Delete ui_channel.rs — relocate types, remove all UiMessage/UiSender plumbing

Types relocated:
- StreamTarget → mind/mod.rs (Mind decides Conversation vs Autonomous)
- SharedActiveTools + shared_active_tools() → agent/tools/mod.rs
- ContextSection + SharedContextState → agent/context.rs (already there)
- StatusInfo + ContextInfo → user/mod.rs (UI display state)

Removed UiSender from: Agent::turn, Mind, learn.rs, all function signatures.
The entire message-passing layer is gone. All state flows through
Agent fields (activities, entries, streaming) read by the UI via try_lock.

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

src/agent/api/mod.rs

@@ -20,7 +20,6 @@ use tokio::sync::mpsc;
 
 use crate::agent::tools::{self as agent_tools, summarize_args, ActiveToolCall};
 pub use types::ToolCall;
-use crate::user::ui_channel::UiSender;
 
 /// A JoinHandle that aborts its task when dropped.
 pub struct AbortOnDrop(tokio::task::JoinHandle<()>);
@@ -107,7 +106,6 @@ impl ApiClient {
         &self,
         messages: &[Message],
         tools: &[agent_tools::Tool],
-        ui_tx: &UiSender,
         reasoning_effort: &str,
         sampling: SamplingParams,
         priority: Option<i32>,
@@ -119,14 +117,13 @@ impl ApiClient {
         let messages = messages.to_vec();
         let tools_json = tools_to_json_str(tools);
         let tools_value: serde_json::Value = serde_json::from_str(&tools_json).unwrap_or_default();
-        let ui_tx = ui_tx.clone();
         let reasoning_effort = reasoning_effort.to_string();
         let base_url = self.base_url.clone();
 
         let handle = tokio::spawn(async move {
             let result = openai::stream_events(
                 &client, &base_url, &api_key, &model,
-                &messages, &tools_value, &tx, &ui_tx,
+                &messages, &tools_value, &tx,
                 &reasoning_effort, sampling, priority,
             ).await;
             if let Err(e) = result {
@@ -141,13 +138,12 @@ impl ApiClient {
         &self,
         messages: &[Message],
         tools: &[agent_tools::Tool],
-        ui_tx: &UiSender,
         reasoning_effort: &str,
         sampling: SamplingParams,
         priority: Option<i32>,
     ) -> Result<(Message, Option<Usage>)> {
         // Use the event stream and accumulate into a message.
-        let (mut rx, _handle) = self.start_stream(messages, tools, ui_tx, reasoning_effort, sampling, priority);
+        let (mut rx, _handle) = self.start_stream(messages, tools, reasoning_effort, sampling, priority);
         let mut content = String::new();
         let mut tool_calls: Vec<ToolCall> = Vec::new();
         let mut usage = None;
@@ -319,14 +315,13 @@ pub(crate) struct SseReader {
     pub sse_lines_parsed: u64,
     pub sse_parse_errors: u64,
     debug: bool,
-    ui_tx: UiSender,
     done: bool,
     /// Serialized request payload — saved to disk on errors for replay debugging.
     pub(crate) request_json: Option<String>,
 }
 
 impl SseReader {
-    pub(crate) fn new(ui_tx: &UiSender) -> Self {
+    pub(crate) fn new() -> Self {
         Self {
             line_buf: String::new(),
             chunk_timeout: Duration::from_secs(crate::config::get().api_stream_timeout_secs),
@@ -335,7 +330,6 @@ impl SseReader {
             sse_lines_parsed: 0,
             sse_parse_errors: 0,
             debug: std::env::var("POC_DEBUG").is_ok(),
-            ui_tx: ui_tx.clone(),
             done: false,
             request_json: None,
         }
@@ -516,7 +510,6 @@ pub fn build_response_message(
 
 /// Log stream diagnostics. Shared by both backends.
 pub(crate) fn log_diagnostics(
-    ui_tx: &UiSender,
     content_len: usize,
     tool_count: usize,
     reasoning_chars: usize,
@@ -619,7 +612,7 @@ pub struct StreamResult {
 pub async fn collect_stream(
     rx: &mut mpsc::UnboundedReceiver<StreamEvent>,
     agent: &std::sync::Arc<tokio::sync::Mutex<super::Agent>>,
-    active_tools: &crate::user::ui_channel::SharedActiveTools,
+    active_tools: &crate::agent::tools::SharedActiveTools,
 ) -> StreamResult {
     let mut content = String::new();
     let mut tool_calls: Vec<ToolCall> = Vec::new();