I use Github Actions triggers to pass flags to a monorepo dagger script to build and test the affected components. For example, if a commit touches the front- and back ends, rebuild both. If it only touches the front end, run integration tests using the latest backend without rebuilding it.
Yea this definitely makes sense for smaller monorepos. For us, we ended up writing our own dependency graph parser to figure out what tests to run (which is easy enough with a single language like python honestly)
We used pants initially (which I believe is similar to bazel). And indeed the dependency graphing it does was very helpful, but other parts of the tool motivated us to create something more bespoke and debuggable (we were only using like 20% or less of the features pants offers)
edit: spell out GHA