feat: Add Python plugins from AutoMetabuilder + restructure workflow folder

Restructure workflow/ for multi-language plugin support:
- Rename src/ to core/ (engine code: DAG executor, registry, types)
- Create executor/{cpp,python,ts}/ for language-specific runtimes
- Consolidate plugins to plugins/{ts,python}/ by language then category

Add 80+ Python plugins from AutoMetabuilder in 14 categories:
- control: bot control, switch logic, state management
- convert: type conversions (json, boolean, dict, list, number, string)
- core: AI requests, context management, tool calls
- dict: dictionary operations (get, set, keys, values, merge)
- list: list operations (concat, find, sort, slice, filter)
- logic: boolean logic (and, or, xor, equals, comparisons)
- math: arithmetic operations (add, subtract, multiply, power, etc.)
- string: string manipulation (concat, split, replace, format)
- notifications: Slack, Discord integrations
- test: assertion helpers and test suite runner
- tools: file operations, git, docker, testing utilities
- utils: filtering, mapping, reducing, condition branching
- var: variable store operations (get, set, delete, exists)
- web: Flask server, environment variables, JSON handling

Add language executor runtimes:
- TypeScript: direct import execution (default, fast startup)
- Python: child process with JSON stdin/stdout communication
- C++: placeholder for native FFI bindings (Phase 3)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

workflow/plugins/python/test/__init__.py

@@ -0,0 +1 @@
+"""Unit testing assertion plugins."""

workflow/plugins/python/test/test_assert_equals.py

@@ -0,0 +1,26 @@
+"""Workflow plugin: assert two values are equal."""
+
+
+def run(_runtime, inputs):
+    """Assert that two values are equal."""
+    actual = inputs.get("actual")
+    expected = inputs.get("expected")
+    message = inputs.get("message", "")
+
+    passed = actual == expected
+
+    if not passed:
+        error_msg = f"Assertion failed: {message}" if message else "Assertion failed"
+        error_msg += f"\n  Expected: {expected}\n  Actual: {actual}"
+        return {
+            "passed": False,
+            "error": error_msg,
+            "expected": expected,
+            "actual": actual
+        }
+
+    return {
+        "passed": True,
+        "expected": expected,
+        "actual": actual
+    }

workflow/plugins/python/test/test_assert_exists.py

@@ -0,0 +1,23 @@
+"""Workflow plugin: assert value exists (is not None/null)."""
+
+
+def run(_runtime, inputs):
+    """Assert that a value exists (is not None)."""
+    value = inputs.get("value")
+    message = inputs.get("message", "")
+
+    passed = value is not None
+
+    if not passed:
+        error_msg = f"Assertion failed: {message}" if message else "Assertion failed"
+        error_msg += f"\n  Expected: non-null value\n  Actual: None"
+        return {
+            "passed": False,
+            "error": error_msg,
+            "value": value
+        }
+
+    return {
+        "passed": True,
+        "value": value
+    }

workflow/plugins/python/test/test_assert_false.py

@@ -0,0 +1,23 @@
+"""Workflow plugin: assert value is false."""
+
+
+def run(_runtime, inputs):
+    """Assert that a value is false."""
+    value = inputs.get("value")
+    message = inputs.get("message", "")
+
+    passed = value is False
+
+    if not passed:
+        error_msg = f"Assertion failed: {message}" if message else "Assertion failed"
+        error_msg += f"\n  Expected: False\n  Actual: {value}"
+        return {
+            "passed": False,
+            "error": error_msg,
+            "value": value
+        }
+
+    return {
+        "passed": True,
+        "value": value
+    }

workflow/plugins/python/test/test_assert_true.py

@@ -0,0 +1,23 @@
+"""Workflow plugin: assert value is true."""
+
+
+def run(_runtime, inputs):
+    """Assert that a value is true."""
+    value = inputs.get("value")
+    message = inputs.get("message", "")
+
+    passed = value is True
+
+    if not passed:
+        error_msg = f"Assertion failed: {message}" if message else "Assertion failed"
+        error_msg += f"\n  Expected: True\n  Actual: {value}"
+        return {
+            "passed": False,
+            "error": error_msg,
+            "value": value
+        }
+
+    return {
+        "passed": True,
+        "value": value
+    }

workflow/plugins/python/test/test_run_suite.py

@@ -0,0 +1,63 @@
+"""Workflow plugin: run a suite of test assertions and report results."""
+
+
+def run(_runtime, inputs):
+    """Run a suite of test assertions and aggregate results.
+
+    Inputs:
+    - results: Array of test result objects (each with 'passed' field)
+    - suite_name: Optional name for the test suite
+
+    Outputs:
+    - passed: Boolean indicating if all tests passed
+    - total: Total number of tests
+    - passed_count: Number of tests that passed
+    - failed_count: Number of tests that failed
+    - failures: Array of failed test details
+    """
+    results = inputs.get("results", [])
+    suite_name = inputs.get("suite_name", "Test Suite")
+
+    if not isinstance(results, list):
+        return {
+            "passed": False,
+            "error": "results must be an array",
+            "total": 0,
+            "passed_count": 0,
+            "failed_count": 0,
+            "failures": []
+        }
+
+    total = len(results)
+    passed_count = 0
+    failed_count = 0
+    failures = []
+
+    for i, result in enumerate(results):
+        if isinstance(result, dict) and result.get("passed") is True:
+            passed_count += 1
+        else:
+            failed_count += 1
+            failure_info = {
+                "test_index": i,
+                "error": result.get("error", "Unknown error") if isinstance(result, dict) else str(result)
+            }
+            if isinstance(result, dict):
+                failure_info.update({
+                    "expected": result.get("expected"),
+                    "actual": result.get("actual")
+                })
+            failures.append(failure_info)
+
+    all_passed = failed_count == 0 and total > 0
+
+    summary = f"{suite_name}: {passed_count}/{total} tests passed"
+
+    return {
+        "passed": all_passed,
+        "total": total,
+        "passed_count": passed_count,
+        "failed_count": failed_count,
+        "failures": failures,
+        "summary": summary
+    }