fix: group selection drop-downs recreation and repopulation logic (#3424)

* fix: include in-memory templates in group participant character list

_getCharacterList() only fetched user templates from the /api/presets/templates
endpoint. When a character was just created in the Character tab, the async
auto-save to the templates API might not have completed by the time the Group
tab loaded its participant dropdown — causing newly created characters to be
missing.

Now also merges the in-memory userTemplates array from presets.js as a
fallback. These are updated as soon as the async save completes (via the
loadUserTemplates callback), so they bridge the gap between character creation
and API persistence.

Fixes #3207

* fix: optimistic userTemplates update on character save

Update the in-memory userTemplates array immediately when saveCustomPreset()
succeeds, before the fire-and-forget templates API POST completes. This
bridges the timing gap where _getCharacterList() calls getUserTemplates()
and gets stale data because loadUserTemplates() hasn't been triggered yet.

* test: verify group participant dropdown merges in-memory templates

Source-level guards for the #3207 fix:
- group.js imports and calls getUserTemplates() to merge in-memory templates
- presets.js exports getUserTemplates and does optimistic in-memory update on save

5 tests ensuring the fix can't be silently reverted.

* fix: generate client-side id for optimistic update, return shallow copy from getUserTemplates

1. New characters now get a 'user-<hex>' id immediately on save, matching
   the server's convention (uuid.uuid4().hex[:8]). Previously the id was ''
   which the merge guard in _getCharacterList filtered as falsy.

2. getUserTemplates() now returns [...userTemplates] so callers cannot
   accidentally mutate module state.

* fix(group.js): fix selection drop-downs behavior

- add an identifier to the selection drop-downs
  based on what type it is.
- fix behavior of continuously adding a row
  when a user clicks the "Group" tab button.
- fix behavior of not repopulating existing
  selection drop-downs whenever a user
  clicks the "Group" tab button.

* fix(#3207): remove duplicate of latest persona

- fix the duplication of the latest persona
  or character being shown in selection
  drop-downs.
- remove unnecessary blocks of code in
  `_getCharacterList()`
- add functionality to show error toast if saving
  a preset template/character fails.
- add functionality to revert optimistic update
  of preset template/character if saving fails.

* chore(group.js,preset.js): fix test & format errors

remove trailing whitespaces in lines 230 and 232
in /static/group.js

add back the expected syntax from
tests/test_group_character_dropdown.py

* fix(presets.js,group.js): fix runtime errors

as stated in a comment by @alteixeira20,
runtime errors exist for the applied fixes.

fixes:

- missing ending `]`
  querySelectorAll("select.preset-input[data-selection-type=character")
  in `group.js`
- spelling error in `modelSelection.vale` in `group.js`
- fix the ordering logic error in optimistic rollback where `Object.assign` is called first before the clone happens in `saveCustomPreset` in `presets.js`.
- add tests for the cloning logic bug with the same format as previous tests by checking the order of LOC in `tests/test_group_character_dropdown.py`.

---------

Co-authored-by: michaelxer <michaelxer@users.noreply.github.com>
Co-authored-by: Alexandre Teixeira <111787685+alteixeira20@users.noreply.github.com>

static/js/presets.js

@@ -830,15 +830,48 @@ export async function saveCustomPreset(showToast, showError) {
       const _selVal = document.getElementById('char-template-select')?.value || '';
       const isBuiltinPreset = PROMPT_TEMPLATES.some(t => t.isPreset && (t.name === name || t.name === _selVal));
       const saveName = isBuiltinPreset ? null : (name || null);
+
       if (saveName) {
-        fetch(`${API_BASE}/api/presets/templates`, {
-          method: 'POST',
+        const _existing = userTemplates.find(t => t.name === saveName);
+        let clone;
+        const _entry = {
+          id: _existing && _existing.id
+            || 'user-' + Math.random().toString(16).slice(2, 10),
+          name: saveName,
+          // use ?? since it's more semantic for null-coalescing
+          system_prompt: system_prompt ?? '',
+          temperature: config.temperature,
+          max_tokens: config.max_tokens,
+        }
+        const ENDPOINT = `${API_BASE}/api/presets/templates`;
+
+        // Optimistically update the in-memory templates list by @michaelxer
+        if (_existing) {
+          // slow but works for now
+          clone = JSON.parse(JSON.stringify(_existing));
+
+          Object.assign(_existing, _entry);
+        } else {
+          userTemplates.push(_entry);
+        }
+
+        fetch(ENDPOINT, {
+          method: "POST",
           headers: { 'Content-Type': 'application/json' },
-          body: JSON.stringify({
-            id: (userTemplates.find(t => t.name === saveName) || {}).id || '',
-            name: saveName, system_prompt, temperature: config.temperature, max_tokens: config.max_tokens,
-          }),
-        }).then(r => { if (r.ok) loadUserTemplates(); }).catch(() => {});
+          body: JSON.stringify(_entry)
+        }).then((r) => {
+          if (r.ok) {
+            loadUserTemplates();
+          }
+        }).catch(() => {
+          if (clone) {
+            Object.assign(_existing, clone);
+          }
+
+          if (showError) {
+            showError(_isInjectStart ? "Something went wrong. Saved prompt has been undone." : "Something went wrong. Saved persona has been undone.");
+          }
+        });
       }
 
       if (showToast) {
@@ -883,6 +916,13 @@ export function getAllPresets() {
   return presets;
 }
 
+/**
+ * Get the in-memory user templates list (may be stale; call loadUserTemplates first if freshness matters).
+ */
+export function getUserTemplates() {
+  return [...userTemplates];
+}
+
 /**
  * Get the character name (if set)
  */
@@ -1099,6 +1139,7 @@ const presetsModule = {
   getSelectedPreset,
   getPreset,
   getAllPresets,
+  getUserTemplates,
   getCharacterName,
   onSessionSwitch,
   isPersistentChat,