fix(mcp): no-response диагностика — не отдавать сырой error.message (утечка host в модель) (внутр. ревью #437)

no-response ветка формата использовала error.code ?? error.message: при
отсутствии code axios-сообщения сетевых ошибок содержат host:port
('connect ECONNREFUSED 127.0.0.1:3000', 'getaddrinfo ENOTFOUND host'), что
нарушает инвариант #437 «host никогда не попадает в видимое модели сообщение».
Теперь только error.code (?? 'network error'); полный нативный текст уходит в
stderr под DEBUG. code проставлен фактически для всех реальных no-response
ошибок. Тест обновлён: сырое host-содержащее сообщение -> нейтральный reason,
плюс ассерт что host в сообщении отсутствует.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts

@@ -729,6 +729,35 @@ export class AiChatToolsService {
           }),
       ),
 
+      // Schema + description live in @docmost/mcp's SHARED_TOOL_SPECS (#423).
+      // meta.hash in the result is the baseHash drawioUpdate requires.
+      drawioGet: sharedTool(
+        sharedToolSpecs.drawioGet,
+        async ({ pageId, node, format }) =>
+          await client.drawioGet(pageId, node, format ?? 'xml'),
+      ),
+
+      // Schema + description live in @docmost/mcp's SHARED_TOOL_SPECS (#423).
+      // The flat schema fields are regrouped into the client's `where` object.
+      drawioCreate: sharedTool(
+        sharedToolSpecs.drawioCreate,
+        async ({ pageId, xml, position, anchorNodeId, anchorText, title }) =>
+          await client.drawioCreate(
+            pageId,
+            { position, anchorNodeId, anchorText },
+            xml,
+            title,
+          ),
+      ),
+
+      // Schema + description live in @docmost/mcp's SHARED_TOOL_SPECS (#423).
+      // baseHash is the optimistic lock: mismatch => structured conflict error.
+      drawioUpdate: sharedTool(
+        sharedToolSpecs.drawioUpdate,
+        async ({ pageId, node, xml, baseHash }) =>
+          await client.drawioUpdate(pageId, node, xml, baseHash),
+      ),
+
       // Schema + description now live in @docmost/mcp's SHARED_TOOL_SPECS (#294).
       // The table reference parameter was unified to `table` (was `tableRef`).
       tableInsertRow: sharedTool(

apps/server/src/core/ai-chat/tools/docmost-client.loader.ts

@@ -168,6 +168,32 @@ export interface DocmostClientLike {
     url: string,
     opts?: { align?: 'left' | 'center' | 'right'; alt?: string },
   ): Promise<Record<string, unknown>>;
+  // --- draw.io diagrams (#423, stage 1) ---
+  // Read a diagram as decoded mxGraph XML (default) or the raw .drawio.svg.
+  // meta.hash is the optimistic-lock key drawioUpdate expects as baseHash.
+  drawioGet(
+    pageId: string,
+    node: string,
+    format?: 'xml' | 'svg',
+  ): Promise<Record<string, unknown>>;
+  // Lint mxGraph XML, build the .drawio.svg attachment and insert a drawio node.
+  drawioCreate(
+    pageId: string,
+    where: {
+      position: 'before' | 'after' | 'append';
+      anchorNodeId?: string;
+      anchorText?: string;
+    },
+    xml: string,
+    title?: string,
+  ): Promise<Record<string, unknown>>;
+  // Optimistic-locked full replacement of a diagram (baseHash from drawioGet).
+  drawioUpdate(
+    pageId: string,
+    node: string,
+    xml: string,
+    baseHash: string,
+  ): Promise<Record<string, unknown>>;
   tableInsertRow(
     pageId: string,
     tableRef: string,

packages/mcp/src/client.ts

@@ -167,6 +167,166 @@ function isUuid(value: string): boolean {
   return typeof value === "string" && UUID_RE.test(value);
 }
 
+// --- Issue #437: central error diagnostics -------------------------------
+// The agent only ever sees the thrown exception's `error.message`, so a failed
+// tool must return an ACTIONABLE message (method, path, status, and the
+// server's own validation text) instead of the opaque "Request failed with
+// status code 400". These helpers + the response interceptor in the
+// constructor are the single authoritative place that text is composed.
+
+// Overall cap on the composed diagnostic message so the model context stays
+// compact and a (whitelisted) server string can never blow up the text.
+const ERROR_MESSAGE_CAP = 300;
+// Only attempt to JSON.parse an arraybuffer body under this size: a larger
+// binary body is never a JSON error envelope, so parsing it just wastes memory
+// (fetchInternalFile uses responseType:"arraybuffer", so a failed file fetch
+// carries the JSON error envelope as raw bytes here).
+const ERROR_BUFFER_PARSE_CAP = 4096;
+
+// Canonical 36-char UUID (8-4-4-4-12 hex). Deliberately version/variant-
+// AGNOSTIC: the ids are UUIDv7 (e.g. 019f499a-9f8c-7d68-...), so only the
+// canonical shape/length is enforced, not the version/variant nibble.
+const FULL_UUID_RE =
+  /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
+
+/**
+ * Throw an actionable error BEFORE any network call when `value` is not a full
+ * canonical UUID. Absorbs #436: a truncated/short comment id used to reach the
+ * server and bounce back as an opaque 400/404 the agent could not self-correct;
+ * failing fast here names the exact fix.
+ */
+export function assertFullUuid(
+  tool: string,
+  param: string,
+  value: string,
+): void {
+  if (typeof value !== "string" || !FULL_UUID_RE.test(value)) {
+    throw new Error(
+      `${tool}: '${param}' must be the FULL comment UUID (36 chars, e.g. ` +
+        `019f499a-9f8c-7d68-b7be-ce100d7c6c56), got '${value}'. Copy the id ` +
+        `verbatim from list_comments / create_comment output.`,
+    );
+  }
+}
+
+// Keep ONLY the pathname of a request (no host, no query string, no fragment)
+// so the message never leaks a host or query params. Resolves a relative
+// config.url against config.baseURL, then discards everything but the path.
+function requestPath(config: any): string {
+  const rawUrl = typeof config?.url === "string" ? config.url : "";
+  const base =
+    typeof config?.baseURL === "string" ? config.baseURL : undefined;
+  try {
+    // A dummy base makes an absolute config.url parse too; its host is dropped.
+    return new URL(rawUrl, base ?? "http://localhost").pathname;
+  } catch {
+    // Malformed url: still strip any query/fragment manually.
+    return rawUrl.split(/[?#]/)[0] || rawUrl;
+  }
+}
+
+/**
+ * Compose the server-facing message from `error.response.data`, using ONLY the
+ * whitelisted `message`/`error` fields or the HTTP statusText. SECURITY: the
+ * raw response body, headers (Authorization!) and config are NEVER read here —
+ * a string/HTML body (e.g. a proxy's 502 page) is deliberately dropped in
+ * favour of the statusText.
+ */
+function extractServerMessage(data: any, statusText: string): string {
+  // class-validator envelope: { message: string | string[], error?: string }.
+  if (
+    data &&
+    typeof data === "object" &&
+    !Buffer.isBuffer(data) &&
+    !(data instanceof ArrayBuffer)
+  ) {
+    const msg = (data as any).message;
+    if (Array.isArray(msg)) {
+      const joined = msg.filter((m) => typeof m === "string").join("; ");
+      if (joined) return joined;
+    } else if (typeof msg === "string" && msg) {
+      return msg;
+    }
+    const err = (data as any).error;
+    if (typeof err === "string" && err) return err;
+    return statusText;
+  }
+
+  // Buffer / ArrayBuffer body: attempt a size-capped, guarded JSON.parse so a
+  // failed arraybuffer fetch still surfaces the server's validation text.
+  if (Buffer.isBuffer(data) || data instanceof ArrayBuffer) {
+    const buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
+    if (buf.length > 0 && buf.length <= ERROR_BUFFER_PARSE_CAP) {
+      try {
+        return extractServerMessage(JSON.parse(buf.toString("utf8")), statusText);
+      } catch {
+        return statusText;
+      }
+    }
+    return statusText;
+  }
+
+  // A raw string / HTML body is never surfaced (may echo server internals).
+  return statusText;
+}
+
+/**
+ * Reformat an AxiosError's `.message` IN PLACE into an actionable diagnostic:
+ *   `<METHOD> <path> failed (<status> <statusText>): <serverMessage>`
+ * or, when the request never got a response:
+ *   `<METHOD> <path> failed: <code> (no response from server)`.
+ *
+ * Mutates the SAME error object (never a custom subclass) so the live
+ * axios.isAxiosError / error.response?.status / config._retry checks around the
+ * client keep working, and sets `_docmostFormatted` as a double-processing
+ * guard. A no-op on a non-axios or already-formatted error.
+ */
+export function formatDocmostAxiosError(error: any): void {
+  if (!error || error._docmostFormatted) return;
+  if (!axios.isAxiosError(error)) return;
+
+  const config: any = error.config ?? {};
+  const method =
+    typeof config.method === "string" ? config.method.toUpperCase() : "";
+  const methodPath = `${method} ${requestPath(config)}`.trim();
+  const response = error.response;
+
+  let message: string;
+  if (response) {
+    const statusText =
+      typeof response.statusText === "string" ? response.statusText : "";
+    const serverMessage = extractServerMessage(response.data, statusText);
+    message = `${methodPath} failed (${response.status} ${statusText}): ${serverMessage}`;
+    // Full body only to stderr under DEBUG (parity with downloadImage).
+    if (process.env.DEBUG) {
+      console.error(
+        "Docmost request failed; response body:",
+        JSON.stringify(response.data),
+      );
+    }
+  } else {
+    // No response at all (ECONNREFUSED / ETIMEDOUT / ECONNRESET / DNS / timeout).
+    // Use ONLY error.code, never the raw error.message: axios network messages
+    // embed host:port ("connect ECONNREFUSED 127.0.0.1:3000", "getaddrinfo
+    // ENOTFOUND host") and #437's invariant is that the host never reaches the
+    // model-visible message. code is set for essentially every real no-response
+    // error (ECONNREFUSED/ETIMEDOUT/ECONNRESET/ENOTFOUND/ECONNABORTED); the full
+    // native message still goes to stderr under DEBUG.
+    const reason = error.code ?? "network error";
+    message = `${methodPath} failed: ${reason} (no response from server)`;
+    if (process.env.DEBUG) {
+      console.error("Docmost request failed; no response:", error.message);
+    }
+  }
+
+  if (message.length > ERROR_MESSAGE_CAP) {
+    message = message.slice(0, ERROR_MESSAGE_CAP - 1) + "…";
+  }
+
+  error.message = message;
+  (error as any)._docmostFormatted = true;
+}
+
 export class DocmostClient {
   private client: AxiosInstance;
   private token: string | null = null;
@@ -295,6 +455,22 @@ export class DocmostClient {
         return Promise.reject(error);
       },
     );
+
+    // Diagnostics interceptor (issue #437). Registered AFTER the re-login
+    // interceptor so a successful re-login retry (which resolves to a real
+    // response) is never seen here as an error; only a genuine failure reaches
+    // this rejection handler. It reformats error.message IN PLACE (see
+    // formatDocmostAxiosError — kept as a mutation, not a custom Error class, so
+    // the surrounding axios.isAxiosError / error.response?.status / config._retry
+    // checks keep working) and re-rejects the SAME error. The _docmostFormatted
+    // flag makes a re-processed retry-failure a no-op.
+    this.client.interceptors.response.use(
+      (response) => response,
+      (error) => {
+        formatDocmostAxiosError(error);
+        return Promise.reject(error);
+      },
+    );
   }
 
   /** Application base URL (API URL without the /api suffix). */
@@ -2324,6 +2500,8 @@ export class DocmostClient {
   }
 
   async getComment(commentId: string) {
+    // Fail fast (#436): reject a truncated id before any network call.
+    assertFullUuid("get_comment", "commentId", commentId);
     await this.ensureAuthenticated();
     const response = await this.client.post("/comments/info", { commentId });
     const comment = response.data.data || response.data;
@@ -2413,6 +2591,12 @@ export class DocmostClient {
     parentCommentId?: string,
     suggestedText?: string,
   ) {
+    // Fail fast (#436): a provided parent id must be a full UUID before any
+    // network call. Validate only when truthy — a falsy parentCommentId means
+    // "top-level comment" (mirrors the isReply computation below), not a reply.
+    if (parentCommentId) {
+      assertFullUuid("create_comment", "parentCommentId", parentCommentId);
+    }
     await this.ensureAuthenticated();
 
     const isReply = !!parentCommentId;
@@ -2695,6 +2879,8 @@ export class DocmostClient {
   }
 
   async updateComment(commentId: string, content: string) {
+    // Fail fast (#436): reject a truncated id before any network call.
+    assertFullUuid("update_comment", "commentId", commentId);
     await this.ensureAuthenticated();
     // NON-canonicalizing on purpose (comment body — see createComment).
     const jsonContent = await markdownToProseMirror(content);
@@ -2710,6 +2896,8 @@ export class DocmostClient {
   }
 
   async deleteComment(commentId: string) {
+    // Fail fast (#436): reject a truncated id before any network call.
+    assertFullUuid("delete_comment", "commentId", commentId);
     await this.ensureAuthenticated();
     return this.client
       .post("/comments/delete", { commentId })
@@ -2722,6 +2910,8 @@ export class DocmostClient {
    * rejects resolving a reply. Hits POST /comments/resolve.
    */
   async resolveComment(commentId: string, resolved: boolean) {
+    // Fail fast (#436): reject a truncated id before any network call.
+    assertFullUuid("resolve_comment", "commentId", commentId);
     await this.ensureAuthenticated();
     const response = await this.client.post("/comments/resolve", {
       commentId,

packages/mcp/src/lib/collab-session.ts

@@ -202,6 +202,21 @@ export class CollabSession {
     this.ydoc = new Y.Doc();
   }
 
+  /**
+   * Shared diagnostic suffix (issue #437) appended to the connect-timeout,
+   * persist-timeout and connection-closed error texts: names the offending
+   * pageId and tells the agent this class of failure is transient (retry once)
+   * vs. a persistent collab-server outage, so it can self-correct instead of
+   * blind-looping. The Yjs-encode error is deliberately NOT touched — it
+   * already names the offending attribute.
+   */
+  private hint(): string {
+    return (
+      `(pageId ${this.pageId}; transient — retry once; persistent failures ` +
+      `mean the collab server is unreachable/overloaded)`
+    );
+  }
+
   /**
    * A cached session may be reused only when it is fully ready, still synced,
    * has not lost its connection, and has not exceeded its max age (invariant 5
@@ -232,7 +247,9 @@ export class CollabSession {
         // The 25s connect timeout: the collab connection never became ready.
         this.opts?.onConnectTimeout?.();
         this.teardown(
-          new Error("Connection timeout to collaboration server"),
+          new Error(
+            `Connection timeout to collaboration server ${this.hint()}`,
+          ),
           false,
         );
       }, CONNECT_TIMEOUT_MS);
@@ -259,7 +276,7 @@ export class CollabSession {
           if (process.env.DEBUG) console.error("WS Disconnect");
           this.teardown(
             new Error(
-              "Collaboration connection closed before the update was persisted/synced",
+              `Collaboration connection closed before the update was persisted/synced ${this.hint()}`,
             ),
             true,
           );
@@ -268,7 +285,7 @@ export class CollabSession {
           if (process.env.DEBUG) console.error("WS Close");
           this.teardown(
             new Error(
-              "Collaboration connection closed before the update was persisted/synced",
+              `Collaboration connection closed before the update was persisted/synced ${this.hint()}`,
             ),
             true,
           );
@@ -403,7 +420,7 @@ export class CollabSession {
         persistTimer = setTimeout(() => {
           localFinish(
             new Error(
-              "Timeout waiting for collaboration server to persist the update",
+              `Timeout waiting for collaboration server to persist the update ${this.hint()}`,
             ),
           );
         }, PERSIST_TIMEOUT_MS);

packages/mcp/test/mock/create-comment.test.mjs

@@ -203,14 +203,16 @@ test("a reply creates without selection or anchoring and is stored as type 'page
     "reply body",
     "inline",
     undefined,
-    "parent-123",
+    // #437: a parentCommentId must be a full canonical UUID.
+    "019f499a-9f8c-7d68-b7be-ce100d7c6c56",
   );
 
   assert.equal(result.success, true, "a reply must resolve successfully");
   assert.ok(createPayload, "/comments/create must have been called");
   assert.equal(
     createPayload.parentCommentId,
-    "parent-123",
+    // #437: a parentCommentId must be a full canonical UUID.
+    "019f499a-9f8c-7d68-b7be-ce100d7c6c56",
     "the reply payload must carry the parentCommentId",
   );
   assert.equal(
@@ -321,7 +323,9 @@ test("suggestedText on a reply is rejected", async () => {
         "body",
         "inline",
         undefined,
-        "parent-1",
+        // #437: use a valid full UUID so the reply+suggestion rejection fires
+        // (not the id-shape guard).
+        "019f499a-9f8c-7d68-b7be-ce100d7c6c56",
         "replacement",
       ),
     /reply/i,

packages/mcp/test/unit/client-host-contract.test.mjs

@@ -81,6 +81,10 @@ const HOST_CONTRACT_METHODS = [
   "insertImage",
   "replaceImage",
   "insertFootnote",
+  // draw.io diagrams (#423, stage 1) — read + create + optimistic-locked update
+  "drawioGet",
+  "drawioCreate",
+  "drawioUpdate",
   // write (comment)
   "createComment",
   "resolveComment",

packages/mcp/test/unit/error-diagnostics.test.mjs

@@ -0,0 +1,450 @@
+// Issue #437: central error diagnostics.
+//
+// Two surfaces are covered here:
+//   1. formatDocmostAxiosError — the pure response-interceptor body that
+//      rewrites an AxiosError's `.message` into an actionable diagnostic.
+//   2. assertFullUuid — the fail-fast comment-id guard (absorbs #436) that must
+//      throw BEFORE any network call.
+// Plus an end-to-end pass over a real (offline) http server to prove the
+// interceptor is wired, that a re-login retry leaves a success untouched, and
+// that a persistent failure gets formatted — and that an invalid comment id
+// short-circuits every comment tool with ZERO network traffic.
+import { test, after } from "node:test";
+import assert from "node:assert/strict";
+import http from "node:http";
+import axios, { AxiosError } from "axios";
+import {
+  DocmostClient,
+  formatDocmostAxiosError,
+  assertFullUuid,
+} from "../../build/client.js";
+
+// Build an AxiosError-shaped object the way the interceptor's rejection handler
+// receives it. Using the real AxiosError ctor makes axios.isAxiosError() true.
+function makeAxiosError({
+  method = "post",
+  url = "/comments/resolve",
+  baseURL = "http://host.example/api",
+  status,
+  statusText,
+  data,
+  code,
+  message = "Request failed",
+}) {
+  const config = { method, url, baseURL };
+  const response =
+    status === undefined
+      ? undefined
+      : { status, statusText, data, headers: {}, config };
+  return new AxiosError(message, code, config, {}, response);
+}
+
+// ---------------------------------------------------------------------------
+// formatDocmostAxiosError: message-body extraction rules.
+// ---------------------------------------------------------------------------
+test("class-validator message array is joined with '; '", () => {
+  const err = makeAxiosError({
+    status: 400,
+    statusText: "Bad Request",
+    data: { message: ["commentId must be a UUID", "resolved must be a boolean"] },
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "POST /comments/resolve failed (400 Bad Request): commentId must be a UUID; resolved must be a boolean",
+  );
+});
+
+test("a string message is used as-is", () => {
+  const err = makeAxiosError({
+    method: "post",
+    url: "/comments/resolve",
+    status: 400,
+    statusText: "Bad Request",
+    data: { message: "commentId must be a UUID" },
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "POST /comments/resolve failed (400 Bad Request): commentId must be a UUID",
+  );
+});
+
+test("falls back to data.error when message is absent", () => {
+  const err = makeAxiosError({
+    method: "get",
+    url: "/pages/info",
+    status: 403,
+    statusText: "Forbidden",
+    data: { error: "Forbidden" },
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(err.message, "GET /pages/info failed (403 Forbidden): Forbidden");
+});
+
+test("empty object body falls back to statusText", () => {
+  const err = makeAxiosError({
+    status: 404,
+    statusText: "Not Found",
+    url: "/comments/info",
+    data: {},
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(err.message, "POST /comments/info failed (404 Not Found): Not Found");
+});
+
+test("HTML/string body is NEVER surfaced — only the statusText", () => {
+  const html = "<html><body>502 Bad Gateway — nginx internals here</body></html>";
+  const err = makeAxiosError({
+    status: 502,
+    statusText: "Bad Gateway",
+    url: "/comments/create",
+    data: html,
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "POST /comments/create failed (502 Bad Gateway): Bad Gateway",
+  );
+  assert.ok(!err.message.includes("nginx"), "raw HTML body must not leak");
+  assert.ok(!err.message.includes("<html>"), "raw HTML body must not leak");
+});
+
+test("Buffer body carrying JSON is parsed for its message", () => {
+  const buf = Buffer.from(JSON.stringify({ message: "file too large" }), "utf8");
+  const err = makeAxiosError({
+    method: "get",
+    url: "/files/abc/x.png",
+    status: 413,
+    statusText: "Payload Too Large",
+    data: buf,
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "GET /files/abc/x.png failed (413 Payload Too Large): file too large",
+  );
+});
+
+test("Buffer body with non-JSON garbage falls back to statusText", () => {
+  const buf = Buffer.from("<<< not json at all >>>", "utf8");
+  const err = makeAxiosError({
+    method: "get",
+    url: "/files/abc/x.png",
+    status: 500,
+    statusText: "Internal Server Error",
+    data: buf,
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "GET /files/abc/x.png failed (500 Internal Server Error): Internal Server Error",
+  );
+  assert.ok(!err.message.includes("not json"), "raw buffer body must not leak");
+});
+
+test("an oversized Buffer body is not parsed (size cap) — statusText only", () => {
+  // A >4KB JSON buffer: even though it IS valid JSON with a message, the size
+  // cap means we do not attempt to parse it, so only the statusText survives.
+  const big = { message: "x".repeat(5000) };
+  const buf = Buffer.from(JSON.stringify(big), "utf8");
+  const err = makeAxiosError({
+    method: "get",
+    url: "/files/abc/x.png",
+    status: 500,
+    statusText: "Internal Server Error",
+    data: buf,
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "GET /files/abc/x.png failed (500 Internal Server Error): Internal Server Error",
+  );
+});
+
+// ---------------------------------------------------------------------------
+// formatDocmostAxiosError: no-response and path/method handling.
+// ---------------------------------------------------------------------------
+test("no response uses error.code + path + 'no response from server'", () => {
+  const err = makeAxiosError({
+    method: "post",
+    url: "/comments/create",
+    status: undefined,
+    code: "ECONNREFUSED",
+    message: "connect ECONNREFUSED 127.0.0.1:3000",
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "POST /comments/create failed: ECONNREFUSED (no response from server)",
+  );
+});
+
+test("no response with no code falls back to a neutral reason (raw message not leaked — it may embed host:port)", () => {
+  const err = makeAxiosError({
+    method: "post",
+    url: "/comments/create",
+    status: undefined,
+    // A raw axios network message like "connect ECONNREFUSED 127.0.0.1:3000"
+    // embeds the host; #437's invariant is that it never reaches the message.
+    message: "connect ECONNREFUSED 10.0.0.5:3000",
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "POST /comments/create failed: network error (no response from server)",
+  );
+  // And the host must NOT appear anywhere in the model-visible message.
+  assert.ok(!err.message.includes("10.0.0.5"));
+});
+
+test("path drops the host and the query string", () => {
+  const err = makeAxiosError({
+    method: "post",
+    url: "/comments/resolve?token=secret&x=1",
+    baseURL: "https://docs.example.com/api",
+    status: 400,
+    statusText: "Bad Request",
+    data: { message: "bad" },
+  });
+  formatDocmostAxiosError(err);
+  assert.equal(
+    err.message,
+    "POST /comments/resolve failed (400 Bad Request): bad",
+  );
+  assert.ok(!err.message.includes("secret"), "query string must not leak");
+  assert.ok(!err.message.includes("docs.example.com"), "host must not leak");
+});
+
+// ---------------------------------------------------------------------------
+// formatDocmostAxiosError: length cap + guard flag + pass-through.
+// ---------------------------------------------------------------------------
+test("the overall message is capped at ~300 chars", () => {
+  const err = makeAxiosError({
+    status: 400,
+    statusText: "Bad Request",
+    data: { message: "y".repeat(1000) },
+  });
+  formatDocmostAxiosError(err);
+  assert.ok(err.message.length <= 300, `expected <=300, got ${err.message.length}`);
+  assert.ok(err.message.endsWith("…"), "a truncated message ends with an ellipsis");
+});
+
+test("a formatted error is not re-processed (guard flag)", () => {
+  const err = makeAxiosError({
+    status: 400,
+    statusText: "Bad Request",
+    data: { message: "first" },
+  });
+  formatDocmostAxiosError(err);
+  const once = err.message;
+  assert.equal(err._docmostFormatted, true);
+  // Mutate the body and re-run: the guard makes it a no-op.
+  err.response.data = { message: "second" };
+  formatDocmostAxiosError(err);
+  assert.equal(err.message, once, "the guard flag prevents double-processing");
+});
+
+test("a non-axios error is passed through untouched", () => {
+  const plain = new Error("boom");
+  formatDocmostAxiosError(plain);
+  assert.equal(plain.message, "boom");
+  assert.equal(plain._docmostFormatted, undefined);
+});
+
+// ---------------------------------------------------------------------------
+// assertFullUuid.
+// ---------------------------------------------------------------------------
+const GOOD_UUID = "019f499a-9f8c-7d68-b7be-ce100d7c6c56";
+
+test("assertFullUuid accepts a full canonical UUID (any version nibble)", () => {
+  assert.doesNotThrow(() => assertFullUuid("resolve_comment", "commentId", GOOD_UUID));
+  // A v4 id also passes (version/variant-agnostic).
+  assert.doesNotThrow(() =>
+    assertFullUuid("get_comment", "commentId", "3d5b7c1e-2f4a-4b6c-8d9e-0f1a2b3c4d5e"),
+  );
+});
+
+test("assertFullUuid rejects a truncated prefix", () => {
+  assert.throws(
+    () => assertFullUuid("resolve_comment", "commentId", "019f499a"),
+    (e) =>
+      e.message.startsWith(
+        "resolve_comment: 'commentId' must be the FULL comment UUID",
+      ) &&
+      e.message.includes("got '019f499a'") &&
+      e.message.includes("Copy the id verbatim"),
+  );
+});
+
+test("assertFullUuid rejects garbage and empty string", () => {
+  assert.throws(
+    () => assertFullUuid("delete_comment", "commentId", "not-a-uuid"),
+    /must be the FULL comment UUID.*got 'not-a-uuid'/s,
+  );
+  assert.throws(
+    () => assertFullUuid("update_comment", "commentId", ""),
+    /must be the FULL comment UUID.*got ''/s,
+  );
+});
+
+// ---------------------------------------------------------------------------
+// End-to-end over an offline http server: interceptor wiring + re-login.
+// ---------------------------------------------------------------------------
+function readBody(req) {
+  return new Promise((resolve) => {
+    let raw = "";
+    req.on("data", (c) => (raw += c));
+    req.on("end", () => resolve(raw));
+  });
+}
+function startServer(handler) {
+  return new Promise((resolve) => {
+    const server = http.createServer(handler);
+    server.listen(0, "127.0.0.1", () => {
+      const { port } = server.address();
+      resolve({ server, baseURL: `http://127.0.0.1:${port}/api` });
+    });
+  });
+}
+function sendJson(res, status, obj, extra = {}) {
+  res.writeHead(status, { "Content-Type": "application/json", ...extra });
+  res.end(JSON.stringify(obj));
+}
+const openServers = [];
+async function spawn(handler) {
+  const { server, baseURL } = await startServer(handler);
+  openServers.push(server);
+  return { baseURL };
+}
+after(async () => {
+  await Promise.all(openServers.map((s) => new Promise((r) => s.close(r))));
+});
+
+test("a 400 on a JSON endpoint is reformatted by the wired interceptor", async () => {
+  const { baseURL } = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      sendJson(res, 200, { success: true }, {
+        "Set-Cookie": "authToken=t; Path=/; HttpOnly",
+      });
+      return;
+    }
+    if (req.url === "/api/pages/info") {
+      sendJson(res, 400, { message: "pageId should not be empty" });
+      return;
+    }
+    sendJson(res, 404, {});
+  });
+
+  const client = new DocmostClient(baseURL, "u@example.com", "pw");
+  await assert.rejects(
+    () => client.getPageRaw("x"),
+    (e) => {
+      assert.ok(axios.isAxiosError(e), "still an AxiosError (mutation, not a subclass)");
+      assert.equal(e.response?.status, 400, "error.response?.status still readable");
+      assert.equal(
+        e.message,
+        "POST /pages/info failed (400 Bad Request): pageId should not be empty",
+      );
+      return true;
+    },
+  );
+});
+
+test("401 -> re-login -> successful retry: the SUCCESS message is untouched", async () => {
+  let infoCalls = 0;
+  const { baseURL } = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      sendJson(res, 200, { success: true }, {
+        "Set-Cookie": "authToken=fresh; Path=/; HttpOnly",
+      });
+      return;
+    }
+    if (req.url === "/api/workspace/info") {
+      infoCalls++;
+      if (infoCalls === 1) sendJson(res, 401, { message: "Unauthorized" });
+      else sendJson(res, 200, { success: true, data: { id: "ws" } });
+      return;
+    }
+    sendJson(res, 404, {});
+  });
+
+  const client = new DocmostClient(baseURL, "u@example.com", "pw");
+  client.token = "stale";
+  client.client.defaults.headers.common["Authorization"] = "Bearer stale";
+
+  const result = await client.getWorkspace();
+  assert.equal(result.success, true, "the retried request resolved successfully");
+  assert.equal(infoCalls, 2, "401 then a successful replay");
+});
+
+test("401 -> re-login -> persistent failure: formatted AND retry guard intact", async () => {
+  let infoCalls = 0;
+  let loginCalls = 0;
+  const { baseURL } = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      loginCalls++;
+      sendJson(res, 200, { success: true }, {
+        "Set-Cookie": "authToken=fresh; Path=/; HttpOnly",
+      });
+      return;
+    }
+    if (req.url === "/api/workspace/info") {
+      infoCalls++;
+      // Always 401, even after a fresh login: the _retry guard must stop here.
+      sendJson(res, 401, { message: "token still invalid" });
+      return;
+    }
+    sendJson(res, 404, {});
+  });
+
+  const client = new DocmostClient(baseURL, "u@example.com", "pw");
+  client.token = "stale";
+  client.client.defaults.headers.common["Authorization"] = "Bearer stale";
+
+  await assert.rejects(
+    () => client.getWorkspace(),
+    (e) => {
+      assert.equal(
+        e.message,
+        "POST /workspace/info failed (401 Unauthorized): token still invalid",
+      );
+      return true;
+    },
+  );
+  // The _retry guard is intact: exactly one replay (2 hits), one re-login.
+  assert.equal(infoCalls, 2, "endpoint hit at most twice (one retry only)");
+  assert.equal(loginCalls, 1, "re-login attempted exactly once");
+});
+
+// ---------------------------------------------------------------------------
+// assertFullUuid application points: NO network call when the id is invalid.
+// A server that counts EVERY request proves the guard short-circuits before
+// even the login round-trip.
+// ---------------------------------------------------------------------------
+test("all 5 comment-id call sites reject a bad id with ZERO network traffic", async () => {
+  let requests = 0;
+  const { baseURL } = await spawn(async (req, res) => {
+    requests++;
+    await readBody(req);
+    sendJson(res, 200, { success: true });
+  });
+
+  const client = new DocmostClient(baseURL, "u@example.com", "pw");
+  const bad = "019f499a"; // truncated
+
+  await assert.rejects(() => client.resolveComment(bad, true), /resolve_comment: 'commentId'/);
+  await assert.rejects(() => client.updateComment(bad, "hi"), /update_comment: 'commentId'/);
+  await assert.rejects(() => client.deleteComment(bad), /delete_comment: 'commentId'/);
+  await assert.rejects(() => client.getComment(bad), /get_comment: 'commentId'/);
+  // createComment validates parentCommentId only when provided.
+  await assert.rejects(
+    () => client.createComment("page-1", "body", "inline", "sel", bad),
+    /create_comment: 'parentCommentId'/,
+  );
+
+  assert.equal(requests, 0, "no request (not even /auth/login) may be issued for a bad id");
+});