story-kit: merge 296_story_track_per_agent_token_usage_for_cost_visibility_and_optimisation

server/src/agents/mod.rs

@@ -3,9 +3,10 @@ pub mod lifecycle;
 pub mod merge;
 mod pool;
 mod pty;
+pub mod token_usage;
 
 use crate::config::AgentConfig;
-use serde::Serialize;
+use serde::{Deserialize, Serialize};
 
 pub use lifecycle::{
     close_bug_to_archive, feature_branch_has_unmerged_changes, move_story_to_archived,
@@ -136,6 +137,45 @@ pub struct CompletionReport {
     pub gate_output: String,
 }
 
+/// Token usage from a Claude Code session's `result` event.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub struct TokenUsage {
+    pub input_tokens: u64,
+    pub output_tokens: u64,
+    pub cache_creation_input_tokens: u64,
+    pub cache_read_input_tokens: u64,
+    pub total_cost_usd: f64,
+}
+
+impl TokenUsage {
+    /// Parse token usage from a Claude Code `result` JSON event.
+    pub fn from_result_event(json: &serde_json::Value) -> Option<Self> {
+        let usage = json.get("usage")?;
+        Some(Self {
+            input_tokens: usage
+                .get("input_tokens")
+                .and_then(|v| v.as_u64())
+                .unwrap_or(0),
+            output_tokens: usage
+                .get("output_tokens")
+                .and_then(|v| v.as_u64())
+                .unwrap_or(0),
+            cache_creation_input_tokens: usage
+                .get("cache_creation_input_tokens")
+                .and_then(|v| v.as_u64())
+                .unwrap_or(0),
+            cache_read_input_tokens: usage
+                .get("cache_read_input_tokens")
+                .and_then(|v| v.as_u64())
+                .unwrap_or(0),
+            total_cost_usd: json
+                .get("total_cost_usd")
+                .and_then(|v| v.as_f64())
+                .unwrap_or(0.0),
+        })
+    }
+}
+
 #[derive(Debug, Serialize, Clone)]
 pub struct AgentInfo {
     pub story_id: String,