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.rs

@@ -41,6 +41,8 @@ pub enum ToolCallDecision {
     Block(String),
     /// Allow the call but replace the tool input with *new_input*.
     ReplaceInput(Value),
+    /// Terminate the entire agent loop immediately (e.g. circuit breaker).
+    AbortLoop(String),
 }
 
 // ---------------------------------------------------------------------------
@@ -194,6 +196,25 @@ impl MiddlewareChain {
         Ok(ToolCallDecision::Allow)
     }
 
+    /// Run all `before_tool_call` hooks with mutable context.
+    pub async fn run_before_tool_call_mut(
+        &self,
+        ctx: &mut MiddlewareContext,
+        tool_name: &str,
+        tool_input: &Value,
+    ) -> Result<ToolCallDecision> {
+        for mw in &self.middlewares {
+            match mw.before_tool_call(ctx, tool_name, tool_input).await? {
+                ToolCallDecision::Allow => {}
+                other => {
+                    tracing::info!("[MiddlewareChain] '{}' decided {:?} for tool '{}'", mw.name(), other, tool_name);
+                    return Ok(other);
+                }
+            }
+        }
+        Ok(ToolCallDecision::Allow)
+    }
+
     /// Run all `after_tool_call` hooks in order.
     pub async fn run_after_tool_call(
         &self,
@@ -245,8 +266,13 @@ impl Default for MiddlewareChain {
 // ---------------------------------------------------------------------------
 
 pub mod compaction;
+pub mod dangling_tool;
 pub mod guardrail;
 pub mod loop_guard;
 pub mod memory;
 pub mod skill_index;
+pub mod subagent_limit;
+pub mod title;
 pub mod token_calibration;
+pub mod tool_error;
+pub mod tool_output_guard;