Is it possible to deny your opponent any reaction windows during your turn by only playing permanents without 'when played' triggers and not initiating showdowns?

Ruling: Yes, if you only play permanents without "when played" triggers and only move units to bases or battlefields you already control without initiating showdowns, there is no window for your opponent to play reactions.

Sequence:

• Play only permanents that lack "when played" triggers
• Move units only to bases or battlefields you already control
• Avoid initiating any showdowns
• This prevents your opponent from gaining priority during your turn

Nuances:

• Permanents with "when played" triggers will open a chain, offering a chance for reactions
• "When" is generally the keyword that indicates a triggered ability that opens a chain
• "As you play" effects (like Clockwork Keeper's draw) are conditional passive abilities, not triggered abilities, and do not open a reaction window