Fixes from testing email search (docs/enhancements-2026-07-07.md):
- New `folders` agent command lists the account's mailboxes (name,
delimiter, selectable), INBOX first, so agents can discover archived
mail outside INBOX.
- `search --all-folders` sweeps every selectable mailbox; each hit
carries a `folder` field, `skipped_folders` reports mailboxes the
server refused, and --limit caps visible results across the sweep.
The sweep deliberately skips EnsureFolderBaseline so a read-only
search never mutates list --new state.
- Empty search results include a generic `data.hint` with next steps.
The hint is a fixed constant per mode, so the invisibility invariant
holds: absent and policy-filtered mail produce byte-identical
envelopes (codified in TestSearchEmptyHintIndistinguishableFromFiltered).
- Skill and user docs: document `--text` full-text search as
best-effort (server-dependent); recommend --subject-contains/--from.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
steve