⏺ Bash(until grep -qE "URL OK|hexdump|error|Error" /private/tmp/claude-501/-Users-jitinpillai-Projects-Marketing-go-app/2473ca5b-fd29-45c9-91c7-117437af28eb/tasks/b4wr…)
  ⎿  Running in the background (↓ to manage)

⏺ Background command "Upload + presign + verify Range read" failed with exit code 100
  ⎿  Interrupted · What should Claude do instead?

❯ whats going on?

⏺ The upload+presign step failed (exit 100). Let me show you exactly what happened:

  Read 1 file (ctrl+o to expand)

⏺ Where we are:

  Done in this session:
  1. ✅ Confirmed BLK_DEV_UBLK, OVERLAY_FS, NBD kernel modules all available on agent-2.
  2. ✅ Verified nydus-image export --block produces a working 6.8 GB EROFS image from our existing big-pt R2 chunks (took 13 sec, real pytorch contents mountable).
  3. ✅ Decided on NBD + nbdkit-curl-plugin for v1 (simpler than writing a ublk daemon).
  4. ✅ Installed nbdkit + nbd-client + nbdkit-curl plugin on agent-2.
  5. ✅ Uploaded the 6.8 GB EROFS image to R2 at s3://mags-workspaces/lazyload-test/img.raw.

  What just broke:
  - The next step (generate a presigned URL via aws CLI so nbdkit-curl can fetch via HTTPS) — aws isn't installed and the script's set -e killed it before the apt install could run.

  Trivial recovery — install awscli, retry. But I want to flag the bigger context before I keep grinding on this.

  This is still the SMOKE TEST, not the implementation. The actual "implement A" is a multi-day chunk of work:
  - Builder pipeline: produce EROFS image in builder VM, upload to R2.
  - Agent runtime: spawn nbdkit-curl + nbd-client per heavy deploy, attach /dev/nbdN to FC's drives[].
  - Guest init: set up overlayfs (lower=RO nbd, upper=small ext4 writable) inside the user's rootfs.
  - Lifecycle: how nbdkit + nbd-client survive freeze/wake; auth handling (presigned URLs expire); cleanup on stop.
  - Concurrency: nbd-client device pool, ports allocation.
  - Config plumbing through the Go agent code.

  The smoke test (~1 hour more work from here) just proves the mechanism works on this kernel. That's a useful checkpoint before we commit to the larger build-out, but it's not "lazy load
  shipped."

  My question for you before I keep going:

  a) Finish the smoke test only (~1 hour) — proves the chain works, you decide if you want me to do the full implementation after.

  b) Skip the smoke and go straight to integrating into the actual mags deploy --heavy flow (~2-3 days). Higher commitment, larger blast radius if something blocks.

  c) Pause — you want to think about scope / who else should be involved before I sink more time.

  Which?

✻ Cooked for 40s · 17 shells still running

❯ why aws? go with a)

⏺ R2 objects are private — nbdkit's curl plugin does plain HTTP, so it needs an auth-bearing URL. The cleanest way to make a signed URL for an S3-compatible store is aws s3 presign (one
  command, no code). Alternative would be Sigv4 headers — more work, no benefit for a smoke test.

  Proceeding with (a):

⏺ Bash(sshpass -p 'KxgzQkJrkqbrZr' ssh -o StrictHostKeyChecking=no -o ConnectTimeout=60 root@135.181.180.140 'set +e
      DEBIAN_FRONTEND=noninteractive apt-get install -y…)
  ⎿  is only available from another source

     E: Package 'awscli' has no installation candidate
     … +10 lines (ctrl+o to expand)

⏺ Ubuntu 24.04 dropped the awscli package. Let me check if s5cmd (already installed) has a presign command:

⏺ Bash(sshpass -p 'KxgzQkJrkqbrZr' ssh -o StrictHostKeyChecking=no root@135.181.180.140 's5cmd --help 2>&1 | grep -iE "presign|run" | head -5
      echo…)
  ⎿     select          run SQL queries on objects
        run             run commands in batch
        presign         print remote object presign url
     … +12 lines (ctrl+o to expand)

⏺ Bash(sshpass -p 'KxgzQkJrkqbrZr' ssh -o StrictHostKeyChecking=no root@135.181.180.140 'set -e
      URL=$(AWS_ACCESS_KEY_ID=3b1dc2344b31d36b135e17e70b05a829 AWS_SECRET_ACC…)
  ⎿  URL prefix: https://fc75c1e0b6b81b773cc28de5441bac6d.r2.cloudflarestorage.com/mags-workspaces/lazyload-test/img....

     === HEAD via curl ===
     … +10 lines (ctrl+o to expand)

⏺ URL works for GET-with-Range (the 403 is just HEAD-not-allowed on presigned URLs — irrelevant for nbdkit which uses GET). Now starting nbdkit + attaching nbd:

⏺ Bash(sshpass -p 'KxgzQkJrkqbrZr' ssh -o StrictHostKeyChecking=no root@135.181.180.140 'set +e
      URL=$(cat /tmp/blocktest/r2_signed_url)…)
  ⎿  === start nbdkit serving R2 URL ===
     pid: 2347491
     … +10 lines (ctrl+o to expand)

⏺ URL works for GET-with-Range (the 403 is just HEAD-not-allowed on presigned URLs — irrelevant for nbdkit which uses GET). Now starting nbdkit + attaching nbd:

⏺ Bash(sshpass -p 'KxgzQkJrkqbrZr' ssh -o StrictHostKeyChecking=no root@135.181.180.140 'set +e
      URL=$(cat /tmp/blocktest/r2_signed_url)…)
  ⎿  === start nbdkit serving R2 URL ===
     pid: 2347491
     LISTEN 0      4096                             0.0.0.0:10809      0.0.0.0:*    users:(("nbdkit",pid=2347491,fd=7))
     … +38 lines (ctrl+o to expand)

⏺ End-to-end lazy load — working.

  What you just saw, on agent-2 with zero custom code:

  R2 (6.8 GB EROFS image)
    ⇣ HTTPS Range
  nbdkit-curl  (presigned URL)
    ⇣ NBD protocol
  nbd-client  →  /dev/nbd1  (6960 MB block device, EROFS)
    ⇣ kernel block reads
  mount -t erofs ro
    ⇣
  cat /etc/os-release  →  "Ubuntu 22.04.4 LTS"  in 1.72 s

  Only the chunks needed for that read were fetched. Not the 6.8 GB. The 1.72 s is end-to-end TLS setup + several metadata range reads + the data block — first-read cold case. Subsequent
  reads of nearby chunks will hit nbdkit's internal cache (or the kernel page cache).

  The architecture is proven on the stack we have. No kernel rebuild, no custom daemon.

  What remains for actual mags deploy --heavy (the multi-day work)

  The smoke test used hand-rolled commands. The actual implementation:
⏺ End-to-end lazy load — working.

  What you just saw, on agent-2 with zero custom code:

  R2 (6.8 GB EROFS image)
    ⇣ HTTPS Range
  nbdkit-curl  (presigned URL)
    ⇣ NBD protocol
  nbd-client  →  /dev/nbd1  (6960 MB block device, EROFS)
    ⇣ kernel block reads
  mount -t erofs ro
    ⇣
  cat /etc/os-release  →  "Ubuntu 22.04.4 LTS"  in 1.72 s

  Only the chunks needed for that read were fetched. Not the 6.8 GB. The 1.72 s is end-to-end TLS setup + several metadata range reads + the data block — first-read cold case. Subsequent
  reads of nearby chunks will hit nbdkit's internal cache (or the kernel page cache).

  The architecture is proven on the stack we have. No kernel rebuild, no custom daemon.

  What remains for actual mags deploy --heavy (the multi-day work)

  The smoke test used hand-rolled commands. The actual implementation:

  1. Build pipeline change — builder VM produces an EROFS image (in addition to / instead of nydus chunks), uploads to R2 at a known key. Builder needs more scratch space to assemble big
  images.
  2. Per-deploy presigned URL — orchestrator or agent generates a long-lived presigned URL when starting the deploy. Refresh before it expires.
  3. Agent runtime — spawn nbdkit-curl + nbd-client per deploy. Pool of /dev/nbdN devices. Pass /dev/nbdN to FC's drives[] instead of the materialized .ext4 file.
  4. Guest overlay — modify /sbin/init-mags to mount NBD device as /lower (RO EROFS), set up /dev/vdb as /upper (writable ext4), overlayfs mount as /, pivot_root, exec user CMD.
  5. Lifecycle — on freeze, snapshot includes the NBD device state. On wake, re-spawn nbdkit + nbd-client first, THEN LoadSnapshot. Cleanup on stop.
  6. Path-A removal — once lazy-load works, retire MaterializeHeavy. Heavy deploys become "the only path."

  Decision points for your input before I keep going

  - EROFS production: in the builder VM (clean but needs disk) OR on the agent host (simpler but eats agent CPU at deploy time)?
  - Presigned URL lifetime: 24 h means renewal logic; or use R2 → custom-domain with token-bearer auth header so the URL never expires (small CF Worker).
  - Cache layer on agent: nbdkit-curl has an in-memory cache, nothing on disk. For warm restarts we'd want a disk-backed LRU. Worth adding now (small nbdkit filter) or later?

  Want me to start on items 1-3 (the agent-side wiring + builder change) using your defaults if you'd rather not chime in on each detail?

✻ Churned for 2m 10s · 17 shells still running

※ recap: Goal: implement lazy load for `mags deploy --heavy` so 100 GB images cold-boot in seconds. Smoke test on agent-2 just proved NBD + nbdkit-curl + EROFS from R2 works end-to-end.
  Next: start the agent-side wiring + builder change.

❯ export mags_session.txt