symposium sync --workspace

Updates .symposium/config.toml to reflect the current workspace dependencies.

Flow

1. Check Cargo.lock mtime — compare the mtime of Cargo.lock against the cached value (stored in the global cache directory). If unchanged, skip the rest — there’s nothing to do.

2. Read workspace dependencies — run cargo metadata to get the full dependency list for the workspace.

3. Load plugin sources — read the user config’s [[plugin-source]] entries and load their plugin manifests. For git sources, fetch/update as needed.

4. Match extensions to dependencies — for each plugin, evaluate skill group crate predicates and individual skill crates frontmatter against the workspace dependencies. Also discover available workflows.

5. Merge with existing config — load the current .symposium/config.toml and reconcile:

   • New extensions: add entries with the resolved sync-default value (from project config if set, else user config).
   • Removed dependencies: remove entries for extensions whose crate predicates no longer match.
   • Existing entries: preserve the user’s on/off choices.

6. Write config — write the updated .symposium/config.toml.

7. Cache mtime — store the current Cargo.lock mtime so future runs can skip work if nothing changed.