runtime: suppress silent-rebuild banner for empty projects

A fresh-launch temp project enters run() with no .db, calls
rebuild_from_text on an empty schema, and used to surface a
"[ok] rebuild — 0 tables and 0 rows will be reconstructed"
note that conveyed no information. Now we only emit the note
when the project actually has tables. The explicit `rebuild`
command still always reports its summary — the user asked.

src/runtime.rs

@@ -133,14 +133,22 @@ pub async fn run(args: Args) -> Result<()> {
         match database.rebuild_from_text(project_path.clone(), None).await {
             Ok(()) => {
                 // Surface the silent rebuild as a system note
-                // so the user sees that the .db was
-                // reconstructed rather than wondering whether
-                // anything happened.
+                // *only* when there was something material to
+                // reconstruct. A fresh-launch temp project
+                // hits this branch with zero tables and zero
+                // rows — the rebuild ran, but nothing
+                // reconstructable existed, so there's nothing
+                // worth telling the user. The explicit
+                // `rebuild` command still always reports its
+                // summary (see spawn_rebuild) since the user
+                // asked.
+                if project_has_content(&project_path) {
                     let summary = summarize_project(&project_path).unwrap_or_else(|_| {
                         "rebuilt playground.db from project.yaml + data/".to_string()
                     });
                     initial_events.push(AppEvent::RebuildSucceeded { summary });
                 }
+            }
             Err(e) => {
                 // The terminal is still in cooked mode here
                 // (we haven't entered the alternate screen
@@ -813,6 +821,27 @@ fn spawn_prepare_rebuild(
     });
 }
 
+/// Does the project at `project_path` actually have any
+/// schema or data?
+///
+/// "Has content" means at least one table is declared in
+/// `project.yaml` OR at least one CSV row exists under
+/// `data/`. A brand-new auto-named temp project, having
+/// neither, returns `false`. Errors reading the project
+/// (corrupt YAML, missing dir) also return `false` —
+/// suppressing a misleading "0 tables reconstructed"
+/// message for a project we can't read is the right default.
+fn project_has_content(project_path: &std::path::Path) -> bool {
+    let yaml_path = project_path.join(crate::project::PROJECT_YAML);
+    let Ok(yaml) = std::fs::read_to_string(&yaml_path) else {
+        return false;
+    };
+    let Ok(snapshot) = crate::persistence::parse_schema(&yaml) else {
+        return false;
+    };
+    !snapshot.tables.is_empty()
+}
+
 fn summarize_project(project_path: &std::path::Path) -> Result<String, String> {
     let yaml_path = project_path.join(crate::project::PROJECT_YAML);
     let yaml = std::fs::read_to_string(&yaml_path).map_err(|e| e.to_string())?;