feat(devbox): add devbox.on_evict eviction notifications (SSE)

[jrvb-rl]

Description

Follow-on to the server-side flex eviction-notification work (monorepo #10325 and its successor SSE endpoint). Adds the object-oriented client surface for eviction notifications.

New API: devbox.on_evict(callback) (and devbox.cancel_on_evict()), on both the sync Devbox and async AsyncDevbox.

How it works (internal state management):

• A per-client EvictionMonitor (sdk/eviction.py, async sdk/async_eviction.py) holds the interest set: {devbox_id -> callback}. Monitors are looked up via a weak client -> monitor registry (monitor_for), so every Devbox built from the same generated client shares one monitor and thus one SSE connection. No Devbox/factory constructor signatures changed.
• The first on_evict across any devbox opens a single account-wide devboxes.watch_evictions() SSE stream on a background thread (sync) / asyncio.Task (async).
• On each event: the id is matched against the interest set; unknown ids are discarded. The devbox is removed before its callback runs, so it fires at most once even if the server repeats a notification.
• When the interest set empties, the stream is closed. Re-registering re-opens it.
• The server replays all currently-pending evictions on connect, so late registrants are still notified.
• RunloopSDK.close() / AsyncRunloopSDK.aclose() tear the monitor down.

Dependency / status

⚠️ Draft. This depends on the Stainless-generated devboxes.watch_evictions method and the DevboxEvictionEvent type (devbox_id, eviction_deadline_ms), which are generated downstream once the server endpoint lands. Those symbols are imported under TYPE_CHECKING and referenced by assumed name — they will be reconciled, and tests + an example added, once generation lands. No generated code was modified.

Testing

Deferred until the generated endpoint exists (see above). New/edited files byte-compile cleanly.

🤖 Generated with Claude Code

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[jrvb-rl]

Reconciled with the endpoint as landed:

• callback is now callback(devbox, eviction_deadline_ms) (the Devbox object + Unix-ms deadline)
• uses the real generated type DevboxEvictionEventView

Ordering: depends on runloopai/runloop#10404, which marks watch_evictions as streaming in openapi.stainless.yml so Stainless generates devboxes.watch_evictions() -> Stream[DevboxEvictionEventView]. Once that merges and Stainless regenerates (the .stats.yml bump lands the method + type), this rebases green.

[gautam-rl]

Async parity gap

EvictionMonitor (sync) got the Accept + reconnect fix, but AsyncEvictionMonitor still has the pre-fix _run:

• calls watch_evictions() with no extra_headers={"Accept": "text/event-stream"}
• runs the stream once and exits (no backoff/reconnect)

That reintroduces the silent “never fires” failure for AsyncDevbox.on_evict — same root causes called out in the sync fix commit.

Please mirror the sync monitor’s connect/reconnect loop in sdk/async_eviction.py before merge.

[jrvb-rl]

Addressed the async parity gap in 7893f59: AsyncEvictionMonitor._run now mirrors the sync monitor — it forces the Accept: text/event-stream header on watch_evictions and reconnects with capped backoff (asyncio.sleep) until no devbox is still interested, exiting quietly on intentional teardown. asyncio.CancelledError propagates cleanly. (Also ruff-formatted sdk/eviction.py, which had a wrapped call that fits on one line.)

Note: the remaining test_devboxes.py::*watch_evictions* failures are unrelated to this wrapper — they're the /v1/devboxes/evictions/watch rename: the generated method targets the new server path, but the bundled OpenAPI spec + prism mock are still on the old path from the pre-rename Stainless regen. They resolve once Stainless regenerates against the current runloop openapi.json.