fix(menubar): surface CLI stdout/stderr on decode failure (#515)

mac/Sources/CodeBurnMenubar/Data/DataClient.swift

@@ -17,6 +17,26 @@ enum DataClientError: Error {
     case outputTooLarge
 }
 
+/// Wraps a `MenubarPayload` decode failure with a bounded snippet of what the CLI
+/// actually wrote to stdout (plus stderr), so a malformed-output failure — for
+/// example a stray Node banner landing on stdout ahead of the JSON (see #515) —
+/// is self-diagnosing in logs and the UI instead of an opaque "not valid JSON".
+struct CLIDecodeFailure: Error, CustomStringConvertible {
+    let underlying: Error
+    let stdoutByteCount: Int
+    let stdoutSnippet: String
+    let stderr: String
+
+    var description: String {
+        var parts = [
+            "decode failed: \(underlying)",
+            "stdout (\(stdoutByteCount) bytes): \(stdoutSnippet.isEmpty ? "<empty>" : stdoutSnippet)",
+        ]
+        if !stderr.isEmpty { parts.append("stderr: \(stderr)") }
+        return parts.joined(separator: " | ")
+    }
+}
+
 /// Runs the CLI via argv (no shell interpretation). See `CodeburnCLI` for why we never route
 /// commands through `/bin/zsh -c` anymore.
 struct DataClient {
@@ -46,7 +66,13 @@ struct DataClient {
         do {
             return try JSONDecoder().decode(MenubarPayload.self, from: result.stdout)
         } catch {
-            throw DataClientError.decode(error)
+            let snippet = String(decoding: result.stdout.prefix(2048), as: UTF8.self)
+            throw DataClientError.decode(CLIDecodeFailure(
+                underlying: error,
+                stdoutByteCount: result.stdout.count,
+                stdoutSnippet: snippet,
+                stderr: result.stderr
+            ))
         }
     }
 

mac/Tests/CodeBurnMenubarTests/AppStoreRefreshRecoveryTests.swift

@@ -14,6 +14,7 @@ private func menubarPayload(cost: Double) -> MenubarPayload {
             inputTokens: 1,
             outputTokens: 1,
             cacheHitPercent: 0,
+            codexCredits: nil,
             topActivities: [],
             topModels: [],
             localModelSavings: LocalModelSavings(totalUSD: 0, calls: 0, byModel: [], byProvider: []),

mac/Tests/CodeBurnMenubarTests/DataClientProcessTests.swift

@@ -38,6 +38,31 @@ final class DataClientProcessTests: XCTestCase {
                        "runProcess deadlocked: \(count) concurrent CLIs starved the cooperative pool")
     }
 
+    /// A decode failure surfaces the CLI's actual stdout/stderr so a stray banner
+    /// on stdout (see #515) is self-diagnosing instead of an opaque "not valid JSON".
+    func testDecodeFailureSurfacesOutput() {
+        struct Boom: Error {}
+        let failure = CLIDecodeFailure(
+            underlying: Boom(),
+            stdoutByteCount: 13,
+            stdoutSnippet: "(node) banner",
+            stderr: "warn: x"
+        )
+        let text = String(describing: failure)
+        XCTAssertTrue(text.contains("(node) banner"), "should include the stdout snippet")
+        XCTAssertTrue(text.contains("13 bytes"), "should include the stdout byte count")
+        XCTAssertTrue(text.contains("warn: x"), "should include stderr")
+    }
+
+    /// Empty stdout is reported distinctly (the JSONDecoder-on-empty-Data case).
+    func testDecodeFailureWithEmptyStdout() {
+        struct Boom: Error {}
+        let failure = CLIDecodeFailure(underlying: Boom(), stdoutByteCount: 0, stdoutSnippet: "", stderr: "")
+        let text = String(describing: failure)
+        XCTAssertTrue(text.contains("0 bytes"))
+        XCTAssertTrue(text.contains("<empty>"))
+    }
+
     /// A normally-exiting process returns its real output and exit code through
     /// the off-pool wait path.
     func testProcessReturnsOutputAndExitCode() async throws {

mac/Tests/CodeBurnMenubarTests/MenubarStatusCacheTests.swift

@@ -16,6 +16,7 @@ struct MenubarStatusCacheTests {
             current: CurrentBlock(
                 label: "Today", cost: cost, calls: 1, sessions: 1, oneShotRate: nil,
                 inputTokens: 1, outputTokens: 1, cacheHitPercent: 0,
+                codexCredits: nil,
                 topActivities: [], topModels: [], localModelSavings: LocalModelSavings(totalUSD: 0, calls: 0, byModel: [], byProvider: []), providers: ["claude": cost],
                 topProjects: [], modelEfficiency: [], topSessions: [],
                 retryTax: RetryTax(totalUSD: 0, retries: 0, editTurns: 0, byModel: []),