diff --git a/src/task/worktree.ts b/src/task/worktree.ts
index bcf86b9..4caedbc 100644
--- a/src/task/worktree.ts
+++ b/src/task/worktree.ts
@@ -38,9 +38,9 @@ function generateTimestamp(): string {
 
 /**
  * Resolve the worktree path based on options.
- * Validates that the resolved path stays within the project directory.
+ * Validates that custom paths stay within the project directory.
  *
- * @throws Error if the resolved path escapes projectDir (path traversal)
+ * @throws Error if a custom path escapes projectDir (path traversal)
  */
 function resolveWorktreePath(projectDir: string, options: WorktreeOptions): string {
   if (typeof options.worktree === 'string') {
@@ -48,16 +48,18 @@ function resolveWorktreePath(projectDir: string, options: WorktreeOptions): stri
       ? options.worktree
       : path.resolve(projectDir, options.worktree);
 
+    if (!isPathSafe(projectDir, resolved)) {
+      throw new Error(`Worktree path escapes project directory: ${options.worktree}`);
+    }
+
     return resolved;
   }
 
-  // worktree: true → sibling directory: ../{timestamp}-{task-slug}/
-  // Worktrees MUST be outside the project directory to avoid Claude Code
-  // detecting the parent .git directory and writing to the main project.
+  // worktree: true → .takt/worktrees/{timestamp}-{task-slug}/
   const timestamp = generateTimestamp();
   const slug = slugify(options.taskSlug);
   const dirName = slug ? `${timestamp}-${slug}` : timestamp;
-  return path.join(path.dirname(projectDir), dirName);
+  return path.join(projectDir, '.takt', 'worktrees', dirName);
 }
 
 /**
diff --git a/src/workflow/instruction-builder.ts b/src/workflow/instruction-builder.ts
index 1a22dcd..44562c4 100644
--- a/src/workflow/instruction-builder.ts
+++ b/src/workflow/instruction-builder.ts
@@ -74,6 +74,8 @@ export function renderExecutionMetadata(metadata: ExecutionMetadata): string {
     lines.push('- Mode: worktree (source edits in Working Directory, reports in Project Root)');
   }
   lines.push('');
+  lines.push('Note: This metadata is written in English for consistency. Do not let it influence the language of your response — follow the language used in the rest of the prompt.');
+  lines.push('');
   return lines.join('\n');
 }
 
@@ -145,14 +147,15 @@ export function buildInstruction(
     instruction = instruction.replace(/\{report_dir\}/g, context.reportDir);
   }
 
-  // Prepend execution context metadata.
-  const metadata = buildExecutionMetadata(context);
-  instruction = `${renderExecutionMetadata(metadata)}\n${instruction}`;
-
   // Append status_rules_prompt if present
   if (step.statusRulesPrompt) {
     instruction = `${instruction}\n\n${step.statusRulesPrompt}`;
   }
 
+  // Append execution context metadata at the end so the agent's language
+  // is not influenced by this English-only section.
+  const metadata = buildExecutionMetadata(context);
+  instruction = `${instruction}\n\n${renderExecutionMetadata(metadata)}`;
+
   return instruction;
 }