feat(dev): detect package manager per project dir instead of hard-coding pnpm

[kaihaase]

Summary

Every lt dev flow that spawned a package-manager call (api/app start in dev up + dev test, build + dev-runner fallbacks in the test session, worktree install on ticket start) used to hard-code pnpm via the legacy LT_PNPM_BIN env var.

In an npm-only monorepo (e.g. document-analyzer, where AGENTS.md explicitly forbids pnpm), the supervised processes died on the first call:

1. pnpm regenerated a foreign pnpm-lock.yaml.
2. pnpm exited non-zero with ERR_PNPM_IGNORED_BUILDS on un-approved scripts (bcrypt, sharp, esbuild).
3. lt dev status reported api: dead + app: dead → user sees a white page behind Caddy.

Mechanics

New src/lib/dev-package-manager.ts exposes pickPackageManager(cwd) with the chain:

1. LT_PM_BIN env (new generic override).
2. LT_PNPM_BIN env (legacy alias — kept so older CI configs don't regress).
3. pnpm-lock.yaml in cwd → pnpm
4. yarn.lock in cwd → yarn
5. package-lock.json in cwd → npm
6. Fallback pnpm (historical default for fresh scaffolds without a lockfile).

Returns a PackageManagerCommand with bin, installArgs, runScript() and exec() so call sites emit ONE argv regardless of manager. exec() inserts -- for npm so option flags (--shard=1/2, --reporter=line) reach the binary instead of being re-parsed as npm's own.

Per-component detection — a monorepo with an npm api + pnpm app drives each component correctly.

Files changed

File	Change
src/lib/dev-package-manager.ts	NEW — pure resolution helper + PackageManagerCommand.
src/commands/dev/up.ts	api start + app dev now per-dir resolved.
src/commands/dev/test.ts	api/app test:e2e, sharded playwright call now per-dir resolved.
src/lib/dev-test-session.ts	api/app build, fallback start/dev, sharded exec now per-dir.
src/lib/dev-ticket.ts	pnpmInstall → installWorktreeDeps, lockfile-aware.
src/commands/ticket/start.ts	calls the renamed helper.
__tests__/dev-package-manager.test.ts	NEW — 14 unit tests.

Test plan

• npx jest __tests__/dev-package-manager.test.ts — 14 / 14 green.
• Affected suites still pass: dev-bootstrap, dev-test-session, dev-ticket, dev-up-soft-migrate, dev-package-manager — 74 / 74 green.
• npm run compile — TypeScript clean.
• Live-verified end-to-end: lt dev up against an npm-only monorepo (document-analyzer) now boots api + app cleanly; previously both died on pnpm install exit 1.
• Smoke-test against a pnpm monorepo on a clean checkout (any one of the lt fullstack starters) to confirm the historical default still applies.
• Smoke-test the worktree-install path with lt ticket start against a yarn project (if any consumer has one).

🤖 Generated with Claude Code