Fix rebuild_and_restart in Docker project containers

CARGO_MANIFEST_DIR is baked at image build time as /app/server, but
project containers (Dockerfile.base) don't copy /app — the source is
bind-mounted at /workspace instead. Fall back to project_root when
the compile-time path doesn't exist.

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

server/src/rebuild.rs

@@ -107,11 +107,25 @@ pub async fn rebuild_and_restart(
 
     // 2. Find the workspace root (parent of the server binary's source).
     //    CARGO_MANIFEST_DIR at compile time points to the `server/` crate;
-    //    the workspace root is its parent.
-    let manifest_dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR"));
-    let workspace_root = manifest_dir
+    //    the workspace root is its parent.  When running inside Docker the
+    //    compile-time path (/app) no longer exists — the source is bind-mounted
+    //    at the project_root instead, so fall back to that.
+    let compile_time_root = std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
         .parent()
-        .ok_or_else(|| "Cannot determine workspace root from CARGO_MANIFEST_DIR".to_string())?;
+        .filter(|p| p.join("Cargo.toml").exists());
+    let workspace_root = match compile_time_root {
+        Some(p) => p.to_path_buf(),
+        None => {
+            if project_root.join("Cargo.toml").exists() {
+                project_root.to_path_buf()
+            } else {
+                return Err(
+                    "Cannot determine workspace root: neither CARGO_MANIFEST_DIR nor project_root contain Cargo.toml".to_string(),
+                );
+            }
+        }
+    };
+    let workspace_root = workspace_root.as_path();
 
     slog!(
         "[rebuild] Building server from workspace root: {}",