fix(trace-path): use portable case-insensitive symbol lookup

REQUIREMENTS.md

@@ -2,7 +2,7 @@
 
 > **Note:** This document is automatically generated and verified against the live test suite by `scripts/generate_requirements.py` and `tests/backend/test_requirements_sync.py`.
 
-**Test Verification Baseline:** **1185 Automated Tests** (821 Pytest Backend + 314 Vitest Frontend + 50 Playwright E2E).
+**Test Verification Baseline:** **1187 Automated Tests** (823 Pytest Backend + 314 Vitest Frontend + 50 Playwright E2E).
 
 ---
 
@@ -1399,6 +1399,10 @@ over the PostgresConnectionAdapter using an initialized test engine._
 - `test_upsert_reports_failure_when_every_record_is_rejected`
 - `test_rejected_record_warnings_do_not_log_the_chunk_text`
 
+#### `tests/test_trace_path_case_insensitive.py` (2 tests)
+- `test_lowercase_symbol_resolves_to_the_indexed_symbol`
+- `test_graph_traversal_sql_has_no_sqlite_only_collation`
+
 #### `tests/test_trace_path_compact.py` (3 tests)
 - `test_trace_nodes_have_no_permalinks_by_default_but_the_target_keeps_one`
 - `test_include_permalinks_returns_them_on_every_node`

app/services/graph_traversal.py

@@ -83,7 +83,7 @@ def trace_symbol_path(
         if not symbols_found:
             nc_query = (
                 "SELECT id, repo, filepath, name, full_symbol, kind, start_line, end_line, signature "
-                "FROM ast_symbols WHERE (name = ? COLLATE NOCASE OR full_symbol = ? COLLATE NOCASE OR full_symbol LIKE ? COLLATE NOCASE)"
+                "FROM ast_symbols WHERE (LOWER(name) = LOWER(?) OR LOWER(full_symbol) = LOWER(?) OR LOWER(full_symbol) LIKE LOWER(?))"
                 + repo_sql
             )
             symbols_found = conn.execute(nc_query, [target_sym, target_sym, f"%.{target_sym}"] + repo_arg).fetchall()
@@ -107,7 +107,7 @@ def trace_symbol_path(
             if not rel_hit:
                 rel_hit = conn.execute(
                     "SELECT source_symbol, target_symbol FROM ast_relationships "
-                    "WHERE (source_symbol = ? COLLATE NOCASE OR target_symbol = ? COLLATE NOCASE)"
+                    "WHERE (LOWER(source_symbol) = LOWER(?) OR LOWER(target_symbol) = LOWER(?))"
                     + repo_sql + " LIMIT 1",
                     [target_sym, target_sym] + repo_arg,
                 ).fetchone()

tests/test_trace_path_case_insensitive.py

@@ -0,0 +1,22 @@
+"""trace_path: a symbol in another letter case resolves, with SQL that PostgreSQL accepts (no SQLite-only COLLATE NOCASE)."""
+
+import inspect
+import json
+
+import app.services.graph_traversal as graph_traversal
+from app.services.graph_traversal import trace_symbol_path
+
+# Same database setup as the DI caller tests: the method rows and CALLS rows of a small C# graph.
+from tests.test_trace_path_di_callers import REPO, di_graph  # noqa: F401  (pytest fixture)
+
+
+def test_lowercase_symbol_resolves_to_the_indexed_symbol(di_graph):  # noqa: F811
+    result = json.loads(trace_symbol_path(symbol="assistantservice.publishinstance", repo=REPO, direction="callers", depth=1))
+    assert "error" not in result
+    assert result["target"]["symbol"] == "AssistantService.PublishInstance"
+    assert [c["symbol"] for c in result["callers"]] == ["AssistantsController.PublishInstance"]
+
+
+def test_graph_traversal_sql_has_no_sqlite_only_collation():
+    # PostgreSQL rejects `COLLATE NOCASE` ("collation nocase for encoding UTF8 does not exist").
+    assert "NOCASE" not in inspect.getsource(graph_traversal).upper()