chore(vendor): import pi 1.3.0

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: 71023aec1546d6d677a65669c5665c0927ce0dd0

third_party/pi/packages/ai/src/providers/opencode-headers.ts

@@ -0,0 +1,25 @@
+import type { ProviderHeaders, ProviderStreams, StreamOptions } from "../types.ts";
+
+const OPENCODE_SESSION_HEADER = "x-opencode-session";
+
+function hasHeader(headers: ProviderHeaders | undefined, name: string): boolean {
+	const expected = name.toLowerCase();
+	return Object.keys(headers ?? {}).some((key) => key.toLowerCase() === expected);
+}
+
+function withSessionHeader<TOptions extends StreamOptions>(options: TOptions | undefined): TOptions | undefined {
+	if (!options?.sessionId || hasHeader(options.headers, OPENCODE_SESSION_HEADER)) return options;
+	return {
+		...options,
+		headers: { ...options.headers, [OPENCODE_SESSION_HEADER]: options.sessionId },
+	};
+}
+
+/** Adds OpenCode's required per-conversation routing header before API dispatch. */
+export function withOpenCodeSessionHeader(streams: ProviderStreams): ProviderStreams {
+	return {
+		...streams,
+		stream: (model, context, options) => streams.stream(model, context, withSessionHeader(options)),
+		streamSimple: (model, context, options) => streams.streamSimple(model, context, withSessionHeader(options)),
+	};
+}