnit(unitId)!;
+        var from = unit.ParentId;
+        DropTools(preview);
+        unit.ParentId = newParentId;
+
+        // The members changed position although not unit: tell them, like a move.
+        var now = DateTime.UtcNow;
+        foreach (var agentId in preview.AffectedAgents)
+        {
+            if (host.AgentAdmin.Find(agentId) is { } agent)
+            {
+                agent.UnitSinceUtc = now;
+                host.AgentAdmin.PersistAgent(agent);
+            }
+        }
+
+        Save(null, "unit_move", new { unitId, from, to = newParentId, toolsLost = preview.ToolsLost }, reason);
+        return AdminResult.Success($"Unit '{unit.Name}' moved under {Describe(newParentId)}.");
+    }
+
+    // ─── tool ceiling ───
+
+    public StructurePreview PreviewToolCeiling(string unitId, IReadOnlyCollection<string>? tools)
+    {
+        var chart = Chart;
+        var problems = new List<string>();
+        if (chart.Unit(unitId) is null)
+            problems.Add($"There is no unit '{unitId}'.");
+
+        var agents = Subtree(chart, unitId).SelectMany(u => chart.MembersOf(u.Id)).Select(a => a.AgentId).ToList();
+        return Preview(agents, targetUnitId: null, movingUnit: null, problems, ceiling: (unitId, tools));
+    }
+
+    /// <summary>
+    /// Sets the ceiling. Lowering it removes the tools beyond it from the members — shown by
+    /// <see cref="PreviewToolCeiling"/> first, and only with <paramref name="dropExcessTools"/>,
+    /// like a move. <c>null</c> lifts the ceiling.
+    /// </summary>
+    public AdminResult SetToolCeiling(
+        string unitId, IReadOnlyCollection<string>? tools, string reason, bool dropExcessTools = false)
+    {
+        var preview = PreviewToolCeiling(unitId, tools);
+        if (Refusal(preview, dropExcessTools) is { } refused)
+            return refused;
+
+        var unit = FindUnit(unitId)!;
+        DropTools(preview);
+        unit.ToolCeiling = tools?.Select(t => t.Trim()).Where(t => t.Length > 0)
+            .Distinct(StringComparer.OrdinalIgnoreCase).ToList();
+
+        Save(null, "unit_ceiling", new { unitId, tools = unit.ToolCeiling, toolsLost = preview.ToolsLost }, reason);
+        return AdminResult.Success(unit.ToolCeiling is null
+            ? $"'{unit.Name}' has no tool ceiling now."
+            : $"Tool ceiling of '{unit.Name}' set: {string.Join(", ", unit.ToolCeiling)}.");
+    }
+
+    /// <summary>
+    /// Whether an agent may be granted a tool — called by <see cref="AgentAdministration"/>
+    /// when writing. <c>null</c> means yes; otherwise the reason.
+    /// </summary>
+    public string? CeilingRefusal(AgentConfig agent, string toolName)
+    {
+        if (Chart.ToolCeiling(agent.UnitId) is not { } ceiling || ceiling.Contains(toolName))
+            return null;
+        return $"'{toolName}' is beyond the tool ceiling of the unit '{Chart.UnitOf(agent.AgentId)?.Name}'. " +
+               "Raise the ceiling of the unit or move the agent.";
+    }
+
+    // ─── unit-wide values ───
+
+    /// <summary>
+    /// What writing a unit-wide value would change, per agent below the unit (sub-units
+    /// included). Outliers are marked and not selected by default: the specialist with a
+    /// deliberately large budget must not be overwritten by accident.
+    /// </summary>
+    public IReadOnlyList<UnitSettingChange> PreviewSetting(
+        string unitId, UnitSetting setting, string value, UnitSettingMode mode = UnitSettingMode.PerAgent)
+    {
+        var chart = Chart;
+        if (chart.Unit(unitId) is null)
+            return [];
+
+        var agents = Subtree(chart, unitId).SelectMany(u => chart.MembersOf(u.Id)).ToList();
+        var numeric = setting is UnitSetting.DailyCostUsd or UnitSetting.DailyTokens;
+
+        if (!numeric)
+        {
+            return agents.Select(a => new UnitSettingChange(
+                a.AgentId, a.DisplayName, CurrentText(a, setting), value.Trim(), Outlier: false,
+                SelectedByDefault: true)).ToList();
+        }
+
+        if (!decimal.TryParse(value, System.Globalization.NumberStyles.Number,
+                System.Globalization.CultureInfo.InvariantCulture, out var number) || number < 0)
+            return [];
+
+        var current = agents.Select(a => CurrentNumber(a, setting)).ToList();
+        var outliers = OutlierFlags(current);
+
+        IReadOnlyList<decimal> proposed;
+        if (mode == UnitSettingMode.Distribute)
+        {
+            // In proportion to the current values, so a specialist keeps its larger share.
+            // Without any current values, evenly.
+            var sum = current.Sum();
+            proposed = current.Select(c => sum > 0 ? number * c / sum : agents.Count == 0 ? 0 : number / agents.Count).ToList();
+        }
+        else
+        {
+            proposed = current.Select(_ => number).ToList();
+        }
+
+        return agents.Select((a, i) => new UnitSettingChange(
+            a.AgentId, a.DisplayName,
+            Format(current[i], setting), Format(proposed[i], setting),
+            outliers[i], SelectedByDefault: !outliers[i])).ToList();
+    }
+
+    /// <summary>
+    /// Writes the values chosen from a preview into the agents, one audit entry each, and —
+    /// with <paramref name="rememberAsDefault"/> — keeps the value as the unit's default for
+    /// agents that join.
+    /// </summary>
+    public AdminResult ApplySetting(
+        string unitId, UnitSetting setting, IReadOnlyDictionary<string, string> valuesByAgent,
+        string reason, string? defaultValue = null)
+    {
+        if (FindUnit(unitId) is not { } unit)
+            return AdminResult.Failure($"There is no unit '{unitId}'.");
+
+        var chart = Chart;
+        var below = Subtree(chart, unitId).SelectMany(u => chart.MembersOf(u.Id))
+            .Select(a => a.AgentId).ToHashSet(StringComparer.OrdinalIgnoreCase);
+
+        var written = 0;
+        foreach (var (agentId, value) in valuesByAgent)
+        {
+            if (!below.Contains(agentId) || host.AgentAdmin.Find(agentId) is not { } agent)
+                return AdminResult.Failure($"'{agentId}' is not below '{unit.Name}'.");
+            if (Write(agent, setting, value) is { } invalid)
+                return AdminResult.Failure(invalid);
+
+            host.AgentAdmin.PersistAgent(agent);
+            Audit(agentId, "unit_setting", new { unitId, setting = setting.ToString(), value }, reason);
+            written++;
+        }
+
+        if (defaultValue is not null)
+            RememberDefault(unit, setting, defaultValue);
+
+        Save(null, "unit_setting_done", new { unitId, setting = setting.ToString(), written, defaultValue }, reason);
+        return AdminResult.Success($"{written} agent(s) in '{unit.Name}' updated.");
+    }
+
+    /// <summary>
+    /// Gives an agent that is new to a unit the unit's defaults — only then. A move does not
+    /// apply them: it would overwrite exactly the values an experienced agent was tuned to.
+    /// </summary>
+    public void ApplyDefaultsToNewAgent(AgentConfig agent)
+    {
+        if (FindUnit(agent.UnitId) is not { } unit)
+            return;
+        var d = unit.Defaults;
+        if (!string.IsNullOrWhiteSpace(d.Model)) agent.Model = d.Model;
+        if (d.DailyCostUsd is { } cost) agent.Budget.DailyCostUsd = cost;
+        if (d.DailyTokens is { } tokens) agent.Budget.DailyTokens = tokens;
+        if (!string.IsNullOrWhiteSpace(d.WhenExhausted)) agent.Budget.WhenExhausted = d.WhenExhausted;
+    }
+
+    // ─── helpers ───
+
+    private StructurePreview Preview(
+        IReadOnlyList<string> agents, string? targetUnitId, (string UnitId, string? NewParent)? movingUnit,
+        List<string> problems, (string UnitId, IReadOnlyCollection<string>? Tools)? ceiling = null)
+    {
+        // The structure as it would be afterwards — the ceiling is computed on that.
+        var units = host.Instance.Units.Select(Clone).ToList();
+        if (movingUnit is { } m && units.FirstOrDefault(u => Same(u.Id, m.UnitId)) is { } moved)
+            moved.ParentId = m.NewParent;
+        if (ceiling is { } c && units.FirstOrDefault(u => Same(u.Id, c.UnitId)) is { } limited)
+            limited.ToolCeiling = c.Tools?.ToList();
+
+        var after = new OrgChart(units, host.Instance.Agents);
+        var lost = new Dictionary<string, IReadOnlyList<string>>(StringComparer.OrdinalIgnoreCase);
+        foreach (var agentId in agents)
+        {
+            if (host.AgentAdmin.Find(agentId) is not { } agent)
+                continue;
+            // Moving an agent: its new unit. Moving a unit or setting a ceiling: every agent
+            // stays in its unit — what changes is the structure above it.
+            var unitAfter = movingUnit is null && ceiling is null ? targetUnitId : agent.UnitId;
+            if (after.ToolCeiling(unitAfter) is { } limit)
+            {
+                var beyond = agent.Tools.Keys.Where(t => !limit.Contains(t)).ToList();
+                if (beyond.Count > 0)
+                    lost[agentId] = beyond;
+            }
+        }
+
+        var running = (host.Engine?.Activity.ActiveRuns() ?? [])
+            .Select(r => r.AgentId)
+            .Where(id => agents.Contains(id, StringComparer.OrdinalIgnoreCase))
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList();
+
+        return new StructurePreview(agents, lost, running, problems);
+    }
+
+    private static AdminResult? Refusal(StructurePreview preview, bool dropExcessTools)
+    {
+        if (preview.Problems.Count > 0)
+            return AdminResult.Failure(string.Join(" ", preview.Problems));
+        if (preview.Running.Count > 0)
+            return AdminResult.Failure(
+                $"Not while {string.Join(", ", preview.Running)} run(s): an agent must not get different rights in the middle of a run. Try again when the run is over.");
+        if (preview.ToolsLost.Count > 0 && !dropExcessTools)
+            return AdminResult.Failure(
+                "The new position has a tool ceiling these agents are beyond: " +
+                string.Join("; ", preview.ToolsLost.Select(kv => $"{kv.Key}: {string.Join(", ", kv.Value)}")) +
+                ". Confirm to remove those tools, or raise the ceiling first.");
+        return null;
+    }
+
+    private void DropTools(StructurePreview preview)
+    {
+        foreach (var (agentId, tools) in preview.ToolsLost)
+        {
+            if (host.AgentAdmin.Find(agentId) is not { } agent)
+                continue;
+            foreach (var tool in tools)
+                agent.Tools.Remove(tool);
+            host.AgentAdmin.PersistAgent(agent);
+        }
+    }
+
+    private static IEnumerable<UnitConfig> Subtree(OrgChart chart, string unitId)
+    {
+        if (chart.Unit(unitId) is not { } root)
+            yield break;
+        var stack = new Stack<UnitConfig>([root]);
+        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        while (stack.Count > 0)
+        {
+            var unit = stack.Pop();
+            if (!seen.Add(unit.Id))
+                continue;
+            yield return unit;
+            foreach (var child in chart.Children(unit.Id))
+                stack.Push(child);
+        }
+    }
+
+    private static bool[] OutlierFlags(IReadOnlyList<decimal> values)
+    {
+        var flags = new bool[values.Count];
+        for (var i = 0; i < values.Count; i++)
+        {
+            var others = values.Where((_, j) => j != i && values[j] > 0).Order().ToList();
+            if (others.Count == 0 || values[i] <= 0)
+                continue;
+            var median = others[others.Count / 2];
+            flags[i] = values[i] >= median * OutlierFactor || values[i] <= median / OutlierFactor;
+        }
+        return flags;
+    }
+
+    private static decimal CurrentNumber(AgentConfig agent, UnitSetting setting) => setting switch
+    {
+        UnitSetting.DailyCostUsd => agent.Budget.DailyCostUsd,
+        UnitSetting.DailyTokens => agent.Budget.DailyTokens,
+        _ => 0
+    };
+
+    private static string CurrentText(AgentConfig agent, UnitSetting setting) => setting switch
+    {
+        UnitSetting.Model => agent.Model,
+        UnitSetting.WhenExhausted => agent.Budget.WhenExhausted,
+        _ => Format(CurrentNumber(agent, setting), setting)
+    };
+
+    private static string Format(decimal value, UnitSetting setting) => setting == UnitSetting.DailyTokens
+        ? decimal.Round(value).ToString(System.Globalization.CultureInfo.InvariantCulture)
+        : decimal.Round(value, 2).ToString("0.00", System.Globalization.CultureInfo.InvariantCulture);
+
+    private static string? Write(AgentConfig agent, UnitSetting setting, string value)
+    {
+        var inv = System.Globalization.CultureInfo.InvariantCulture;
+        switch (setting)
+        {
+            case UnitSetting.DailyCostUsd when decimal.TryParse(value, System.Globalization.NumberStyles.Number, inv, out var cost) && cost >= 0:
+                agent.Budget.DailyCostUsd = cost;
+                return null;
+            case UnitSetting.DailyTokens when long.TryParse(value, System.Globalization.NumberStyles.Number, inv, out var tokens) && tokens >= 0:
+                agent.Budget.DailyTokens = tokens;
+                return null;
+            case UnitSetting.Model when !string.IsNullOrWhiteSpace(value):
+                agent.Model = value.Trim();
+                return null;
+            case UnitSetting.WhenExhausted when value.Trim() is "expire" or "catchUpOnce":
+                agent.Budget.WhenExhausted = value.Trim();
+                return null;
+            default:
+                return $"'{value}' is not a valid value for {setting}.";
+        }
+    }
+
+    private static void RememberDefault(UnitConfig unit, UnitSetting setting, string value)
+    {
+        var inv = System.Globalization.CultureInfo.InvariantCulture;
+        switch (setting)
+        {
+            case UnitSetting.DailyCostUsd: unit.Defaults.DailyCostUsd = decimal.Parse(value, inv); break;
+            case UnitSetting.DailyTokens: unit.Defaults.DailyTokens = long.Parse(value, inv); break;
+            case UnitSetting.Model: unit.Defaults.Model = value.Trim(); break;
+            case UnitSetting.WhenExhausted: unit.Defaults.WhenExhausted = value.Trim(); break;
+        }
+    }
+
+    private UnitConfig? FindUnit(string? unitId)
+        => unitId is null ? null : host.Instance.Units.FirstOrDefault(u => Same(u.Id, unitId));
+
+    private string Describe(string? unitId)
+        => FindUnit(unitId) is { } unit ? $"'{unit.Name}'" : "the top level";
+
+    private static UnitConfig Clone(UnitConfig u) => new()
+    {
+        Id = u.Id, Name = u.Name, ParentId = u.ParentId, LeaderAgentId = u.LeaderAgentId,
+        Goal = u.Goal, ToolCeiling = u.ToolCeiling?.ToList(), Defaults = u.Defaults
+    };
+
+    private static bool Same(string? a, string? b) => string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
+
+    private static string? NullIfEmpty(string? value) => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+
+    private void Save(string? agentId, string action, object details, string reason)
+    {
+        host.SaveInstance(new InstanceChange(InstanceChangeKind.Agents, agentId));
+        Audit(agentId ?? "", action, details, reason);
+    }
+
+    private void Audit(string agentId, string action, object details, string reason)
+    {
+        if (host.AuditRepository is not { } audit)
+            return;
+        try
+        {
+            audit.AppendAsync(new AuditEntry
+            {
+                RunId = "",
+                AgentId = agentId,
+                Source = "admin",
+                Tool = "Organisation",
+                Arguments = JsonSerializer.Serialize(new { action, details }),
+                Status = AuditStatus.Ok,
+                Summary = string.IsNullOrWhiteSpace(reason) ? action : $"{action}: {reason.Trim()}",
+                OccurredAt = DateTime.UtcNow
+            }, CancellationToken.None).GetAwaiter().GetResult();
+        }
+        catch (Exception ex)
+        {
+            // The change itself is saved; a missing audit line must not undo it.
+            logger.LogError(ex, "Organisation change {Action} could not be written to the audit log", action);
+        }
+    }
+}
diff --git a/src/ClawdDotNet.Core/Config/AgentConfig.cs b/src/ClawdDotNet.Core/Config/AgentConfig.cs
index 39b2039..9c2d06a 100644
--- a/src/ClawdDotNet.Core/Config/AgentConfig.cs
+++ b/src/ClawdDotNet.Core/Config/AgentConfig.cs
@@ -21,6 +21,13 @@ public sealed class AgentConfig
     [JsonPropertyName("unitSinceUtc")]
     public DateTime? UnitSinceUtc { get; set; }
 
+    /// <summary>
+    /// #683: The unit the agent left with its last move — so the lead it left is told as
+    /// well as the one it joined. <c>null</c> after the first placement.
+    /// </summary>
+    [JsonPropertyName("previousUnitId")]
+    public string? PreviousUnitId { get; set; }
+
     [JsonPropertyName("model")]
     public string Model { get; set; } = "anthropic/claude-sonnet-4-5";
 
diff --git a/src/ClawdDotNet.Core/Organisation/OrgBriefing.cs b/src/ClawdDotNet.Core/Organisation/OrgBriefing.cs
index 5eda4f2..33fe1cb 100644
--- a/src/ClawdDotNet.Core/Organisation/OrgBriefing.cs
+++ b/src/ClawdDotNet.Core/Organisation/OrgBriefing.cs
@@ -73,6 +73,16 @@ public static class OrgBriefing
                 .ToList();
             if (joined.Count > 0)
                 sb.AppendLine("New in your unit: " + string.Join(", ", joined.Select(m => $"{m.AgentId} since {m.UnitSinceUtc:yyyy-MM-dd}")) + ".");
+
+            // The lead that was left is told as well as the one that was joined.
+            var left = org.Agents
+                .Where(a => string.Equals(a.PreviousUnitId, led.Id, StringComparison.OrdinalIgnoreCase)
+                            && a.UnitSinceUtc is { } s && nowUtc - s < RecentChange)
+                .ToList();
+            if (left.Count > 0)
+                sb.AppendLine("Left your unit recently: " + string.Join(", ", left.Select(a =>
+                    $"{a.AgentId} (now in {(org.UnitOf(a.AgentId) is { } u ? u.Name : "the top level")})")) +
+                    ". Hand over what is still open with them.");
         }
 
         var contacts = org.AddressBook(agentId)
diff --git a/src/ClawdDotNet.Core/Organisation/OrgChart.cs b/src/ClawdDotNet.Core/Organisation/OrgChart.cs
index b11693e..afc3060 100644
--- a/src/ClawdDotNet.Core/Organisation/OrgChart.cs
+++ b/src/ClawdDotNet.Core/Organisation/OrgChart.cs
@@ -64,6 +64,8 @@ public sealed class OrgChart
 
     public IReadOnlyCollection<UnitConfig> Units => _units.Values;
 
+    public IReadOnlyCollection<AgentConfig> Agents => _agents.Values;
+
     public UnitConfig? Unit(string? unitId)
         => unitId is not null && _units.TryGetValue(unitId, out var unit) ? unit : null;
 
diff --git a/tests/ClawdDotNet.App.Tests/Services/OrgAdministrationTests.cs b/tests/ClawdDotNet.App.Tests/Services/OrgAdministrationTests.cs
new file mode 100644
index 0000000..2b4eea4
--- /dev/null
+++ b/tests/ClawdDotNet.App.Tests/Services/OrgAdministrationTests.cs
@@ -0,0 +1,252 @@
+using ClawdDotNet.App.Services;
+using ClawdDotNet.Core.Config;
+using Shouldly;
+
+namespace ClawdDotNet.App.Tests.Services;
+
+/// <summary>
+/// #683: Units in the administration — create, lead, move, limit, write unit-wide values.
+/// </summary>
+public sealed class OrgAdministrationTests : IDisposable
+{
+    private readonly TestHost _test;
+
+    public OrgAdministrationTests()
+    {
+        _test = new TestHost(
+            Agent("marketing-lead", "WebFetch", "AgentComm", "Taskboard"),
+            Agent("ads", "WebFetch", "Taskboard"),
+            Agent("listing", "WebFetch", "Taskboard"),
+            Agent("specialist", "WebFetch", "Taskboard", "Database"),
+            Agent("bookkeeper", "Database", "Taskboard"));
+    }
+
+    public void Dispose() => _test.Dispose();
+
+    private static AgentConfig Agent(string id, params string[] tools)
+        => new() { AgentId = id, DisplayName = id, Tools = tools.ToDictionary(t => t, _ => new Dictionary<string, object?>()) };
+
+    private OrgAdministration Org => _test.Host.Organisation;
+
+    private AgentConfig Find(string id) => _test.Host.AgentAdmin.Find(id)!;
+
+    private void BuildMarketing()
+    {
+        Org.CreateUnit("marketing", "Marketing", null, "Sell more.").Ok.ShouldBeTrue();
+        Org.CreateUnit("amazon", "Amazon", "marketing").Ok.ShouldBeTrue();
+        Org.MoveAgent("marketing-lead", "marketing", "setup").Ok.ShouldBeTrue();
+        Org.SetLeader("marketing", "marketing-lead").Ok.ShouldBeTrue();
+        foreach (var id in new[] { "ads", "listing", "specialist" })
+            Org.MoveAgent(id, "amazon", "setup").Ok.ShouldBeTrue();
+    }
+
+    // ═══════════════════ units ═══════════════════
+
+    [Fact]
+    public void A_unit_needs_a_valid_id_a_name_and_an_existing_parent()
+    {
+        Org.CreateUnit("bad id", "X", null).Ok.ShouldBeFalse();
+        Org.CreateUnit("x", " ", null).Ok.ShouldBeFalse();
+        Org.CreateUnit("x", "X", "nowhere").Ok.ShouldBeFalse();
+        Org.CreateUnit("x", "X", null).Ok.ShouldBeTrue();
+        Org.CreateUnit("x", "Again", null).Ok.ShouldBeFalse("ids are unique");
+    }
+
+    [Fact]
+    public void Only_a_member_can_lead_a_unit()
+    {
+        Org.CreateUnit("marketing", "Marketing", null);
+
+        Org.SetLeader("marketing", "ads").Ok.ShouldBeFalse();
+        Org.MoveAgent("ads", "marketing", "join");
+        Org.SetLeader("marketing", "ads").Ok.ShouldBeTrue();
+    }
+
+    [Fact]
+    public void Only_an_empty_unit_can_be_deleted()
+    {
+        BuildMarketing();
+
+        Org.DeleteUnit("amazon").Ok.ShouldBeFalse("it has members");
+        foreach (var id in new[] { "ads", "listing", "specialist" })
+            Org.MoveAgent(id, null, "leave");
+        Org.DeleteUnit("amazon").Ok.ShouldBeTrue();
+    }
+
+    // ═══════════════════ moves ═══════════════════
+
+    [Fact]
+    public void A_move_records_since_when_and_where_from()
+    {
+        BuildMarketing();
+
+        Org.MoveAgent("ads", "marketing", "promoted").Ok.ShouldBeTrue();
+
+        var ads = Find("ads");
+        ads.UnitId.ShouldBe("marketing");
+        ads.PreviousUnitId.ShouldBe("amazon");
+        ads.UnitSinceUtc.ShouldNotBeNull();
+    }
+
+    [Fact]
+    public void A_lead_that_moves_leaves_its_unit_without_lead()
+    {
+        BuildMarketing();
+
+        Org.MoveAgent("marketing-lead", "amazon", "reorg").Ok.ShouldBeTrue();
+
+        Org.Current().LeaderOf("marketing").ShouldBeNull();
+    }
+
+    [Fact]
+    public void A_unit_cannot_be_moved_under_itself()
+    {
+        BuildMarketing();
+
+        Org.MoveUnit("marketing", "amazon", "oops").Ok.ShouldBeFalse();
+        Org.MoveUnit("marketing", "marketing", "oops").Ok.ShouldBeFalse();
+    }
+
+    [Fact]
+    public void A_moved_unit_takes_its_members_along_and_tells_them()
+    {
+        BuildMarketing();
+        Org.CreateUnit("marketplaces", "Marketplaces", "marketing");
+        var before = Find("ads").UnitSinceUtc;
+
+        Org.MoveUnit("amazon", "marketplaces", "a new level in between").Ok.ShouldBeTrue();
+
+        Find("ads").UnitId.ShouldBe("amazon", "the unit is the same");
+        Org.Current().PathOf("amazon").ShouldBe("Marketing / Marketplaces / Amazon");
+        Find("ads").UnitSinceUtc.ShouldNotBe(before, "the position changed, so the briefing says so");
+    }
+
+    // ═══════════════════ tool ceiling ═══════════════════
+
+    [Fact]
+    public void A_move_under_a_lower_ceiling_is_refused_until_confirmed()
+    {
+        BuildMarketing();
+        Org.SetToolCeiling("amazon", ["WebFetch", "Taskboard"], "no databases in ads").Ok.ShouldBeFalse(
+            "the specialist has Database — that has to be confirmed via the preview first");
+
+        var preview = Org.PreviewToolCeiling("amazon", ["WebFetch", "Taskboard"]);
+        preview.ToolsLost.Keys.ShouldBe(["specialist"]);
+        preview.ToolsLost["specialist"].ShouldBe(["Database"]);
+    }
+
+    [Fact]
+    public void Lowering_a_ceiling_removes_the_tools_beyond_it_from_the_members()
+    {
+        BuildMarketing();
+        Org.MoveAgent("specialist", null, "out first").Ok.ShouldBeTrue();
+
+        Org.SetToolCeiling("amazon", ["WebFetch", "Taskboard"], "no databases in ads").Ok.ShouldBeTrue();
+
+        // And from now on it cannot be granted.
+        var refused = _test.Host.AgentAdmin.SetToolEnabled("ads", "Database", true);
+        refused.Ok.ShouldBeFalse();
+        refused.Message.ShouldContain("ceiling");
+    }
+
+    [Fact]
+    public void Moving_into_a_ceiling_needs_the_tools_beyond_it_dropped_explicitly()
+    {
+        Org.CreateUnit("amazon", "Amazon", null);
+        Org.SetToolCeiling("amazon", ["WebFetch", "Taskboard"], "setup").Ok.ShouldBeTrue();
+
+        var refused = Org.MoveAgent("specialist", "amazon", "join");
+        refused.Ok.ShouldBeFalse();
+        refused.Message.ShouldContain("Database");
+        Find("specialist").UnitId.ShouldBeNull("nothing happened");
+
+        Org.MoveAgent("specialist", "amazon", "join", dropExcessTools: true).Ok.ShouldBeTrue();
+        Find("specialist").Tools.Keys.ShouldNotContain("Database");
+    }
+
+    [Fact]
+    public void A_ceiling_higher_up_limits_the_units_below()
+    {
+        BuildMarketing();
+        Org.MoveAgent("specialist", null, "out first");
+        Org.SetToolCeiling("marketing", ["WebFetch", "Taskboard", "AgentComm"], "setup").Ok.ShouldBeTrue();
+
+        _test.Host.AgentAdmin.SetToolEnabled("ads", "Database", true).Ok.ShouldBeFalse(
+            "amazon has no ceiling of its own, but marketing above it has");
+    }
+
+    // ═══════════════════ unit-wide values ═══════════════════
+
+    [Fact]
+    public void A_unit_wide_budget_marks_the_specialist_as_an_outlier_and_leaves_it_unselected()
+    {
+        BuildMarketing();
+        Find("ads").Budget.DailyCostUsd = 5;
+        Find("listing").Budget.DailyCostUsd = 4;
+        Find("specialist").Budget.DailyCostUsd = 40; // deliberately large
+        Find("marketing-lead").Budget.DailyCostUsd = 6;
+
+        var preview = Org.PreviewSetting("marketing", UnitSetting.DailyCostUsd, "10");
+
+        preview.Count.ShouldBe(4, "the unit and its sub-units");
+        var specialist = preview.Single(c => c.AgentId == "specialist");
+        specialist.Outlier.ShouldBeTrue();
+        specialist.SelectedByDefault.ShouldBeFalse();
+        preview.Where(c => c.AgentId != "specialist").ShouldAllBe(c => c.SelectedByDefault && c.Proposed == "10.00");
+    }
+
+    [Fact]
+    public void A_distributed_total_keeps_the_proportions()
+    {
+        BuildMarketing();
+        Find("ads").Budget.DailyCostUsd = 10;
+        Find("listing").Budget.DailyCostUsd = 10;
+        Find("specialist").Budget.DailyCostUsd = 20;
+        Find("marketing-lead").Budget.DailyCostUsd = 0;
+
+        var preview = Org.PreviewSetting("amazon", UnitSetting.DailyCostUsd, "80", UnitSettingMode.Distribute);
+
+        preview.Single(c => c.AgentId == "specialist").Proposed.ShouldBe("40.00");
+        preview.Single(c => c.AgentId == "ads").Proposed.ShouldBe("20.00");
+    }
+
+    [Fact]
+    public void Applying_writes_only_the_chosen_agents_and_remembers_the_default()
+    {
+        BuildMarketing();
+        Find("specialist").Budget.DailyCostUsd = 40;
+
+        var result = Org.ApplySetting("amazon", UnitSetting.DailyCostUsd,
+            new Dictionary<string, string> { ["ads"] = "10", ["listing"] = "10" }, "budget round", defaultValue: "10");
+
+        result.Ok.ShouldBeTrue(result.Message);
+        Find("ads").Budget.DailyCostUsd.ShouldBe(10);
+        Find("specialist").Budget.DailyCostUsd.ShouldBe(40, "not chosen, not touched");
+        Org.Current().Unit("amazon")!.Defaults.DailyCostUsd.ShouldBe(10);
+    }
+
+    [Fact]
+    public void An_agent_outside_the_unit_cannot_be_written_through_it()
+    {
+        BuildMarketing();
+
+        Org.ApplySetting("amazon", UnitSetting.DailyCostUsd,
+            new Dictionary<string, string> { ["bookkeeper"] = "1" }, "sneaky").Ok.ShouldBeFalse();
+    }
+
+    [Fact]
+    public void A_new_agent_placed_in_a_unit_starts_with_its_defaults_but_a_moved_one_keeps_its_values()
+    {
+        BuildMarketing();
+        Org.ApplySetting("amazon", UnitSetting.DailyCostUsd, new Dictionary<string, string>(), "defaults", defaultValue: "7");
+        Find("bookkeeper").Budget.DailyCostUsd = 30;
+
+        Org.MoveAgent("bookkeeper", "amazon", "moved").Ok.ShouldBeTrue();
+        Find("bookkeeper").Budget.DailyCostUsd.ShouldBe(30, "a move does not overwrite tuned values");
+
+        var created = _test.Host.AgentAdmin.Add(new NewAgent("newbie", "Newbie", "test/model", UnitId: "amazon"));
+        created.Ok.ShouldBeTrue(created.Message);
+        Find("newbie").Budget.DailyCostUsd.ShouldBe(7);
+        Find("newbie").UnitId.ShouldBe("amazon");
+    }
+}