fix(signal): outbound formatting and markdown IR rendering improvements (#9781)

* fix: Signal and markdown formatting improvements

Markdown IR fixes:
- Fix list-paragraph spacing (extra newline between list items and following paragraphs)
- Fix nested list indentation and newline handling
- Fix blockquote_close emitting redundant newline (inner content handles spacing)
- Render horizontal rules as visible ─── separator instead of silent drop
- Strip inner cell styles in code-mode tables to prevent overlapping with code_block span

Signal formatting fixes:
- Normalize URLs for dedup comparison (strip protocol, www., trailing slash)
- Render headings as bold text (headingStyle: 'bold')
- Add '> ' prefix to blockquotes for visual distinction
- Re-chunk after link expansion to respect chunk size limits

Tests:
- 51 new tests for markdown IR (spacing, lists, blockquotes, tables, HR)
- 18 new tests for Signal formatting (URL dedup, headings, blockquotes, HR, chunking)
- Update Slack nested list test expectation to match corrected IR output

* refactor: style-aware Signal text chunker

Replace indexOf-based chunk position tracking with deterministic
cursor tracking. The new splitSignalFormattedText:

- Splits at whitespace/newline boundaries within the limit
- Avoids breaking inside parentheses (preserves expanded link URLs)
- Slices style ranges at chunk boundaries with correct local offsets
- Tracks position via offset arithmetic instead of fragile indexOf

Removes dependency on chunkText from auto-reply/chunk.

Tests: 19 new tests covering style preservation across chunk boundaries,
edge cases (empty text, under limit, exact split points), and integration
with link expansion.

* fix: correct Signal style offsets with multiple link expansions

applyInsertionsToStyles() was using original coordinates for each
insertion without tracking cumulative shift from prior insertions.
This caused bold/italic/etc styles to drift to wrong text positions
when multiple markdown links expanded in a single message.

Added cumulative shift tracking and a regression test.

* test: clean up test noise and fix ineffective assertions

- Remove console.log from ir.list-spacing and ir.hr-spacing tests
- Fix ir.nested-lists.test.ts: remove ineffective regex assertion
- Fix ir.hr-spacing.test.ts: add actual assertions to edge case test

* refactor: split Signal formatting tests (#9781) (thanks @heyhudson)

---------

Co-authored-by: Hudson <258693705+hudson-rivera@users.noreply.github.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/signal/format.chunking.test.ts

@@ -0,0 +1,390 @@
+import { describe, expect, it } from "vitest";
+import { markdownToSignalTextChunks } from "./format.js";
+
+describe("splitSignalFormattedText", () => {
+  // We test the internal chunking behavior via markdownToSignalTextChunks with
+  // pre-rendered SignalFormattedText. The helper is not exported, so we test
+  // it indirectly through integration tests and by constructing scenarios that
+  // exercise the splitting logic.
+
+  describe("style-aware splitting - basic text", () => {
+    it("text with no styles splits correctly at whitespace", () => {
+      // Create text that exceeds limit and must be split
+      const limit = 20;
+      const markdown = "hello world this is a test";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks.length).toBeGreaterThan(1);
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+      // Verify all text is preserved (joined chunks should contain all words)
+      const joinedText = chunks.map((c) => c.text).join(" ");
+      expect(joinedText).toContain("hello");
+      expect(joinedText).toContain("world");
+      expect(joinedText).toContain("test");
+    });
+
+    it("empty text returns empty array", () => {
+      // Empty input produces no chunks (not an empty chunk)
+      const chunks = markdownToSignalTextChunks("", 100);
+      expect(chunks).toEqual([]);
+    });
+
+    it("text under limit returns single chunk unchanged", () => {
+      const markdown = "short text";
+      const chunks = markdownToSignalTextChunks(markdown, 100);
+
+      expect(chunks).toHaveLength(1);
+      expect(chunks[0].text).toBe("short text");
+    });
+  });
+
+  describe("style-aware splitting - style preservation", () => {
+    it("style fully within first chunk stays in first chunk", () => {
+      // Create a message where bold text is in the first chunk
+      const limit = 30;
+      const markdown = "**bold** word more words here that exceed limit";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks.length).toBeGreaterThan(1);
+      // First chunk should contain the bold style
+      const firstChunk = chunks[0];
+      expect(firstChunk.text).toContain("bold");
+      expect(firstChunk.styles.some((s) => s.style === "BOLD")).toBe(true);
+      // The bold style should start at position 0 in the first chunk
+      const boldStyle = firstChunk.styles.find((s) => s.style === "BOLD");
+      expect(boldStyle).toBeDefined();
+      expect(boldStyle!.start).toBe(0);
+      expect(boldStyle!.length).toBe(4); // "bold"
+    });
+
+    it("style fully within second chunk has offset adjusted to chunk-local position", () => {
+      // Create a message where the styled text is in the second chunk
+      const limit = 30;
+      const markdown = "some filler text here **bold** at the end";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks.length).toBeGreaterThan(1);
+      // Find the chunk containing "bold"
+      const chunkWithBold = chunks.find((c) => c.text.includes("bold"));
+      expect(chunkWithBold).toBeDefined();
+      expect(chunkWithBold!.styles.some((s) => s.style === "BOLD")).toBe(true);
+
+      // The bold style should have chunk-local offset (not original text offset)
+      const boldStyle = chunkWithBold!.styles.find((s) => s.style === "BOLD");
+      expect(boldStyle).toBeDefined();
+      // The offset should be the position within this chunk, not the original text
+      const boldPos = chunkWithBold!.text.indexOf("bold");
+      expect(boldStyle!.start).toBe(boldPos);
+      expect(boldStyle!.length).toBe(4);
+    });
+
+    it("style spanning chunk boundary is split into two ranges", () => {
+      // Create text where a styled span crosses the chunk boundary
+      const limit = 15;
+      // "hello **bold text here** end" - the bold spans across chunk boundary
+      const markdown = "hello **boldtexthere** end";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks.length).toBeGreaterThan(1);
+
+      // Both chunks should have BOLD styles if the span was split
+      const chunksWithBold = chunks.filter((c) => c.styles.some((s) => s.style === "BOLD"));
+      // At least one chunk should have the bold style
+      expect(chunksWithBold.length).toBeGreaterThanOrEqual(1);
+
+      // For each chunk with bold, verify the style range is valid for that chunk
+      for (const chunk of chunksWithBold) {
+        for (const style of chunk.styles.filter((s) => s.style === "BOLD")) {
+          expect(style.start).toBeGreaterThanOrEqual(0);
+          expect(style.start + style.length).toBeLessThanOrEqual(chunk.text.length);
+        }
+      }
+    });
+
+    it("style starting exactly at split point goes entirely to second chunk", () => {
+      // Create text where style starts right at where we'd split
+      const limit = 10;
+      const markdown = "abcdefghi **bold**";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks.length).toBeGreaterThan(1);
+
+      // Find chunk with bold
+      const chunkWithBold = chunks.find((c) => c.styles.some((s) => s.style === "BOLD"));
+      expect(chunkWithBold).toBeDefined();
+
+      // Verify the bold style is valid within its chunk
+      const boldStyle = chunkWithBold!.styles.find((s) => s.style === "BOLD");
+      expect(boldStyle).toBeDefined();
+      expect(boldStyle!.start).toBeGreaterThanOrEqual(0);
+      expect(boldStyle!.start + boldStyle!.length).toBeLessThanOrEqual(chunkWithBold!.text.length);
+    });
+
+    it("style ending exactly at split point stays entirely in first chunk", () => {
+      const limit = 10;
+      const markdown = "**bold** rest of text";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // First chunk should have the complete bold style
+      const firstChunk = chunks[0];
+      if (firstChunk.text.includes("bold")) {
+        const boldStyle = firstChunk.styles.find((s) => s.style === "BOLD");
+        expect(boldStyle).toBeDefined();
+        expect(boldStyle!.start + boldStyle!.length).toBeLessThanOrEqual(firstChunk.text.length);
+      }
+    });
+
+    it("multiple styles, some spanning boundary, some not", () => {
+      const limit = 25;
+      // Mix of styles: italic at start, bold spanning boundary, monospace at end
+      const markdown = "_italic_ some text **bold text** and `code`";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks.length).toBeGreaterThan(1);
+
+      // Verify all style ranges are valid within their respective chunks
+      for (const chunk of chunks) {
+        for (const style of chunk.styles) {
+          expect(style.start).toBeGreaterThanOrEqual(0);
+          expect(style.start + style.length).toBeLessThanOrEqual(chunk.text.length);
+          expect(style.length).toBeGreaterThan(0);
+        }
+      }
+
+      // Collect all styles across chunks
+      const allStyles = chunks.flatMap((c) => c.styles.map((s) => s.style));
+      // We should have at least italic, bold, and monospace somewhere
+      expect(allStyles).toContain("ITALIC");
+      expect(allStyles).toContain("BOLD");
+      expect(allStyles).toContain("MONOSPACE");
+    });
+  });
+
+  describe("style-aware splitting - edge cases", () => {
+    it("handles zero-length text with styles gracefully", () => {
+      // Edge case: empty markdown produces no chunks
+      const chunks = markdownToSignalTextChunks("", 100);
+      expect(chunks).toHaveLength(0);
+    });
+
+    it("handles text that splits exactly at limit", () => {
+      const limit = 10;
+      const markdown = "1234567890"; // exactly 10 chars
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      expect(chunks).toHaveLength(1);
+      expect(chunks[0].text).toBe("1234567890");
+    });
+
+    it("preserves style through whitespace trimming", () => {
+      const limit = 30;
+      const markdown = "**bold**  some text that is longer than limit";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // Bold should be preserved in first chunk
+      const firstChunk = chunks[0];
+      if (firstChunk.text.includes("bold")) {
+        expect(firstChunk.styles.some((s) => s.style === "BOLD")).toBe(true);
+      }
+    });
+
+    it("handles repeated substrings correctly (no indexOf fragility)", () => {
+      // This test exposes the fragility of using indexOf to find chunk positions.
+      // If the same substring appears multiple times, indexOf finds the first
+      // occurrence, not necessarily the correct one.
+      const limit = 20;
+      // "word" appears multiple times - indexOf("word") would always find first
+      const markdown = "word **bold word** word more text here to chunk";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // Verify chunks are under limit
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+
+      // Find chunk(s) with bold style
+      const chunksWithBold = chunks.filter((c) => c.styles.some((s) => s.style === "BOLD"));
+      expect(chunksWithBold.length).toBeGreaterThanOrEqual(1);
+
+      // The bold style should correctly cover "bold word" (or part of it if split)
+      // and NOT incorrectly point to the first "word" in the text
+      for (const chunk of chunksWithBold) {
+        for (const style of chunk.styles.filter((s) => s.style === "BOLD")) {
+          const styledText = chunk.text.slice(style.start, style.start + style.length);
+          // The styled text should be part of "bold word", not the initial "word"
+          expect(styledText).toMatch(/^(bold( word)?|word)$/);
+          expect(style.start).toBeGreaterThanOrEqual(0);
+          expect(style.start + style.length).toBeLessThanOrEqual(chunk.text.length);
+        }
+      }
+    });
+
+    it("handles chunk that starts with whitespace after split", () => {
+      // When text is split at whitespace, the next chunk might have leading
+      // whitespace trimmed. Styles must account for this.
+      const limit = 15;
+      const markdown = "some text **bold** at end";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // All style ranges must be valid
+      for (const chunk of chunks) {
+        for (const style of chunk.styles) {
+          expect(style.start).toBeGreaterThanOrEqual(0);
+          expect(style.start + style.length).toBeLessThanOrEqual(chunk.text.length);
+        }
+      }
+    });
+
+    it("deterministically tracks position without indexOf fragility", () => {
+      // This test ensures the chunker doesn't rely on finding chunks via indexOf
+      // which can fail when chunkText trims whitespace or when duplicates exist.
+      // Create text with lots of whitespace and repeated patterns.
+      const limit = 25;
+      const markdown = "aaa   **bold**   aaa   **bold**   aaa extra text to force split";
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // Multiple chunks expected
+      expect(chunks.length).toBeGreaterThan(1);
+
+      // All chunks should respect limit
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+
+      // All style ranges must be valid within their chunks
+      for (const chunk of chunks) {
+        for (const style of chunk.styles) {
+          expect(style.start).toBeGreaterThanOrEqual(0);
+          expect(style.start + style.length).toBeLessThanOrEqual(chunk.text.length);
+          // The styled text at that position should actually be "bold"
+          if (style.style === "BOLD") {
+            const styledText = chunk.text.slice(style.start, style.start + style.length);
+            expect(styledText).toBe("bold");
+          }
+        }
+      }
+    });
+  });
+});
+
+describe("markdownToSignalTextChunks", () => {
+  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
+      const limit = 100;
+      // Create text that's 90 chars, leaving only 10 chars of headroom
+      const filler = "x".repeat(80);
+      // This link will expand from "[link](url)" to "link (https://example.com/very/long/path)"
+      const markdown = `${filler} [link](https://example.com/very/long/path/that/will/exceed/limit)`;
+
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+    });
+
+    it("handles multiple links near chunk boundary", () => {
+      const limit = 100;
+      const filler = "x".repeat(60);
+      const markdown = `${filler} [a](https://a.com) [b](https://b.com) [c](https://c.com)`;
+
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+    });
+  });
+
+  describe("link expansion with style preservation", () => {
+    it("long message with links that expand beyond limit preserves all text", () => {
+      const limit = 80;
+      const filler = "a".repeat(50);
+      const markdown = `${filler} [click here](https://example.com/very/long/path/to/page) more text`;
+
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // All chunks should be under limit
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+
+      // Combined text should contain all original content
+      const combined = chunks.map((c) => c.text).join("");
+      expect(combined).toContain(filler);
+      expect(combined).toContain("click here");
+      expect(combined).toContain("example.com");
+    });
+
+    it("styles (bold, italic) survive chunking correctly after link expansion", () => {
+      const limit = 60;
+      const markdown =
+        "**bold start** text [link](https://example.com/path) _italic_ more content here to force chunking";
+
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // Should have multiple chunks
+      expect(chunks.length).toBeGreaterThan(1);
+
+      // All style ranges should be valid within their chunks
+      for (const chunk of chunks) {
+        for (const style of chunk.styles) {
+          expect(style.start).toBeGreaterThanOrEqual(0);
+          expect(style.start + style.length).toBeLessThanOrEqual(chunk.text.length);
+          expect(style.length).toBeGreaterThan(0);
+        }
+      }
+
+      // Verify styles exist somewhere
+      const allStyles = chunks.flatMap((c) => c.styles.map((s) => s.style));
+      expect(allStyles).toContain("BOLD");
+      expect(allStyles).toContain("ITALIC");
+    });
+
+    it("multiple links near chunk boundary all get properly chunked", () => {
+      const limit = 50;
+      const markdown =
+        "[first](https://first.com/long/path) [second](https://second.com/another/path) [third](https://third.com)";
+
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // All chunks should respect limit
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+
+      // All link labels should appear somewhere
+      const combined = chunks.map((c) => c.text).join("");
+      expect(combined).toContain("first");
+      expect(combined).toContain("second");
+      expect(combined).toContain("third");
+    });
+
+    it("preserves spoiler style through link expansion and chunking", () => {
+      const limit = 40;
+      const markdown =
+        "||secret content|| and [link](https://example.com/path) with more text to chunk";
+
+      const chunks = markdownToSignalTextChunks(markdown, limit);
+
+      // All chunks should respect limit
+      for (const chunk of chunks) {
+        expect(chunk.text.length).toBeLessThanOrEqual(limit);
+      }
+
+      // Spoiler style should exist and be valid
+      const chunkWithSpoiler = chunks.find((c) => c.styles.some((s) => s.style === "SPOILER"));
+      expect(chunkWithSpoiler).toBeDefined();
+
+      const spoilerStyle = chunkWithSpoiler!.styles.find((s) => s.style === "SPOILER");
+      expect(spoilerStyle).toBeDefined();
+      expect(spoilerStyle!.start).toBeGreaterThanOrEqual(0);
+      expect(spoilerStyle!.start + spoilerStyle!.length).toBeLessThanOrEqual(
+        chunkWithSpoiler!.text.length,
+      );
+    });
+  });
+});

src/signal/format.links.test.ts

@@ -0,0 +1,58 @@
+import { describe, expect, it } from "vitest";
+import { markdownToSignalText } from "./format.js";
+
+describe("markdownToSignalText", () => {
+  describe("duplicate URL display", () => {
+    it("does not duplicate URL when label matches URL without protocol", () => {
+      // [selfh.st](http://selfh.st) should render as "selfh.st" not "selfh.st (http://selfh.st)"
+      const res = markdownToSignalText("[selfh.st](http://selfh.st)");
+      expect(res.text).toBe("selfh.st");
+    });
+
+    it("does not duplicate URL when label matches URL without https protocol", () => {
+      const res = markdownToSignalText("[example.com](https://example.com)");
+      expect(res.text).toBe("example.com");
+    });
+
+    it("does not duplicate URL when label matches URL without www prefix", () => {
+      const res = markdownToSignalText("[www.example.com](https://example.com)");
+      expect(res.text).toBe("www.example.com");
+    });
+
+    it("does not duplicate URL when label matches URL without trailing slash", () => {
+      const res = markdownToSignalText("[example.com](https://example.com/)");
+      expect(res.text).toBe("example.com");
+    });
+
+    it("does not duplicate URL when label matches URL with multiple trailing slashes", () => {
+      const res = markdownToSignalText("[example.com](https://example.com///)");
+      expect(res.text).toBe("example.com");
+    });
+
+    it("does not duplicate URL when label includes www but URL does not", () => {
+      const res = markdownToSignalText("[example.com](https://www.example.com)");
+      expect(res.text).toBe("example.com");
+    });
+
+    it("handles case-insensitive domain comparison", () => {
+      const res = markdownToSignalText("[EXAMPLE.COM](https://example.com)");
+      expect(res.text).toBe("EXAMPLE.COM");
+    });
+
+    it("still shows URL when label is meaningfully different", () => {
+      const res = markdownToSignalText("[click here](https://example.com)");
+      expect(res.text).toBe("click here (https://example.com)");
+    });
+
+    it("handles URL with path - should show URL when label is just domain", () => {
+      // Label is just domain, URL has path - these are meaningfully different
+      const res = markdownToSignalText("[example.com](https://example.com/page)");
+      expect(res.text).toBe("example.com (https://example.com/page)");
+    });
+
+    it("does not duplicate when label matches full URL with path", () => {
+      const res = markdownToSignalText("[example.com/page](https://example.com/page)");
+      expect(res.text).toBe("example.com/page");
+    });
+  });
+});

src/signal/format.test.ts

@@ -21,6 +21,18 @@ describe("markdownToSignalText", () => {
     expect(res.styles).toEqual([]);
   });
 
+  it("keeps style offsets correct with multiple expanded links", () => {
+    const markdown =
+      "[first](https://example.com/first) **bold** [second](https://example.com/second)";
+    const res = markdownToSignalText(markdown);
+
+    const expectedText =
+      "first (https://example.com/first) bold second (https://example.com/second)";
+
+    expect(res.text).toBe(expectedText);
+    expect(res.styles).toEqual([{ start: expectedText.indexOf("bold"), length: 4, style: "BOLD" }]);
+  });
+
   it("applies spoiler styling", () => {
     const res = markdownToSignalText("hello ||secret|| world");
 

src/signal/format.ts

@@ -34,6 +34,17 @@ type Insertion = {
   length: number;
 };
 
+function normalizeUrlForComparison(url: string): string {
+  let normalized = url.toLowerCase();
+  // Strip protocol
+  normalized = normalized.replace(/^https?:\/\//, "");
+  // Strip www. prefix
+  normalized = normalized.replace(/^www\./, "");
+  // Strip trailing slashes
+  normalized = normalized.replace(/\/+$/, "");
+  return normalized;
+}
+
 function mapStyle(style: MarkdownStyle): SignalTextStyle | null {
   switch (style) {
     case "bold":
@@ -100,15 +111,17 @@ function applyInsertionsToStyles(
   }
   const sortedInsertions = [...insertions].toSorted((a, b) => a.pos - b.pos);
   let updated = spans;
+  let cumulativeShift = 0;
 
   for (const insertion of sortedInsertions) {
+    const insertionPos = insertion.pos + cumulativeShift;
     const next: SignalStyleSpan[] = [];
     for (const span of updated) {
-      if (span.end <= insertion.pos) {
+      if (span.end <= insertionPos) {
         next.push(span);
         continue;
       }
-      if (span.start >= insertion.pos) {
+      if (span.start >= insertionPos) {
         next.push({
           start: span.start + insertion.length,
           end: span.end + insertion.length,
@@ -116,15 +129,15 @@ function applyInsertionsToStyles(
         });
         continue;
       }
-      if (span.start < insertion.pos && span.end > insertion.pos) {
-        if (insertion.pos > span.start) {
+      if (span.start < insertionPos && span.end > insertionPos) {
+        if (insertionPos > span.start) {
           next.push({
             start: span.start,
-            end: insertion.pos,
+            end: insertionPos,
             style: span.style,
           });
         }
-        const shiftedStart = insertion.pos + insertion.length;
+        const shiftedStart = insertionPos + insertion.length;
         const shiftedEnd = span.end + insertion.length;
         if (shiftedEnd > shiftedStart) {
           next.push({
@@ -136,6 +149,7 @@ function applyInsertionsToStyles(
       }
     }
     updated = next;
+    cumulativeShift += insertion.length;
   }
 
   return updated;
@@ -161,16 +175,26 @@ function renderSignalText(ir: MarkdownIR): SignalFormattedText {
     const href = link.href.trim();
     const label = text.slice(link.start, link.end);
     const trimmedLabel = label.trim();
-    const comparableHref = href.startsWith("mailto:") ? href.slice("mailto:".length) : href;
 
     if (href) {
       if (!trimmedLabel) {
         out += href;
         insertions.push({ pos: link.end, length: href.length });
-      } else if (trimmedLabel !== href && trimmedLabel !== comparableHref) {
-        const addition = ` (${href})`;
-        out += addition;
-        insertions.push({ pos: link.end, length: addition.length });
+      } else {
+        // Check if label is similar enough to URL that showing both would be redundant
+        const normalizedLabel = normalizeUrlForComparison(trimmedLabel);
+        let comparableHref = href;
+        if (href.startsWith("mailto:")) {
+          comparableHref = href.slice("mailto:".length);
+        }
+        const normalizedHref = normalizeUrlForComparison(comparableHref);
+
+        // Only show URL if label is meaningfully different from it
+        if (normalizedLabel !== normalizedHref) {
+          const addition = ` (${href})`;
+          out += addition;
+          insertions.push({ pos: link.end, length: addition.length });
+        }
       }
     }
 
@@ -214,13 +238,136 @@ export function markdownToSignalText(
   const ir = markdownToIR(markdown ?? "", {
     linkify: true,
     enableSpoilers: true,
-    headingStyle: "none",
-    blockquotePrefix: "",
+    headingStyle: "bold",
+    blockquotePrefix: "> ",
     tableMode: options.tableMode,
   });
   return renderSignalText(ir);
 }
 
+function sliceSignalStyles(
+  styles: SignalTextStyleRange[],
+  start: number,
+  end: number,
+): SignalTextStyleRange[] {
+  const sliced: SignalTextStyleRange[] = [];
+  for (const style of styles) {
+    const styleEnd = style.start + style.length;
+    const sliceStart = Math.max(style.start, start);
+    const sliceEnd = Math.min(styleEnd, end);
+    if (sliceEnd > sliceStart) {
+      sliced.push({
+        start: sliceStart - start,
+        length: sliceEnd - sliceStart,
+        style: style.style,
+      });
+    }
+  }
+  return sliced;
+}
+
+/**
+ * Split Signal formatted text into chunks under the limit while preserving styles.
+ *
+ * This implementation deterministically tracks cursor position without using indexOf,
+ * which is fragile when chunks are trimmed or when duplicate substrings exist.
+ * Styles spanning chunk boundaries are split into separate ranges for each chunk.
+ */
+function splitSignalFormattedText(
+  formatted: SignalFormattedText,
+  limit: number,
+): SignalFormattedText[] {
+  const { text, styles } = formatted;
+
+  if (text.length <= limit) {
+    return [formatted];
+  }
+
+  const results: SignalFormattedText[] = [];
+  let remaining = text;
+  let offset = 0; // Track position in original text for style slicing
+
+  while (remaining.length > 0) {
+    if (remaining.length <= limit) {
+      // Last chunk - take everything remaining
+      const trimmed = remaining.trimEnd();
+      if (trimmed.length > 0) {
+        results.push({
+          text: trimmed,
+          styles: mergeStyles(sliceSignalStyles(styles, offset, offset + trimmed.length)),
+        });
+      }
+      break;
+    }
+
+    // Find a good break point within the limit
+    const window = remaining.slice(0, limit);
+    let breakIdx = findBreakIndex(window);
+
+    // If no good break point found, hard break at limit
+    if (breakIdx <= 0) {
+      breakIdx = limit;
+    }
+
+    // Extract chunk and trim trailing whitespace
+    const rawChunk = remaining.slice(0, breakIdx);
+    const chunk = rawChunk.trimEnd();
+
+    if (chunk.length > 0) {
+      results.push({
+        text: chunk,
+        styles: mergeStyles(sliceSignalStyles(styles, offset, offset + chunk.length)),
+      });
+    }
+
+    // Advance past the chunk and any whitespace separator
+    const brokeOnWhitespace = breakIdx < remaining.length && /\s/.test(remaining[breakIdx]);
+    const nextStart = Math.min(remaining.length, breakIdx + (brokeOnWhitespace ? 1 : 0));
+
+    // Chunks are sent as separate messages, so we intentionally drop boundary whitespace.
+    // Keep `offset` in sync with the dropped characters so style slicing stays correct.
+    remaining = remaining.slice(nextStart).trimStart();
+    offset = text.length - remaining.length;
+  }
+
+  return results;
+}
+
+/**
+ * Find the best break index within a text window.
+ * Prefers newlines over whitespace, avoids breaking inside parentheses.
+ */
+function findBreakIndex(window: string): number {
+  let lastNewline = -1;
+  let lastWhitespace = -1;
+  let parenDepth = 0;
+
+  for (let i = 0; i < window.length; i++) {
+    const char = window[i];
+
+    if (char === "(") {
+      parenDepth++;
+      continue;
+    }
+    if (char === ")" && parenDepth > 0) {
+      parenDepth--;
+      continue;
+    }
+
+    // Only consider break points outside parentheses
+    if (parenDepth === 0) {
+      if (char === "\n") {
+        lastNewline = i;
+      } else if (/\s/.test(char)) {
+        lastWhitespace = i;
+      }
+    }
+  }
+
+  // Prefer newline break, fall back to whitespace
+  return lastNewline > 0 ? lastNewline : lastWhitespace;
+}
+
 export function markdownToSignalTextChunks(
   markdown: string,
   limit: number,
@@ -229,10 +376,22 @@ export function markdownToSignalTextChunks(
   const ir = markdownToIR(markdown ?? "", {
     linkify: true,
     enableSpoilers: true,
-    headingStyle: "none",
-    blockquotePrefix: "",
+    headingStyle: "bold",
+    blockquotePrefix: "> ",
     tableMode: options.tableMode,
   });
   const chunks = chunkMarkdownIR(ir, limit);
-  return chunks.map((chunk) => renderSignalText(chunk));
+  const results: SignalFormattedText[] = [];
+
+  for (const chunk of chunks) {
+    const rendered = renderSignalText(chunk);
+    // If link expansion caused the chunk to exceed the limit, re-chunk it
+    if (rendered.text.length > limit) {
+      results.push(...splitSignalFormattedText(rendered, limit));
+    } else {
+      results.push(rendered);
+    }
+  }
+
+  return results;
 }

src/signal/format.visual.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, it } from "vitest";
+import { markdownToSignalText } from "./format.js";
+
+describe("markdownToSignalText", () => {
+  describe("headings visual distinction", () => {
+    it("renders headings as bold text", () => {
+      const res = markdownToSignalText("# Heading 1");
+      expect(res.text).toBe("Heading 1");
+      expect(res.styles).toContainEqual({ start: 0, length: 9, style: "BOLD" });
+    });
+
+    it("renders h2 headings as bold text", () => {
+      const res = markdownToSignalText("## Heading 2");
+      expect(res.text).toBe("Heading 2");
+      expect(res.styles).toContainEqual({ start: 0, length: 9, style: "BOLD" });
+    });
+
+    it("renders h3 headings as bold text", () => {
+      const res = markdownToSignalText("### Heading 3");
+      expect(res.text).toBe("Heading 3");
+      expect(res.styles).toContainEqual({ start: 0, length: 9, style: "BOLD" });
+    });
+  });
+
+  describe("blockquote visual distinction", () => {
+    it("renders blockquotes with a visible prefix", () => {
+      const res = markdownToSignalText("> This is a quote");
+      // Should have some kind of prefix to distinguish it
+      expect(res.text).toMatch(/^[│>]/);
+      expect(res.text).toContain("This is a quote");
+    });
+
+    it("renders multi-line blockquotes with prefix", () => {
+      const res = markdownToSignalText("> Line 1\n> Line 2");
+      // Should start with the prefix
+      expect(res.text).toMatch(/^[│>]/);
+      expect(res.text).toContain("Line 1");
+      expect(res.text).toContain("Line 2");
+    });
+  });
+
+  describe("horizontal rule rendering", () => {
+    it("renders horizontal rules as a visible separator", () => {
+      const res = markdownToSignalText("Para 1\n\n---\n\nPara 2");
+      // Should contain some kind of visual separator like ───
+      expect(res.text).toMatch(/[─—-]{3,}/);
+    });
+
+    it("renders horizontal rule between content", () => {
+      const res = markdownToSignalText("Above\n\n***\n\nBelow");
+      expect(res.text).toContain("Above");
+      expect(res.text).toContain("Below");
+      // Should have a separator
+      expect(res.text).toMatch(/[─—-]{3,}/);
+    });
+  });
+});