chore: bump version to v0.50.51, update CHANGELOG

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Hermes Web UI -- Changelog
 
+## [v0.50.51] — 2026-04-15
+
+### Fixed
+- **Orphaned tool messages** — conversation histories containing `role: tool` messages with no matching `tool_call_id` in a prior assistant message are now silently stripped before sending to the provider API. Fixes 400 errors from strictly-conformant providers (Mercury-2/Inception, newer OpenAI models). Adds 13 regression tests. (Fixes #534)
+
 ## [v0.50.50] — 2026-04-15
 
 ### Fixed

static/index.html

@@ -552,7 +552,7 @@
                 <div class="settings-section-title">System</div>
                 <div class="settings-section-meta">Instance version and access controls.</div>
               </div>
-              <span class="settings-version-badge">v0.50.50</span>
+              <span class="settings-version-badge">v0.50.51</span>
             </div>
             <div class="settings-field" style="border-top:1px solid var(--border);padding-top:12px;margin-top:8px">
               <label for="settingsPassword" data-i18n="settings_label_password">Access Password</label>