feat: add design_prompt meta-prompt for implementation planningv0.21.0

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

3 files changed, 87 insertions, 5 deletions

diff --git a/docs/mcp-prompts.md b/docs/mcp-prompts.md
index 777af5b..260760b 100644
--- a/docs/mcp-prompts.md
+++ b/docs/mcp-prompts.md
@@ -203,6 +203,61 @@ Claude: (Updates the prompt using MCP prompts/update)
 
 **Tags**: meta, prompt-management, interactive
 
+### design_prompt
+Interactively design a brand new prompt template from scratch with minimal questions.
+
+**How it works**:
+1) Claude asks what the prompt should do (1-2 sentences)
+2) Claude asks what arguments it needs (if any)
+3) Claude asks for metadata (name, title, tags)
+4) Claude shows a preview of the complete prompt
+5) After you approve, Claude saves it using the MCP prompts/create method
+
+**Arguments**: None (fully interactive)
+
+**Usage Example**:
+```
+You: /design_prompt
+
+Claude: What should this prompt do?
+
+You: Review database schemas and suggest optimizations for performance and best practices
+
+Claude: What arguments does it need?
+
+You: schema (required), db_type (optional)
+
+Claude: Prompt name, title, and tags?
+
+You: Name: review_db_schema
+     Title: Database Schema Review
+     Tags: database, schema, review
+
+Claude: Here's your prompt:
+
+        ```json
+        {
+          "name": "review_db_schema",
+          "title": "Database Schema Review",
+          "description": "Review database schemas and suggest optimizations for performance and best practices",
+          "arguments": [
+            {"name": "schema", "required": true},
+            {"name": "db_type", "required": false}
+          ],
+          "messages": [...],
+          "tags": ["database", "schema", "review"]
+        }
+        ```
+
+        Should I save this?
+
+You: Yes
+
+Claude: (Saves the prompt using MCP prompts/create)
+```
+
+**Tags**: meta, prompt-management, interactive, creation
+
 **Note**: Built-in prompts (including these meta-prompts) cannot be modified or deleted. If you need to customize a built-in, create a new prompt with a different name.
 
 ## Creating Custom Prompts
diff --git a/internal/promptstore/default_prompts.go b/internal/promptstore/default_prompts.go
index acfbe9a..f8edefc 100644
--- a/internal/promptstore/default_prompts.go
+++ b/internal/promptstore/default_prompts.go
@@ -6,8 +6,8 @@ import (
 )
 
 // DefaultPrompts returns the built-in meta-prompts for prompt management.
-// These prompts help users create and update prompts interactively using Claude's
-// access to conversation context.
+// These prompts help users create, update, delete, and design prompts interactively
+// using Claude's access to conversation context.
 func DefaultPrompts() []Prompt {
 	now := time.Now()
 
@@ -181,5 +181,32 @@ Ask me to confirm the deletion of '{{prompt_name}}'.`,
 			Created: now,
 			Updated: now,
 		},
+		{
+			Name:        "design_prompt",
+			Title:       "Design New Prompt from Scratch",
+			Description: "Interactively design a brand new prompt template through guided questions. Claude will help you define the purpose, arguments, message flow, and metadata step by step, show a preview, and wait for approval before saving.",
+			Arguments:   []PromptArgument{},
+			Messages: []PromptMessage{
+				{
+					Role: "user",
+					Content: MessageContent{
+						Type: "text",
+						Text: `I want to design a brand new prompt template from scratch.
+
+Please ask me:
+1) What should this prompt do? (describe the task/purpose in 1-2 sentences)
+2) What arguments does it need? (if any - use {{argument}} syntax)
+3) Prompt name (lowercase, underscores only), title, and tags
+
+Then show me a preview and save it after I approve.
+
+Keep questions brief and focused.`,
+					},
+				},
+			},
+			Tags:    []string{"meta", "prompt-management", "interactive", "creation"},
+			Created: now,
+			Updated: now,
+		},
 	}
 }
diff --git a/internal/promptstore/store_test.go b/internal/promptstore/store_test.go
index 2c95ad7..1ec784a 100644
--- a/internal/promptstore/store_test.go
+++ b/internal/promptstore/store_test.go
@@ -84,9 +84,9 @@ func TestJSONLStore_List(t *testing.T) {
 		t.Fatalf("List() error = %v", err)
 	}
 
-	// Should have all prompts (7 user + 3 built-ins)
-	if len(prompts) != 10 {
-		t.Errorf("List() got %d prompts, want 10 (7 user + 3 built-ins)", len(prompts))
+	// Should have all prompts (7 user + 4 built-ins)
+	if len(prompts) != 11 {
+		t.Errorf("List() got %d prompts, want 11 (7 user + 4 built-ins)", len(prompts))
 	}
 
 	// No cursor for full list