fix: negative token savings caused by passthrough pollution and wrong avg (#3)

- Stop tracking passthrough commands (0/0 tokens is noise)
- Skip tracking when input_tokens == 0 (no output captured)
- Use weighted avg savings: SUM(saved)/SUM(input)*100 instead of AVG(pct)

Fixes #2

Author: edouard-claude

internal/engine/pipeline.go

@@ -81,33 +81,30 @@ func (p *Pipeline) Run(command string, args []string) int {
 		fmt.Fprint(os.Stderr, result.Stderr)
 	}
 
-	// Track
-	originalCmd := command + " " + strings.Join(fullArgs, " ")
-	snipCmd := command + " " + strings.Join(finalArgs, " ")
+	// Track (skip if no input — nothing meaningful to measure)
 	inputTokens := utils.EstimateTokens(result.Stdout)
-	outputTokens := utils.EstimateTokens(filtered)
-	if err := timed.Track(originalCmd, snipCmd, inputTokens, outputTokens); err != nil {
-		fmt.Fprintf(os.Stderr, "snip: tracking error: %v\n", err)
+	if inputTokens > 0 {
+		originalCmd := command + " " + strings.Join(fullArgs, " ")
+		snipCmd := command + " " + strings.Join(finalArgs, " ")
+		outputTokens := utils.EstimateTokens(filtered)
+		if err := timed.Track(originalCmd, snipCmd, inputTokens, outputTokens); err != nil {
+			fmt.Fprintf(os.Stderr, "snip: tracking error: %v\n", err)
+		}
 	}
 
 	return result.ExitCode
 }
 
 // Passthrough runs a command directly without filtering.
+// Passthrough commands are not tracked because the output goes directly
+// to stdout — snip never captures it, so token counts would be 0/0.
 func (p *Pipeline) Passthrough(command string, args []string) int {
-	timed := tracking.Start(p.Tracker)
-
 	code, err := Passthrough(command, args)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "snip: %v\n", err)
 		return 1
 	}
 
-	cmd := command + " " + strings.Join(args, " ")
-	if err := timed.TrackPassthrough(cmd, 0); err != nil {
-		fmt.Fprintf(os.Stderr, "snip: tracking error: %v\n", err)
-	}
-
 	return code
 }
 

internal/tracking/schema.go

@@ -25,7 +25,7 @@ const summarySQL = `
 SELECT
 	COUNT(*) as total_commands,
 	COALESCE(SUM(saved_tokens), 0) as total_saved,
-	COALESCE(AVG(savings_pct), 0) as avg_savings,
+	COALESCE(SUM(saved_tokens) * 100.0 / NULLIF(SUM(input_tokens), 0), 0) as avg_savings,
 	COALESCE(SUM(exec_time_ms), 0) as total_time_ms
 FROM commands;
 `
@@ -37,7 +37,7 @@ SELECT
 	SUM(input_tokens) as input_tokens,
 	SUM(output_tokens) as output_tokens,
 	SUM(saved_tokens) as saved_tokens,
-	AVG(savings_pct) as avg_savings
+	COALESCE(SUM(saved_tokens) * 100.0 / NULLIF(SUM(input_tokens), 0), 0) as avg_savings
 FROM commands
 WHERE timestamp >= datetime('now', ? || ' days')
 GROUP BY date(timestamp)