feat: add change_title MCP tool support to OpenCode

cli/src/opencode/utils/opencodeConfig.ts

@@ -0,0 +1,81 @@
+/**
+ * OpenCode configuration file generator.
+ *
+ * Generates opencode.json with MCP server configuration and instructions
+ * for the hapi change_title tool.
+ */
+
+import { mkdirSync, readFileSync, writeFileSync } from 'node:fs';
+import { join } from 'node:path';
+
+const CONFIG_FILENAME = 'opencode.json';
+const INSTRUCTIONS_FILENAME = 'hapi-instructions.md';
+
+interface McpServerEntry {
+    command: string;
+    args: string[];
+}
+
+interface OpencodeConfig {
+    $schema: string;
+    mcp: Record<string, {
+        type: string;
+        command: string[];
+        enabled: boolean;
+    }>;
+    instructions: string[];
+}
+
+/**
+ * Ensures the opencode.json config file exists with MCP server and instructions.
+ *
+ * @param rootPath - The OPENCODE_CONFIG_DIR path
+ * @param mcpServer - The hapi MCP server command configuration
+ * @param instructions - The instruction text to write to the instructions file
+ */
+export function ensureOpencodeConfig(
+    rootPath: string,
+    mcpServer: McpServerEntry,
+    instructions: string
+): { configPath: string; instructionsPath: string } {
+    mkdirSync(rootPath, { recursive: true });
+
+    // Write instructions file
+    const instructionsPath = join(rootPath, INSTRUCTIONS_FILENAME);
+    writeFileSafe(instructionsPath, instructions);
+
+    // Build opencode.json config
+    // Use absolute path for instructions since OpenCode resolves paths relative to project root
+    const config: OpencodeConfig = {
+        $schema: 'https://opencode.ai/config.json',
+        mcp: {
+            hapi: {
+                type: 'local',
+                command: [mcpServer.command, ...mcpServer.args],
+                enabled: true
+            }
+        },
+        instructions: [instructionsPath]
+    };
+
+    const configPath = join(rootPath, CONFIG_FILENAME);
+    const configJson = JSON.stringify(config, null, 2);
+    writeFileSafe(configPath, configJson);
+
+    return { configPath, instructionsPath };
+}
+
+/**
+ * Write file only if content has changed.
+ */
+function writeFileSafe(filePath: string, content: string): void {
+    try {
+        const current = readFileSync(filePath, 'utf-8');
+        if (current === content) {
+            return;
+        }
+    } catch {
+        // Ignore missing or unreadable file
+    }
+    writeFileSync(filePath, content, 'utf-8');
+}

cli/src/opencode/utils/systemPrompt.ts

@@ -0,0 +1,20 @@
+/**
+ * OpenCode-specific system prompt for change_title tool.
+ *
+ * OpenCode exposes MCP tools with the naming pattern: <server-name>_<tool-name>
+ * The hapi MCP server exposes `change_title`, so it's called as `hapi_change_title`.
+ */
+
+import { trimIdent } from '@/utils/trimIdent';
+
+/**
+ * Title instruction for OpenCode to call the hapi MCP tool.
+ */
+export const TITLE_INSTRUCTION = trimIdent(`
+    ALWAYS when you start a new chat - you must call the tool "hapi_change_title" to set a chat title. When you think chat title is not relevant anymore - call the tool again to change it. When chat name is too generic and you have a chance to make it more specific - call the tool again to change it. This title is needed to easily find the chat in the future. Help human.
+`);
+
+/**
+ * The system prompt to inject for OpenCode sessions.
+ */
+export const opencodeSystemPrompt = TITLE_INSTRUCTION;