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.test.ts

@@ -178,6 +178,39 @@ describe("buildPartialRunError", () => {
     expect(msg).toContain("code 2");
   });
 
+  it("skips assistant events and surfaces model hint (FAR-32: MiniMax-M2.7 output_tokens=0)", () => {
+    // Reproduces the exact failure: init event + assistant event with only a
+    // thinking block and output_tokens=0, no result event.  The assistant JSON
+    // blob must not be surfaced verbatim as the error message.
+    const assistantEvent = JSON.stringify({
+      type: "assistant",
+      message: {
+        id: "063ad6038e4c889faa7c95168e007d73",
+        type: "message",
+        role: "assistant",
+        content: [{ type: "thinking", thinking: "Let me start…", signature: "abc123" }],
+        model: "MiniMax-M2.7",
+        stop_reason: null,
+        stop_sequence: null,
+        usage: { input_tokens: 11013, output_tokens: 0, cache_creation_input_tokens: 0, cache_read_input_tokens: 0 },
+      },
+    });
+    const stdout = [initLine, assistantEvent].join("\n");
+    const msg = buildPartialRunError(null, "MiniMax-M2.7", stdout);
+    expect(msg).toContain("MiniMax-M2.7");
+    expect(msg).toContain("did not produce a result");
+    expect(msg).not.toContain("063ad6038e4c889faa7c95168e007d73");
+    expect(msg).not.toContain("output_tokens");
+    expect(msg).not.toContain("thinking");
+  });
+
+  it("skips user events alongside system events", () => {
+    const userEvent = JSON.stringify({ type: "user", message: { role: "user", content: [] } });
+    const stdout = [initLine, userEvent, "Error: API quota exceeded"].join("\n");
+    const msg = buildPartialRunError(1, "claude-sonnet-4-6", stdout);
+    expect(msg).toBe("Claude exited with code 1: Error: API quota exceeded");
+  });
+
   it("null exitCode renders as -1 in message", () => {
     const msg = buildPartialRunError(null, "", "Some plain error text");
     expect(msg).toBe("Claude exited with code -1: Some plain error text");