Module sidecar 

Long-lived local server (“sidecar”) lifecycle for picoframe apps.

A sidecar is a persistent localhost HTTP server (e.g. a Bun process) spawned once at app startup, so substantial non-Rust business logic runs in-process without per-call subprocess cold-start. This module owns the full lifecycle:

• spawn the bundled binary (Tauri externalBin, resolved next to the app exe) or a dev command (bun run server.ts) when the compiled binary is absent under tauri dev;
• handshake — the child binds an ephemeral 127.0.0.1 port and writes a 0600 {port,token,pid} file we poll; the token is a per-spawn shared secret we generate;
• health — poll GET /health (bearer auth) until ready or timeout;
• stream — hold an SSE connection to GET /events and re-emit each progress record as the Tauri event "<event_prefix>/progress";
• supervise — if the child exits unexpectedly and restart is set, respawn it;
• shutdown — kill the child on app exit. (The child also self-exits if it sees the parent pid disappear, covering the SIGKILL case that a parent-side kill cannot.)

Transport is loopback TCP + a shared-secret bearer token rather than a Unix socket, so the same code path works on Windows, macOS and Linux.

Structs

Sidecar

A running, supervised sidecar. Cheaply cloneable (Arc inside); dropping the last clone kills the child.

SidecarOptions

Configuration for a supervised sidecar.