Strip non-schema message fields for Mistral chat requests

app/L0/_all/mod/_core/mistral/AGENTS.md

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+# AGENTS
+
+## Purpose
+
+`_core/mistral/` owns Mistral-specific frontend request customization.
+
+It is a headless helper module. It does not own chat UI or prompt assembly. It owns reusable Mistral endpoint detection plus extension files that patch API-mode chat requests for the first-party chat surfaces.
+
+Mistral's chat completions API uses strict Pydantic validation (`extra="forbid"`) and rejects any field on a message object that is not part of its defined schema. Space Agent's prompt pipeline attaches internal bookkeeping fields such as `tokenCount`, `kind`, and `source` to message objects for prompt budgeting and UI display. These fields must be stripped before the request reaches Mistral. This module performs that strip at the API-request seam.
+
+Documentation is top priority for this module. After any change under this subtree, update this file and any affected parent or consumer docs in the same session.
+
+## Ownership
+
+This module owns:
+
+- `request.js`: shared Mistral endpoint detection and request-body mutation helpers
+- `ext/js/_core/onscreen_agent/api.js/prepareOnscreenAgentApiRequest/end/mistral.js`: overlay-chat API request customization
+- `ext/js/_core/admin/views/agent/api.js/prepareAdminAgentApiRequest/end/mistral.js`: admin-chat API request customization
+
+## Local Contracts
+
+- this module contributes behavior only through JS extension hooks and shared helpers; it must not fork or duplicate the admin or onscreen chat runtimes
+- Mistral detection should use the configured upstream API endpoint, not the proxied fetch URL, because frontend fetches may be rerouted through `/api/proxy`
+- the two shipped extension hooks may mutate the prepared API request object, including headers, body, URL, method, or extra fetch-init fields, but they must leave non-Mistral requests untouched
+- the body rewrite preserves only the message fields accepted by Mistral's schema: `role`, `content`, `name`, `tool_calls`, `tool_call_id`
+- provider-specific HTTP policy belongs here or in similar headless provider modules, not hard-coded into `_core/onscreen_agent/llm.js` or `_core/admin/views/agent/api.js`
+
+## Development Guidance
+
+- keep provider detection small and explicit
+- prefer one shared helper for endpoint matching and body mutation so the admin and onscreen hooks stay in sync
+- if Mistral expands its accepted message schema, extend `ALLOWED_MESSAGE_FIELDS` in `request.js` rather than removing the strip entirely
+- if additional Mistral request shaping is needed later (e.g. header mutation, endpoint rewriting), extend the prepared request object here instead of reintroducing per-surface hard-coded branches

app/L0/_all/mod/_core/mistral/ext/js/_core/admin/views/agent/api.js/prepareAdminAgentApiRequest/end/mistral.js

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+import { applyMistralBodyRewrite, isMistralEndpoint } from "/mod/_core/mistral/request.js";
+
+export default async function mistralAdminRequestHook(hookContext) {
+  const apiRequest = hookContext?.result;
+
+  if (!apiRequest || typeof apiRequest !== "object") {
+    return;
+  }
+
+  if (!isMistralEndpoint(apiRequest.apiEndpoint || apiRequest.settings?.apiEndpoint || "")) {
+    return;
+  }
+
+  hookContext.result = applyMistralBodyRewrite(apiRequest);
+}

app/L0/_all/mod/_core/mistral/ext/js/_core/onscreen_agent/api.js/prepareOnscreenAgentApiRequest/end/mistral.js

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+import { applyMistralBodyRewrite, isMistralEndpoint } from "/mod/_core/mistral/request.js";
+
+export default async function mistralOnscreenRequestHook(hookContext) {
+  const apiRequest = hookContext?.result;
+
+  if (!apiRequest || typeof apiRequest !== "object") {
+    return;
+  }
+
+  if (!isMistralEndpoint(apiRequest.apiEndpoint || apiRequest.settings?.apiEndpoint || "")) {
+    return;
+  }
+
+  hookContext.result = applyMistralBodyRewrite(apiRequest);
+}

app/L0/_all/mod/_core/mistral/request.js

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+const MISTRAL_HOST = "mistral.ai";
+
+const ALLOWED_MESSAGE_FIELDS = ["role", "content", "name", "tool_calls", "tool_call_id"];
+
+export function isMistralEndpoint(endpoint = "") {
+  const normalizedEndpoint = String(endpoint || "").trim();
+
+  if (!normalizedEndpoint) {
+    return false;
+  }
+
+  try {
+    const url = new URL(normalizedEndpoint, globalThis.location?.origin || "http://localhost");
+    return url.hostname === MISTRAL_HOST || url.hostname.endsWith(`.${MISTRAL_HOST}`);
+  } catch {
+    return normalizedEndpoint.includes(MISTRAL_HOST);
+  }
+}
+
+function stripMessage(message) {
+  if (!message || typeof message !== "object") {
+    return message;
+  }
+
+  const stripped = {};
+
+  for (const field of ALLOWED_MESSAGE_FIELDS) {
+    if (message[field] !== undefined) {
+      stripped[field] = message[field];
+    }
+  }
+
+  return stripped;
+}
+
+export function applyMistralBodyRewrite(apiRequest = {}) {
+  const requestBody =
+    apiRequest?.requestBody && typeof apiRequest.requestBody === "object"
+      ? apiRequest.requestBody
+      : null;
+
+  if (!requestBody || !Array.isArray(requestBody.messages)) {
+    return apiRequest;
+  }
+
+  return {
+    ...apiRequest,
+    requestBody: {
+      ...requestBody,
+      messages: requestBody.messages.map((message) => stripMessage(message))
+    }
+  };
+}