fix(markdown-core): treat infinity chunk limit as unbounded

Fix render-aware markdown chunking so `Number.POSITIVE_INFINITY` is treated as an explicit unbounded chunk limit instead of falling back to `1`.

This preserves full Signal media captions and disabled Signal text chunking while keeping invalid non-finite limits on the existing fallback path.

Fixes #92734.
Thanks @yhterrance for the report and fix.

extensions/signal/src/format.chunking.test.ts

@@ -296,6 +296,16 @@ describe("splitSignalFormattedText", () => {
 });
 
 describe("markdownToSignalTextChunks", () => {
+  it("treats Infinity as unbounded for media captions", () => {
+    const markdown = "Here's **another** photo from today's walk.";
+
+    const chunks = markdownToSignalTextChunks(markdown, Number.POSITIVE_INFINITY);
+
+    expect(chunks).toHaveLength(1);
+    expect(chunks[0]?.text).toBe("Here's another photo from today's walk.");
+    expect(chunks[0]?.styles.map((style) => style.style)).toContain("BOLD");
+  });
+
   describe("link expansion chunk limit", () => {
     it("does not exceed chunk limit after link expansion", () => {
       // Create text that is close to limit, with a link that will expand

packages/markdown-core/src/render-aware-chunking.test.ts

@@ -84,4 +84,18 @@ describe("renderMarkdownIRChunksWithinLimit", () => {
     expect(chunks.map((chunk) => chunk.source.text)).toEqual(["a", "b", "c"]);
     expect(chunks.every((chunk) => chunk.rendered.length <= 1)).toBe(true);
   });
+
+  it("treats Infinity as no size cap and returns a single chunk", () => {
+    const text = "one two three four five six seven eight nine ten";
+    const ir = markdownToIR(text);
+    const chunks = renderMarkdownIRChunksWithinLimit({
+      ir,
+      limit: Number.POSITIVE_INFINITY,
+      renderChunk: renderEscapedHtml,
+      measureRendered: (rendered) => rendered.length,
+    });
+
+    expect(chunks).toHaveLength(1);
+    expect(chunks[0]?.source.text).toBe(text);
+  });
 });

packages/markdown-core/src/render-aware-chunking.ts

@@ -47,6 +47,13 @@ export function renderMarkdownIRChunksWithinLimit<TRendered>(
     return [];
   }
 
+  // Callers pass Infinity to mean "no size cap" (e.g. a media caption that must not be
+  // split). resolveIntegerOption rejects non-finite values and would fall back to 1,
+  // shattering the text into one chunk per character; emit the whole IR as one chunk.
+  if (options.limit === Number.POSITIVE_INFINITY) {
+    return [{ source: options.ir, rendered: options.renderChunk(options.ir) }];
+  }
+
   const normalizedLimit = resolveIntegerOption(options.limit, 1, { min: 1 });
   const pending = chunkMarkdownIR(options.ir, normalizedLimit);
   const finalized: MarkdownIR[] = [];