Frontend builds triggered from the castle web app run inside the castle-api
systemd service, whose PATH omits nvm's versioned node dir — so `pnpm build`
died with `node: not found` even though it worked from an interactive shell.
Introduce a per-program node convention: a program declares its version the
ecosystem-standard way (.node-version / .nvmrc / package.json engines.node),
and castle_core.toolchains.resolve_node_bin() maps it to a concrete nvm bin dir
(CASTLE_NODE_VERSIONS_DIR, default ~/.nvm/versions/node; newest match wins).
The same resolver feeds both sites that run a program's node:
- build time: stacks._build_env() prepends the pinned node for the dev-verb
subprocess (keyed on the source dir), so `castle program build` uses the
program's node regardless of caller.
- run time: deploy._build_deployed() stores it in Deployment.path_prepend,
which the systemd generator puts ahead of the default unit PATH — so a
`launcher: node` service runs its program's node.
A pinned-but-uninstalled version fails loud with an `nvm install` hint instead
of a cryptic `node: not found`. Unpinned → no injection (no guessing).
Also: the systemd generator now honors an explicit PATH in defaults.env as a
full override instead of clobbering it with a trailing Environment=PATH line
(systemd's last-assignment-wins rule had silently defeated the documented
escape hatch).
Pins app/.node-version and documents the convention in the react-vite stack.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
