huskies: merge 1183 story Config parse error hints at misplaced top-level keys after [[component]]

server/src/config/mod.rs

@@ -506,7 +506,7 @@ impl ProjectConfig {
             Err(_) => {
                 // New format failed — try legacy
                 let legacy: LegacyProjectConfig =
-                    toml::from_str(content).map_err(|e| format!("Parse config: {e}"))?;
+                    toml::from_str(content).map_err(|e| format_parse_error(&e))?;
                 if let Some(agent) = legacy.agent {
                     slog!(
                         "[config] Warning: [agent] table is deprecated. \
@@ -659,6 +659,26 @@ impl ProjectConfig {
     }
 }
 
+/// Format a `toml::de::Error` for display, appending a hint when the error is
+/// an "unknown field" rejection (raised by `ComponentConfig`'s
+/// `deny_unknown_fields`). Such errors most commonly happen when a top-level
+/// setting is placed after the last `[[component]]` header — TOML attaches
+/// trailing bare keys to the table above them, so the setting silently lands
+/// inside `ComponentConfig` instead of `ProjectConfig`. The same hint is also
+/// shown for a genuine typo'd field inside `[[component]]`, since the error
+/// text can't distinguish the two cases.
+fn format_parse_error(e: &toml::de::Error) -> String {
+    let mut msg = format!("Parse config: {e}");
+    if e.to_string().contains("unknown field") {
+        msg.push_str(
+            "\n\nhint: top-level settings must appear before the first `[[component]]` \
+             section in project.toml — keys placed after a `[[component]]` table are \
+             attached to that component instead of the project.",
+        );
+    }
+    msg
+}
+
 /// Validate agent configs: no duplicate names, no empty names, positive budgets/turns.
 fn validate_agents(agents: &[AgentConfig]) -> Result<(), String> {
     let mut names = HashSet::new();