feat(FN-3815): quiet stderr logging for clean-exit MCP processes in pi-clau

Adds a changeset for FN-3815. The core change reclassifies clean-exit stderr output in the pi-claude-cli provider to reduce noisy logging, with corresponding test coverage distinguishing between clean and non-zero exit stderr handling.

Fusion-Task-Id: FN-3815

.changeset/fn-3815-quiet-pi-mcp-loading.md

@@ -0,0 +1,7 @@
+---
+"@runfusion/fusion": patch
+---
+
+Quiet benign Claude Code CLI stderr on clean shutdown by routing it to debug-only logs in `pi-claude-cli`.
+
+This prevents MCP loading/initialization lines from surfacing as warning/error-level entries in the TUI Logs tab when Claude exits cleanly, while preserving warning/error surfacing for non-zero Claude CLI exits and authentication-related failures.

packages/pi-claude-cli/src/__tests__/provider.test.ts

@@ -1188,28 +1188,42 @@ describe("streamViaCli", { timeout: 90_000 }, () => {
       expect(doneEvent.message.content).toBeDefined();
     });
 
-    it("logs stderr at warn level on close even with exit code 0", async () => {
+    it.each([
-      const model = mockModels[0] as any;
+      { code: 0, shouldWarn: false },
-      const context = {
+      { code: 42, shouldWarn: true },
-        messages: [{ role: "user", content: "Hello" }],
+    ])(
-      };
+      "FN-3815: routes close stderr logging by exit code=$code",
+      async ({ code, shouldWarn }) => {
+        const model = mockModels[0] as any;
+        const context = {
+          messages: [{ role: "user", content: "Hello" }],
+        };
 
-      const warnSpy = vi.spyOn(console, "warn");
+        const warnSpy = vi.spyOn(console, "warn");
 
-      streamViaCli(model, context);
+        streamViaCli(model, context);
-      await vi.advanceTimersByTimeAsync(0);
+        await vi.advanceTimersByTimeAsync(0);
 
-      const proc = (spawn as any).mock.results[0].value;
+        const proc = (spawn as any).mock.results[0].value;
 
-      proc.stderr.emit("data", Buffer.from("minor warning from cli"));
+        proc.stderr.emit("data", Buffer.from("minor warning from cli"));
-      proc.emit("close", 0, null);
+        proc.emit("close", code, null);
-      proc.stdout.end();
+        proc.stdout.end();
-      await vi.advanceTimersByTimeAsync(100);
+        await vi.advanceTimersByTimeAsync(100);
 
-      expect(warnSpy).toHaveBeenCalledWith(
+        const stderrWarnCalls = warnSpy.mock.calls.filter(([message]) =>
-        expect.stringContaining("minor warning from cli"),
+          typeof message === "string" &&
-      );
+          message.includes("[pi-claude-cli] Claude CLI stderr on close:"),
-    });
+        );
+
+        if (shouldWarn) {
+          expect(stderrWarnCalls).toHaveLength(1);
+          expect(stderrWarnCalls[0]?.[0]).toContain("minor warning from cli");
+        } else {
+          expect(stderrWarnCalls).toHaveLength(0);
+        }
+      },
+    );
 
     it("warns when subprocess closes successfully with no content events", async () => {
       const model = mockModels[0] as any;

packages/pi-claude-cli/src/provider.ts

@@ -252,7 +252,13 @@ export function streamViaCli(
         if (broken) return; // Break-early kill, expected
         const stderr = getStderr().trim();
         if (stderr) {
-          console.warn(`[pi-claude-cli] Claude CLI stderr on close: ${stderr}`);
+          if (code === 0 || code === null) {
+            // FN-3815: Claude CLI writes benign MCP bring-up diagnostics to stderr
+            // on clean/abort shutdown; keep these debug-only to avoid false TUI warnings.
+            debugLog(`Claude CLI stderr on close (clean exit): ${stderr}`);
+          } else {
+            console.warn(`[pi-claude-cli] Claude CLI stderr on close: ${stderr}`);
+          }
         }
         if (code !== 0 && code !== null) {
           const message = stderr