Exit 130 and say so when a command is interrupted (closes #267)

Ctrl-C or SIGTERM during snapshot create, restore or verify exited 0
with no error line (1, also silent, under snapshot verify --json), so
an unfinished --cron backup looked like a success. RunOperation now
records whether op returned while the Vaultik context was still live;
a run where it had not by the time RunWithApp returned is interrupted,
whatever op returned. It used to look for context.Canceled in op's
error, which verify --json does not return. Entry prints "interrupted
before the command finished" on stderr for it and returns 130, under
--cron and --json too.

SIGTERM also gives 130, as the issue asks, not 143.
The test does not cover an op still running when the 30s shutdown
timeout ends.

Model: opus-5-5

internal/cli/entry.go

@@ -15,6 +15,11 @@ import (
 // the startup banner.
 const shortCommitLen = 12
 
+// exitCodeInterrupted is the exit status of a command that SIGINT or
+// SIGTERM stopped. It is 128 plus SIGINT's number, 2, which is what a
+// shell reports for a command stopped by Ctrl-C.
+const exitCodeInterrupted = 130
+
 // Entry is the main entry point for the CLI application.
 // It prints the startup banner to stderr (unless a banner-suppressing
 // flag is present in os.Args — see bannerSuppressedInArgs), executes the
@@ -23,9 +28,10 @@ const shortCommitLen = 12
 // The banner goes to stderr because stdout carries only the output the
 // user asked for, such as a completion script or a `config get` value.
 //
-// It returns the process exit code (0 on success, 1 on error) rather
-// than calling os.Exit, so that main's deferred profile writers run
-// before the process ends. See run in cmd/vaultik/main.go.
+// It returns the process exit code (0 on success, 130 when interrupted,
+// 1 on any other error) rather than calling os.Exit, so that main's
+// deferred profile writers run before the process ends. See run in
+// cmd/vaultik/main.go.
 func Entry() int {
 	emitStartupBanner(os.Args[1:], os.Stderr)
 
@@ -39,11 +45,16 @@ func Entry() int {
 		// document instead); errReported says so. Printing it again
 		// here would double the error line.
 		// Every other error — bad arguments, a config that would not
-		// load — reaches Entry unreported, so it is shown here.
+		// load, an interrupt — reaches Entry unreported, so it is shown
+		// here.
 		if !errors.Is(err, errReported) {
 			ReportErrorf("%s", err.Error())
 		}
 
+		if errors.Is(err, errInterrupted) {
+			return exitCodeInterrupted
+		}
+
 		return 1
 	}