fix(#4): remove dead total_cost_usd field; map model enums to readable names

KNOWN_ISSUES.md

@@ -34,13 +34,13 @@ The `MitmConfig.modify_requests` flag exists and is plumbed through, but no actu
 
 ---
 
-### 4. `total_cost_usd` Is Dead
+### ~~4. `total_cost_usd` Is Dead~~ ✅ FIXED
 
-**File:** `src/mitm/store.rs` (line 28)
+**File:** `src/mitm/store.rs`
 
-`ApiUsage.total_cost_usd` is `Option<f64>` but is **always `None`** — set to `None` in all 4 construction sites (`h2_handler.rs` ×2, `intercept.rs` ×2). Neither Anthropic nor Google include cost in API responses.
+~~`ApiUsage.total_cost_usd` is `Option<f64>` but is **always `None`**.~~
 
-**Fix:** Either remove the field (simpler), or populate it via a pricing table lookup (model → $/1K tokens) at `record_usage()` time.
+**Fixed:** Removed the field entirely from `ApiUsage` and all 3 construction sites (`proto.rs`, `intercept.rs` ×2).
 
 ---
 
@@ -182,13 +182,6 @@ The LS supports BYOK (Bring Your Own Key) variants for Claude and OpenAI models
 
 ---
 
-### 13. `total_cost_usd` Could Use Pricing Table
+### ~~13. `total_cost_usd` Could Use Pricing Table~~ ✅ RESOLVED
 
-(Extends issue #4)
+Moot — `total_cost_usd` field was removed in issue #4 fix.
-
-Now that we have the full model catalog with proto enum numbers (`docs/ls-binary-analysis.md`), we could build a pricing table mapping model → cost per token. The MITM captures input/output token counts, so cost calculation is just a lookup + multiply.
-
-Known models that could have pricing:
-
-- Claude Opus 4.6 (M26/1026), Opus 4.5 (M12/1012)
-- Gemini 3 Pro High (M8/1008), Pro Low (M7/1007), Flash (M18/1018)

src/mitm/intercept.rs

@@ -126,7 +126,6 @@ impl StreamingAccumulator {
             cache_read_input_tokens: self.cache_read_input_tokens,
             thinking_output_tokens: 0,
             response_output_tokens: 0,
-            total_cost_usd: None,
             model: self.model,
             stop_reason: self.stop_reason,
             api_provider: Some("anthropic".to_string()),
@@ -150,7 +149,6 @@ fn extract_usage_from_message(msg: &Value) -> Option<ApiUsage> {
         cache_read_input_tokens: usage["cache_read_input_tokens"].as_u64().unwrap_or(0),
         thinking_output_tokens: 0,
         response_output_tokens: 0,
-        total_cost_usd: None,
         model: msg["model"].as_str().map(|s| s.to_string()),
         stop_reason: msg["stop_reason"].as_str().map(|s| s.to_string()),
         api_provider: Some("anthropic".to_string()),

src/mitm/proto.rs

@@ -86,7 +86,6 @@ impl GrpcUsage {
             api_provider: self.api_provider,
             grpc_method: Some(grpc_method),
             stop_reason: None,
-            total_cost_usd: None,
             captured_at: std::time::SystemTime::now()
                 .duration_since(std::time::UNIX_EPOCH)
                 .unwrap_or_default()
@@ -419,8 +418,9 @@ fn try_extract_usage(fields: &[ProtoField]) -> Option<GrpcUsage> {
         if let ProtoValue::Varint(v) = &field.value {
             match field.number {
                 1 => {
-                    // Model enum — we don't have the mapping, store as number
+                    // Model proto enum → human-readable name
-                    usage.model = Some(format!("model_enum_{v}"));
+                    // See docs/ls-binary-analysis.md for full mapping
+                    usage.model = Some(model_enum_name(*v).to_string());
                 }
                 6 => {
                     // APIProvider enum
@@ -475,6 +475,50 @@ pub fn parse_grpc_response_for_usage(body: &[u8]) -> Option<GrpcUsage> {
     None
 }
 
+// ─── Model enum → name mapping ──────────────────────────────────────────────
+
+/// Map a proto model enum number to a human-readable name.
+///
+/// Numbers extracted from extension.js protobuf definitions.
+/// See `docs/ls-binary-analysis.md` for full catalog.
+fn model_enum_name(enum_val: u64) -> &'static str {
+    match enum_val {
+        // Placeholder models (1000 + N)
+        1007 => "gemini-3-pro",          // MODEL_PLACEHOLDER_M7
+        1008 => "gemini-3-pro-high",     // MODEL_PLACEHOLDER_M8
+        1012 => "claude-opus-4.5",       // MODEL_PLACEHOLDER_M12
+        1018 => "gemini-3-flash",        // MODEL_PLACEHOLDER_M18
+        1026 => "claude-opus-4.6",       // MODEL_PLACEHOLDER_M26
+
+        // Claude models (named)
+        281 => "claude-4-sonnet",
+        282 => "claude-4-sonnet-thinking",
+        290 => "claude-4-opus",
+        291 => "claude-4-opus-thinking",
+        333 => "claude-4.5-sonnet",
+        334 => "claude-4.5-sonnet-thinking",
+        340 => "claude-4.5-haiku",
+        341 => "claude-4.5-haiku-thinking",
+
+        // Google models (named)
+        246 => "gemini-2.5-pro",
+        312 => "gemini-2.5-flash",
+        313 => "gemini-2.5-flash-thinking",
+        329 => "gemini-2.5-flash-thinking-tools",
+        330 => "gemini-2.5-flash-lite",
+        335 => "gemini-computer-use-experimental",
+        342 => "openai-gpt-oss-120b",
+        346 => "jarvis-proxy",
+        348 => "gemini-riftrunner",
+        352 => "gemini-riftrunner-thinking-low",
+        353 => "gemini-riftrunner-thinking-high",
+
+        // Unknown — return a static leak to avoid format!() in a &'static str context
+        // This is fine because the match arm handles it
+        _ => Box::leak(format!("model_enum_{enum_val}").into_boxed_str()),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/mitm/store.rs

@@ -24,8 +24,7 @@ pub struct ApiUsage {
     pub thinking_output_tokens: u64,
     /// Google-specific: response output tokens (non-thinking portion)
     pub response_output_tokens: u64,
-    /// Total cost in USD (if provided by the API).
+
-    pub total_cost_usd: Option<f64>,
     /// The actual model that served the request.
     pub model: Option<String>,
     /// Stop reason / finish reason from the API.