Why I Stopped Writing tap() Inside rxResource Streams

There's a pattern I see a lot in Angular codebases that adopted Signals early: a developer discovers rxResource , loves that it handles loading and error state automatically, and then immediately reaches for tap() to write a signal inside the stream. private readonly resource = rxResource ({ params : () => this . paramsSignal (), stream : ({ params }) => this . api . fetch ( params ). pipe ( tap ( data => this . sideSignal . set ( data . meta )) // 💥 ) }); This looks harmless. It runs in development without complaint in zone-based Angular. Then you enable zoneless — or Angular tightens its reactive graph enforcement — and you get NG0600: Writing to signals is not allowed in a reactive context . The rxResource stream runs inside Angular's reactive scheduler. Signal writes there aren't just discouraged — they're illegal by design. The scheduler assumes computed signals and reactive contexts are read-only during evaluation. A write mid-computation breaks the glitch-free guarantee Angular's signal graph is built on. The fix I landed on: make the stream return everything it needs to return, as a single typed value. interface ResourceValue { readonly sections : Section []; readonly meta : Meta ; } private readonly resource = rxResource < ResourceValue , Params > ({ stream : ({ params }) => this . api . fetch ( params ). pipe ( map ( data => ({ sections : transform ( data ), meta : data . meta })) ) }); No tap . No side signal. Everything the rest of the store needs lives in resource.value() and can be read via computed . The lesson isn't "don't use tap". The lesson is that rxResource has a contract: it is a read primitive . Its stream is for fetching and transforming. If you're writing signals inside it, you're treating it as a command bus — and that's a different tool. Originally published on ysndmr.com .