tools: delete ToolDef and FunctionDef

ToolDef and FunctionDef are gone. Tool definitions are static strings
on the Tool struct. The API layer builds JSON from Tool::to_json().

- ChatRequest.tools is now Option<serde_json::Value>
- start_stream takes &[Tool] instead of Option<&[ToolDef]>
- openai::stream_events takes &serde_json::Value for tools
- memory_and_journal_tools() returns Vec<Tool> for subconscious agents
- Subconscious agents filter by t.name instead of t.function.name

No more runtime JSON construction for tool definitions.
No more ToolDef::new(). No more FunctionDef.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/api/openai.rs

@@ -8,7 +8,6 @@ use anyhow::Result;
 use reqwest::Client;
 use tokio::sync::mpsc;
 
-use crate::agent::tools::ToolDef;
 use super::types::*;
 use crate::user::ui_channel::{UiMessage, UiSender};
 use super::StreamEvent;
@@ -22,18 +21,19 @@ pub(super) async fn stream_events(
     api_key: &str,
     model: &str,
     messages: &[Message],
-    tools: Option<&[ToolDef]>,
+    tools_json: &serde_json::Value,
     tx: &mpsc::UnboundedSender<StreamEvent>,
     ui_tx: &UiSender,
     reasoning_effort: &str,
     sampling: super::SamplingParams,
     priority: Option<i32>,
 ) -> Result<()> {
+    let has_tools = tools_json.as_array().map_or(false, |a| !a.is_empty());
     let request = ChatRequest {
         model: model.to_string(),
         messages: messages.to_vec(),
-        tool_choice: tools.map(|_| "auto".to_string()),
-        tools: tools.map(|t| t.to_vec()),
+        tool_choice: if has_tools { Some("auto".to_string()) } else { None },
+        tools: if has_tools { Some(tools_json.clone()) } else { None },
         max_tokens: Some(16384),
         temperature: Some(sampling.temperature),
         top_p: Some(sampling.top_p),