Regenerates the project's context index (index.yaml) from the YAML frontmatter across every context file, grouping entries by typology (findings/plans/goals/evidence/guides/follow-ups/merge-requests/tickets/decisions/notes/research), and validates that each file carries the required frontmatter fields. Also computes which active files are ready to work on, from optional typed `blocks`/`blocked-by` dependency links (scripts/context-ready.sh). Use when the index is stale, context files were added, renamed, or removed, a pre-commit gate blocks a commit because a context file is missing frontmatter, or someone asks what's ready/unblocked/blocked across the context backlog. Do not use it to create new context files (use create-context-file instead), to hand-edit the index, or as a substitute for fixing frontmatter at the source.