Lab 3 — Sessions: continue, resume, fork
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Lab 3 — Sessions: continue, resume, fork

Start from: app/ at tag lab02b-done, with the Lab 0 setup loaded (see Working in app/).

Goal: a session is the conversation (messages, tool calls, results), saved on disk by the harness. It is not a snapshot of your files. You pause work, change the repo behind Claude’s back, then continue, resume and fork the conversation, and watch what it does and doesn’t know.

1. Start a named session and investigate

claude -n low-stock-threshold

The low-stock threshold is hardcoded. Investigate how it's used and write NOTES.md with a short plan to make it configurable (CLI flag and/or environment variable). Don't change any code yet.

Exit with /exit. The session is saved under ~/.claude/projects/<encoded-app-path>/.

2. Change the repo while Claude isn’t looking

In the same terminal, act as a teammate:

git add NOTES.md ; git commit -m "docs: threshold notes"
(Get-Content catalog.csv) -replace '^(P4,[^,]+,\d+),\d+$', '${1},2' | Set-Content catalog.csv
git commit -am "chore: restock data from warehouse sync"

git add NOTES.md && git commit -m "docs: threshold notes"
sed -i.bak -E 's/^(P4,[^,]+,[0-9]+),[0-9]+$/\1,2/' catalog.csv && rm catalog.csv.bak
git commit -am "chore: restock data from warehouse sync"

3. Continue the most recent session

claude -c

Continue: implement the plan from NOTES.md, with tests. Before you start, tell me which products are currently low on stock.

Observe: the conversation is restored, so it remembers the plan without re-reading everything. But does it trust its memory of catalog.csv or re-read the file? Is P4 (stock now 2) in its list? A restored session can hold stale facts about files that changed since. Note whether it re-checks. Exit when the feature is done and tests pass; commit it.

4. Resume by name, and fork an alternative

claude --resume low-stock-threshold

--resume with a name or search term opens the session picker; with no argument it lists recent sessions. Now fork that conversation, so you can try a different design without polluting the original history:

git switch -c try/env-only
claude --resume low-stock-threshold --fork-session

Alternative design: drop the CLI flag and support only an environment variable LOW_STOCK_THRESHOLD. Implement it and run the tests.

Exit, and check the /resume picker: the original and the fork are separate entries. Decide which design you prefer, then switch back to main and delete the branch you’re not keeping (git switch main; git branch -D try/env-only).

Record

Checkpoint

git switch main ; python -m pytest -q
git tag lab03-done