infra(spikes): add README for LIT-2888 EC2 spike

Documents how to run the spike, what AWS resources are required (subnet,
SG, IAM instance profile), the cost envelope, and how to clean up the
one-time infra after Epic B ships.

infra/spikes/README.md

@@ -0,0 +1,89 @@
+# EC2 provisioning spike (LIT-2888)
+
+Spike for Epic B (Cursor SDK on LiteLLM, full-VM provisioning). Proves end-to-end
+that LiteLLM can launch an EC2 in the *customer's* AWS account, push a hydrate
+command to the running instance, and tear it down — all without holding AWS
+credentials server-side beyond what BYOC config supplies.
+
+**This is throwaway code.** It exists to produce one number: warm-attach latency.
+That number decides B2's hydrate transport design.
+
+## Files
+
+- `ec2_provision_poc.py` — main spike. Launches one t3.large, fires user-data
+  callback, sends an SSM RunCommand, terminates. Always cleans up via `finally`.
+- `callback_receiver.py` — 5-line Flask app on port 3333. Logs every callback
+  and exposes them at `/callbacks` for the spike script to poll.
+
+## What you need before running
+
+A one-time AWS setup (B0 already did this for the LiteLLM PoC account):
+
+| Resource | Value (us-west-2) |
+| --- | --- |
+| AMI | `ami-06c6960215cdac78d` (Ubuntu 24.04) |
+| Subnet | `subnet-071fed49c5887c37d` (default VPC, public, auto-public-IP) |
+| Security group | `sg-01fcce386c017c9e7` (egress all, ingress none) |
+| IAM instance profile | `litellm-ec2-poc` (attached `AmazonSSMManagedInstanceCore`) |
+
+All resources are tagged `litellm-spike=b0` so they're easy to find / clean up
+later.
+
+## How to run
+
+```bash
+# Terminal 1 — Flask receiver
+uv run python infra/spikes/callback_receiver.py
+
+# Terminal 2 — ngrok tunnel
+ngrok http 3333
+# Copy the https://xxx.ngrok-free.app URL.
+
+# Terminal 3 — the spike
+export CALLBACK_URL="https://xxx.ngrok-free.app/spike"
+uv run python infra/spikes/ec2_provision_poc.py
+
+# Or 5 back-to-back for the consistency validation:
+for i in 1 2 3 4 5; do
+  uv run python infra/spikes/ec2_provision_poc.py || exit 1
+done
+```
+
+The script prints a `SUMMARY:{...}` JSON line on stdout at the end of each run.
+Pipe through `jq` to collect timings across runs.
+
+## Safety
+
+Every `RunInstances` is paired with `TerminateInstances` in a `finally` block.
+If termination fails, the script attempts a tag-scoped emergency cleanup
+(everything tagged `litellm-spike=<this-run-id>`).
+
+If a script run is killed mid-way (Ctrl-C, SIGKILL), confirm no leftovers with:
+
+```bash
+aws ec2 describe-instances --profile litellm-poc --region us-west-2 \
+  --filters Name=tag:litellm-spike,Values=* \
+            Name=instance-state-name,Values=pending,running,stopping,stopped \
+  --query 'Reservations[].Instances[].[InstanceId,State.Name,Tags]' --output table
+```
+
+## Cost
+
+t3.large in us-west-2 = $0.0832/hr. One spike cycle ≈ 4–5 min wall clock, so
+~$0.007 per run. Budget for the full spike (5 runs + 2 failure-mode tests) is
+under $0.10 — well below the $1 hard cap.
+
+## Tearing down the one-time infra (after Epic B is done)
+
+```bash
+aws iam remove-role-from-instance-profile --profile litellm-poc \
+  --instance-profile-name litellm-ec2-poc --role-name litellm-ec2-poc
+aws iam delete-instance-profile --profile litellm-poc \
+  --instance-profile-name litellm-ec2-poc
+aws iam detach-role-policy --profile litellm-poc \
+  --role-name litellm-ec2-poc \
+  --policy-arn arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore
+aws iam delete-role --profile litellm-poc --role-name litellm-ec2-poc
+aws ec2 delete-security-group --profile litellm-poc --region us-west-2 \
+  --group-id sg-01fcce386c017c9e7
+```