docs: add agent loop example — durable sessions on Cloudflare Artifacts via exgit

[ivarvong]

Adds examples/agent_artifacts_session.exs: durable, forkable agent memory — pure Elixir top to bottom. The sandbox is JustBash, the git client is exgit (clone, commit, push implemented in Elixir), and each session is one Cloudflare Artifacts repo. No git binary, no subprocess, no host filesystem, no credential in argv.

The session repo is cloned in memory and mounted into the sandbox at /work, so the agent's bash writes land directly in a git workspace. A checkpoint is Workspace.commit + Exgit.push — one commit per turn, labeled with the commands that ran. Kill the process, switch machines, come back later:

$ elixir examples/agent_artifacts_session.exs demo "create a csv with sample sales data at sales.csv"
$ elixir examples/agent_artifacts_session.exs demo "add a total_arr column (mrr*12) using awk"   # remembers everything

Memory is a plain git repo — commits pushed by exgit are cloned and audited with stock git, one commit per command:

$ git log --oneline
f5a8630 turn 1: cd /work && awk -F',' 'BEGIN{OFS=","} NR==1{print $0,"total_arr"; next} ...' sales.csv
845b4a0 turn 1: mkdir -p /work && cat > /work/sales.csv << 'EOF' sale_id,customer_name,company,plan,...

State flows both ways (push files with a write-scoped token; the agent sees them on resume), and sessions fork like repos do:

$ elixir examples/agent_artifacts_session.exs demo --fork demo-experiment
$ elixir examples/agent_artifacts_session.exs demo-experiment "try the risky transformation here"

Robustness: sandbox output is scrubbed to valid UTF-8 (arbitrary bytes and truncation cannot corrupt the transcript), the durable transcript is complete while the model sees a recent window cut at prompt boundaries, and a rejected push (concurrent run of one session) fails with a clear error instead of merging.

Depends on two fixes now in flight: ivarvong/exgit#9 (Workspace.write over an unborn ref, for the first checkpoint of a fresh repo) and #48 (mkdir/rm report backend errors instead of crashing — git trees cannot hold empty directories, and agents love mkdir -p). The example installs both libraries from GitHub main, so it runs once those merge.

🤖 Generated with Claude Code

https://claude.ai/code/session_01FpxHS5iGm9ktgpnL9QZu9x