Arch Index

Build and validate .arch/index.json — a committed map from each architectural component of this repository to the real directories and files that implement it, pinned to a git commit, with every path verified to exist. Also detects structural drift between that index and the current code. Use when asked to map a codebase, produce a component or code-ownership index, find which files implement a component, check whether architecture docs are stale, or detect architecture drift after a refactor. Triggers include 'map the codebase', 'component index', 'which files implement X', 'is the architecture still accurate', 'architecture drift', 'refresh the architecture index'.