fix(targets): reject special path targets in preflight

[sylvesterkaczmarek]

Summary

Reject special filesystem nodes as path scan targets during local target normalization instead of allowing them to fail later in bundled scan setup.

Fixes #548.

Reproduction / evidence

Current upstream main at 37bf87a692fc72d41f7312cc48808d699d204fba checks only that a path target exists, resolves it, and stays inside the repository. It does not check whether the resolved target is a file or directory.

On POSIX, a Unix-domain socket inside the repository therefore passes normalizeTarget() and is returned as a valid paths target.

The bundled generate_rank_input.py scope resolver later rejects the same node because it explicitly requires is_dir() or is_file().

That contradicts the public preflight boundary, which validates local inputs before runtime initialization.

Root cause

Existence and containment checks were present, but filesystem type validation was deferred to a later Python setup helper.

Fix

After canonicalizing each path target, stat() the resolved path and require it to be a regular file or directory. A special node now raises InvalidTargetError during local target validation.

Tests / validation

Added path-target-special-files.test.ts:

• POSIX regression creates a real Unix-domain socket inside the repository and requires normalizeTarget() to reject it;
• a control verifies ordinary file and directory targets still normalize normally.

The branch is based directly on current upstream main at 37bf87a692fc72d41f7312cc48808d699d204fba and is not behind it. Production change: 14 additions, 0 deletions.

Full repository tests cannot be run in this execution environment because the repository cannot be cloned here. Pushed-head CI remains the authoritative full-suite validation.

Risk

Low. The accepted target set now matches the file/directory invariant already enforced by bundled scan setup. Normal files, directories, and in-repository symlink targets that resolve to either remain supported.