Replace the Phase 3 stub with a working rolling implementation.
Flow:
- Capture previous deployment's per-index container ids up front.
- For i = 0..replicas-1:
- Start new[i] (gen-suffixed name, coexists with old[i]).
- Wait for new[i] healthy (new waitForOneHealthy helper).
- On success: stop old[i] if present, continue.
- On failure: stop in-flight new[0..i], leave un-replaced old[i+1..N]
running, mark FAILED. Already-replaced old replicas are not
restored — rolling is not reversible; user redeploys to recover.
- After the loop: sweep any leftover old replicas (when replica count
shrank) and mark the old deployment STOPPED.
Resource peak: replicas + 1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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