modularize bin/gtr into libraries and add BATS test suite

.github/instructions/ai.instructions.md

@@ -2,11 +2,26 @@
 applyTo: adapters/ai/**/*.sh
 ---
 
-# AI Instructions
+# AI Adapter Instructions
 
-## Adding Features
+## When to Use a File vs Registry
 
-### New AI Tool Adapter (`adapters/ai/<name>.sh`)
+Most AI tools are defined as **registry entries** in `lib/adapters.sh` — no adapter file needed.
+Only create an adapter file in `adapters/ai/` for tools that need **custom behavior** beyond the standard builder (see `claude.sh` or `cursor.sh` for examples).
+
+## Adding a Standard AI Tool (Registry)
+
+Add a line to `_AI_REGISTRY` in `lib/adapters.sh`:
+
+```
+yourname|yourcmd|ToolName not found. Install with: ...|Extra info;More info
+```
+
+Format: `name|cmd|err_msg|info_lines` (info lines are semicolon-separated)
+
+## Adding a Custom AI Tool (File Override)
+
+Create `adapters/ai/<name>.sh` implementing:
 
 ```bash
 #!/usr/bin/env bash
@@ -27,7 +42,9 @@ ai_start() {
 }
 ```
 
-**Also update**: Same as editor adapters (README, completions, help text)
+File-based adapters take precedence over registry entries of the same name.
+
+**Also update**: README, completions (bash/zsh/fish), help text in `lib/commands/help.sh`
 
 ## Contract & Guidelines
 
@@ -38,5 +55,4 @@ ai_start() {
 - Accept extra args after `--`: preserve ordering (`ai_start` receives already-shifted args).
 - Prefer fast startup; heavy initialization belongs in hooks (`postCreate`), not adapters.
 - When adding adapter: update `cmd_help`, README tool list, and completions (bash/zsh/fish).
-- Test manually: `bash -c 'source adapters/ai/<tool>.sh && ai_can_start && echo OK'`.
 - Inspect function definition if needed: `declare -f ai_start`.

.github/instructions/editor.instructions.md

@@ -2,11 +2,28 @@
 applyTo: adapters/editor/**/*.sh
 ---
 
-# Editor Instructions
+# Editor Adapter Instructions
 
-## Adding Features
+## When to Use a File vs Registry
 
-### New Editor Adapter (`adapters/editor/<name>.sh`)
+Most editors are defined as **registry entries** in `lib/adapters.sh` — no adapter file needed.
+Only create an adapter file in `adapters/editor/` for editors that need **custom behavior** beyond what the standard/terminal builders provide (see `nano.sh` for an example).
+
+## Adding a Standard Editor (Registry)
+
+Add a line to `_EDITOR_REGISTRY` in `lib/adapters.sh`:
+
+```
+yourname|yourcmd|standard|EditorName not found. Install from https://...|flags
+```
+
+Format: `name|cmd|type|err_msg|flags`
+- `type`: `standard` (GUI app) or `terminal` (runs in terminal)
+- `flags`: comma-separated — `workspace` (supports .code-workspace), `background` (terminal bg)
+
+## Adding a Custom Editor (File Override)
+
+Create `adapters/editor/<name>.sh` implementing:
 
 ```bash
 #!/usr/bin/env bash
@@ -26,20 +43,21 @@ editor_open() {
 }
 ```
 
+File-based adapters take precedence over registry entries of the same name.
+
 **Also update**:
 
 - README.md (setup instructions)
 - All three completion files: `completions/gtr.bash`, `completions/_git-gtr`, `completions/gtr.fish`
-- Help text in `bin/gtr` (`cmd_help` function)
+- Help text in `lib/commands/help.sh` (`cmd_help` function)
 
 ## Contract & Guidelines
 
 - Required functions: `editor_can_open` (probe via `command -v`), `editor_open <path>`.
 - Quote all paths; support spaces. Avoid changing PWD globally—no subshell needed (editor opens path).
 - Use `log_error` with actionable install guidance if command missing.
 - Keep adapter lean: no project scans, no blocking prompts.
-- Naming: file name = tool name (`zed.sh` → `zed` flag). Avoid uppercase.
+- Naming: file/registry name = tool name (`zed` → `zed` flag). Avoid uppercase.
 - Update: README editor list, completions (bash/zsh/fish), help (`Available editors:`), optional screenshots.
-- Manual test: `bash -c 'source adapters/editor/<tool>.sh && editor_can_open && editor_open . || echo fail'`.
 - Fallback behavior: if editor absent, fail clearly; do NOT silently defer to file browser.
 - Inspect function definition if needed: `declare -f editor_open`.

.github/instructions/lib.instructions.md

@@ -21,7 +21,7 @@ applyTo: lib/**/*.sh
 
 ## Change Guidelines
 
-- Preserve adapter contracts; do not rename exported functions used by `bin/gtr`.
+- Preserve adapter contracts; do not rename exported functions used by command handlers in `lib/commands/`.
 - Add new config keys with `gtr.<name>` prefix; avoid collisions.
 - For performance-sensitive loops (e.g. directory scans) prefer built-ins (`find`, `grep`) with minimal subshells.
 - Any new Git command: add fallback for older versions or guard with detection.

.github/workflows/lint.yml

@@ -0,0 +1,33 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  shellcheck:
+    name: ShellCheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install ShellCheck
+        run: sudo apt-get update && sudo apt-get install -y shellcheck
+
+      - name: Run ShellCheck
+        run: |
+          shellcheck bin/gtr bin/git-gtr lib/*.sh lib/commands/*.sh adapters/editor/*.sh adapters/ai/*.sh
+
+  test:
+    name: Tests
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install BATS
+        run: sudo apt-get update && sudo apt-get install -y bats
+
+      - name: Run tests
+        run: bats tests/

CLAUDE.md

@@ -12,9 +12,14 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 - **Development/testing**: `./bin/gtr <command>` (direct execution)
 - **User-facing docs**: Always reference `git gtr`, never `./bin/gtr`
 
-## CRITICAL: No Automated Tests
+## Testing
 
-This project has **no test suite**. All testing is manual. After any change, run the relevant smoke tests:
+This project uses **BATS tests** for core functions and **manual smoke tests** for end-to-end workflows. CI runs ShellCheck + BATS automatically on PRs (`.github/workflows/lint.yml`).
+
+1. Run automated tests: `bats tests/`
+2. Run a single test file: `bats tests/config.bats`
+3. Run a single test by name: `bats tests/config.bats --filter "cfg_map_to_file_key"`
+4. Run relevant manual smoke tests:
 
 ```bash
 ./bin/gtr new test-feature          # Create worktree
@@ -25,7 +30,9 @@ This project has **no test suite**. All testing is manual. After any change, run
 ./bin/gtr rm test-feature           # Clean up
 ```
 
-For exhaustive testing (hooks, copy patterns, adapters, `--force`, `--from-current`, etc.), see the full checklist in CONTRIBUTING.md or `.github/instructions/testing.instructions.md`.
+For exhaustive manual testing (hooks, copy patterns, adapters, `--force`, `--from-current`, etc.), see the full checklist in CONTRIBUTING.md or `.github/instructions/testing.instructions.md`.
+
+**Test files**: `adapters`, `config`, `copy_safety`, `integration_lifecycle`, `parse_args`, `provider`, `resolve_base_dir`, `sanitize_branch_name` (all in `tests/`). Shared fixtures in `tests/test_helper.bash`.
 
 **Tip**: Use a disposable repo for testing to avoid polluting your working tree:
 
@@ -39,28 +46,35 @@ mkdir -p /tmp/gtr-test && cd /tmp/gtr-test && git init && git commit --allow-emp
 ### Binary Structure
 
 - `bin/git-gtr` — Thin wrapper enabling `git gtr` subcommand invocation
-- `bin/gtr` — Main script (~1960 lines), contains `main()` dispatcher + all `cmd_*` handlers
+- `bin/gtr` — Entry point: sources libraries and commands, contains `main()` dispatcher
 
 ### Module Structure
 
-| File              | Purpose                                                                                                     |
-| ----------------- | ----------------------------------------------------------------------------------------------------------- |
-| `lib/core.sh`     | Worktree CRUD: `create_worktree`, `remove_worktree`, `list_worktrees`, `resolve_target`, `resolve_base_dir` |
-| `lib/config.sh`   | Git config wrapper with precedence: `cfg_get`, `cfg_default`, `cfg_get_all`                                 |
-| `lib/copy.sh`     | File/directory copying with glob patterns: `copy_patterns`, `copy_directories`                              |
-| `lib/hooks.sh`    | Hook execution: `run_hooks_in` for postCreate/preRemove/postRemove                                          |
-| `lib/ui.sh`       | Logging (`log_error`, `log_info`, `log_warn`), prompts, formatting                                          |
-| `lib/platform.sh` | OS detection, GUI helpers                                                                                   |
+| File                | Purpose                                                                                                     |
+| ------------------- | ----------------------------------------------------------------------------------------------------------- |
+| `lib/ui.sh`         | Logging (`log_error`, `log_info`, `log_warn`), prompts, formatting                                          |
+| `lib/args.sh`       | Shared argument parser: flag specs (`--flag`, `--flag: val`, aliases), populates `_arg_*` vars              |
+| `lib/config.sh`     | Git config wrapper with precedence: `cfg_get`, `cfg_default`, `cfg_get_all`                                 |
+| `lib/platform.sh`   | OS detection, GUI helpers                                                                                   |
+| `lib/core.sh`       | Worktree CRUD: `create_worktree`, `remove_worktree`, `list_worktrees`, `resolve_target`, `resolve_base_dir` |
+| `lib/copy.sh`       | File/directory copying with glob patterns: `copy_patterns`, `copy_directories`                              |
+| `lib/hooks.sh`      | Hook execution: `run_hooks_in` for postCreate/preRemove/postRemove                                          |
+| `lib/provider.sh`   | Remote hosting detection (GitHub/GitLab) and CLI integration for `clean --merged`                           |
+| `lib/adapters.sh`   | Adapter registry, builder functions, generic fallbacks, loader functions                                    |
+| `lib/launch.sh`     | Editor/AI launch orchestration: `_open_editor`, `_auto_launch_editor`, `_auto_launch_ai`                    |
+| `lib/commands/*.sh` | One file per subcommand: `cmd_create`, `cmd_remove`, etc. (16 files)                                        |
+
+Libraries are sourced in the order listed above (ui → args → config → ... → launch → commands/\*.sh glob).
 
 ### Adapters
 
-Editor adapters in `adapters/editor/` and AI adapters in `adapters/ai/` are dynamically sourced via `load_editor_adapter()` and `load_ai_adapter()` in `bin/gtr`.
+Most adapters are defined declaratively in the **adapter registry** (`lib/adapters.sh`) using pipe-delimited entries. Custom adapters that need special logic remain as override files in `adapters/editor/` and `adapters/ai/`.
 
-**Editor adapters** (atom, cursor, emacs, idea, nano, nvim, pycharm, sublime, vim, vscode, webstorm, zed): implement `editor_can_open()` + `editor_open(path)`.
+**Registry-defined adapters**: atom, cursor, emacs, idea, nvim, pycharm, sublime, vim, vscode, webstorm, zed (editors) and aider, auggie, codex, continue, copilot, gemini, opencode (AI).
 
-**AI adapters** (aider, auggie, claude, codex, continue, copilot, cursor, gemini, opencode): implement `ai_can_start()` + `ai_start(path, args...)`.
+**Custom adapter files**: `adapters/editor/nano.sh`, `adapters/ai/claude.sh`, `adapters/ai/cursor.sh` — these implement `editor_can_open()`/`editor_open()` or `ai_can_start()`/`ai_start()` directly.
 
-**Generic fallback**: `GTR_EDITOR_CMD` / `GTR_AI_CMD` env vars allow custom tools without adapter files.
+**Loading order**: file override → registry → generic PATH fallback. `GTR_EDITOR_CMD` / `GTR_AI_CMD` env vars allow custom tools without adapters.
 
 ### Command Flow
 
@@ -106,15 +120,17 @@ cmd_editor() → resolve_target() → load_editor_adapter() → editor_open()
 
 ### Adding a New Command
 
-1. Add `cmd_<name>()` function in `bin/gtr`
-2. Add case entry in `main()` dispatcher (around line 71)
-3. Add help text in `cmd_help()`
+1. Create `lib/commands/<name>.sh` with `cmd_<name>()` function
+2. Add case entry in `main()` dispatcher in `bin/gtr`
+3. Add help text in `lib/commands/help.sh`
 4. Update all three completion files: `completions/gtr.bash`, `completions/_git-gtr`, `completions/git-gtr.fish`
 5. Update README.md
 
 ### Adding an Adapter
 
-Create `adapters/{editor,ai}/<name>.sh` implementing the two required functions (see existing adapters for patterns). Then update: help text in `cmd_help()` and `load_*_adapter()`, all three completions, README.md.
+**Standard adapters** (just a command name + error message): Add an entry to `_EDITOR_REGISTRY` or `_AI_REGISTRY` in `lib/adapters.sh`. Then update: help text in `lib/commands/help.sh`, all three completions, README.md.
+
+**Custom adapters** (special logic needed): Create `adapters/{editor,ai}/<name>.sh` implementing the two required functions (see `adapters/ai/claude.sh` for an example). File-based adapters take priority over registry entries.
 
 ### Updating the Version
 
@@ -128,6 +144,17 @@ When adding commands or flags, update all three files:
 - `completions/_git-gtr` (Zsh)
 - `completions/git-gtr.fish` (Fish)
 
+## Critical Gotcha: `set -e`
+
+`bin/gtr` runs with `set -e`. Any unguarded non-zero return silently exits the entire script. When calling functions that may `return 1`, guard with `|| true`:
+
+```bash
+result=$(my_func) || true           # Prevents silent exit
+if my_func; then ...; fi            # Also safe (if guards the return)
+```
+
+This is the most common source of subtle bugs in this codebase.
+
 ## Code Style
 
 - Shebang: `#!/usr/bin/env bash`