Split context_state_summary: ContextBudget for compaction, UI-only for display

context_state_summary() was used for both compaction decisions (just
needs token counts) and debug screen display (needs full tree with
labels). Split into:

- Agent::context_budget() -> ContextBudget: cheap token counting by
  category, used by compact(), restore_from_log(), mind event loop
- ContextBudget::format(): replaces sections_budget_string() which
  fragily pattern-matched on section name strings
- context_state_summary(): now UI-only, formatting code stays here

Also extracted entry_sections() as shared helper with include_memories
param — false for context_state_summary (memories have own section),
true for conversation_sections_from() (subconscious screen shows all).

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

src/agent/context.rs

@@ -336,33 +336,29 @@ impl ContextState {
     }
 }
 
-/// Total tokens used across all context sections.
-pub fn sections_used(sections: &[ContextSection]) -> usize {
-    sections.iter().map(|s| s.tokens).sum()
+/// Token budget per context category — cheap to compute, no formatting.
+pub struct ContextBudget {
+    pub system: usize,
+    pub identity: usize,
+    pub journal: usize,
+    pub memory: usize,
+    pub conversation: usize,
 }
 
-/// Budget status string derived from context sections.
-pub fn sections_budget_string(sections: &[ContextSection]) -> String {
-    let window = context_window();
-    if window == 0 { return String::new(); }
-    let used: usize = sections.iter().map(|s| s.tokens).sum();
-    let free = window.saturating_sub(used);
-    let pct = |n: usize| if n == 0 { 0 } else { ((n * 100) / window).max(1) };
-    let parts: Vec<String> = sections.iter()
-        .map(|s| {
-            // Short label from section name
-            let label = match s.name.as_str() {
-                n if n.starts_with("System") => "sys",
-                n if n.starts_with("Personality") => "id",
-                n if n.starts_with("Journal") => "jnl",
-                n if n.starts_with("Working") => "stack",
-                n if n.starts_with("Memory") => "mem",
-                n if n.starts_with("Conversation") => "conv",
-                _ => return String::new(),
-            };
-            format!("{}:{}%", label, pct(s.tokens))
-        })
-        .filter(|s| !s.is_empty())
-        .collect();
-    format!("{} free:{}%", parts.join(" "), pct(free))
+impl ContextBudget {
+    pub fn total(&self) -> usize {
+        self.system + self.identity + self.journal + self.memory + self.conversation
+    }
+
+    pub fn format(&self) -> String {
+        let window = context_window();
+        if window == 0 { return String::new(); }
+        let used = self.total();
+        let free = window.saturating_sub(used);
+        let pct = |n: usize| if n == 0 { 0 } else { ((n * 100) / window).max(1) };
+        format!("sys:{}% id:{}% jnl:{}% mem:{}% conv:{}% free:{}%",
+            pct(self.system), pct(self.identity), pct(self.journal),
+            pct(self.memory), pct(self.conversation), pct(free))
+    }
 }
+