## What
`startRunAttempt` — the run controller's first call when a run starts —
had no retry on transient connection errors. A brief connection blip on
that call would abandon the start and send the run back through the
queue, delaying its first attempt.
This adds a jittered backoff retry, matching the existing
`continueRunExecution` path with a shorter budget, so a transient blip
is ridden out in place instead of bouncing the run.
## Why a shorter budget
The continue path retries generously. Start-attempt keeps a tighter
budget (6 attempts, ~25-40s jittered) so it rides out a transient blip
but never keeps retrying past the point the run would already have been
requeued.
## Safety
Retrying is safe: start-attempt is guarded server-side by the snapshot
id — a retry after a start has already committed is rejected, so it can
never double-start an attempt. A pure connection error (the common case)
never reached the server.
## Scope
One retry-options object on `startRunAttempt`; no other behavior change.
Warm starts share this path and get the same resilience.
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