feat: agent-agnostic codex support + bats test framework (#52)

## Summary

- **Agent abstraction layer**: Crabcode now natively supports codex
alongside claude. Projects configure `agent: codex` (or `agent: claude`,
the default) in their YAML config
- **~180 LOC helper functions** centralize all agent-specific CLI
differences (command building, session resume, system prompts,
non-interactive mode)
- **All callsites updated**: workspace open/continue, WIP
save/restore/list, session start/resume, review, handoff — all use the
new helpers
- **Bats-core test framework** vendored as git submodules with 36 unit
tests for the agent layer
- **CI workflow** runs unit tests + shellcheck on every PR

## Agent CLI mapping

| Operation | Claude | Codex |
|---|---|---|
| Base command | `claude --dangerously-skip-permissions` | `codex
--full-auto` |
| Continue session | `--continue` | `codex resume --last` |
| Resume specific | `--resume <id>` | `codex resume <id>` |
| Non-interactive | `claude --print` | `codex exec` |
| System prompt | `.claude/CLAUDE.md` | `AGENTS.md` |

## Out of scope
- Court review (hardcoded Claude judge + Codex reviewer B) — separate PR

## Test plan
- [x] 36 bats unit tests pass locally (`make test-unit`)
- [x] Bash syntax check passes (`bash -n src/crabcode`)
- [ ] CI runs on this PR (first run — watch it)
- [x] Backward compat: existing projects without `agent:` field default
to claude
- [x] Source guard enables testing without executing main

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: MrFlounder

.github/workflows/test.yml

@@ -0,0 +1,41 @@
+name: test
+run-name: tests by @${{ github.actor }}
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: test-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  unit:
+    name: Unit tests (bats)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Install yq
+        run: |
+          sudo wget -qO /usr/local/bin/yq https://github.com/mikefarah/yq/releases/latest/download/yq_linux_amd64
+          sudo chmod +x /usr/local/bin/yq
+
+      - name: Run unit tests
+        run: make test-unit
+
+  lint:
+    name: Shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Run shellcheck
+        run: shellcheck --severity=error src/crabcode

.gitmodules

@@ -0,0 +1,9 @@
+[submodule "tests/bats"]
+	path = tests/bats
+	url = https://github.com/bats-core/bats-core.git
+[submodule "tests/test_helper/bats-support"]
+	path = tests/test_helper/bats-support
+	url = https://github.com/bats-core/bats-support.git
+[submodule "tests/test_helper/bats-assert"]
+	path = tests/test_helper/bats-assert
+	url = https://github.com/bats-core/bats-assert.git

Makefile

@@ -1,17 +1,25 @@
-.PHONY: test test-docker test-e2e install lint help
+.PHONY: test test-unit test-integration test-docker test-e2e install lint help
 
 help:
 	@echo "Crabcode Makefile"
 	@echo ""
 	@echo "Commands:"
-	@echo "  make test        Run unit tests"
-	@echo "  make test-docker Run tests in Docker"
-	@echo "  make test-e2e    Run end-to-end tests in Docker (full promptfoo-cloud simulation)"
-	@echo "  make install     Install crabcode to /usr/local/bin"
-	@echo "  make lint        Run shellcheck"
+	@echo "  make test             Run all tests (unit + integration)"
+	@echo "  make test-unit        Run bats unit tests only"
+	@echo "  make test-integration Run integration tests only"
+	@echo "  make test-docker      Run integration tests in Docker"
+	@echo "  make test-e2e         Run end-to-end tests in Docker (full promptfoo-cloud simulation)"
+	@echo "  make install          Install crabcode to /usr/local/bin"
+	@echo "  make lint             Run shellcheck"
 	@echo ""
 
-test:
+test: test-unit test-integration
+
+test-unit:
+	@git submodule update --init --recursive tests/bats tests/test_helper/bats-support tests/test_helper/bats-assert 2>/dev/null || true
+	@./tests/bats/bin/bats tests/unit/
+
+test-integration:
 	@chmod +x tests/run.sh
 	@./tests/run.sh