Add GPT-5.6 Sol xhigh agent mode

.amp/plugins/sol-mode.ts

@@ -0,0 +1,30 @@
+// @amp-agent-mode {"key":"sol-xhigh","label":"sol-xhigh"}
+
+import type { PluginAPI } from '@ampcode/plugin'
+
+export default function (amp: PluginAPI) {
+	const solXHigh = amp.createAgent({
+		name: 'sol-xhigh',
+		model: 'openai/gpt-5.6-sol',
+		// Rules inspired by Ponytail: https://github.com/DietrichGebert/ponytail/blob/main/skills/ponytail/SKILL.md#rules
+		instructions: [
+			'Work as an autonomous software engineer. Investigate carefully, make the smallest correct change, and verify the result before reporting it.',
+			'Rules:',
+			'No unrequested abstractions: no interface with one implementation, no factory for one product, no config for a value that never changes.',
+			'No boilerplate, no scaffolding "for later", later can scaffold for itself.',
+			'Deletion over addition. Boring over clever, clever is what someone decodes at 3am.',
+			"Fewest files possible. Shortest working diff wins — but only once you understand the problem. The smallest change in the wrong place isn't lazy, it's a second bug.",
+			'Complex request? Ship the lazy version and question it in the same response, "Did X; Y covers it. Need full X? Say so." Never stall on an answer you can default.',
+			"Two stdlib options, same size? Take the one that's correct on edge cases. Lazy means writing less code, not picking the flimsier algorithm.",
+		].join(' '),
+		tools: 'all',
+		reasoningEffort: 'xhigh',
+	})
+
+	amp.registerAgentMode({
+		key: 'sol-xhigh',
+		label: 'sol-xhigh',
+		description: 'GPT-5.6 Sol with all tools and xhigh reasoning.',
+		agent: solXHigh.definition,
+	})
+}