Replace every open-coded separator translation across the installer/hooks
source with named, tested seams in shell-command-projection.cts (the platform
seam), removing all hardcoded `/`+`\` from path handling:
- toPosixPath(p) — this machine's native path → POSIX (running-OS relative;
for local filesystem paths).
- toNativePath(p) — POSIX → native (collapses the win32 `/\//g,'\\'` ternary).
- posixNormalize(p)— unconditional `\`→`/`, OS-independent; for emitting paths
to a POSIX/bash TARGET (which may differ from the running
OS) and for parsing mixed-separator input.
core-utils.toPosixPath now delegates to the seam, so its 20+ existing consumers
resolve to one implementation; no duplicate helper.
- ~47 sites across runtime-hooks-surface, runtime-artifact-conversion,
runtime-artifact-install-plan, drift, init, worktree-safety,
installer-migrations, installer-migration-authoring, install-engine, surface,
verify, runtime-artifact-layout, schema-detect, check-command-router.
- Closes the latent POSIX-literal-backslash corruption class (the regex form
corrupts a POSIX path containing a literal backslash; split(path.sep) does not).
- New unit + fast-check property tests for all three helpers.
Closes#2246
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
