Why: the five builtin tools could not express file discovery (no glob),
code search (literal-only grep), paged reads (200 KiB silent
truncation), or batch edits, capping the kernel below general coding-
agent parity.
Evidence: go vet ./... clean; go test ./... all ok. New cases cover
numbered line ranges and beyond-EOF rejection, regex/include/
ignore_case grep with invalid-regex errors, double-star glob
(**/*.go, docs/**, no-match), workspace confinement of glob, and
multi_edit atomicity (failed batch leaves the file untouched).
Impact: WorkspaceTools now registers 7 tools (adds glob, multi_edit);
read_file gains optional offset/limit and announces truncation; grep
gains regex/include/ignore_case while keeping literal default
behavior; existing callers see only additive changes.
Refs: docs/parity-matrix.md #3 (tool semantics negatives, Batch2).
