feat(ai): add Cloudflare Workers AI as a provider (#3851)

* feat(ai): add Cloudflare Workers AI as a provider

Cloudflare Workers AI hosts open-weight LLMs (Kimi K2.6, GPT-OSS,
GLM-4.7, Llama 4, Gemma 4, Nemotron 3) on Cloudflare's GPU network with
an OpenAI-compatible endpoint. Reuses the openai-completions API
protocol; the per-account URL contains a {CLOUDFLARE_ACCOUNT_ID}
placeholder resolved at request time by a small helper.

Pi automatically sets x-session-affinity for prefix caching:
https://developers.cloudflare.com/workers-ai/features/prompt-caching/

Auth: CLOUDFLARE_API_KEY (matches pi's *_API_KEY convention) +
CLOUDFLARE_ACCOUNT_ID. The User-Agent identifies traffic as
'pi-coding-agent' in Cloudflare analytics.

Verified end-to-end against a real Cloudflare account: 17 e2e tests
pass across stream/empty/tokens/unicode/tool-call-without-result/
total-tokens against @cf/moonshotai/kimi-k2.6.

Cloudflare AI Gateway is a separate, larger change (it requires routing
through provider-specific subpaths with the matching API protocol per
upstream) and will land in a follow-up PR.

* refactor(ai): move Cloudflare User-Agent and session-affinity flag to per-model metadata

Instead of conditionally setting them in openai-completions.ts based on
provider detection, declare them as model-level fields in the catalog
(headers + compat). This is consistent with how the github-copilot and
kimi-coding entries already declare their static headers.

  packages/ai/scripts/generate-models.ts: emit headers and compat fields
  on each cloudflare-workers-ai entry (CLOUDFLARE_STATIC_HEADERS).
  packages/ai/src/providers/openai-completions.ts: drop the
  isCloudflareProvider conditional that injected User-Agent and the
  isCloudflareWorkersAI override of sendSessionAffinityHeaders.
  packages/ai/src/models.generated.ts: re-spliced 8 cloudflare-workers-ai
  entries with headers + compat.

Behavior is unchanged - verified via fetch interceptor that User-Agent
and x-session-affinity / session_id / x-client-request-id are still sent
on outbound requests. 5/5 e2e tests pass.

packages/ai/scripts/generate-models.ts

@@ -3,6 +3,7 @@
 import { writeFileSync } from "fs";
 import { join, dirname } from "path";
 import { fileURLToPath } from "url";
+import { CLOUDFLARE_WORKERS_AI_BASE_URL } from "../src/providers/cloudflare.js";
 import {
 	Api,
 	type AnthropicMessagesCompat,
@@ -63,6 +64,10 @@ const KIMI_STATIC_HEADERS = {
 	"User-Agent": "KimiCLI/1.5",
 } as const;
 
+const CLOUDFLARE_STATIC_HEADERS = {
+	"User-Agent": "pi-coding-agent",
+} as const;
+
 const AI_GATEWAY_MODELS_URL = "https://ai-gateway.vercel.sh/v1";
 const AI_GATEWAY_BASE_URL = "https://ai-gateway.vercel.sh";
 const ZAI_TOOL_STREAM_UNSUPPORTED_MODELS = new Set(["glm-4.5", "glm-4.5-air", "glm-4.5-flash", "glm-4.5v"]);
@@ -376,6 +381,34 @@ async function loadModelsDevData(): Promise<Model<any>[]> {
 			}
 		}
 
+		// Process Cloudflare Workers AI models
+		if (data["cloudflare-workers-ai"]?.models) {
+			for (const [modelId, model] of Object.entries(data["cloudflare-workers-ai"].models)) {
+				const m = model as ModelsDevModel;
+				if (m.tool_call !== true) continue;
+
+				models.push({
+					id: modelId,
+					name: m.name || modelId,
+					api: "openai-completions",
+					provider: "cloudflare-workers-ai",
+					baseUrl: CLOUDFLARE_WORKERS_AI_BASE_URL,
+					reasoning: m.reasoning === true,
+					input: m.modalities?.input?.includes("image") ? ["text", "image"] : ["text"],
+					cost: {
+						input: m.cost?.input || 0,
+						output: m.cost?.output || 0,
+						cacheRead: m.cost?.cache_read || 0,
+						cacheWrite: m.cost?.cache_write || 0,
+					},
+					contextWindow: m.limit?.context || 4096,
+					maxTokens: m.limit?.output || 4096,
+					headers: { ...CLOUDFLARE_STATIC_HEADERS },
+					compat: { sendSessionAffinityHeaders: true },
+				});
+			}
+		}
+
 		// Process xAi models
 		if (data.xai?.models) {
 			for (const [modelId, model] of Object.entries(data.xai.models)) {