feat: add AI fix service with prompt building and validation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/tests/test_ai_fix_service.py

@@ -0,0 +1,224 @@
+"""Unit tests for AI fix service helper functions.
+
+Tests pure Python helpers only — no AI mocking needed.
+"""
+
+import pytest
+
+from app.core.ai_fix_service import (
+    _find_node_by_id,
+    _find_parent_node,
+    _serialize_tree_outline,
+    _strip_markdown_fences,
+    _replace_node_in_tree,
+    _describe_fix,
+)
+
+
+# ── Sample tree ──
+
+SAMPLE_TREE = {
+    "id": "root",
+    "type": "decision",
+    "question": "Is the server up?",
+    "options": [
+        {"id": "opt-yes", "label": "Yes", "next_node_id": "check-logs"},
+        {"id": "opt-no", "label": "No", "next_node_id": "restart"},
+    ],
+    "children": [
+        {
+            "id": "check-logs",
+            "type": "action",
+            "title": "Check Logs",
+            "description": "Review logs.",
+            "next_node_id": "logs-ok",
+        },
+        {
+            "id": "logs-ok",
+            "type": "solution",
+            "title": "Logs OK",
+            "description": "Issue in logs.",
+        },
+        {
+            "id": "restart",
+            "type": "decision",
+            "question": "Did restart work?",
+            "options": [{"id": "opt-r", "label": "Yes", "next_node_id": "done"}],
+            "children": [
+                {
+                    "id": "done",
+                    "type": "solution",
+                    "title": "Done",
+                    "description": "Fixed.",
+                }
+            ],
+        },
+    ],
+}
+
+
+# ── _find_node_by_id ──
+
+
+class TestFindNodeById:
+    def test_finds_root(self):
+        node = _find_node_by_id(SAMPLE_TREE, "root")
+        assert node is not None
+        assert node["id"] == "root"
+        assert node["type"] == "decision"
+
+    def test_finds_nested_child(self):
+        node = _find_node_by_id(SAMPLE_TREE, "done")
+        assert node is not None
+        assert node["id"] == "done"
+        assert node["type"] == "solution"
+
+    def test_finds_direct_child(self):
+        node = _find_node_by_id(SAMPLE_TREE, "check-logs")
+        assert node is not None
+        assert node["title"] == "Check Logs"
+
+    def test_returns_none_for_missing(self):
+        node = _find_node_by_id(SAMPLE_TREE, "nonexistent")
+        assert node is None
+
+    def test_returns_none_for_non_dict(self):
+        assert _find_node_by_id("not a dict", "root") is None
+
+
+# ── _find_parent_node ──
+
+
+class TestFindParentNode:
+    def test_root_has_no_parent(self):
+        parent = _find_parent_node(SAMPLE_TREE, "root")
+        assert parent is None
+
+    def test_finds_parent_of_direct_child(self):
+        parent = _find_parent_node(SAMPLE_TREE, "check-logs")
+        assert parent is not None
+        assert parent["id"] == "root"
+
+    def test_finds_parent_of_deeply_nested(self):
+        parent = _find_parent_node(SAMPLE_TREE, "done")
+        assert parent is not None
+        assert parent["id"] == "restart"
+
+    def test_returns_none_for_missing(self):
+        parent = _find_parent_node(SAMPLE_TREE, "nonexistent")
+        assert parent is None
+
+    def test_returns_none_for_non_dict(self):
+        assert _find_parent_node("not a dict", "root") is None
+
+
+# ── _serialize_tree_outline ──
+
+
+class TestSerializeTreeOutline:
+    def test_produces_readable_outline(self):
+        outline = _serialize_tree_outline(SAMPLE_TREE)
+        assert "- [decision] Is the server up?" in outline
+        assert "  - [action] Check Logs" in outline
+        assert "  - [solution] Logs OK" in outline
+        assert "    - [solution] Done" in outline
+
+    def test_marks_error_node(self):
+        outline = _serialize_tree_outline(SAMPLE_TREE, error_node_id="restart")
+        assert "<<< ERROR HERE" in outline
+        # Only the restart node should be marked
+        lines = outline.split("\n")
+        error_lines = [l for l in lines if "ERROR HERE" in l]
+        assert len(error_lines) == 1
+        assert "Did restart work?" in error_lines[0]
+
+    def test_no_error_marker_when_none(self):
+        outline = _serialize_tree_outline(SAMPLE_TREE)
+        assert "ERROR HERE" not in outline
+
+    def test_handles_non_dict(self):
+        assert _serialize_tree_outline("not a dict") == ""
+
+    def test_indentation_increases_with_depth(self):
+        outline = _serialize_tree_outline(SAMPLE_TREE)
+        lines = outline.split("\n")
+        # Root has no indentation
+        assert lines[0].startswith("- [decision]")
+        # Children have 2-space indent
+        child_lines = [l for l in lines if "Check Logs" in l]
+        assert child_lines[0].startswith("  - ")
+
+
+# ── _strip_markdown_fences ──
+
+
+class TestStripMarkdownFences:
+    def test_strips_json_fences(self):
+        text = '```json\n{"key": "value"}\n```'
+        assert _strip_markdown_fences(text) == '{"key": "value"}'
+
+    def test_strips_plain_fences(self):
+        text = '```\n{"key": "value"}\n```'
+        assert _strip_markdown_fences(text) == '{"key": "value"}'
+
+    def test_passes_through_plain_json(self):
+        text = '{"key": "value"}'
+        assert _strip_markdown_fences(text) == '{"key": "value"}'
+
+
+# ── _replace_node_in_tree ──
+
+
+class TestReplaceNodeInTree:
+    def test_replaces_root(self):
+        import copy
+
+        tree = copy.deepcopy(SAMPLE_TREE)
+        replacement = {"id": "root", "type": "decision", "question": "New question"}
+        assert _replace_node_in_tree(tree, "root", replacement) is True
+        assert tree["question"] == "New question"
+        assert "children" not in tree  # cleared and replaced
+
+    def test_replaces_nested_node(self):
+        import copy
+
+        tree = copy.deepcopy(SAMPLE_TREE)
+        replacement = {"id": "done", "type": "solution", "title": "All Done", "description": "Complete."}
+        assert _replace_node_in_tree(tree, "done", replacement) is True
+        found = _find_node_by_id(tree, "done")
+        assert found["title"] == "All Done"
+
+    def test_returns_false_for_missing(self):
+        import copy
+
+        tree = copy.deepcopy(SAMPLE_TREE)
+        assert _replace_node_in_tree(tree, "nonexistent", {"id": "x"}) is False
+
+
+# ── _describe_fix ──
+
+
+class TestDescribeFix:
+    def test_describes_added_children(self):
+        original = {"id": "n1", "children": [{"id": "c1"}]}
+        fixed = {"id": "n1", "children": [{"id": "c1"}, {"id": "c2"}]}
+        desc = _describe_fix(original, fixed)
+        assert "1 child node" in desc
+
+    def test_describes_added_options(self):
+        original = {"id": "n1", "options": [{"id": "o1"}]}
+        fixed = {"id": "n1", "options": [{"id": "o1"}, {"id": "o2"}]}
+        desc = _describe_fix(original, fixed)
+        assert "1 option" in desc
+
+    def test_describes_added_next_node_id(self):
+        original = {"id": "n1", "type": "action"}
+        fixed = {"id": "n1", "type": "action", "next_node_id": "n2"}
+        desc = _describe_fix(original, fixed)
+        assert "next_node_id" in desc
+
+    def test_fallback_description(self):
+        original = {"id": "n1", "type": "solution"}
+        fixed = {"id": "n1", "type": "solution"}
+        desc = _describe_fix(original, fixed)
+        assert "fixed structural issue" in desc.lower()