implement six-skill gstack 2 runtime

compat/guard.md

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+<!-- GENERATED by scripts/gstack2/generate-skill-tree.ts; do not edit. -->
+# Compatibility alias: /guard
+
+This is not a public/discoverable skill. Route the legacy invocation to `$debug --mode Diagnose-only --module guard`, then read [the preserved module](../skills/debug/references/legacy/guard.md) in full.
+
+- Tree: `debug`
+- Public mode: `Diagnose-only`
+- Legacy internal alias: `guard`
+- Dispatcher role: `internal`
+- Mandatory specialist input: `false`