Add guarded Text alias rename with complete preview and editor reuse

docs/language.html

@@ -2650,6 +2650,45 @@ limits. If sources change, stale rows cannot navigate: run the query again.
 Navigation MUST preserve the accepted model and every source draft, and select
 locations in the original UTF-8 bytes. Displayed locations use one-based lines
 and UTF-8 byte columns.</p>
+<p><strong>Rename alias</strong> (<span class="docutils literal">F2</span> while the source editor has focus) changes the alias
+under the caret or its exact selection. It requires a unique authored identity
+in the complete accepted source bundle, with no pending source, property or
+behavior drafts and no extra loaded detached files. Accepted but unsaved source
+is eligible. The operation MUST NOT implicitly apply a draft or allocate an ID.
+The engineering name and UUID remain unchanged.</p>
+<p>The <strong>Source alias</strong> field does not trim or normalize the entered alias. Pasting
+line breaks, tabs or other control characters is explicitly rejected as a whole:
+the field and its selection remain unchanged, and any previous preview approval
+is invalidated. <strong>Preview</strong>
+prepares a typed alias change and displays every changed file and source line;
+comments, strings, engineering data, file membership and declaration ownership
+remain unchanged. Enter in the field requests Preview, never confirmation.
+The preview is for this operation against accepted source, so a later Save may
+also contain earlier accepted edits. A changing rename requires enough model
+history capacity to retain its immediate Undo. An invalid, identical, stale or
+oversized candidate cannot enable confirmation.</p>
+<p>The preview MUST provide access to all admitted files, hunks, lines and long-line
+segments. Refuse a candidate whose complete preview exceeds the editor's bounds:
+256 changed files, 50,000 changed lines or 8 MiB of displayed source bytes
+(both versions of changed/context lines and file paths). Index metadata is
+separately bounded to seven retained line records per changed line. These
+limits do not restrict the language itself. A changed-line count is not a count
+of semantic references. Cancel, Preview and Rename alias remain reachable
+outside the independently scrolling source preview.</p>
+<p>Explicit <strong>Rename alias</strong> confirms the current preview once, as one accepted
+model/source transaction. A source, document, recovery or replacement change
+invalidates its approval even if later bytes match the old preview. Closing the
+form cancels approval; a late worker result MUST NOT reopen it. Rejected,
+canceled and unchanged operations preserve accepted bytes, drafts, save state,
+revisions, selection and both histories. Successful rename selects the new alias
+at the original occurrence rather than the first matching spelling in the file.
+Editing the replacement permits a new Preview in the same form. After a source
+context change, close the form and invoke Rename again on the current alias.</p>
+<p><strong>Undo rename</strong> is guarded against intervening edits and uses model history;
+the persistent <strong>Undo model</strong> and <strong>Redo model</strong> controls restore the complete
+accepted snapshots. Text <span class="docutils literal">Ctrl+Z</span> remains <strong>Undo text</strong>. Save is separate and
+uses the ordinary guarded source-save contract. An unconfirmed preview and Undo
+history are not persisted on reopening.</p>
 <p>Changing a graphical UUID must atomically update map keys and every reference.
 Alias changes preserve UUID identity. Deletion must account for owned elements,
 incident relationships, ordered occurrences, and diagram placements without