feat: add mypy command with grouped error output

.claude/hooks/rtk-rewrite.sh

@@ -170,6 +170,10 @@ elif echo "$MATCH_CMD" | grep -qE '^pip[[:space:]]+(list|outdated|install|show)(
   REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^pip /rtk pip /')"
 elif echo "$MATCH_CMD" | grep -qE '^uv[[:space:]]+pip[[:space:]]+(list|outdated|install|show)([[:space:]]|$)'; then
   REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^uv pip /rtk pip /')"
+elif echo "$MATCH_CMD" | grep -qE '^mypy([[:space:]]|$)'; then
+  REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^mypy/rtk mypy/')"
+elif echo "$MATCH_CMD" | grep -qE '^python[[:space:]]+-m[[:space:]]+mypy([[:space:]]|$)'; then
+  REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^python -m mypy/rtk mypy/')"
 
 # --- Go tooling ---
 elif echo "$MATCH_CMD" | grep -qE '^go[[:space:]]+test([[:space:]]|$)'; then

CLAUDE.md

@@ -219,6 +219,7 @@ rtk gain --history | grep proxy
 | pnpm_cmd.rs | pnpm package manager | Compact dependency trees (70-90% reduction) |
 | ruff_cmd.rs | Ruff linter/formatter | JSON for check, text for format (80%+ reduction) |
 | pytest_cmd.rs | Pytest test runner | State machine text parser (90%+ reduction) |
+| mypy_cmd.rs | Mypy type checker | Group by file/error code (80% reduction) |
 | pip_cmd.rs | pip/uv package manager | JSON parsing, auto-detect uv (70-85% reduction) |
 | go_cmd.rs | Go commands | NDJSON for test, text for build/vet (80-90% reduction) |
 | golangci_cmd.rs | golangci-lint | JSON parsing, group by rule (85% reduction) |
@@ -312,3 +313,10 @@ GitHub Actions workflow (.github/workflows/release.yml):
 - DEB/RPM package generation
 - Automated releases on version tags (v*)
 - Checksums for binary verification
+
+## Active Technologies
+- Rust 2021 edition + regex (1), lazy_static (1.4), anyhow (1.0) -- all already in Cargo.toml (001-mypy-cmd)
+- SQLite via rusqlite (existing tracking.rs) (001-mypy-cmd)
+
+## Recent Changes
+- 001-mypy-cmd: Added Rust 2021 edition + regex (1), lazy_static (1.4), anyhow (1.0) -- all already in Cargo.toml

hooks/rtk-rewrite.sh

@@ -170,6 +170,10 @@ elif echo "$MATCH_CMD" | grep -qE '^pip[[:space:]]+(list|outdated|install|show)(
   REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^pip /rtk pip /')"
 elif echo "$MATCH_CMD" | grep -qE '^uv[[:space:]]+pip[[:space:]]+(list|outdated|install|show)([[:space:]]|$)'; then
   REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^uv pip /rtk pip /')"
+elif echo "$MATCH_CMD" | grep -qE '^mypy([[:space:]]|$)'; then
+  REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^mypy/rtk mypy/')"
+elif echo "$MATCH_CMD" | grep -qE '^python[[:space:]]+-m[[:space:]]+mypy([[:space:]]|$)'; then
+  REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^python -m mypy/rtk mypy/')"
 
 # --- Go tooling ---
 elif echo "$MATCH_CMD" | grep -qE '^go[[:space:]]+test([[:space:]]|$)'; then

specs/001-mypy-cmd/checklists/requirements.md

@@ -0,0 +1,37 @@
+# Specification Quality Checklist: RTK Mypy Command
+
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: 2026-02-13
+**Feature**: [spec.md](../spec.md)
+
+## Content Quality
+
+- [x] No implementation details (languages, frameworks, APIs)
+- [x] Focused on user value and business needs
+- [x] Written for non-technical stakeholders
+- [x] All mandatory sections completed
+
+## Requirement Completeness
+
+- [x] No [NEEDS CLARIFICATION] markers remain
+- [x] Requirements are testable and unambiguous
+- [x] Success criteria are measurable
+- [x] Success criteria are technology-agnostic (no implementation details)
+- [x] All acceptance scenarios are defined
+- [x] Edge cases are identified
+- [x] Scope is clearly bounded
+- [x] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [x] All functional requirements have clear acceptance criteria
+- [x] User scenarios cover primary flows
+- [x] Feature meets measurable outcomes defined in Success Criteria
+- [x] No implementation details leak into specification
+
+## Notes
+
+- All items pass. Spec is ready for `/speckit.plan`.
+- FR-001 through FR-009 cover the core filter function (testable with unit tests on raw strings).
+- FR-010 through FR-013 cover the command execution wrapper (testable with integration patterns).
+- FR-014 and FR-015 cover discovery and hook integration (testable with registry unit tests and hook script assertions).

specs/001-mypy-cmd/plan.md

@@ -0,0 +1,203 @@
+# Implementation Plan: RTK Mypy Command
+
+**Branch**: `001-mypy-cmd` | **Date**: 2026-02-13 | **Spec**: [spec.md](spec.md)
+**Input**: Feature specification from `/specs/001-mypy-cmd/spec.md`
+
+## Summary
+
+Add `rtk mypy` command that filters and compresses mypy type-checker output by parsing errors, grouping by file (most errors first), displaying a summary header with total counts and top error codes, and preserving every individual error. Follows the exact same structural pattern as `tsc_cmd.rs`. Includes discover registry pattern, auto-rewrite hook entry, and comprehensive TDD tests.
+
+## Technical Context
+
+**Language/Version**: Rust 2021 edition
+**Primary Dependencies**: regex (1), lazy_static (1.4), anyhow (1.0) -- all already in Cargo.toml
+**Storage**: SQLite via rusqlite (existing tracking.rs)
+**Testing**: cargo test with embedded `#[cfg(test)] mod tests`
+**Target Platform**: macOS, Linux (cross-platform CLI)
+**Project Type**: Single Rust binary (existing)
+**Performance Goals**: N/A (output filtering is string processing on small inputs)
+**Constraints**: No new dependencies. Must follow existing module patterns exactly.
+**Scale/Scope**: 6 files modified/created total
+
+## Constitution Check
+
+*No constitution file exists. Skipping gate check.*
+
+## Project Structure
+
+### Documentation (this feature)
+
+```text
+specs/001-mypy-cmd/
+├── spec.md
+├── plan.md              # This file
+├── research.md          # Phase 0 output
+├── checklists/
+│   └── requirements.md  # Already created
+└── tasks.md             # Phase 2 output (created by /speckit.tasks)
+```
+
+### Source Code (repository root)
+
+```text
+src/
+├── mypy_cmd.rs          # NEW: mypy command module (filter + run)
+├── main.rs              # MODIFY: add Mypy variant to Commands enum + match arm
+├── discover/
+│   └── registry.rs      # MODIFY: add mypy + python3 -m mypy patterns and rules
+
+.claude/hooks/
+└── rtk-rewrite.sh       # MODIFY: add mypy rewrite patterns
+
+hooks/
+└── rtk-rewrite.sh       # MODIFY: mirror of .claude/hooks/rtk-rewrite.sh
+```
+
+**Structure Decision**: This is a leaf module addition following the exact pattern of `tsc_cmd.rs`, `ruff_cmd.rs`, and `pytest_cmd.rs`. No new directories, no new dependencies, no architectural changes.
+
+## Design
+
+### mypy_cmd.rs -- Core Module
+
+**Pattern**: Mirrors `tsc_cmd.rs` exactly.
+
+**Public API**:
+```
+pub fn run(args: &[String], verbose: u8) -> Result<()>
+```
+
+**Internal filter function** (unit-testable):
+```
+fn filter_mypy_output(output: &str) -> String
+```
+
+**Mypy output format** (the input we parse):
+```
+src/module.py:12: error: Incompatible return value type  [return-value]
+src/module.py:12:5: error: Incompatible return value type  [return-value]
+src/module.py:15: note: Expected "int"
+src/other.py:8: error: Name "foo" is not defined  [name-defined]
+Found 3 errors in 2 files (checked 10 source files)
+```
+
+**Key patterns**:
+- Error line regex: `^(.+?):(\d+)(?::(\d+))?: (error|warning|note): (.+?)(?:\s+\[(.+)\])?$`
+- Continuation: `note:` lines attach to the preceding error
+- File-less errors: Lines matching `error:` without a file path prefix (e.g., mypy config errors) -- display verbatim at top
+- Summary line: `Found N errors in M files` -- replaced by our header
+
+**RTK output format** (what we produce):
+```
+mypy: 3 errors in 2 files
+=======================================
+Top codes: return-value (1x), name-defined (1x)
+
+src/module.py (2 errors)
+  L12: [return-value] Incompatible return value type
+    Expected "int"
+  L15: [some-code] Another error
+
+src/other.py (1 error)
+  L8: [name-defined] Name "foo" is not defined
+```
+
+**Command execution flow**:
+1. Try `mypy` directly via `Command::new("mypy")`
+2. If not found, try `python3 -m mypy` as fallback (same pattern as pytest_cmd.rs)
+3. Forward all user args
+4. Capture stdout + stderr, combine
+5. Strip ANSI codes via `utils::strip_ansi()`
+6. Filter through `filter_mypy_output()`
+7. Track via `tracking::TimedExecution`
+8. Exit with mypy's exit code via `std::process::exit()`
+
+### main.rs -- Wiring
+
+Add to `Commands` enum (alphabetical placement near other Python tools):
+```
+Mypy {
+    #[arg(trailing_var_arg = true, allow_hyphen_values = true)]
+    args: Vec<String>,
+}
+```
+
+Add match arm:
+```
+Commands::Mypy { args } => {
+    mypy_cmd::run(&args, cli.verbose)?;
+}
+```
+
+Add module declaration:
+```
+mod mypy_cmd;
+```
+
+### discover/registry.rs -- Discovery
+
+Add pattern after the existing Python tool patterns (after ruff, before docker):
+```
+r"^(python3?\s+-m\s+)?mypy(\s|$)"
+```
+
+Add corresponding rule:
+```
+RtkRule {
+    rtk_cmd: "rtk mypy",
+    category: "Build",
+    savings_pct: 80.0,
+    subcmd_savings: &[],
+    subcmd_status: &[],
+}
+```
+
+### rtk-rewrite.sh -- Hook (both locations)
+
+Add after the ruff rewrite block in the "Python tooling" section:
+```bash
+elif echo "$MATCH_CMD" | grep -qE '^mypy([[:space:]]|$)'; then
+  REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^mypy/rtk mypy/')"
+elif echo "$MATCH_CMD" | grep -qE '^python[[:space:]]+-m[[:space:]]+mypy([[:space:]]|$)'; then
+  REWRITTEN="${ENV_PREFIX}$(echo "$CMD_BODY" | sed 's/^python -m mypy/rtk mypy/')"
+```
+
+## File Change Summary
+
+| File | Action | Lines (est.) | Risk |
+|------|--------|-------------|------|
+| `src/mypy_cmd.rs` | CREATE | ~200 | Low -- follows tsc_cmd.rs pattern |
+| `src/main.rs` | MODIFY | +6 (mod decl, enum variant, match arm) | Low |
+| `src/discover/registry.rs` | MODIFY | +10 (pattern + rule + test) | Low |
+| `.claude/hooks/rtk-rewrite.sh` | MODIFY | +4 (two elif blocks) | Low |
+| `hooks/rtk-rewrite.sh` | MODIFY | +4 (mirror) | Low |
+
+**Total**: 1 new file, 4 modified files. ~224 new lines.
+
+## Testing Strategy
+
+All tests follow TDD (Red-Green-Refactor) per project conventions.
+
+**Unit tests in mypy_cmd.rs** (embedded `#[cfg(test)] mod tests`):
+
+| Test | Validates |
+|------|-----------|
+| `test_filter_mypy_errors_grouped_by_file` | FR-001, FR-003, FR-004: Multi-file errors grouped correctly |
+| `test_filter_mypy_with_column_numbers` | FR-002: Extended format `file:line:col:` parsed |
+| `test_filter_mypy_top_codes_summary` | FR-005: Top codes shown when 2+ distinct codes |
+| `test_filter_mypy_single_code_no_summary` | FR-005: Top codes omitted with 1 code |
+| `test_filter_mypy_every_error_shown` | FR-006: No error messages collapsed |
+| `test_filter_mypy_note_continuation` | FR-007: note: lines preserved as context |
+| `test_filter_mypy_fileless_errors` | FR-008: Config errors shown verbatim at top |
+| `test_filter_mypy_no_errors` | FR-013: Success message for clean output |
+| `test_filter_mypy_no_file_limit` | All files shown (mirrors tsc test) |
+
+**Unit tests in discover/registry.rs** (added to existing test module):
+
+| Test | Validates |
+|------|-----------|
+| `test_classify_mypy` | FR-014: `mypy src/` classified as Supported |
+| `test_classify_python_m_mypy` | FR-014: `python3 -m mypy` classified as Supported |
+
+## Complexity Tracking
+
+No constitution violations. No complexity justification needed.

specs/001-mypy-cmd/research.md

@@ -0,0 +1,34 @@
+# Research: RTK Mypy Command
+
+**Date**: 2026-02-13
+**Status**: Complete
+
+## Findings
+
+### Mypy Output Format Stability
+
+- **Decision**: Parse the standard `file:line: severity: message [code]` format.
+- **Rationale**: This format has been stable since mypy 0.9 (2020). The optional column format (`file:line:col:`) was added later but is backwards-compatible. Both formats coexist in modern mypy (1.x).
+- **Alternatives considered**: Parsing mypy's `--output json` flag was considered but rejected -- it would require RTK to inject flags, which conflicts with the argument passthrough design (FR-010). The text format is sufficient and avoids modifying user intent.
+
+### Command Discovery (mypy vs python -m mypy)
+
+- **Decision**: Try `mypy` directly first, fall back to `python3 -m mypy`.
+- **Rationale**: This is the same pattern used by `pytest_cmd.rs` (lines 18-25). Users who install mypy via pip have it on PATH. Users in virtualenvs or poetry/pipx may only have it via `python -m mypy`.
+- **Alternatives considered**: Only supporting `mypy` directly was considered but would miss users who haven't activated their virtualenv.
+
+### ANSI Stripping
+
+- **Decision**: Reuse existing `utils::strip_ansi()` (src/utils.rs:47).
+- **Rationale**: Mypy colorizes output when stdout is a TTY. Since RTK captures via `Command::output()` (not a TTY), mypy typically does not emit ANSI. However, users may have `MYPY_FORCE_COLOR=1` or `--color-output` set, so stripping is a safety measure.
+- **Alternatives considered**: None -- the utility already exists.
+
+### Error Code Format
+
+- **Decision**: Display error codes in bracket format `[error-code]` matching mypy's native format.
+- **Rationale**: Mypy uses bracketed codes like `[return-value]`, `[name-defined]`, `[assignment]`. This differs from tsc which uses `TS2322` style. Using brackets preserves the code as-is for easy copy-paste into mypy configuration (`# type: ignore[error-code]`).
+- **Alternatives considered**: Stripping brackets was considered but reduces utility for suppression comments.
+
+## No Unresolved Unknowns
+
+All technical decisions are resolved. No NEEDS CLARIFICATION items remain.