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
counts an op as interrupted when the Vaultik context was cancelled
before it returned, rather than when its error wraps context.Canceled,
which verify --json does not. 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 reach the branch for 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
 	}