worktrees

name	worktrees
description	Run parallel tasks in isolated git worktrees, each with its own databases, ports, env files, and dev server. Use when creating or removing worktrees, running parallel tasks or agents, starting a dev server for a specific worktree, running browser tests against an isolated server, or when the user mentions worktree, parallel lanes, or isolated environments.

Worktrees

Each worktree is a fully isolated copy of the app: its own git checkout, its own development and test databases on the shared local Postgres, its own ports, and its own maildev. Parallel tasks never share state, so dev servers, unit tests, E2E tests, and browser sessions can run concurrently across worktrees.

Lifecycle

Create

From the main checkout (or any worktree — the scripts resolve the main repository):

pnpm run worktree:setup <lane>
pnpm run worktree:setup <lane> --branch feature/name   # custom branch (default worktree/<lane>)
pnpm run worktree:setup <lane> --base origin/main      # custom base (default origin/main)
pnpm run worktree:setup <lane> --skip-seed             # skip the dev seed

Setup is idempotent: re-running reuses the registered worktree, its ports, and its databases. It prints a summary with every port and database name. Claude Code's WorktreeCreate/WorktreeRemove hooks (wired in .claude/settings.json) run the same scripts automatically for harness-created worktrees.

What setup does: creates the worktree at ../app-worktrees/<lane> from origin/main, copies .env and .env.test from the main checkout and rewrites the managed keys, creates and migrates both databases, runs pnpm install, and seeds the development database (only when it was just created — the seed is not re-runnable).

Work

Everything runs from inside the worktree directory with the usual commands — the worktree's .env files carry the isolation:

cd ../app-worktrees/<lane>
pnpm run dev          # dev server + maildev on this worktree's ports
pnpm run dev:worker   # graphile-worker against this worktree's database
pnpm run test:unit    # resets and migrates only this worktree's test database
pnpm run build && pnpm run test:e2e tests/<spec>.spec.ts   # E2E needs a build first (test server runs the production build)

Run only the specs the lane touches — the full E2E suite is the PR's CI job, not a local step.

The setup summary (and the worktree's .env/.env.test) tells you the ports. To read them later:

grep -A 10 'managed by scripts/worktree' .env .env.test

Browser testing

Point agent-browser at the worktree's dev server port, and read emails from the worktree's own maildev REST API (login is passwordless, so magic links arrive there):

agent-browser open http://localhost:<PORT>/auth/email --session <lane>
curl -s http://localhost:<MAILDEV_WEB_PORT>/email | ...   # fetch the magic link

Use one agent-browser --session per worktree so cookies never mix.

Teardown

pnpm run worktree:teardown <lane>            # refuses if the worktree has uncommitted changes
pnpm run worktree:teardown <lane> --force    # removes anyway

Teardown kills processes listening on the worktree's ports — the whole E2E block included, so a worker stack orphaned by a killed run cannot outlive the lane — drops both databases, and removes the worktree. It never touches the branch (it may back a PR). The WorktreeRemove hook does the same minus the directory removal (the harness handles that) and never blocks.

Run teardown from the main repo checkout, never from inside the worktree being removed — removal deletes the shell's working directory, so every later command in the same chain fails (git exits 128 on a vanished cwd).

Never chain teardown behind a prerequisite with ; — it runs even when the prerequisite failed. Confirm the merge (or whatever the teardown waits on) actually succeeded, then tear down as its own command.

Give teardown a generous timeout (ten minutes) or run it in the background — never a default two-minute command budget. On a loaded machine the port sweep alone (lsof per port) can eat minutes, and a kill that lands mid-git worktree remove leaves a half-deleted tree that the next attempt's uncommitted-changes check refuses to touch. If that happens, confirm the branch's commits are merged, then git worktree remove --force by hand.

Naming and isolation model

Resource	Convention	Example (lane task-a)
Worktree directory	../app-worktrees/<lane>	../app-worktrees/task-a
Branch	worktree/<lane>	worktree/task-a
Dev database	app_wt_<slug>_development	app_wt_task_a_development
Test database	app_wt_<slug>_test	app_wt_task_a_test
Dev server / HMR	PORT / HMR_PORT in .env	7100+ / 26700+
Dev maildev SMTP / web	MAILDEV_PORT / MAILDEV_WEB_PORT in .env	15100+ / 16100+
Test server / maildev	same keys in .env.test	8100+ (four ports) / 17100+ / 18100+

Ports are spread deterministically by a hash of the lane slug, then probed for availability. The lane's test PORT heads a four-port block rather than a single port: an E2E run serves the product once per Playwright worker, on PORT through PORT + 3. Planning hands out and reserves whole blocks — including the blocks it reads back from sibling lanes' env files, and the hash itself steps in whole blocks — so two lanes can run their suites at the same time. The main checkout keeps its defaults (7002, 26680, 1047, 1087, app_development, app_test) — worktree isolation lives entirely in the worktrees' gitignored env files.

Shared across worktrees (by design): the local Postgres server, the pnpm store (installs are hardlinks, so they are fast), and external service credentials copied from .env (DigitalOcean Spaces). Anything a task does against those external services is visible to other worktrees.

The shared Postgres also shares its connection budget (max_connections, typically 100). Several lanes running test suites at once can exhaust it: unit tests fail with sorry, too many clients already or plain timeouts yet pass in isolation, and pages drop to the error boundary under load. That is host contention, not a defect in the branch — do not chase it; re-run alone or let the PR's CI, which has the database to itself, be the arbiter.

Guardrails and gotchas

• Start a worktree's dev server and worker as their own background tasks — never with & inside another task's shell. Stopping that wrapper task kills its entire process group, the server included.
• NEVER run git stash inside a worktree. The stash is one stack shared by the main repo and every worktree, so a concurrent lane's push/pop can silently swap or drop another lane's uncommitted work. To shelve work, use git diff > <file>.patch (restore with git apply) or a WIP commit.
• When the main checkout is parked on a non-main branch (a parallel session owns it), never answer repo-state questions from its working tree — grep, Read, and file listings there report the parked branch's state, not main's, and the difference reads as convincingly real. Query the ref directly instead: git fetch origin main, then git grep <pattern> origin/main -- <path> and git show origin/main:<file>.
• Run post-merge routines (pull, pnpm install, migrate, seed, baseline tests) only from the main checkout — inside a worktree, the branch tracks the lane ref and db:migrate hits the lane's isolated database. Always include pnpm install: a merged PR can add a dependency, and unit tests can stay green while tsc fails on the missing module.
• Push each successive slice of a lane under a fresh remote branch name instead of force-pushing over an already-merged tip.
• After rebasing a long-lived worktree onto main, diff app/env.server.ts/app/framework/env.server.ts against your lane's base commit — a newly-required env var must be mirrored into the worktree's gitignored .env/.env.test or the dev server and test global-setup crash.
• If a configured port is already bound, never kill the listener to reclaim it — it may be a sibling lane's live server. Start on a different free port with an overridden PORT/HMR_PORT instead. The exception is your own lane's zombie: a dead pnpm run dev task can leave maildev holding the port ("dev:maildev exited with 1") — find it with lsof -iTCP:<port> and kill it.
• db:migrate/db:rollback install the graphile_worker schema before regenerating types. If you ever run kysely-codegen/db:generate by hand against a database, make sure that schema exists first — otherwise every interface silently vanishes from while tsc stays green.