feat: phase 2 — coûts par session (stats --costs) + am monitor TUI (closes #49 #50)

src/sessions.rs

@@ -29,6 +29,14 @@ pub struct SessionRecord {
     /// RFC 3339 end timestamp (None while running).
     #[serde(default)]
     pub ended_at: Option<String>,
+    /// Tokens billed once the agent exposed its usage (issue #49).
+    #[serde(default)]
+    pub tokens_in: Option<u64>,
+    #[serde(default)]
+    pub tokens_out: Option<u64>,
+    /// Estimated cost in USD (issue #49).
+    #[serde(default)]
+    pub cost_usd: Option<f64>,
     #[serde(default)]
     pub exit_code: Option<i32>,
     #[serde(default)]
@@ -125,6 +133,9 @@ pub fn start_agent(
             project,
             started_at: crate::installers::now_rfc3339(),
             ended_at: None,
+            tokens_in: None,
+            tokens_out: None,
+            cost_usd: None,
             exit_code: None,
             log,
             args,
@@ -151,6 +162,9 @@ pub fn start_repl(app: &App, id: &str, cwd: Option<String>) -> Result<()> {
             project: None,
             started_at: crate::installers::now_rfc3339(),
             ended_at: None,
+            tokens_in: None,
+            tokens_out: None,
+            cost_usd: None,
             exit_code: None,
             log: None,
             args: Vec::new(),
@@ -184,12 +198,15 @@ pub fn finish_agent(app: &App, agent: &str, pid: Option<u32>, exit_code: i32, ok
         candidates.first().cloned()
     };
     if let Some(k) = key {
+        let cwd = sf.sessions.get(&k).and_then(|r| r.cwd.clone());
         if let Some(r) = sf.sessions.get_mut(&k) {
             r.ended_at = Some(crate::installers::now_rfc3339());
             r.exit_code = Some(exit_code);
             r.status = if ok { "stopped" } else { "failed" }.to_string();
         }
         save(app, &sf)?;
+        // Issue #49: collect the token usage the agent exposed and price it.
+        let _ = crate::costs::record_session_usage(app, agent, &k, cwd.as_deref());
     }
     Ok(())
 }