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/prompt/builder.rs

@@ -0,0 +1,120 @@
+use std::fmt::Write;
+
+use crate::driver::ToolDefinition;
+
+/// Runtime context that determines which prompt sections are included.
+pub struct PromptContext {
+    /// Base system prompt from AgentConfig
+    pub base_prompt: Option<String>,
+    /// Custom agent personality (SOUL.md equivalent)
+    pub soul: Option<String>,
+    /// Whether thinking/extended reasoning is enabled
+    pub thinking_enabled: bool,
+    /// Whether plan mode is active
+    pub plan_mode: bool,
+    /// Tool definitions available for dynamic injection
+    pub tool_definitions: Vec<ToolDefinition>,
+    /// Agent name for personalization
+    pub agent_name: Option<String>,
+}
+
+/// A single section in the assembled prompt.
+pub struct PromptSection {
+    pub name: &'static str,
+    pub template: String,
+    pub priority: u32,
+}
+
+/// Builds structured system prompts from conditional sections.
+pub struct PromptBuilder {
+    sections: Vec<PromptSection>,
+}
+
+impl PromptBuilder {
+    pub fn new() -> Self {
+        Self {
+            sections: Vec::new(),
+        }
+    }
+
+    /// Add a section unconditionally.
+    pub fn add_section(
+        mut self,
+        name: &'static str,
+        template: impl Into<String>,
+        priority: u32,
+    ) -> Self {
+        self.sections.push(PromptSection {
+            name,
+            template: template.into(),
+            priority,
+        });
+        self
+    }
+
+    /// Assemble the final system prompt based on runtime context.
+    pub fn build(&self, ctx: &PromptContext) -> String {
+        let mut sections: Vec<&PromptSection> = self.sections.iter().collect();
+        sections.sort_by_key(|s| s.priority);
+
+        let mut result = String::with_capacity(4096);
+
+        // Base prompt (always included)
+        if let Some(ref base) = ctx.base_prompt {
+            result.push_str(base);
+        } else {
+            result.push_str("You are a helpful AI assistant.");
+        }
+
+        // Soul/personality section
+        if let Some(ref soul) = ctx.soul {
+            result.push_str("\n\n## Agent Personality\n\n");
+            result.push_str(soul);
+        }
+
+        // Agent name personalization
+        if let Some(ref name) = ctx.agent_name {
+            let _ = write!(result, "\n\nYou are known as \"{name}\". Respond in character.");
+        }
+
+        // Dynamic tool descriptions
+        if !ctx.tool_definitions.is_empty() {
+            result.push_str("\n\n## Available Tools\n\n");
+            for tool in &ctx.tool_definitions {
+                let _ = writeln!(result, "- **{}**: {}", tool.name, tool.description);
+            }
+        }
+
+        // Thinking style guidance
+        if ctx.thinking_enabled {
+            result.push_str("\n\n## Reasoning Mode\n\n");
+            result.push_str(
+                "Extended reasoning is enabled. Think step-by-step before responding. \
+                 Show your reasoning process, then provide the final answer.",
+            );
+        }
+
+        // Plan mode instructions
+        if ctx.plan_mode {
+            result.push_str("\n\n## Plan Mode\n\n");
+            result.push_str(
+                "You are in plan mode. Before executing any actions, create a detailed plan. \
+                 Present the plan to the user for approval before proceeding.",
+            );
+        }
+
+        // Additional registered sections
+        for section in sections {
+            result.push_str("\n\n");
+            result.push_str(&section.template);
+        }
+
+        result
+    }
+}
+
+impl Default for PromptBuilder {
+    fn default() -> Self {
+        Self::new()
+    }
+}

crates/zclaw-runtime/src/prompt/mod.rs

@@ -0,0 +1,9 @@
+//! Dynamic prompt assembly module.
+//!
+//! Inspired by DeerFlow's conditional section-based prompt composition.
+//! The `PromptBuilder` assembles a structured system prompt from multiple
+//! conditional sections before the middleware chain further modifies it.
+
+mod builder;
+
+pub use builder::{PromptBuilder, PromptContext, PromptSection};