construct: auto-start the daemon from the TUI when none is running#398
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Now that `construct` is one binary that can also be the daemon, running the TUI with no daemon is a setup mistake rather than a user intent — so instead of erroring with a bare "connect <socket>" failure, the TUI spawns a detached `construct daemon run` in the background and waits for the socket. Opt out with CONSTRUCT_NO_AUTOSTART=1. Auto-start makes two `construct` launches able to race to start a daemon, which the old bind path handled badly: `server::serve` unconditionally unlinks the socket before binding, so a second daemon would *steal* a live socket and orphan the first's clients. Fix that race (and the same latent bug for a stray second `daemon run`) with a single-instance advisory lock: - The daemon takes an exclusive `flock` keyed to its socket path (`<socket>.lock`) before binding. The loser exits cleanly instead of stealing the socket. Held for the process lifetime; released across the restart exec() (CLOEXEC fd) and re-acquired by the new image. Daemons on different sockets don't contend. - `spawn_detached_daemon` (in the agentd lib) launches `<current exe> daemon run [--socket …]` in a new session (setsid) with logs to state_dir/daemon.log, so it survives the TUI's exit / terminal SIGHUP. - The TUI's `ensure_daemon_running` probes the socket, spawns if dead, and polls ~5s for readiness. Best-effort: on failure the normal connect error still surfaces. One-shot control subcommands (list/ping/…) intentionally do NOT auto-start — only the interactive TUI does. Updates spec 0026, README. Verified: TUI with no daemon auto-starts a detached daemon that binds the socket and survives the TUI exit; a second daemon on the same socket refuses and exits 0 while the first keeps serving.
edwin-zvs
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Jun 8, 2026
The daemon has had no unique role since #396/#398: `construct daemon run` runs it and the TUI auto-starts one. `constructd` was just a thin alias, so drop it — the daemon crate (`agentd`) is now library-only and the daemon ships solely inside `construct`. - crates/daemon: remove the `[[bin]] constructd` target and delete the `main.rs` shim; the crate is lib-only now. - e2e harness: spawn `construct daemon run` (and copy `construct` as the relocatable daemon binary) instead of `constructd run`. - scripts/test_agentd.sh, scripts/smoke.sh: launch via `construct daemon run`. - release.yml + install.sh: drop `constructd` from BINS (and `-p agentd` from the release build). The release tarball KEEPS its historical `constructd-<target>` asset name — already-released install.sh / `construct upgrade` builds fetch that exact name, so renaming it would break the download URL. - Docs/spec/comments updated; spec 0026 records that there is no standalone daemon binary and notes the one-time upgrade caveat below. Upgrade caveat (one-time): an `install.sh` baked into an *older* binary lists `constructd` in its `BINS` and aborts when it's absent from the new tarball, so `construct upgrade` across this single version hop fails — re-run the install one-liner instead. New installs and subsequent upgrades are unaffected. Verified: `cargo build --workspace` produces no `constructd`; `cargo test -p agentd` (66) and the e2e restart suite (3, incl. `restart_reloads_updated_binary`) pass with the daemon spawned as `construct daemon run`.
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Problem
After the binary consolidation (#396), running
constructwith no daemon up just errors:Now that one binary is both client and daemon, that's a setup mistake, not user intent — the TUI should just start one.
What
construct(the TUI) now auto-starts a daemon in the background when none is listening, then attaches. Opt out withCONSTRUCT_NO_AUTOSTART=1.This was the explicit non-goal in
specs/0026because a naive version is unsafe:server::serveunconditionallyremove_files the socket before binding (server.rs:30), so two racing daemons would steal each other's socket and orphan clients. This PR adds auto-start and fixes that race.How
crates/daemon/src/lib.rs): the daemon takes an exclusiveflockkeyed to its socket path (<socket>.lock) before binding. The loser exits cleanly instead of stealing the socket. Held for process lifetime; released across the restartexec()(CLOEXEC fd) and re-acquired by the new image. Daemons on different sockets don't contend. This also fixes the same latent bug for a stray secondconstruct daemon run.spawn_detached_daemon(agentd lib): launches<current exe> daemon run [--socket …]in a new session (setsid), stdio →state_dir/daemon.log, so it survives the TUI's exit / terminal SIGHUP.ensure_daemon_running(crates/cli): probes the socket, spawns if dead, polls ~5s for readiness. Best-effort — on failure the original connect error still surfaces.list/ping/…) intentionally do not auto-start; only the interactive TUI does (a scripted one-shot should fail fast, not leave a lingering daemon).specs/0026(auto-start moves from non-goal → decision, with the lock) and the README quick-start.Verification
cargo build(full workspace) ✓ ·cargo test -p agentd→ 66 passed ✓construct daemon run, which bound the socket, wrotedaemon.log, answeredping, and survived the TUI being killed ✓🤖 Generated with Claude Code