fix(#3493): confine key_links from:/to: to the project directory (#3506)

`cmdVerifyKeyLinks` resolved `from:` and `to:` with `path.join(cwd, <value>)` where the value comes verbatim from plan YAML. `path.join` normalizes `../` rather than rejecting it, so a plan travelling with a repository could name any file the process can read, and the command reports whether the link's `pattern` matched it — an arbitrary-file-read oracle reachable from `verify-phase`.

Both reads now go through `validatePath` in src/security.cts, the existing realpath-based confinement seam already used at 11 call sites. Not a missing capability — a bypassed one.

Two defects in that seam, found by adversarial review and fixed here because they affect all 11 callers:

1. A dangling in-project symlink escaped confinement. A link to an EXISTING outside path was refused (realpath lands outside) while a link to a MISSING outside path took the parent-resolution fallback and was accepted — an existence oracle for arbitrary absolute paths. lstat succeeds on a dangling link and throws ENOENT on a truly absent path; an unresolvable link is now refused. A symlink resolving inside the project is still accepted.

2. A canonicalized base was compared against an uncanonicalized path when a file and its parent were both missing, wrongly refusing legitimate in-project paths on any non-canonical cwd (every macOS temp dir). This was a live regression in this PR: the wave-pending classification (#1202) depends on the not-yet-created case. Resolution now walks up to the nearest existing ancestor.

Two adjacent aborts fixed: the from: read sat outside the per-link try, so a non-ENOENT errno killed the whole command; and an empty from: read the cwd directory, throwing EISDIR. Both now fail per-link.

The issue was filed as a fourth ADR-0174 consolidation loss. It is not one — validatePath/requireSafePath never went away, only the SDK's name for the concept did. This is an instance of epic #3473's F2 family. The ADR-0174 loss count is three.

Closes #3493

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/CLI-TOOLS.md

@@ -547,6 +547,8 @@ node gsd-tools.cjs verify artifacts <plan-file>
 node gsd-tools.cjs verify key-links <plan-file>
 ```
 
+`verify key-links` confines each link's `from:`/`to:` to the project directory (#3493): a path that resolves outside the project (via `../` traversal, an absolute path, or a symlink) is never read. That link's `links[]` entry reports `path_rejected: "from"` or `path_rejected: "to"` (whichever field was rejected) alongside `verified: false`, without echoing the underlying path-confinement error (which would embed an absolute host path). A rejected link fails independently — it does not abort evaluation of the other links in the same plan, and does not set `path_rejected` on links whose paths resolve inside the project.
+
 ---
 
 ## Validation Commands