[Bug] Ampersand (&) does not trigger background task mode

Bug Description
& does not trigger background task mode

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.1.59
• Feedback ID: 69111051-db36-425a-864f-27f630e94b41

Errors

[{"error":"Error: Plugin pyright-lsp has an invalid manifest file at /Users/ryan/.claude/plugins/cache/claude-plugins-official/pyright-lsp/1.0.0/.claude-plugin/plugin.json.\n\nValidation errors: : Unrecognized keys: \"source\", \"category\", \"strict\"\n\nPlease fix the manifest or remove it. The plugin cannot load with an invalid manifest.\n    at MNR (/$bunfs/root/claude:1930:11452)\n    at async WBB (/$bunfs/root/claude:1938:378)\n    at async Ec7 (/$bunfs/root/claude:1938:8942)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-26T12:56:54.204Z"},{"error":"Error: Plugin plugin-dev has an invalid manifest file at /Users/ryan/.claude/plugins/cache/claude-plugins-official/plugin-dev/55b58ec6e564/.claude-plugin/plugin.json.\n\nValidation errors: : Unrecognized keys: \"source\", \"category\"\n\nPlease fix the manifest or remove it. The plugin cannot load with an invalid manifest.\n    at MNR (/$bunfs/root/claude:1930:11452)\n    at async WBB (/$bunfs/root/claude:1938:378)\n    at async Ec7 (/$bunfs/root/claude:1938:8942)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-26T12:56:54.204Z"}]