Function build_wasm_canisters_cached_with_progress 

pub fn build_wasm_canisters_cached_with_progress<F>(
    spec: &WasmBuildSpec,
    config: WasmBuildProgressConfig,
    observer: F,
) -> Result<WasmBuildOutcome, WasmBuildError>
where
    F: FnMut(WasmBuildProgressEvent),

Build or reuse one exact Wasm set while streaming structured progress.

Cargo output remains captured for WasmBuildError::CommandFailed and is additionally forwarded as raw chunks when enabled. Quiet Cargo processes emit periodic heartbeats, so a legitimate cold build need not appear stalled. Observer panics propagate after terminating the child process and preserving normal incomplete-entry cleanup.