Send reasoning content back to the model across turns via the reasoning_content API field (#21036)

* webui: send reasoning_content back to model in context

Preserve assistant reasoning across turns by extracting it from
internal tags and sending it as a separate reasoning_content field
in the API payload. The server and Jinja templates handle native
formatting (e.g. <think> tags for Qwen, GLM, DeepSeek...).

Adds "Exclude reasoning from context" toggle in Settings > Developer
(off by default, so reasoning is preserved). Includes unit tests.

* webui: add syncable parameter for excludeReasoningFromContext

* chore: update webui build output

tools/server/webui/src/lib/constants/settings-config.ts

@@ -10,6 +10,7 @@ export const SETTING_CONFIG_DEFAULT: Record<string, string | number | boolean |
 	theme: ColorMode.SYSTEM,
 	showThoughtInProgress: false,
 	disableReasoningParsing: false,
+	excludeReasoningFromContext: false,
 	showRawOutputSwitch: false,
 	keepStatsVisible: false,
 	showMessageStats: true,
@@ -106,6 +107,8 @@ export const SETTING_CONFIG_INFO: Record<string, string> = {
 	showThoughtInProgress: 'Expand thought process by default when generating messages.',
 	disableReasoningParsing:
 		'Send reasoning_format=none to prevent server-side extraction of reasoning tokens into separate field',
+	excludeReasoningFromContext:
+		'Strip reasoning content from previous messages before sending to the model. When unchecked, reasoning is sent back via the reasoning_content field so the model can see its own chain-of-thought across turns.',
 	showRawOutputSwitch:
 		'Show toggle button to display messages as plain text instead of Markdown-formatted content',
 	keepStatsVisible: 'Keep processing statistics visible after generation finishes.',