My #1071 made IsRunning return (false, err) on all error paths, but that
breaks a2a_proxy which depends on Docker provisioner's (true, err) contract.
Without this fix, any brief CP outage causes a2a_proxy to mark workspaces
offline and trigger restart cascades across every tenant.
Contract now matches Docker.IsRunning:
transport error → (true, err) — alive, degraded signal
non-2xx response → (true, err) — alive, degraded signal
JSON decode error → (true, err) — alive, degraded signal
2xx state!=running → (false, nil)
2xx state==running → (true, nil)
healthsweep.go is also happy with this — it skips on err regardless.
Adds TestIsRunning_ContractCompat_A2AProxy as regression guard that
asserts each error path explicitly against the a2a_proxy expectations.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
25b560960a