feat(#1820): spec-optional predicate rail — author probe predicates into must_haves when SPEC omits them

docs/INVENTORY-MANIFEST.json

@@ -261,6 +261,7 @@
       "sketch-theme-system.md",
       "sketch-tooling.md",
       "sketch-variant-patterns.md",
+      "specless-probe-fallback.md",
       "spidr-splitting.md",
       "tdd.md",
       "thinking-models-debug.md",
@@ -407,6 +408,7 @@
       "semver-compare.cjs",
       "shell-command-projection.cjs",
       "smart-entry.cjs",
+      "spec-section.cjs",
       "stale-bake-guard.cjs",
       "state-command-router.cjs",
       "state-document.cjs",