replace panic with os.Exit and error log in cmd/filewriter

Panics in non-setup code violate the AGENTS.md convention. Replace all
three panic(err) calls with fmt.Fprintf(os.Stderr, ...) + os.Exit(1) so
the process exits cleanly with a human-readable message instead of a
stack trace.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/cmd/filewriter/main.go b/cmd/filewriter/main.go
index 25f5cb7..b175371 100644
--- a/cmd/filewriter/main.go
+++ b/cmd/filewriter/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"os"
 	"time"
 )
@@ -9,7 +10,8 @@ func main() {
 	// Open the file in append mode, create it if it doesn't exist
 	file, err := os.OpenFile("output.txt", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 	if err != nil {
-		panic(err)
+		fmt.Fprintf(os.Stderr, "filewriter: failed to open output file: %v\n", err)
+		os.Exit(1)
 	}
 	defer file.Close()
 
@@ -20,13 +22,15 @@ func main() {
 	for {
 		_, err := file.Write(data)
 		if err != nil {
-			panic(err)
+			fmt.Fprintf(os.Stderr, "filewriter: failed to write data: %v\n", err)
+			os.Exit(1)
 		}
 
 		// Flush writes to stable storage
 		err = file.Sync()
 		if err != nil {
-			panic(err)
+			fmt.Fprintf(os.Stderr, "filewriter: failed to sync file: %v\n", err)
+			os.Exit(1)
 		}
 
 		// Wait for 3 seconds