`dx serve --hotpatch` fails with build error `Missing rustc args for replay`

[rami3l]

Problem

Upstreamed from Pangpang-Studio/monoxide#158.

Our workspace setup worked last month when we were using Dioxus CLI 0.7.4, so some regression must have happened since then.

When trying to trigger a --hotpatch reloading dx serve in the playground "example" binary target of the workspace, subsecond's DAG scan somehow thinks that the root binary target also needs to be rebuilt.

However, playground doesn't rely on the root binary target at all so it wasn't built. Thus, when dx is trying to replay the build, this will give a [dev] Build failed: Missing rustc args for replay error.

Manually rebuilding with r works, but this is against the point of enabling --hotpatch.

Expected behavior

The workspace reloads correctly.

Actual behavior

We see verbose error logs like so:

[dev] Verbose logging is now on 
[dev] Patch rebuild: changed_crates=["monoxide_font"], modified_crates={"monoxide_font", "playground", "monoxide"} 
[dev] Changed crates dag using {"monoxide_font", "playground", "monoxide"} 
[dev] replaying crates: ["monoxide_font", "monoxide"] 
[dev] Setting builder to failed state 
[dev] Build failed: Missing rustc args for replay: 'monoxide' 

... and the hotpatch never succeeded.

Steps To Reproduce

To make the investigation simpler, I have made a minimal reproduction that mirrors the basic structure of our project monoxide under the repros/issue-158-hmr subdirectory.

• Download this reproducer: https://github.com/Pangpang-Studio/monoxide/tree/3eac434ec9bc245d59177cbc0b9e9da53155d397/repros/issue-158-hmr
• Follow the reproducing instructions in https://github.com/Pangpang-Studio/monoxide/blob/3eac434ec9bc245d59177cbc0b9e9da53155d397/repros/issue-158-hmr/README.md
• Observe logs like so:

  Patch rebuild: changed_crates=["mini_font"], modified_crates={"mini_font", "mini_monoxide", "playground"}
  replaying crates: ["mini_font", "mini_monoxide"]
  Build failed: Missing rustc args for replay: 'mini_monoxide'

Environment:

• Dioxus version: 0.7.9
• Rust version: 1.95.0 stable
• OS info: macOS 26.4.1
• App platform: subsecond-only, not using Dioxus