refactor(crates): kernel/generation module split + DeerFlow optimizations + middleware + dead code cleanup

- Split zclaw-kernel/kernel.rs (1486 lines) into 9 domain modules
- Split zclaw-kernel/generation.rs (1080 lines) into 3 modules
- Add DeerFlow-inspired middleware: DanglingTool, SubagentLimit, ToolError, ToolOutputGuard
- Add PromptBuilder for structured system prompt assembly
- Add FactStore (zclaw-memory) for persistent fact extraction
- Add task builtin tool for agent task management
- Driver improvements: Anthropic/OpenAI extended thinking, Gemini safety settings
- Replace let _ = with proper log::warn! across SaaS handlers
- Remove unused dependency (url) from zclaw-hands

crates/zclaw-runtime/src/middleware/title.rs

@@ -5,22 +5,29 @@
 //! "新对话" or truncating the user's first message.
 //!
 //! Priority 180 — runs after compaction (100) and memory (150), before skill index (200).
+//!
+//! NOTE: This is a structural placeholder. Full implementation requires an LLM driver
+//! reference to generate titles asynchronously, which will be wired through the
+//! middleware context in a future iteration. For now it simply passes through.
 
 use async_trait::async_trait;
-use zclaw_types::Result;
-use crate::middleware::{AgentMiddleware, MiddlewareContext};
+use crate::middleware::{AgentMiddleware, MiddlewareDecision};
 
 /// Middleware that auto-generates conversation titles after the first exchange.
+///
+/// When fully implemented, this will:
+/// 1. Detect the first user-assistant exchange (via message count)
+/// 2. Call the LLM with a short prompt to generate a descriptive title
+/// 3. Update the session title via the middleware context
+///
+/// For now, it serves as a registered placeholder in the middleware chain.
 pub struct TitleMiddleware {
-    /// Whether a title has been generated for the current session.
-    titled: std::sync::atomic::AtomicBool,
+    _reserved: (),
 }
 
 impl TitleMiddleware {
     pub fn new() -> Self {
-        Self {
-            titled: std::sync::atomic::AtomicBool::new(false),
-        }
+        Self { _reserved: () }
     }
 }
 
@@ -34,4 +41,9 @@ impl Default for TitleMiddleware {
 impl AgentMiddleware for TitleMiddleware {
     fn name(&self) -> &str { "title" }
     fn priority(&self) -> i32 { 180 }
+
+    // All hooks default to Continue — placeholder until LLM driver is wired in.
+    async fn before_completion(&self, _ctx: &mut crate::middleware::MiddlewareContext) -> zclaw_types::Result<MiddlewareDecision> {
+        Ok(MiddlewareDecision::Continue)
+    }
 }