Compute ContextBudget on demand from typed sources

Remove cached context_budget field and measure_budget(). Budget
is computed on demand via budget() which calls
ContextState::budget(). Each bucket counted from its typed source.
Memory split from conversation by identifying memory tool calls.

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

src/agent/runner.rs

@@ -62,8 +62,6 @@ pub struct Agent {
     pub reasoning_effort: String,
     /// Persistent conversation log — append-only record of all messages.
     conversation_log: Option<ConversationLog>,
-    /// Current context window budget breakdown.
-    pub context_budget: ContextBudget,
     /// BPE tokenizer for token counting (cl100k_base — close enough
     /// for Claude and Qwen budget allocation, ~85-90% count accuracy).
     tokenizer: CoreBPE,
@@ -116,7 +114,6 @@ impl Agent {
             process_tracker: ProcessTracker::new(),
             reasoning_effort: "none".to_string(),
             conversation_log,
-            context_budget: ContextBudget::default(),
             tokenizer,
             context,
             shared_context,
@@ -126,7 +123,6 @@ impl Agent {
 
         agent.load_startup_journal();
         agent.load_working_stack();
-        agent.measure_budget();
         agent.publish_context_state();
         agent
     }
@@ -183,28 +179,11 @@ impl Agent {
     /// Push a context-only message (system prompt, identity context,
     /// journal summaries). Not logged — these are reconstructed on
     /// every startup/compaction.
-    /// Measure context window usage by category. Uses the BPE tokenizer
-    /// for direct token counting (no chars/4 approximation).
-    fn measure_budget(&mut self) {
-        let count = |s: &str| self.tokenizer.encode_with_special_tokens(s).len();
-
-        let id_tokens = count(&self.context.system_prompt)
-            + self.context.personality.iter()
-                .map(|(_, content)| count(content)).sum::<usize>();
-        let jnl_tokens: usize = self.context.journal.iter()
-            .map(|e| count(&e.content)).sum();
-        let mem_tokens: usize = self.context.loaded_nodes.iter()
-            .map(|node| count(&node.render())).sum();
-        let conv_tokens: usize = self.context.messages.iter()
-            .map(|m| crate::agent::context::msg_token_count(&self.tokenizer, m)).sum();
-
-        self.context_budget = ContextBudget {
-            identity_tokens: id_tokens,
-            memory_tokens: mem_tokens,
-            journal_tokens: jnl_tokens,
-            conversation_tokens: conv_tokens,
-            window_tokens: crate::agent::context::model_context_window(&self.client.model),
-        };
+    pub fn budget(&self) -> ContextBudget {
+        let count_str = |s: &str| self.tokenizer.encode_with_special_tokens(s).len();
+        let count_msg = |m: &Message| crate::agent::context::msg_token_count(&self.tokenizer, m);
+        let window = crate::agent::context::model_context_window(&self.client.model);
+        self.context.budget(&count_str, &count_msg, window)
     }
 
     /// Send a user message and run the agent loop until the model
@@ -372,7 +351,7 @@ impl Agent {
 
             if let Some(usage) = &usage {
                 self.last_prompt_tokens = usage.prompt_tokens;
-                self.measure_budget();
+                
                 self.publish_context_state();
                 let _ = ui_tx.send(UiMessage::StatusUpdate(StatusInfo {
                     dmn_state: String::new(), // filled by main loop
@@ -382,7 +361,7 @@ impl Agent {
                     completion_tokens: usage.completion_tokens,
                     model: self.client.model.clone(),
                     turn_tools: 0, // tracked by TUI from ToolCall messages
-                    context_budget: self.context_budget.status_string(),
+                    context_budget: self.budget().status_string(),
                 }));
             }
 
@@ -547,7 +526,7 @@ impl Agent {
             if output.text.starts_with("Error:") {
                 ds.tool_errors += 1;
             }
-            self.measure_budget();
+            
             self.publish_context_state();
             return;
         }
@@ -826,7 +805,7 @@ impl Agent {
 
     /// Called after any change to context state (working stack, etc).
     fn refresh_context_state(&mut self) {
-        self.measure_budget();
+        
         self.publish_context_state();
         self.save_working_stack();
     }
@@ -849,8 +828,16 @@ impl Agent {
 
     /// Push the current context summary to the shared state for the TUI to read.
     fn publish_context_state(&self) {
+        let summary = self.context_state_summary();
+        if let Ok(mut dbg) = std::fs::OpenOptions::new().create(true).append(true)
+                .open("/tmp/poc-journal-debug.log") {
+            use std::io::Write;
+            for s in &summary {
+                let _ = writeln!(dbg, "[publish] {} ({} tokens, {} children)", s.name, s.tokens, s.children.len());
+            }
+        }
         if let Ok(mut state) = self.shared_context.write() {
-            *state = self.context_state_summary();
+            *state = summary;
         }
     }
 
@@ -978,7 +965,7 @@ impl Agent {
         self.context.journal = journal::parse_journal_text(&journal);
         self.context.messages = messages;
         self.last_prompt_tokens = 0;
-        self.measure_budget();
+        
         self.publish_context_state();
     }
 
@@ -1041,7 +1028,7 @@ impl Agent {
         self.context.messages = messages;
         dbglog!("[restore] built context window: {} messages", self.context.messages.len());
         self.last_prompt_tokens = 0;
-        self.measure_budget();
+        
         self.publish_context_state();
         true
     }