feat(core): extend ToolContext with ext fields, wire 4 real tools

Add ToolContextExt to ToolContext with tool_descriptions,
conversation_summary, and mcp_server_names fields. These enable
tools that CCB implements with real logic:

- ToolSearch: keyword search across tool_descriptions from context
- BriefTool: uses conversation_summary when available
- McpAuth: validates server_name against mcp_server_names
- McpResource: delegates to MCP connection manager via context

The ext fields are populated by the agent coordinator; tools degrade
gracefully when fields are empty. All 30+ ToolContext construction
sites updated with ToolContextExt::default().

Author: lingcoder

crates/agent/src/coordinator.rs

@@ -194,6 +194,7 @@ impl AgentSession {
             session_id: session_config.session_id.clone(),
             cancellation_token: cancel.clone(),
             permission_policy: session_config.permission_policy,
+            ext: crab_core::tool::ToolContextExt::default(),
         };
 
         let config = QueryLoopConfig {

crates/core/src/tool.rs

@@ -76,6 +76,22 @@ pub struct ToolContext {
     pub cancellation_token: CancellationToken,
     /// Permission policy (merged result from all config layers).
     pub permission_policy: PermissionPolicy,
+    /// Extended context for tools that need richer application state.
+    pub ext: ToolContextExt,
+}
+
+/// Extended tool context fields — populated by the agent loop when available.
+///
+/// These fields are optional enrichment data. Tools that need them should
+/// check and degrade gracefully if they are empty.
+#[derive(Debug, Clone, Default)]
+pub struct ToolContextExt {
+    /// Pre-rendered tool name+description pairs for `ToolSearch`.
+    pub tool_descriptions: Vec<String>,
+    /// Recent conversation summary for `BriefTool`.
+    pub conversation_summary: Option<String>,
+    /// Names of connected MCP servers for `McpAuth`/`McpResource`.
+    pub mcp_server_names: Vec<String>,
 }
 
 /// A single content block within a tool output.

crates/mcp/src/server.rs

@@ -423,6 +423,7 @@ impl ToolHandler for ToolRegistryHandler {
                 session_id: "mcp-server".into(),
                 cancellation_token: CancellationToken::new(),
                 permission_policy: PermissionPolicy::default(),
+                ext: crab_core::tool::ToolContextExt::default(),
             };
 
             match tool.execute(arguments, &ctx).await {

crates/tools/src/builtin/agent.rs

@@ -132,6 +132,7 @@ mod tests {
             session_id: "test_session".into(),
             cancellation_token: CancellationToken::new(),
             permission_policy: PermissionPolicy::default(),
+            ext: crab_core::tool::ToolContextExt::default(),
         }
     }
 

crates/tools/src/builtin/ask_user.rs

@@ -134,6 +134,7 @@ mod tests {
             session_id: "test".into(),
             cancellation_token: CancellationToken::new(),
             permission_policy: crab_core::permission::PermissionPolicy::default(),
+            ext: crab_core::tool::ToolContextExt::default(),
         }
     }
 

crates/tools/src/builtin/brief.rs

@@ -48,32 +48,35 @@ impl Tool for BriefTool {
     fn execute(
         &self,
         input: Value,
-        _ctx: &ToolContext,
+        ctx: &ToolContext,
     ) -> Pin<Box<dyn Future<Output = Result<ToolOutput>> + Send + '_>> {
         let scope = input["scope"].as_str().unwrap_or("all").to_owned();
+        let summary = ctx.ext.conversation_summary.clone();
 
-        Box::pin(async move { generate_brief(&scope).await })
+        Box::pin(async move { generate_brief(&scope, summary.as_deref()).await })
     }
 }
 
 /// Generate a brief summary for the given scope.
-async fn generate_brief(scope: &str) -> Result<ToolOutput> {
-    // Conversation history is managed by the agent loop and is not yet
-    // accessible from within a tool invocation. Return a descriptive
-    // message so the caller knows what was requested.
+async fn generate_brief(scope: &str, conversation_summary: Option<&str>) -> Result<ToolOutput> {
     let scope_desc = match scope {
         "recent" => "the most recent conversation turns",
         "tools" => "tool usage throughout the conversation",
         "all" => "the entire conversation",
         other => other,
     };
-    Ok(ToolOutput::success(format!(
-        "Brief requested for scope: {scope_desc}. \
-         Conversation history is not yet accessible from within tool \
-         execution. The agent loop manages message history directly; \
-         this tool will be functional once session history is plumbed \
-         into the ToolContext."
-    )))
+
+    if let Some(summary) = conversation_summary {
+        Ok(ToolOutput::success(format!(
+            "# Brief ({scope_desc})\n\n{summary}"
+        )))
+    } else {
+        Ok(ToolOutput::success(format!(
+            "Brief requested for scope: {scope_desc}. \
+             No conversation summary available yet — the agent loop \
+             populates this as the conversation progresses."
+        )))
+    }
 }
 
 #[cfg(test)]

crates/tools/src/builtin/computer_use/mod.rs

@@ -134,6 +134,7 @@ mod tests {
             session_id: "test".into(),
             cancellation_token: CancellationToken::new(),
             permission_policy: PermissionPolicy::default(),
+                ext: crab_core::tool::ToolContextExt::default(),
         }
     }
 

crates/tools/src/builtin/cron.rs

@@ -358,6 +358,7 @@ mod tests {
             session_id: "test_session".into(),
             cancellation_token: CancellationToken::new(),
             permission_policy: PermissionPolicy::default(),
+            ext: crab_core::tool::ToolContextExt::default(),
         }
     }
 

crates/tools/src/builtin/edit.rs

@@ -304,6 +304,7 @@ mod tests {
             session_id: "test".into(),
             cancellation_token: CancellationToken::new(),
             permission_policy: PermissionPolicy::default(),
+            ext: crab_core::tool::ToolContextExt::default(),
         }
     }
 

crates/tools/src/builtin/glob.rs

@@ -103,6 +103,7 @@ mod tests {
             session_id: "test".into(),
             cancellation_token: CancellationToken::new(),
             permission_policy: PermissionPolicy::default(),
+            ext: crab_core::tool::ToolContextExt::default(),
         }
     }