P1 invariant: the REPL works out of the box — no daemon, no config, no latency change

[justrach]

The standing guarantee that gates the entire detachment arc (#420, built on #422). Typing graff in a directory must always give exactly today's experience: one process, no daemon, no socket, no setup step, in-process rendering at in-process latency. Detachment is strictly opt-in (backgrounding a session, graff attach), never the default path.

Concretely, every slice of #422/#420 is bound by:

1. In-process TuiSink stays the default transport. The event contract is the same either way; the socket is an alternative sink transport, not a replacement. A Phase-2 PR that makes the plain REPL depend on a daemon, a socket handshake, or any background service violates this issue.
2. Behavior gate: the golden eval harness (byte-identical --json + PTY transcripts) rides every conversion PR, as it has for feat(engine): #422 slice 1 — typed event vocabulary + EngineSink inversion for agent_stream #423/feat(engine): #422 slice 1b — agent_ws and argstream emit typed events; spinner aliases and inline notices gone #426.
3. Latency gate (from the first transport milestone): the same scripted session run in-process vs attached must byte-match its rendered transcript, and a delta-to-paint benchmark (p99) must show no regression on the in-process default.
4. Cold start: no measurable startup regression on the plain graff path (no daemon probe on the hot path; discovery of background sessions happens in graff agents, not at REPL boot).

This issue stays open for the life of the arc; close it only when #420 ships with all gates in CI.

[justrach]

Cluster links: umbrella #420 · output completion #429 · input inversion #430 · lease prereq #413 · milestone 1 #431 · epic #422. This invariant gates all of them.

[justrach]

Triage 2026-08-28. This issue’s own close rule still holds: stay open for the life of the #420 arc.

Checked today: default graff is still one in-process REPL (ADR 0041: same-process ACP client, no child graff acp, no boot-time daemon probe). #431 (graff agents / graff attach) has not shipped, so the attach-parity + delta-to-paint gates are not in CI.

Leaving open.