Implement v0.4 subscriptions + v0.5 theming and plugin slots

- SSE and WebSocket fetchers via graphql-sse and graphql-ws,
  returning AsyncIterable results
- SessionStore.run consumes AsyncIterable streams with
  subscriptionMode "append" (timestamped) or "replace" and
  honors an AbortSignal for cancellation
- Chrome CSS variables documented in styles/theme.scss with
  prefers-color-scheme light/dark gating and .graphiql-light override
- Svelte 5 snippet slots on GraphiQL: toolbarExtras, tabExtras,
  resultFooter

1 files changed, 51 insertions, 2 deletions

diff --git a/source/library/state/session.svelte.ts b/source/library/state/session.svelte.ts
index d9f52ff..9345d29 100644
--- a/source/library/state/session.svelte.ts
+++ b/source/library/state/session.svelte.ts
@@ -3,7 +3,7 @@
 
 /*** UTILITY ------------------------------------------ ***/
 
-import type { Fetcher } from "../fetcher/types.ts";
+import type { Fetcher, FetcherResult } from "../fetcher/types.ts";
 import {
   deriveTitle,
   parseOperations,
@@ -13,6 +13,12 @@ import type { Storage } from "./storage.ts";
 
 const STORAGE_KEY = "session";
 
+function isAsyncIterable<T>(value: unknown): value is AsyncIterable<T> {
+  return typeof value === "object" &&
+    value !== null &&
+    typeof (value as AsyncIterable<T>)[Symbol.asyncIterator] === "function";
+}
+
 type Snapshot = {
   activeId: string;
   tabs: Tab[];
@@ -40,6 +46,13 @@ export type TabSeed = {
   variables?: string;
 };
 
+export type SubscriptionMode = "append" | "replace";
+
+export type RunOptions = {
+  signal?: AbortSignal;
+  subscriptionMode?: SubscriptionMode;
+};
+
 export class SessionStore {
   activeId = $state<string>("");
   tabs = $state<Tab[]>([]);
@@ -115,12 +128,15 @@ export class SessionStore {
     tab.titleDirty = true;
   }
 
-  async run(fetcher: Fetcher): Promise<boolean> {
+  async run(fetcher: Fetcher, options: RunOptions = {}): Promise<boolean> {
     const tab = this.active;
 
     if (!tab)
       return false;
 
+    const mode = options.subscriptionMode ?? "append";
+    const signal = options.signal;
+
     try {
       const variables = tab.variables.trim() ? JSON.parse(tab.variables) : {};
       const headers = tab.headers.trim() ? JSON.parse(tab.headers) : {};
@@ -132,6 +148,39 @@ export class SessionStore {
         variables
       });
 
+      if (isAsyncIterable<FetcherResult>(result)) {
+        tab.result = "";
+        const iterator = result[Symbol.asyncIterator]();
+
+        try {
+          while (true) {
+            if (signal?.aborted) {
+              await iterator.return?.();
+              break;
+            }
+
+            const step = await iterator.next();
+
+            if (step.done)
+              break;
+
+            const payload = JSON.stringify(step.value, null, 2);
+
+            if (mode === "append") {
+              const stamp = new Date().toISOString();
+              const chunk = `// ${stamp}\n${payload}\n`;
+              tab.result = tab.result ? `${tab.result}\n${chunk}` : chunk;
+            } else {
+              tab.result = payload;
+            }
+          }
+        } finally {
+          await iterator.return?.();
+        }
+
+        return true;
+      }
+
       tab.result = JSON.stringify(result, null, 2);
       return true;
     } catch(err) {