fix: do not persist zero dimension after a zero-chunk parse

A parse producing no chunks (e.g. whitespace-only content) reached the
dimension persistence block with ctx->dimension still 0, writing
dimension=0 to dbmem_settings and latching dimension_saved. Later real
embeddings then updated the dimension in memory only, so a reopened
connection that only searches saw dimension=0 and reported that no
content has been indexed.

Persist the dimension only when at least one real embedding was
computed (chunks_added > 0), which guarantees ctx->dimension is set.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: andinux

src/sqlite-memory.c

@@ -3016,7 +3016,9 @@ static int dbmem_process_buffer (dbmem_context *ctx, const char *buffer, int64_t
         rc = dbmem_database_add_vault_sentinel(ctx);
     }
 
-    if (rc == SQLITE_OK && !ctx->dimension_saved) {
+    // persist the dimension only after a real embedding established it:
+    // a zero-chunk parse would latch dimension=0 and block the real write
+    if (rc == SQLITE_OK && ctx->chunks_added > 0 && !ctx->dimension_saved) {
         // make sure to serialize dimension
         dbmem_settings_write_int(db, DBMEM_SETTINGS_KEY_DIMENSION, ctx->dimension);
         ctx->dimension_saved = true;

test/unittest.c

@@ -5407,6 +5407,39 @@ TEST(sqlite_memory_zero_chunk_content_marks_processed_with_sentinel) {
     sqlite3_close(db);
 }
 
+TEST(sqlite_memory_zero_chunk_first_add_does_not_persist_zero_dimension) {
+    sqlite3 *db = open_test_db();
+    ASSERT(db != NULL);
+
+    dbmem_provider_t prov = { .init = dummy_init, .compute = dummy_compute, .free = dummy_free };
+    int rc = sqlite3_memory_register_provider(db, "dummy", &prov);
+    ASSERT_EQ(rc, SQLITE_OK);
+
+    sqlite3_int64 result = 0;
+    rc = exec_get_int(db, "SELECT memory_set_model('dummy', 'test-model');", &result);
+    ASSERT_EQ(rc, SQLITE_OK);
+
+    // a zero-chunk first add must not latch dimension=0 into dbmem_settings
+    rc = exec_get_int(db, "SELECT memory_add_content('docs/blank.md', '  ' || char(10) || char(9));", &result);
+    ASSERT_EQ(rc, SQLITE_OK);
+
+    sqlite3_int64 count = -1;
+    rc = exec_get_int(db, "SELECT COUNT(*) FROM dbmem_settings WHERE key = 'dimension';", &count);
+    ASSERT_EQ(rc, SQLITE_OK);
+    ASSERT_EQ(count, 0);
+
+    // the first real embedding persists the provider dimension
+    rc = exec_get_int(db, "SELECT memory_add_content('docs/real.md', '# Title' || char(10) || 'Real body text.');", &result);
+    ASSERT_EQ(rc, SQLITE_OK);
+
+    sqlite3_int64 dimension = -1;
+    rc = exec_get_int(db, "SELECT value FROM dbmem_settings WHERE key = 'dimension';", &dimension);
+    ASSERT_EQ(rc, SQLITE_OK);
+    ASSERT_EQ(dimension, 4);
+
+    sqlite3_close(db);
+}
+
 #ifndef DBMEM_OMIT_LOCAL_ENGINE
 TEST(sqlite_local_logger_ignores_stale_user_data) {
     dbmem_logger(GGML_LOG_LEVEL_WARN, "ignored warning", (void *)1);
@@ -5637,6 +5670,7 @@ int main(int argc, char *argv[]) {
     RUN_TEST(sqlite_memory_defer_embeddings_requires_save_content);
     RUN_TEST(sqlite_memory_embed_pending_embeds_deferred_content_in_batches);
     RUN_TEST(sqlite_memory_zero_chunk_content_marks_processed_with_sentinel);
+    RUN_TEST(sqlite_memory_zero_chunk_first_add_does_not_persist_zero_dimension);
 
 #ifndef DBMEM_OMIT_REMOTE_ENGINE
     RUN_TEST(sqlite_set_model_releases_previous_engine_on_class_switch);