feat(coding-agent): export project config dir name

packages/coding-agent/docs/extensions.md

@@ -898,6 +898,20 @@ Current run mode: `"tui"`, `"rpc"`, `"json"`, or `"print"`. Use `ctx.mode === "t
 
 Current working directory.
 
+Use `CONFIG_DIR_NAME` instead of hardcoding `.pi` when constructing project-local config paths. Rebranded distributions can use a different config directory name.
+
+```typescript
+import { CONFIG_DIR_NAME, type ExtensionAPI } from "@earendil-works/pi-coding-agent";
+import { join } from "node:path";
+
+export default function (pi: ExtensionAPI) {
+  pi.on("session_start", (_event, ctx) => {
+    const projectConfigPath = join(ctx.cwd, CONFIG_DIR_NAME, "my-extension.json");
+    // ...
+  });
+}
+```
+
 ### ctx.isProjectTrusted()
 
 Returns whether project-local trust is active for the current session context. This includes temporary trust decisions and CLI trust overrides, not just saved decisions in the global trust store.