Runtime paths and platform isolation

One path contract

Every installer sources install/_lib.sh, which derives runtime paths from LOCAL_PLAT. In the ordinary flat layout that is ~/.local; with DF_USE_PLAT=1, it is ~/.local/$PLAT. The latter is for one NFS-shared home used from machines with incompatible architectures, not a general performance setting.

Variable	Purpose
ARCH_BIN	executable destination: $LOCAL_PLAT/bin
CARGO_HOME, RUSTUP_HOME	Rust tools and toolchains
NVM_DIR	Node versions and global npm package tree
UV_TOOL_DIR, PYTHON_ENV	uv tool environments and managed Python
ELAN_HOME	Lean toolchains and shims
GOPATH, GOCACHE, GOBIN	Go source/cache and executable destination

The exact derivations are in _lib.sh. Platform detection chooses the highest matching install/plat/ specification; the lightweight runtime helper resolves ~/.local through a scratch symlink before adding the optional platform directory (source).

# Normal single-machine layout
./bootstrap.sh

# Only for an NFS-shared HOME across architectures
DF_USE_PLAT=1 ./bootstrap.sh

In PLAT mode, failure to find a matching platform specification is fatal. In flat mode, detection still supplies capability flags when available but no matching specification is acceptable (source).

Shell and scratch convergence

Generated login profiles use the same layout: they put the selected runtime bin ahead of Homebrew and export the language-specific homes (zprofile source). Confirm what the current shell actually resolves before diagnosing a tool:

printf '%s\n' "$DF_USE_PLAT" "${_LOCAL_PLAT:-unset}"
command -v cargo node python lean
bash ~/dotfiles/install/verify-path.sh

DF_SCRATCH can redirect large writable directories to bulk storage. The scratch installer copies, verifies entries, and only then replaces a real directory with a symlink (source). It intentionally keeps managed ~/.claude and ~/.codex directories real and moves selected unmanaged Claude subdirectories instead (source). See PLAT setup and scratch setup before enabling either feature on a populated home.

Machine-specific inputs come from host configuration. DF_TOOLS_ROOT overrides the tool base before PLAT is appended. DF_STATE_ROOT is a separate persistent host-local root, currently consumed by Codex as CODEX_HOME=$DF_STATE_ROOT/codex. Tools can be shared by compatible machines; WAL databases, locks, and daemon sockets cannot.