Probe server/discover once, persist the DiscoverResult, and reconnect with zero round-trips. The first client connects at mode="auto" (one server/discover request inside __aenter__); a second client at mode=LATEST_MODERN_VERSION, prior_discover=<cached> enters with no wire traffic and has server_info / server_capabilities available immediately.

Run it

# over HTTP — Streamable HTTP only; in-memory has no "round-trip" to skip.
# The client self-hosts the server on a free port, runs, then tears it down.
uv run python -m stories.reconnect.client --http
# same, against the lowlevel-API server variant
uv run python -m stories.reconnect.client --http --server server_lowlevel

What to look at

client.py — the first Client(targets(), mode="auto"). The mode="auto" connect ladder runs server/discover inside __aenter__; client.session.discover_result is the cached result. Round-trip it through model_dump_json() / DiscoverResult.model_validate_json() to model an on-disk cache.
client.py — Client(targets(), mode=LATEST_MODERN_VERSION, prior_discover=rehydrated). A version pin plus a prior DiscoverResult installs the cached state via ClientSession.adopt() with no initialize and no server/discover on the wire — the era-neutral client.server_info / .server_capabilities accessors are populated before the first request.
client.py — targets(). A Client cannot be re-entered after exit; each call yields a fresh target against the same server, so the reconnect is a genuinely new connection.

Caveats

mode=<version-pin> without prior_discover= synthesizes a placeholder whose server_info is Implementation(name="", version=""). Pass the cached result to get real identity on reconnect. Whether Client should expose a public synthesizer (or refuse the bare pin) is open.
client.session.discover_result is a one-hop reach into the mechanics layer; Client does not yet surface the cached result directly.
The wire-level proof that the second entry sends zero requests lives in the interaction suite (test_prior_discover_populates_state_with_zero_connect_time_traffic); this story asserts only what's observable through the public Client surface.

README.md

reconnect

Run it

What to look at

Caveats

Spec

See also