fix: skip assistant/user events in buildPartialRunError to avoid raw JSON blobs in error messages (FAR-32)

When a model produces assistant events with output_tokens=0 but no result
event (e.g. MiniMax-M2.7 thinking-only output), the partial-run error
previously surfaced the raw assistant JSON blob verbatim, producing an
unreadable message like "Claude exited with code -1: {\"type\":\"assistant\",...}".

Fix: extend the content-line filter in buildPartialRunError to also skip
assistant and user event types (intermediate streaming events), in addition
to system events. result events are still retained since they may carry
useful terminal error details. When all stdout lines are filtered, the
existing initOnlyOutput branch triggers and surfaces a clean diagnostic:
"Claude started but did not produce a result (model: MiniMax-M2.7) — check
API credentials, model support, and adapter config".

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/server/execute.ts

@@ -117,22 +117,30 @@ export function buildPartialRunError(
 ): string {
   if (exitCode === 0) return "Failed to parse Claude JSON output";
 
-  // Walk stdout lines, skip system events, return the first real content line.
+  // Walk stdout lines, skip system and intermediate streaming events, return
+  // the first human-readable content line.  assistant/user events are
+  // intermediate and contain raw JSON blobs that make poor error messages;
+  // result events are retained because they may carry useful error details
+  // (e.g. rate-limit messages).
   const firstContentLine = stdout.split(/\r?\n/)
     .map((l) => l.trim())
     .find((l) => {
       if (!l) return false;
       try {
         const obj = JSON.parse(l);
-        if (typeof obj === "object" && obj !== null && (obj as Record<string, unknown>).type === "system") return false;
+        if (typeof obj === "object" && obj !== null) {
+          const t = (obj as Record<string, unknown>).type;
+          if (t === "system" || t === "assistant" || t === "user") return false;
+        }
       } catch {
         // not JSON — treat as content
       }
       return true;
     }) ?? "";
 
-  // If we only have system/init events and nothing else, surface the model
-  // name so the operator can diagnose missing credentials or unsupported model.
+  // If the stream contains only system/init and intermediate events with no
+  // plain-text or result output, surface the model name so the operator can
+  // diagnose missing credentials or unsupported model.
   const initOnlyOutput = stdout.trim() !== "" && model !== "" && !firstContentLine;
   if (initOnlyOutput) {
     const modelHint = model ? ` (model: ${model})` : "";