feat(grep): add agent-safe and JSON output modes

[isink17]

Summary

• add opt-in agent-safe grep output with explicit total-match, per-file, context-row, and line-length limits
• add files-only, count-by-file, top-files, and stable JSON result modes
• preserve existing grep defaults, native rg behavior, argument ordering, stdin handling, and child exit codes

Compatibility

• default rtk grep behavior remains unchanged unless a new mode, explicit limit, environment opt-in, or config opt-in is used
• rtk rg --json remains native ripgrep JSON
• explicit CLI limits override agent-safe, environment, and config defaults
• --all and --full-lines independently disable match caps and line clipping
• default piped match output remains live; piped structured and JSON modes emit after EOF
• --context-only remains an RTK option and is supported before or after the pattern/path
• native help and version behavior remains available without enabling structured processing

Agent-safe output

--agent-safe defaults to:

• 80 total matches
• 5 matches per file
• 240 Unicode scalar values per line

Match and context rows are accounted for separately. Context output remains associated with displayed matches and cannot bypass configured bounds.

JSON

• emits one deterministic newline-terminated rtk.grep.v1 object
• supports matches, files-only, count-by-file, top-files, zero-match, capped, clipped, context, partial-result, and error cases
• preserves machine-openable paths, exact forwarded recovery argv, and native grep exit codes
• emits no human text or ANSI on stdout
• partial output plus an engine error preserves parseable results and includes a non-null error
• rtk rg --json remains native ripgrep JSON

Parser safety

• NUL-separated grep output is preferred through --null or -Z
• Windows grep without NUL support uses a platform-limited ordinary parser
• native context rows require NUL-safe grep output; ordinary Windows fallback rejects context modes before child execution rather than guessing around valid -digits- filenames
• native grep operands are tracked by argv role; incomplete required native options fail closed before child execution in RTK-owned modes
• POSIX grep without NUL-safe filename output fails closed for RTK-owned structured modes
• parser-unavailable JSON emits a typed error object and exit 2 without executing the child
• parser-unavailable non-JSON structured modes return a clear error without passthrough
• default legacy grep behavior remains unchanged

Safety

• structured capture uses fixed-size reads and bounds retained stdout and stderr to 10 MiB per stream
• capture overflow fails closed with a partial-result error
• ambiguous ordinary colon-separated POSIX paths are never parsed as structured records
• forced ANSI output and incompatible native shape modes are rejected before structured execution
• active RTK processing modes cannot silently fall through to native output

Validation

• focused search tests: 122 passed, 2499 filtered
• config tests: 12 passed, 2609 filtered
• grep integration tests: 1 passed, 10 filtered
• exact no-match guard: 1 passed, 10 filtered
• cargo check --all-targets: passed
• cargo fmt --all -- --check: passed
• cargo clippy --all-targets: passed
• full suite: 2636 passed, 8 ignored
• manual checks passed for native operand-role preservation, incomplete native operand rejection, separated forced-color handling, shape-flag rejection, Windows filenames and labels, ordinary-context fail-closed behavior, bounded capture and live-stream decoding, child draining/reaping, piped --context-only, partial-result JSON, invalid regex, ANSI rejection, Unicode handling, PowerShell JSON parsing, and native rtk rg --json

[MiVi29]

sorry, did by mistake.