app/engine/model.ts

Ladder Summary

file The module defines a `ModelBackend` interface for a single‑purpose summarisation operation and supplies three concrete implementations: a wrapper around any `ChatBackend` (`createChatSummaryBackend`), a no‑op “null” backend (`createNullBackend`), and an HTTP‑based Ollama backend (`createOllamaBackend`). It also exports `resolveModelBackend`, which selects the appropriate backend at runtime based on the requested provider, environment variables, and Ollama server reachability. **Exported symbols** - `ModelBackend` (interface) - `createChatSummaryBackend` (function) - `createNullBackend` (function) - `createOllamaBackend` (function) - `resolveModelBackend` (function)

// BYO model, local only for now: a configured Ollama server. No backend

// here ever shells out to the `claude` CLI -- that's what caused the

// quota incident this replaces. A remote/API-key backend is deferred to

// later, not built here.

export interface ModelBackend {

name: string;

summarize(prompt: string): Promise<string | null>; // null = unreachable; caller falls back to mechanical text

}

export function createNullBackend(): ModelBackend {

return { name: "null", summarize: async () => null };

}

export function createOllamaBackend(baseUrl: string, model: string): ModelBackend {

return {

name: `ollama:${model}`,

async summarize(prompt: string): Promise<string | null> {

try {

const res = await fetch(`${baseUrl}/api/generate`, {

method: "POST",

headers: { "content-type": "application/json" },

body: JSON.stringify({ model, prompt, stream: false }),

});

if (!res.ok) return null;

const data = (await res.json()) as { response?: string };

return data.response?.trim() || null;

} catch {

return null;

}

};

}

/** Ollama if ZZ_OLLAMA_MODEL is set (or the default) and reachable; otherwise the null backend. */

export async function resolveModelBackend(): Promise<ModelBackend> {

const baseUrl = process.env.ZZ_OLLAMA_HOST ?? "http://localhost:11434";

const model = process.env.ZZ_OLLAMA_MODEL ?? "qwen2.5:14b-instruct";

const backend = createOllamaBackend(baseUrl, model);

try {

const res = await fetch(`${baseUrl}/api/tags`, { signal: AbortSignal.timeout(2000) });

if (res.ok) return backend;

} catch {

// fall through to null backend

}

console.error(`(ollama at ${baseUrl} not reachable; falling back to mechanical text)`);

return createNullBackend();

}