# Regression Review Report

**Branch**: feat/176-tmux-abstraction-layer -> main
**Date**: 2026-05-17
**Focus**: Regression (removed exports, changed signatures, altered behavior, breaking changes)

## Summary

This branch adds a new tmux abstraction layer as a purely additive module. The regression risk is minimal. Two shared files were modified (`src/core/errors.ts` and `package.json`), but both modifications are strictly additive -- no existing exports, enum values, function signatures, or script behaviors were removed or altered.

## Analysis

### src/core/errors.ts

- **Existing exports**: 16 exports on main, 20 on HEAD. All 16 original exports are preserved unchanged.
- **Enum additions**: 4 new `ErrorCode` enum values added at the end (`TMUX_SESSION_FAILED`, `TMUX_VALIDATION_FAILED`, `TMUX_HOOK_FAILED`, `TMUX_SEND_KEYS_FAILED`). Appending to the end of a string enum is non-breaking -- no existing numeric ordinals shift.
- **Factory function additions**: 4 new factory functions added (`tmuxSessionFailed`, `tmuxValidationFailed`, `tmuxHookFailed`, `tmuxSendKeysFailed`). These are new named exports that do not conflict with any existing names.
- **No removed lines**: Confirmed zero deletions in the diff for this file.
- **No signature changes**: All pre-existing functions retain their original parameter types and return types.

### package.json (scripts)

- **test:all**: Appends `&& npm run test:tmux && npm run test:tmux:integration` to the chain. Existing suites execute identically; the new suites run after them. If tmux tests fail, `test:all` will fail -- but this is intentional (new tests should gate CI).
- **test:implementations**: Adds `--exclude='**/tmux/**'` to prevent tmux tests from running in this group (they have their own dedicated group). This is correct and non-breaking -- existing tests in the implementations group are unaffected.
- **test:integration**: Adds `--exclude='**/tmux/**'` for the same reason. Existing integration tests are unaffected.
- **New scripts**: `test:tmux` and `test:tmux:integration` are purely additive. They do not conflict with any existing script names.
- **Safeguard message**: The blocked `npm test` warning message still lists the original safe commands. It does not yet mention `test:tmux` -- this is a documentation gap but not a regression (the new commands work fine, they just are not advertised in the warning).

### Barrel Export (src/implementations/tmux/index.ts)

- This is a new file with no higher-level re-export. Neither `src/core/index.ts`, `src/implementations/index.ts`, nor any root `src/index.ts` imports from `src/implementations/tmux/`.
- No risk of name shadowing or collision with existing exports. All exported names use the `Tmux` prefix or tmux-specific constants.

### .features/index.json

- Previously contained `{"version":1,"features":{}}`. Now contains two tmux feature entries. This is additive and the schema version remains `1`. No existing feature entries were removed.

## Findings

No regression issues found. All changes are purely additive.

## Issues in Your Changes (BLOCKING)

### CRITICAL
(none)

### HIGH
(none)

### MEDIUM
(none)

## Issues in Code You Touched (Should Fix)

(none)

## Pre-existing Issues (Not Blocking)

(none)

## Suggestions (Lower Confidence)

- **Safeguard warning omits test:tmux** - `package.json` "test" script (Confidence: 65%) -- The blocked `npm test` message lists safe commands but does not include the new `test:tmux` or `test:tmux:integration`. Users in Claude Code might not discover these groups exist. Low priority since these are new-module tests with no existing consumers.

## Summary

| Category | CRITICAL | HIGH | MEDIUM | LOW |
|----------|----------|------|--------|-----|
| Blocking | 0 | 0 | 0 | 0 |
| Should Fix | 0 | 0 | 0 | 0 |
| Pre-existing | 0 | 0 | 0 | 0 |

**Regression Score**: 10/10
**Recommendation**: APPROVED

## Rationale

1. No exports removed from any shared module.
2. No function signatures changed in any existing code.
3. No default values altered.
4. No side effects removed from existing event handlers or lifecycle hooks.
5. Enum additions are append-only to a string enum (non-breaking).
6. Test script changes use exclusion patterns that isolate new tests from existing groups.
7. The barrel export is self-contained with no upstream re-export chain.
8. No existing consumers of the tmux module exist (it is brand new).

This is a clean, additive feature branch with zero regression risk to existing functionality.
