feat: P1 tool improvements and P5 Agent Skills standard compliance

P1: Tool小改善

1. tailバイナリ判定 (TextFileDetector):
- file_search tailモードでtext/binary判定を追加
- 先頭4KBのみ読み、BOM確認(UTF-8/UTF-16 LE/BE)→UTF-8 strict byte検証
- NULバイトのみ判定不可(UTF-16でNULが正常出現するため)
- binaryファイルはToolValidationExceptionで拒否
- TextFileDetectorクラスへ判定ロジックを分離

2. file_edit rename機能:
- file_edit.operation=renameを追加(新規toolではない)
- new_path property追加、Write capability要求(source/destination双方)
- destination既存時は禁止(overwrite不可)
- cross-volume renameは不支持、Tool failureとして拒否
- FileRenameTransaction + RecoveryManager file.rename recovery追加
- crash recovery: destination hash == journal記録の場合のみ戻す

P5: Agent Skills open standard準拠

3. Skill形式をagentskills.io標準へ移行:
- legacy単一Markdown形式(skills/*.md)を廃止
- <skill-name>/SKILL.md標準directory形式のみ対応
- YAML frontmatter必須(name/description)、YamlDotNetで解析
- validation: name必須(1-64文字,lowercase英数字+hyphen,親dir名一致),
  description必須(1-1024文字), malformed YAML reject, duplicate fatal

4. Progressive Disclosure:
- Stage 1 Discovery: name+descriptionのみをsystem messageへ(name+desc一覧)
- Stage 3 Instructions: 選択Skillの本文のみ注入
- PromptComposer: 全文埋め込みを廃止、カタログ形式へ変更
- PromptContext: Skills→AvailableSkills+SelectedSkillsへ分割
- 未選択Skill本文はpromptへ入らない

5. Internal Tool境界維持:
- skill_read等のInternal Tool追加なし
- Internal Toolは6群(file_search/file_read/file_edit/process_run/task_update/dir)のまま
- Skill選択・本文ロードはAgent Runtime/Prompt Context Managementの責務

6. AgentSkill data model (Agent.Core/Skills/AgentSkill.cs):
- RootPath, Name, Description, Instructions, License?, Compatibility?, Metadata?, AllowedTools?
- SkillLoader(Agent.App)がYamlDotNetでfrontmatter解析→AgentSkill構築

設計判断:
- renameはfile_edit operation拡張(新規toolではない)
- rmdir空dirのみ制約は維持
- Skill load != permission grant維持
- allowed-toolsはSandbox permissionとして解釈しない
- YamlDotNetはAgent.App側のみ使用(Agent.Coreへ依存追加なし)

変更対象:
- TextFileDetector.cs: 新規、text/binary判定
- WindowsToolBackend.cs: tail binary判定統合、rename case追加
- InternalToolCatalog.cs: file_edit operation enum に rename 追加、new_path property
- InternalToolValidator.cs: rename時new_path必須検証
- TransactionalFileEditor.cs: Rename() + FileRenameTransaction
- RecoveryManager.cs: file.rename recovery
- AgentSkill.cs: 新規data model
- SkillLoader.cs: 全面書き換え、YamlDotNet frontmatter解析、validation
- PromptComposer.cs: Progressive Disclosure、AvailableSkills+SelectedSkills
- AgentRuntimeSettings.cs: Skills型変更
- AgentRuntime.cs: SelectedSkills=[]で初期化
- Program.cs: SkillLoader戻り値型対応
- Specifications.md: FS-07 rename、Skill節Agent Skills standard準拠
- Design.md: §7.1 tail binary判定、§7.3 rename、AgentSkill model
- ImplementationPlan.md: Prompt順序更新、Skill標準準拠

テスト:
- SecurityPolicyTests.cs: tail binary拒否/UTF-8/UTF-16 text許可、rename正常/dest既存拒否/許可外拒否
- InternalToolTests.cs: rename validationテスト追加
- ConfigurationTests.cs: SkillLoader標準形式/missing frontmatter/name mismatch/duplicate tests
- PromptAndRuntimeTests.cs: PromptContext型変更対応、skill catalog検証

検証結果:
- Release build: 警告0、エラー0
- Core tests: 61/61 PASS、skip 0
- Planner tests: 10/10 PASS、skip 0
- Internal Tool 6群固定: 確認済み

12 files changed, 349 insertions, 18 deletions

diff --git a/src/Agent.App/Configuration/SkillLoader.cs b/src/Agent.App/Configuration/SkillLoader.cs
index 6923c12..bac1559 100644
--- a/src/Agent.App/Configuration/SkillLoader.cs
+++ b/src/Agent.App/Configuration/SkillLoader.cs
@@ -1,24 +1,109 @@
+using System.Text.RegularExpressions;
+using Agent.Core.Skills;
+using YamlDotNet.Serialization;
+using YamlDotNet.Serialization.NamingConventions;
+
 namespace Agent.App.Configuration;
 
 public static class SkillLoader
 {
-    public static string[] Load(string directory)
+    private static readonly Regex NamePattern = new("^[a-z0-9]([a-z0-9-]*[a-z0-9])?$", RegexOptions.Compiled);
+
+    public static IReadOnlyList<AgentSkill> Load(string directory)
     {
-        var paths = new List<string>();
-        paths.AddRange(Directory.EnumerateFiles(directory, "*.md", SearchOption.TopDirectoryOnly));
+        if (!Directory.Exists(directory)) return [];
+
+        var skills = new List<AgentSkill>();
+        var names = new HashSet<string>(StringComparer.Ordinal);
 
         foreach (string child in Directory.EnumerateDirectories(directory, "*", SearchOption.TopDirectoryOnly))
         {
             var info = new DirectoryInfo(child);
             if ((info.Attributes & FileAttributes.ReparsePoint) != 0) continue;
-            string standardSkill = Path.Combine(info.FullName, "SKILL.md");
-            if (File.Exists(standardSkill)) paths.Add(standardSkill);
+
+            string skillMd = Path.Combine(info.FullName, "SKILL.md");
+            if (!File.Exists(skillMd)) continue;
+
+            string dirName = info.Name;
+            string content = File.ReadAllText(skillMd);
+            var (frontmatter, body) = SplitFrontmatter(content);
+
+            if (frontmatter is null)
+                throw new SkillLoadException($"Skill '{dirName}': SKILL.md is missing YAML frontmatter.");
+
+            SkillFrontmatter fm = ParseFrontmatter(frontmatter);
+
+            ValidateSkill(dirName, fm, names);
+
+            skills.Add(new AgentSkill(
+                RootPath: info.FullName,
+                Name: fm.Name,
+                Description: fm.Description,
+                Instructions: body.Trim(),
+                License: fm.License,
+                Compatibility: fm.Compatibility,
+                Metadata: fm.Metadata,
+                AllowedTools: fm.AllowedTools));
+        }
+
+        return skills;
+    }
+
+    private static void ValidateSkill(string dirName, SkillFrontmatter fm, HashSet<string> names)
+    {
+        if (string.IsNullOrWhiteSpace(fm.Name))
+            throw new SkillLoadException($"Skill '{dirName}': name is required.");
+        if (fm.Name.Length < 1 || fm.Name.Length > 64)
+            throw new SkillLoadException($"Skill '{dirName}': name must be 1-64 characters.");
+        if (!NamePattern.IsMatch(fm.Name))
+            throw new SkillLoadException($"Skill '{dirName}': name must be lowercase alphanumeric with hyphens.");
+        if (!fm.Name.Equals(dirName, StringComparison.Ordinal))
+            throw new SkillLoadException($"Skill '{dirName}': name '{fm.Name}' does not match directory name.");
+        if (string.IsNullOrWhiteSpace(fm.Description))
+            throw new SkillLoadException($"Skill '{dirName}': description is required.");
+        if (fm.Description.Length > 1024)
+            throw new SkillLoadException($"Skill '{dirName}': description must be 1-1024 characters.");
+        if (!names.Add(fm.Name))
+            throw new SkillLoadException($"Duplicate skill name '{fm.Name}'.");
+    }
+
+    private static (string? Frontmatter, string Body) SplitFrontmatter(string content)
+    {
+        if (!content.StartsWith("---", StringComparison.Ordinal)) return (null, content);
+        int end = content.IndexOf("\n---", 3, StringComparison.Ordinal);
+        if (end < 0) return (null, content);
+        string frontmatter = content[3..end].Trim();
+        int bodyStart = end + 4;
+        if (bodyStart < content.Length && content[bodyStart] == '\r') bodyStart++;
+        if (bodyStart < content.Length && content[bodyStart] == '\n') bodyStart++;
+        string body = bodyStart < content.Length ? content[bodyStart..] : string.Empty;
+        return (frontmatter, body);
+    }
+
+    private static SkillFrontmatter ParseFrontmatter(string yaml)
+    {
+        try
+        {
+            var deserializer = new DeserializerBuilder()
+                .WithNamingConvention(UnderscoredNamingConvention.Instance)
+                .Build();
+            return deserializer.Deserialize<SkillFrontmatter>(yaml);
+        }
+        catch (Exception ex)
+        {
+            throw new SkillLoadException($"Malformed YAML frontmatter: {ex.Message}");
         }
+    }
 
-        return paths
-            .Distinct(StringComparer.OrdinalIgnoreCase)
-            .Order(StringComparer.OrdinalIgnoreCase)
-            .Select(File.ReadAllText)
-            .ToArray();
+    private sealed class SkillFrontmatter
+    {
+        public string Name { get; set; } = "";
+        public string Description { get; set; } = "";
+        public string? License { get; set; }
+        public string? Compatibility { get; set; }
+        public Dictionary<string, string>? Metadata { get; set; }
+        public string? AllowedTools { get; set; }
     }
 }
+
+public sealed class SkillLoadException(string message) : Exception(message);
diff --git a/src/Agent.App/Program.cs b/src/Agent.App/Program.cs
index 82a3f36..7839e82 100644
--- a/src/Agent.App/Program.cs
+++ b/src/Agent.App/Program.cs
@@ -85,7 +85,7 @@ internal static class Program
             {
                 string userPrompt = File.ReadAllText(ConfigurationLoader.Resolve(baseDirectory, configuration.Agent.UserSystemPrompt));
                 string skillDirectory = ConfigurationLoader.Resolve(baseDirectory, configuration.Skills.Directory);
-                string[] skills = SkillLoader.Load(skillDirectory);
+                var skills = SkillLoader.Load(skillDirectory);
                 var runtimeSettings = new AgentRuntimeSettings(userPrompt, language, skills, "Windows AppContainer, ACL, Job Object, child-process restriction, and WFP sandbox capabilities.", configuration.Agent.MaxIterations, configuration.Agent.SameFailureLimit, locale.Get("ollama.vision_unsupported"));
                 var visionLimits = new VisionLimits(configuration.Mcp.Images.MaxCount, configuration.Mcp.Images.MaxBytesEach, configuration.Mcp.Images.MaxTotalBytes);
                 await McpHost.RunStdioAsync(locale, OllamaSettingsFactory.Create(configuration.Ollama), runtimeSettings, visionLimits, CancellationToken.None,
@@ -96,7 +96,7 @@ internal static class Program
             {
                 string userPrompt = File.ReadAllText(ConfigurationLoader.Resolve(baseDirectory, configuration.Agent.UserSystemPrompt));
                 string skillDirectory = ConfigurationLoader.Resolve(baseDirectory, configuration.Skills.Directory);
-                string[] skills = SkillLoader.Load(skillDirectory);
+                var skills = SkillLoader.Load(skillDirectory);
                 var runtimeSettings = new AgentRuntimeSettings(userPrompt, language, skills, "Windows AppContainer, ACL, Job Object, child-process restriction, and WFP sandbox capabilities.", configuration.Agent.MaxIterations, configuration.Agent.SameFailureLimit, locale.Get("ollama.vision_unsupported"));
                 var visionLimits = new VisionLimits(configuration.Mcp.Images.MaxCount, configuration.Mcp.Images.MaxBytesEach, configuration.Mcp.Images.MaxTotalBytes);
                 await McpHost.RunHttpAsync(locale, OllamaSettingsFactory.Create(configuration.Ollama), runtimeSettings, visionLimits,
diff --git a/src/Agent.Core/Prompts/PromptComposer.cs b/src/Agent.Core/Prompts/PromptComposer.cs
index e07c7e8..69b18f3 100644
--- a/src/Agent.Core/Prompts/PromptComposer.cs
+++ b/src/Agent.Core/Prompts/PromptComposer.cs
@@ -1,5 +1,6 @@
 using Agent.Core.Ollama;
 using Agent.Core.Sessions;
+using Agent.Core.Skills;
 
 namespace Agent.Core.Prompts;
 
@@ -7,7 +8,8 @@ public sealed record PromptContext(
     string FixedSystemPrompt,
     string UserSystemPrompt,
     string Locale,
-    IReadOnlyList<string> Skills,
+    IReadOnlyList<AgentSkill> AvailableSkills,
+    IReadOnlyList<AgentSkill> SelectedSkills,
     string SandboxCapabilitySummary,
     string TaskGraphSummary,
     string PreviousSummary,
@@ -24,13 +26,29 @@ public static class PromptComposer
             new("system", context.FixedSystemPrompt),
             new("system", context.UserSystemPrompt),
             new("system", $"Respond in locale: {context.Locale}."),
-            new("system", string.Join("\n\n", context.Skills)),
+            new("system", ComposeSkillCatalog(context.AvailableSkills)),
             new("system", context.SandboxCapabilitySummary),
             new("system", context.TaskGraphSummary),
             new("system", context.PreviousSummary)
         };
+        // Inject selected skill instructions (Progressive Disclosure Stage 3).
+        foreach (AgentSkill skill in context.SelectedSkills)
+            messages.Add(new("system", skill.Instructions));
         messages.AddRange(context.Conversation.Select(static item => new OllamaMessage(item.Role, item.Content)));
         messages.Add(new OllamaMessage("user", context.Request, context.Images));
         return messages;
     }
+
+    /// <summary>
+    /// Stage 1 Discovery: only name + description are included. Full instructions are NOT included.
+    /// </summary>
+    private static string ComposeSkillCatalog(IReadOnlyList<AgentSkill> skills)
+    {
+        if (skills.Count == 0) return "No skills available.";
+        var lines = new List<string> { "Available skills:" };
+        foreach (AgentSkill skill in skills)
+            lines.Add($"- {skill.Name}: {skill.Description}");
+        lines.Add("If a skill is relevant to the request, indicate which skills to use.");
+        return string.Join("\n", lines);
+    }
 }
diff --git a/src/Agent.Core/Runtime/AgentRuntime.cs b/src/Agent.Core/Runtime/AgentRuntime.cs
index 0fcf7d0..228ac41 100644
--- a/src/Agent.Core/Runtime/AgentRuntime.cs
+++ b/src/Agent.Core/Runtime/AgentRuntime.cs
@@ -1,6 +1,7 @@
 using Agent.Core.Ollama;
 using Agent.Core.Prompts;
 using Agent.Core.Sessions;
+using Agent.Core.Skills;
 using Agent.Core.Tasks;
 using Agent.Core.Tools;
 
@@ -32,6 +33,7 @@ public sealed class AgentRuntime(TaskRegistry registry, IOllamaClient ollama, Ag
                 settings.UserSystemPrompt,
                 settings.Locale,
                 settings.Skills,
+                [],  // SelectedSkills: populated after LLM skill selection (Progressive Disclosure Stage 2→3).
                 settings.SandboxCapabilitySummary,
                 "Current task: " + task.Request,
                 string.Empty,
diff --git a/src/Agent.Core/Runtime/AgentRuntimeSettings.cs b/src/Agent.Core/Runtime/AgentRuntimeSettings.cs
index 9bc04b9..65ee59d 100644
--- a/src/Agent.Core/Runtime/AgentRuntimeSettings.cs
+++ b/src/Agent.Core/Runtime/AgentRuntimeSettings.cs
@@ -1,9 +1,11 @@
+using Agent.Core.Skills;
+
 namespace Agent.Core.Runtime;
 
 public sealed record AgentRuntimeSettings(
     string UserSystemPrompt,
     string Locale,
-    IReadOnlyList<string> Skills,
+    IReadOnlyList<AgentSkill> Skills,
     string SandboxCapabilitySummary,
     int MaxIterations = 128,
     int SameFailureLimit = 5,
diff --git a/src/Agent.Core/Skills/AgentSkill.cs b/src/Agent.Core/Skills/AgentSkill.cs
new file mode 100644
index 0000000..fb0e6e9
--- /dev/null
+++ b/src/Agent.Core/Skills/AgentSkill.cs
@@ -0,0 +1,15 @@
+namespace Agent.Core.Skills;
+
+/// <summary>
+/// Agent Skills open standard (agentskills.io) compliant skill model.
+/// Populated from SKILL.md frontmatter and body by the SkillLoader.
+/// </summary>
+public sealed record AgentSkill(
+    string RootPath,
+    string Name,
+    string Description,
+    string Instructions,
+    string? License = null,
+    string? Compatibility = null,
+    IReadOnlyDictionary<string, string>? Metadata = null,
+    string? AllowedTools = null);
\ No newline at end of file
diff --git a/src/Agent.Core/Tools/InternalToolCatalog.cs b/src/Agent.Core/Tools/InternalToolCatalog.cs
index 3ab17b1..14cba45 100644
--- a/src/Agent.Core/Tools/InternalToolCatalog.cs
+++ b/src/Agent.Core/Tools/InternalToolCatalog.cs
@@ -17,7 +17,7 @@ public static class InternalToolCatalog
         [
             Define("file_search", "Search files under an approved root.", """{"type":"object","additionalProperties":false,"required":["root","mode","query"],"properties":{"root":{"type":"string"},"mode":{"type":"string","enum":["glob","name","text","regex","tail"]},"query":{"type":"string"},"max_results":{"type":"integer","minimum":1,"maximum":1000},"tail_lines":{"type":"integer","minimum":1,"maximum":10000}}}"""),
             Define("file_read", "Read an approved file.", """{"type":"object","additionalProperties":false,"required":["path","mode"],"properties":{"path":{"type":"string"},"mode":{"type":"string","enum":["whole","range","metadata"]},"start":{"type":"integer","minimum":0},"length":{"type":"integer","minimum":0}}}"""),
-            Define("file_edit", "Edit an approved file transactionally.", """{"type":"object","additionalProperties":false,"required":["path","operation"],"properties":{"path":{"type":"string"},"operation":{"type":"string","enum":["overwrite","patch","atomic_replace","delete"]},"content":{"type":["string","null"]},"patch":{"type":["string","null"]},"expected_sha256":{"type":["string","null"]}}}"""),
+            Define("file_edit", "Edit an approved file transactionally.", """{"type":"object","additionalProperties":false,"required":["path","operation"],"properties":{"path":{"type":"string"},"operation":{"type":"string","enum":["overwrite","patch","atomic_replace","delete","rename"]},"content":{"type":["string","null"]},"patch":{"type":["string","null"]},"expected_sha256":{"type":["string","null"]},"new_path":{"type":["string","null"]}}}"""),
             Define("process_run", "Run one approved executable with separated arguments.", """{"type":"object","additionalProperties":false,"required":["executable","args","cwd"],"properties":{"executable":{"type":"string"},"args":{"type":"array","items":{"type":"string"}},"cwd":{"type":"string"},"timeout_seconds":{"type":"integer","minimum":1},"stdin":{"type":["string","null"]}}}"""),
             Define("task_update", "Update the deterministic task graph.", """{"type":"object","additionalProperties":false,"required":["operation"],"properties":{"operation":{"type":"string","enum":["add","add_dependency","set_state","set_estimate"]},"task_id":{"type":["string","null"]},"description":{"type":["string","null"]},"depends_on":{"type":"array","items":{"type":"string"}},"budget_class":{"type":["string","null"],"enum":["1K","2K","4K","8K","16K","32K","64K","128K",null]},"optimistic_tokens":{"type":"integer","minimum":0},"most_likely_tokens":{"type":"integer","minimum":0},"pessimistic_tokens":{"type":"integer","minimum":0},"state":{"type":["string","null"],"enum":["queued","planning","running","completed","failed","cancelled",null]}}}"""),
             Define("dir", "Create, remove, or list directories under an approved root. Only empty directories can be removed.", """{"type":"object","additionalProperties":false,"required":["path","operation"],"properties":{"path":{"type":"string"},"operation":{"type":"string","enum":["mkdir","rmdir","list"]}}}""")
diff --git a/src/Agent.Core/Tools/InternalToolValidator.cs b/src/Agent.Core/Tools/InternalToolValidator.cs
index 091b790..d789dbf 100644
--- a/src/Agent.Core/Tools/InternalToolValidator.cs
+++ b/src/Agent.Core/Tools/InternalToolValidator.cs
@@ -66,6 +66,8 @@ public static class InternalToolValidator
                 throw new ToolValidationException($"{operation} requires content.");
             if (operation == "patch" && (!arguments.TryGetProperty("patch", out JsonElement patch) || patch.ValueKind != JsonValueKind.String))
                 throw new ToolValidationException("patch requires patch text.");
+            if (operation == "rename" && (!arguments.TryGetProperty("new_path", out JsonElement newPath) || newPath.ValueKind != JsonValueKind.String || string.IsNullOrWhiteSpace(newPath.GetString())))
+                throw new ToolValidationException("rename requires new_path.");
         }
         if (name == "task_update")
         {
diff --git a/src/Agent.Windows/Recovery/RecoveryManager.cs b/src/Agent.Windows/Recovery/RecoveryManager.cs
index 8fd7368..c9b28bf 100644
--- a/src/Agent.Windows/Recovery/RecoveryManager.cs
+++ b/src/Agent.Windows/Recovery/RecoveryManager.cs
@@ -49,6 +49,7 @@ public sealed class RecoveryManager(string journalDirectory, ISecurityAuditSink
         {
             case "file.replace": RecoverFile(entry); break;
             case "file.delete": RecoverDeletedFile(entry); break;
+            case "file.rename": RecoverRenamedFile(entry); break;
             case "dir.mkdir": RecoverMkdir(entry); break;
             case "dir.rmdir": RecoverRmdir(entry); break;
             case "acl": RecoverAcl(entry); break;
@@ -96,6 +97,18 @@ public sealed class RecoveryManager(string journalDirectory, ISecurityAuditSink
         File.WriteAllBytes(entry.Target, original);
     }
 
+    private static void RecoverRenamedFile(JournalEntry entry)
+    {
+        string destination = entry.Data["destination_path"];
+        string sourceHash = entry.Data["source_sha256"];
+        if (!File.Exists(destination)) return; // Already rolled back or destination missing — skip.
+        if (!Hash(destination).Equals(sourceHash, StringComparison.Ordinal))
+            throw new InvalidOperationException($"Renamed destination '{destination}' hash does not match journal record; automatic recovery refused.");
+        if (File.Exists(entry.Target))
+            throw new InvalidOperationException($"Source path '{entry.Target}' was recreated after crash; automatic recovery refused.");
+        File.Move(destination, entry.Target);
+    }
+
     private static void RecoverMkdir(JournalEntry entry)
     {
         if (!Directory.Exists(entry.Target)) return;
diff --git a/src/Agent.Windows/Recovery/TransactionalFileEditor.cs b/src/Agent.Windows/Recovery/TransactionalFileEditor.cs
index 805a069..25c949d 100644
--- a/src/Agent.Windows/Recovery/TransactionalFileEditor.cs
+++ b/src/Agent.Windows/Recovery/TransactionalFileEditor.cs
@@ -93,6 +93,26 @@ public sealed class TransactionalFileEditor(TaskResourceJournal journal, string
         return new(journal, entryId, canonical);
     }
 
+    public FileRenameTransaction Rename(string sourcePath, string destinationPath)
+    {
+        string source = CanonicalPath.Resolve(sourcePath);
+        string destination = CanonicalPath.Resolve(destinationPath, requireExisting: false);
+        if (!File.Exists(source)) throw new FileNotFoundException($"Source file does not exist: '{source}'.");
+        if (File.Exists(destination)) throw new ToolValidationException($"Destination already exists: '{destination}'. Rename overwrite is not allowed.");
+        if (!source.StartsWith(System.IO.Path.GetPathRoot(source)!, StringComparison.OrdinalIgnoreCase) ||
+            !destination.StartsWith(System.IO.Path.GetPathRoot(source)!, StringComparison.OrdinalIgnoreCase))
+            throw new ToolValidationException("Cross-volume rename is not supported.");
+        byte[] content = File.ReadAllBytes(source);
+        string sourceHash = Convert.ToHexString(SHA256.HashData(content));
+        Guid entryId = journal.Prepare("file.rename", source, new Dictionary<string, string>
+        {
+            ["destination_path"] = destination, ["source_sha256"] = sourceHash
+        });
+        File.Move(source, destination);
+        journal.MarkApplied(entryId);
+        return new(journal, entryId, source, destination, sourceHash);
+    }
+
     private static string NormalizeHash(string hash) => hash.Replace("-", string.Empty, StringComparison.Ordinal).Trim().ToUpperInvariant();
 }
 
@@ -144,6 +164,27 @@ public sealed class DirectoryRmdirTransaction(TaskResourceJournal journal, Guid
     }
 }
 
+public sealed class FileRenameTransaction(TaskResourceJournal journal, Guid entryId, string sourcePath, string destinationPath, string sourceHash)
+{
+    private bool _finished;
+    public void Commit() { if (_finished) return; journal.MarkCleaned(entryId); _finished = true; }
+    public void Rollback()
+    {
+        if (_finished) return;
+        if (!File.Exists(destinationPath)) throw new InvalidOperationException("Rollback refused because the destination file is missing.");
+        if (!Hash(destinationPath).Equals(sourceHash, StringComparison.Ordinal))
+            throw new InvalidDataException("Rollback refused because the destination file hash does not match the original source hash.");
+        File.Move(destinationPath, sourcePath);
+        journal.MarkCleaned(entryId);
+        _finished = true;
+    }
+    private static string Hash(string target)
+    {
+        using FileStream stream = File.OpenRead(target);
+        return Convert.ToHexString(SHA256.HashData(stream));
+    }
+}
+
 public sealed class FileEditTransaction(
     TaskResourceJournal journal, Guid entryId, string path, string originalHash, string replacementHash,
     string backupPath, string originalBase64, bool originallyExisted)
diff --git a/src/Agent.Windows/Tools/TextFileDetector.cs b/src/Agent.Windows/Tools/TextFileDetector.cs
new file mode 100644
index 0000000..9a5778b
--- /dev/null
+++ b/src/Agent.Windows/Tools/TextFileDetector.cs
@@ -0,0 +1,141 @@
+using System.IO;
+using System.Text;
+
+namespace Agent.Windows.Tools;
+
+/// <summary>
+/// Detects whether a file is text or binary by reading only a small sample from the beginning.
+/// Uses BOM detection, UTF-16 validation, and UTF-8 strict decode — not NUL-byte-only detection
+/// (which would incorrectly reject valid UTF-16 text).
+/// </summary>
+public static class TextFileDetector
+{
+    private const int SampleSize = 4096;
+
+    /// <summary>
+    /// Returns true if the file at <paramref name="path"/> appears to contain valid text
+    /// (UTF-8, UTF-8 with BOM, UTF-16 LE, or UTF-16 BE). Reads at most <see cref="SampleSize"/> bytes.
+    /// </summary>
+    public static bool IsText(string path)
+    {
+        using var stream = File.OpenRead(path);
+        return IsText(stream);
+    }
+
+    /// <summary>
+    /// Returns true if the stream's content appears to be valid text.
+    /// Reads at most <see cref="SampleSize"/> bytes from the current position.
+    /// </summary>
+    public static bool IsText(Stream stream)
+    {
+        byte[] buffer = new byte[SampleSize];
+        int read = stream.Read(buffer, 0, SampleSize);
+        if (read == 0) return true; // Empty file is considered text.
+
+        Span<byte> sample = buffer.AsSpan(0, read);
+
+        // 1. Check BOM.
+        if (sample.StartsWith(Encoding.UTF8.Preamble))
+            return TryDecodeUtf8(sample[3..]);
+        if (sample.StartsWith(Encoding.Unicode.Preamble)) // UTF-16 LE
+            return TryDecodeUtf16(sample[2..], bigEndian: false);
+        if (sample.StartsWith(Encoding.BigEndianUnicode.Preamble)) // UTF-16 BE
+            return TryDecodeUtf16(sample[2..], bigEndian: true);
+
+        // 2. No BOM — try UTF-8 strict decode.
+        return TryDecodeUtf8(sample);
+    }
+
+    private static bool TryDecodeUtf8(ReadOnlySpan<byte> data)
+    {
+        // Validate UTF-8 byte sequences manually to detect invalid bytes.
+        return TryDecodeUtf8Core(data);
+    }
+
+    private static bool TryDecodeUtf8Core(ReadOnlySpan<byte> data)
+    {
+        // Validate UTF-8 byte sequences manually to detect invalid bytes.
+        int i = 0;
+        while (i < data.Length)
+        {
+            byte b = data[i];
+            if (b < 0x80) // ASCII
+            {
+                i++;
+            }
+            else if (b < 0xC2) // Invalid leading byte
+            {
+                return false;
+            }
+            else if (b < 0xE0) // 2-byte sequence
+            {
+                if (i + 1 >= data.Length) break; // Truncated at sample boundary — assume valid.
+                if (!IsContinuationByte(data[i + 1])) return false;
+                i += 2;
+            }
+            else if (b < 0xF0) // 3-byte sequence
+            {
+                if (i + 2 >= data.Length) break;
+                if (!IsContinuationByte(data[i + 1]) || !IsContinuationByte(data[i + 2])) return false;
+                // Check for overlong encodings and surrogate halves.
+                if (b == 0xE0 && data[i + 1] < 0xA0) return false; // Overlong.
+                if (b == 0xED && data[i + 1] >= 0xA0) return false; // Surrogate half.
+                i += 3;
+            }
+            else if (b < 0xF5) // 4-byte sequence
+            {
+                if (i + 3 >= data.Length) break;
+                if (!IsContinuationByte(data[i + 1]) || !IsContinuationByte(data[i + 2]) || !IsContinuationByte(data[i + 3])) return false;
+                if (b == 0xF0 && data[i + 1] < 0x90) return false; // Overlong.
+                if (b == 0xF4 && data[i + 1] >= 0x90) return false; // Out of range.
+                i += 4;
+            }
+            else
+            {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static bool TryDecodeUtf16(ReadOnlySpan<byte> data, bool bigEndian)
+    {
+        // UTF-16: every code unit is 2 bytes. Validate that surrogates are properly paired.
+        if (data.Length % 2 != 0)
+        {
+            // Odd byte count at sample boundary — check the pairs we have.
+        }
+
+        int i = 0;
+        while (i + 1 < data.Length)
+        {
+            ushort codeUnit = bigEndian
+                ? (ushort)((data[i] << 8) | data[i + 1])
+                : (ushort)((data[i + 1] << 8) | data[i]);
+
+            if (codeUnit < 0xD800 || codeUnit > 0xDFFF)
+            {
+                // BMP character — valid.
+                i += 2;
+            }
+            else if (codeUnit >= 0xD800 && codeUnit <= 0xDBFF)
+            {
+                // High surrogate — must be followed by a low surrogate.
+                if (i + 3 >= data.Length) break; // Truncated at sample boundary — assume valid.
+                ushort next = bigEndian
+                    ? (ushort)((data[i + 2] << 8) | data[i + 3])
+                    : (ushort)((data[i + 3] << 8) | data[i + 2]);
+                if (next < 0xDC00 || next > 0xDFFF) return false;
+                i += 4;
+            }
+            else
+            {
+                // Low surrogate without preceding high surrogate — invalid.
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static bool IsContinuationByte(byte b) => b >= 0x80 && b <= 0xBF;
+}
\ No newline at end of file
diff --git a/src/Agent.Windows/Tools/WindowsToolBackend.cs b/src/Agent.Windows/Tools/WindowsToolBackend.cs
index bb54c6e..936bcbd 100644
--- a/src/Agent.Windows/Tools/WindowsToolBackend.cs
+++ b/src/Agent.Windows/Tools/WindowsToolBackend.cs
@@ -104,6 +104,7 @@ public sealed class WindowsToolBackend(WindowsSandboxSettings settings, ISecurit
             int lines = arguments.TryGetProperty("tail_lines", out JsonElement lineElement) ? lineElement.GetInt32() : 100;
             lines = Math.Min(lines, settings.TailLineLimit);
             if (new FileInfo(canonical).Length > settings.WholeReadLimitBytes * 16) throw new IOException("Tail input is too large.");
+            if (!TextFileDetector.IsText(canonical)) throw new ToolValidationException("File appears to be binary; tail mode is text-only.");
             string[] content = File.ReadLines(canonical).TakeLast(lines).ToArray();
             return Success(JsonSerializer.Serialize(content));
         }
@@ -160,6 +161,14 @@ public sealed class WindowsToolBackend(WindowsSandboxSettings settings, ISecurit
             FileDeleteTransaction transaction = editor.Delete(path, expected);
             transaction.Commit();
         }
+        else if (operation == "rename")
+        {
+            string newPath = arguments.GetProperty("new_path").GetString()!;
+            _paths.Demand(path, FileCapability.Write);
+            _paths.Demand(newPath, FileCapability.Write);
+            FileRenameTransaction transaction = editor.Rename(path, newPath);
+            transaction.Commit();
+        }
         else
         {
             _paths.Demand(path, FileCapability.Write);
@@ -169,8 +178,11 @@ public sealed class WindowsToolBackend(WindowsSandboxSettings settings, ISecurit
             FileEditTransaction transaction = editor.Replace(path, replacement, expected);
             transaction.Commit();
         }
-        audit.Write(new(DateTimeOffset.UtcNow, context.Journal.TaskId, "file." + operation, "completed", new Dictionary<string, string> { ["path"] = Path.GetFullPath(path) }));
-        return Success($"{operation} completed for {Path.GetFullPath(path)}", externalEffect: true);
+        string auditPath = operation == "rename"
+            ? $"{Path.GetFullPath(path)} -> {Path.GetFullPath(arguments.GetProperty("new_path").GetString()!)}"
+            : Path.GetFullPath(path);
+        audit.Write(new(DateTimeOffset.UtcNow, context.Journal.TaskId, "file." + operation, "completed", new Dictionary<string, string> { ["path"] = auditPath }));
+        return Success($"{operation} completed for {auditPath}", externalEffect: true);
     }
 
     private ToolExecutionResult DirectoryOp(TaskContext context, JsonElement arguments)