fix(cli): migrate meta's catch rethrows the exit signal by the house predicate

`test/exit-signal.pin.test.ts` holds every catch that a this.exit() inside its
try can reach to open with `if (isExitSignal(error)) throw error;`. The --write
failure exits added two such calls, and the catch opened with a hand-rolled
`oclif.exit` check instead; the pin named both lines. Same behaviour, the one
spelling the pin reads.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RWZbGvPFcRKvUqASZtunCU

Author: claude

packages/cli/src/commands/migrate/meta.ts

@@ -29,6 +29,7 @@ import {
   createTimer,
   emitJson,
   errorCodeFields,
+  isExitSignal,
   isReportedError,
 } from '../../utils/format.js';
 import { bootSchemaStack } from '../../utils/schema-migrate.js';
@@ -857,8 +858,7 @@ export default class MigrateMeta extends Command {
       // A write refused or undone is a failed run, reported above.
       if (write && write.status !== 'written') this.exit(1);
     } catch (error: any) {
-      // `this.exit()` throws; a `--write` failure exits from inside the try.
-      if (typeof error?.oclif?.exit === 'number') throw error;
+      if (isExitSignal(error)) throw error;
       if (error instanceof MigrationFloorError) {
         if (flags.json) {
           await emitJson({ error: 'unsupported_from_major', message: error.message }, 0, { compact: true });