Changes touching this path

• loot grep grows the options that make a search usable, and two of the ticket's acceptance criteria turned out to ask for something this verb already did unconditionally: -n wants line numbers, which loot grep has printed since #391 with no flag at all, so making them conditional would silently change the output of every invocation ever typed and -n ships instead as a pinned compatibility spelling of the default, exactly as -F now spells out the fixed-string matcher that stays the default with the regex behind -E. the same compatibility argument decides the row shape, so the change column is printed only when the selector was a REVSET, a thing this verb could not search before, while a point selector keeps the three-column row it always had. the pathspec is the declared option group and not a fourth hand-rolled one, which cost the leaf its NO_PATHS declaration first: a group's trailing list begins where the leaf's own arity ends, so grep declares two opaque positionals and attaches PATHSPEC, and because its selector is optional a bare trailing path still reads as the selector and the operator says which they meant with the separator. -E is a hand-written POSIX ERE over bytes rather than the regex crate, which is loot-cli's standing dependency-light no-clap stance applied rather than a new decision; that stance is argued in the ctrlc note in the workspace manifest, not by adr 0041, which governs loot-core and the server-side dependencies and does not reach this; and the cost is measured rather than guessed, by resolving regex alone and diffing its closure against this lock: three new entries, regex and regex-syntax and aho-corasick, since memchr and regex-automata are already in the graph through bstr from gix, though regex-automata is linked there with default features off and carries no dependencies at all in this lock, so regex would compile far more of it than anything does today, all to serve one optional flag on one read verb. AC7 is a real requirement and it is keyed on the content address rather than the path, since repo.put mints a fresh address per call and only a carried tree entry reuses one: measured, a two-change revset over three paths each opens four objects where the natural walk opens six and returns byte-identical rows, which is why the pin counts ObjectGets instead of reading the answer. AC6's aggregation needed a fixture the engine refuses to build the obvious way, because a path this identity cannot open cannot be re-captured while it sits on disk, and the count is per change and path, so one sealed path carried through two changes is two skips. the per-object read is loot-core's own readable_tree classification lifted out rather than copied, so grep and surface cannot come to disagree about what a burned path is (#1500) c1ad796e · dbf3dbe6…

Renames are not followed. loot's tree maps a path to an address, so a rename is a delete and an add. This list is the history of the name, not of the bytes.