Document mixed filesystem validation in the language guide

docs/language.html

@@ -649,6 +649,14 @@ parse/compile/update APIs, CLI commands, desktop and server flows remain separat
 a read result does not grant their typed editing or save authority. Generic and
 typed depth policies and platform qualification limits remain unchanged. This
 staged capability does not replace the broader conformance obligations below.</p>
+<p>For filesystem input, <span class="docutils literal">arcadia <span class="pre">check-mixed</span> ROOT <span class="pre">[--json]</span></span> discovers included
+files with the same mixed grammar and the existing disk/path/journal safeguards,
+then checks the complete captured bundle. It requires explicit UUIDs and schema8;
+<span class="docutils literal"><span class="pre">--write</span></span> is rejected. The discovery pass shares a conservative cumulative
+resource budget across files and ends before a fresh complete-validation pass.
+It does not claim one combined numeric-work allowance or an atomic snapshot
+against concurrent external edits. Ordinary check/lint/edit commands retain their
+existing contracts. See <a class="reference external" href="source-cli.md">Source CLI</a> for command use and limits.</p>
 </section>
 <section id="scope-and-conformance">
 <h2>1. Scope and conformance</h2>

docs/language.rst

@@ -26,6 +26,15 @@ a read result does not grant their typed editing or save authority. Generic and
 typed depth policies and platform qualification limits remain unchanged. This
 staged capability does not replace the broader conformance obligations below.
 
+For filesystem input, ``arcadia check-mixed ROOT [--json]`` discovers included
+files with the same mixed grammar and the existing disk/path/journal safeguards,
+then checks the complete captured bundle. It requires explicit UUIDs and schema8;
+``--write`` is rejected. The discovery pass shares a conservative cumulative
+resource budget across files and ends before a fresh complete-validation pass.
+It does not claim one combined numeric-work allowance or an atomic snapshot
+against concurrent external edits. Ordinary check/lint/edit commands retain their
+existing contracts. See `Source CLI <source-cli.md>`_ for command use and limits.
+
 1. Scope and conformance
 ------------------------