fix(doctor): report a missing --format value as MISSING_OUTPUT_VALUE (#6489)

`mcp doctor --format` and `--format=` reported VALIDATION_ERROR
"Invalid output format: missing", although docs/cli.md documents
MISSING_OUTPUT_VALUE for valued output flags without a value and
`capabilities` already returns it. Classify absent and empty values as
missing, share the existing missing-value message, and keep
VALIDATION_ERROR for a present but unsupported format.

Fixes #6455


Claude-Session: https://claude.ai/code/session_01LjhoPGpqAwHwcCgectzRsp

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/cliOutput.ts

@@ -241,6 +241,10 @@ const hasUnclosedFilterSlice = (expression: string): boolean => {
   return unclosed;
 };
 
+/** Name a valued output flag that was given without a value. */
+export const missingCliOutputValueMessage = (flag: string): string =>
+  `${flag} requires a value, as in ${flag} <value> or ${flag}=<value>.`;
+
 /** Reject output controls that cannot safely produce a complete result. */
 export const validateCliOutputArguments = (
   arguments_: readonly string[],
@@ -273,7 +277,7 @@ export const validateCliOutputArguments = (
       ok: false,
       format: format === "yaml" || format === "jsonl" ? format : "json",
       code: "MISSING_OUTPUT_VALUE",
-      message: `${missingValue} requires a value, as in ${missingValue} <value> or ${missingValue}=<value>.`,
+      message: missingCliOutputValueMessage(missingValue),
     };
   return { ok: true };
 };

src/mcpDoctor.ts

@@ -7,6 +7,7 @@ import { StringDecoder } from "node:string_decoder";
 
 import { createCatalogIdentity } from "./catalogIdentity.js";
 import { jsonOutputParts } from "./cli/jsonOutput.js";
+import { missingCliOutputValueMessage } from "./cliOutput.js";
 import {
   compactPresentationForMcpInputSchemaProfile,
   parseMcpInputSchemaProfile,
@@ -338,7 +339,7 @@ export const runProductionMcpDoctorCli = async (
       return { output: `${renderMcpDoctorHelp()}\n`, exitCode: 0 };
     return {
       output: renderOutput(
-        { code: "VALIDATION_ERROR", message: parsed.message },
+        { code: parsed.code, message: parsed.message },
         parsed.format,
         input.stdoutIsTerminal,
       ),
@@ -442,6 +443,7 @@ type McpDoctorArguments =
       readonly ok: false;
       readonly help: false;
       readonly format: OutputFormat;
+      readonly code: "MISSING_OUTPUT_VALUE" | "VALIDATION_ERROR";
       readonly message: string;
     };
 
@@ -476,12 +478,21 @@ const parseOutputArguments = (
     if (argument === "--format" || inline !== undefined) {
       const candidate = inline ?? arguments_[index + 1];
       if (inline === undefined) index += 1;
+      if (candidate === undefined || candidate === "")
+        return {
+          ok: false,
+          help: false,
+          format,
+          code: "MISSING_OUTPUT_VALUE",
+          message: missingCliOutputValueMessage("--format"),
+        };
       if (!isOutputFormat(candidate))
         return {
           ok: false,
           help: false,
           format,
-          message: `Invalid output format: ${candidate ?? "missing"}`,
+          code: "VALIDATION_ERROR",
+          message: `Invalid output format: ${candidate}`,
         };
       format = candidate;
       continue;
@@ -495,6 +506,7 @@ const parseOutputArguments = (
       ok: false,
       help: false,
       format,
+      code: "VALIDATION_ERROR",
       message: `Unknown mcp doctor option: ${argument ?? "missing"}`,
     };
   }

tests/boundary/cli/mcpDoctorHelpCli.test.ts

@@ -83,4 +83,34 @@ describe("MCP doctor help boundary", () => {
     },
     CLI_INTEGRATION_TIMEOUT_MS,
   );
+
+  workspaceCliTest(
+    "reports an absent or empty --format value as a missing output value",
+    async ({ cli }) => {
+      const message =
+        "--format requires a value, as in --format <value> or --format=<value>.";
+      for (const arguments_ of [
+        ["mcp", "doctor", "--format"],
+        ["mcp", "doctor", "--format="],
+      ]) {
+        const result = await cli.run({ arguments: arguments_ });
+        expect(result).toMatchObject({
+          exitCode: 1,
+          stdout: `code: MISSING_OUTPUT_VALUE\nmessage: "${message}"\n`,
+        });
+      }
+      for (const arguments_ of [
+        ["mcp", "doctor", "--json", "--format"],
+        ["mcp", "doctor", "--json", "--format="],
+      ]) {
+        const result = await cli.run({ arguments: arguments_ });
+        expect(result.exitCode).toBe(1);
+        expect(JSON.parse(result.stdout)).toEqual({
+          code: "MISSING_OUTPUT_VALUE",
+          message,
+        });
+      }
+    },
+    CLI_INTEGRATION_TIMEOUT_MS,
+  );
 });