feat(chat): add local-first conversation workspace

chat/lib/incremental-markdown-cache.test.mjs

@@ -0,0 +1,73 @@
+import {describe, expect, test} from "bun:test";
+import {IncrementalMarkdownCache} from "./incremental-markdown-cache.ts";
+
+describe("incremental markdown cache", () => {
+  test("never parses a stable prefix again", () => {
+    const cache = new IncrementalMarkdownCache();
+    const calls = [];
+    const render = (source, type, index, stable) => {
+      calls.push({source, type, index, stable});
+      return {rendered: source.toUpperCase()};
+    };
+
+    cache.render("message", "first", render);
+    const afterFirst = calls.length;
+    const closed = cache.render("message", "first\n\n", render);
+    const afterClosed = calls.length;
+    const growingTail = cache.render("message", "first\n\nsecond", render);
+    const longerTail = cache.render("message", "first\n\nsecond grows", render);
+
+    expect(afterFirst).toBe(1);
+    expect(afterClosed).toBe(2);
+    expect(closed.blocks[0].stable).toBe(true);
+    expect(growingTail.reused).toBe(1);
+    expect(growingTail.parsed).toBe(1);
+    expect(longerTail.reused).toBe(1);
+    expect(longerTail.parsed).toBe(1);
+    expect(calls.filter((call) => call.source === "first")).toHaveLength(2);
+  });
+
+  test("assigns stable indexes as blocks become frozen", () => {
+    const cache = new IncrementalMarkdownCache();
+    const render = () => ({});
+    const first = cache.render("message", "one\n\ntwo", render);
+    const second = cache.render("message", "one\n\ntwo\n\nthree", render);
+
+    expect(first.blocks.map((block) => [block.index, block.stable])).toEqual([[0, true], [1, false]]);
+    expect(second.blocks.map((block) => [block.index, block.stable])).toEqual([[0, true], [1, true], [2, false]]);
+  });
+
+  test("resets when the source is edited before the stable prefix", () => {
+    const cache = new IncrementalMarkdownCache();
+    const render = (source) => ({rendered: source});
+    cache.render("message", "one\n\ntwo", render);
+    const result = cache.render("message", "changed\n\ntwo", render);
+    expect(result.reused).toBe(0);
+    expect(result.blocks[0].source).toBe("changed");
+  });
+
+  test("moves cached blocks when a working message receives its immutable id", () => {
+    const cache = new IncrementalMarkdownCache();
+    const render = (source) => ({rendered: source});
+    cache.render("working", "first\n\n", render);
+
+    cache.move("working", "immutable");
+    const result = cache.render("immutable", "first\n\nsecond", render);
+
+    expect(cache.has("working")).toBe(false);
+    expect(cache.has("immutable")).toBe(true);
+    expect(result.reused).toBe(1);
+    expect(result.blocks.map((block) => block.index)).toEqual([0, 1]);
+  });
+
+  test("freezes the final open block when the stream completes", () => {
+    const cache = new IncrementalMarkdownCache();
+    const render = (source) => ({rendered: source});
+    cache.render("message", "last paragraph", render);
+
+    const result = cache.render("message", "last paragraph", render, undefined, true);
+
+    expect(result.blocks).toHaveLength(1);
+    expect(result.blocks[0].stable).toBe(true);
+  });
+});