Probe connection health through a per-connection atom

[RhysSullivan]

Fixes the client-side health-probe churn seen in production on 2026-09-18, and adds a browser scenario that reproduces it.

Symptom

One signed-in browser with many non-healthy connections sent hundreds of /api/connections/.../health POSTs and /api/connections GETs per minute for as long as the dashboard stayed open. Most were aborted client-side, but hundreds per minute reached the server and upstreams. The server annotated every verdict as unchanged.

Cause

checkConnectionHealth is one shared mutation atom. useAtomSet(..., { mode: "promiseExit" }) calls registry.set and then awaits that atom's next settled result. The health hook fires one probe per list row in a loop, so each call interrupts the previous one and every row's promise resolves with the last row's verdict. Rows compare a foreign verdict against their own persisted status, see a change, refresh the connections cache, and re-probe.

Fix

checkConnectionHealthFor(address): an Atom.family of per-connection probe atoms. The hooks set and await the connection's own atom, so each probe has its own fiber and its own result. Manual "Check now" keeps its reactivity keys.

Evidence

e2e/scenarios/health-probe-churn.test.ts: 8 integrations, 4 with a probe that reads degraded, 4 with none (unknown), verdicts persisted before the browser opens, one mount of the integrations list.

	Before	After
Health POSTs sent	28	8
Connections-list GETs sent	17	2
Aborted client-side	34	0

connection-health-verdict.test.ts still passes.

🤖 Generated with Claude Code

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