fix(incremental): name File nodes by basename, matching the full pipeline

The incremental path passed changed_files[i].rel_path as the File node NAME,
while the full pipeline names File nodes by basename (pipeline.c "Create File
node"). Node upserts match by qualified name, so an incremental re-index of a
touched file RENAMED its File node in place ("applications.py" ->
"fastapi/applications.py"). File nodes are USAGE-edge sources, so:

- the same tree yields different graphs depending on whether it was indexed
  fresh or incrementally, and the divergence grows as files are edited
  (add AND modify both rename);
- name-based traversal dead-ends at any touched file's node (e.g. walking
  inbound USAGE transitively misses everything that reaches a target through
  a recently added/modified class).

Mirror the full pipeline's node shape at the incremental call site: basename
as the name, and the same {"extension": ...} props (previously "{}").

Adds incr_file_node_name_stays_basename to the incremental suite: modify a
file, incremental re-index, then assert no File node name contains '/'.
Red without the fix, green with it; full incremental suite 162/162.

Signed-off-by: Tommy Corbett <spde89@gmail.com>

Author: Tommy Corbett

src/pipeline/pipeline_incremental.c

@@ -848,8 +848,19 @@ int cbm_pipeline_run_incremental(cbm_pipeline_t *p, const char *db_path, cbm_fil
     for (int i = 0; i < ci; i++) {
         char *file_qn = cbm_pipeline_fqn_compute(project, changed_files[i].rel_path, "__file__");
         if (file_qn) {
-            cbm_gbuf_upsert_node(existing, "File", changed_files[i].rel_path, file_qn,
-                                 changed_files[i].rel_path, 0, 0, "{}");
+            /* Mirror the full pipeline's File-node shape (pipeline.c "Create
+             * File node"): name is the BASENAME, not the repo-relative path.
+             * The upsert matches the existing node by QN, so passing rel_path
+             * here RENAMED the node in place — an incrementally re-indexed
+             * file's File node (a USAGE-edge source) diverged from what a full
+             * build produces, and the graph drifted as files were touched. */
+            const char *rel = changed_files[i].rel_path;
+            const char *slash = strrchr(rel, '/');
+            const char *basename = slash ? slash + SKIP_ONE : rel;
+            char props[CBM_SZ_256];
+            const char *ext = strrchr(basename, '.');
+            snprintf(props, sizeof(props), "{\"extension\":\"%s\"}", ext ? ext : "");
+            cbm_gbuf_upsert_node(existing, "File", basename, file_qn, rel, 0, 0, props);
             free(file_qn);
         }
     }

tests/test_incremental.c

@@ -950,6 +950,38 @@ static int resp_lacks_key(const char *resp, const char *key) {
 
 /* ── list_projects ─────────────────────────────────────────────── */
 
+TEST(incr_file_node_name_stays_basename) {
+    /* Regression: the incremental path passed rel_path as the File node NAME
+     * (full build uses the basename). The upsert matches by QN, so a touched
+     * file's File node was RENAMED in place ("applications.py" ->
+     * "fastapi/applications.py") and the graph diverged from a full build as
+     * files were edited. Assert no File node name contains a path separator
+     * after an incremental re-index of a modified file. */
+    char path[512];
+    snprintf(path, sizeof(path), "%s/fastapi/applications.py", g_repodir);
+    FILE *f = fopen(path, "a");
+    ASSERT(f != NULL);
+    fprintf(f, "\n# incr_file_node_name_stays_basename touch\n");
+    fclose(f);
+
+    char *resp = index_repo();
+    ASSERT(resp != NULL);
+    free(resp);
+
+    double ms;
+    char *r = call_tool_timed("query_graph", &ms,
+                              "{\"project\":\"%s\","
+                              "\"query\":\"MATCH (n:File) WHERE n.name CONTAINS '/'"
+                              " RETURN n.name LIMIT 5\"}",
+                              g_project);
+    TOOL_OK(r, ms);
+    /* No File node may carry a path separator in its name; the query engine
+     * returns an empty rows array when nothing matches. */
+    ASSERT(strstr(r, "\"rows\":[]") != NULL || strstr(r, "\\\"rows\\\":[]") != NULL);
+    free(r);
+    PASS();
+}
+
 TEST(tool_list_projects_basic) {
     double ms;
     char *r = call_tool_timed("list_projects", &ms, "{}");
@@ -2956,6 +2988,7 @@ SUITE(incremental) {
 
     /* Phase 3: Incremental deltas */
     RUN_TEST(incr_modify_file);
+    RUN_TEST(incr_file_node_name_stays_basename);
     RUN_TEST(incr_formatter_run);
     RUN_TEST(incr_add_file);
     RUN_TEST(incr_delete_file);