fix(adapter-slack): replace empty table cells with single space

.changeset/slack-empty-table-cells.md

@@ -0,0 +1,5 @@
+---
+"@chat-adapter/slack": patch
+---
+
+Fix empty table cells causing `invalid_blocks` error from Slack API. Empty cells now fall back to a single space to satisfy the Block Kit requirement that cell text must be more than 0 characters.

packages/adapter-slack/src/cards.test.ts

@@ -797,4 +797,31 @@ describe("cardToBlockKit with CardLink", () => {
     expect(blocks[1].type).toBe("section");
     expect(blocks[1].text.text).toContain("```");
   });
+
+  it("replaces empty table cells with a space to satisfy Slack API", () => {
+    const card = Card({
+      children: [
+        Table({
+          headers: ["Kind", ""],
+          rows: [
+            ["FORM", "Form Submission"],
+            ["and more...", ""],
+          ],
+        }),
+      ],
+    });
+
+    const blocks = cardToBlockKit(card);
+    const tableBlock = blocks[0];
+    expect(tableBlock.type).toBe("table");
+    // Every cell must have non-empty text (Slack rejects empty strings)
+    for (const row of tableBlock.rows) {
+      for (const cell of row) {
+        expect(cell.text.length).toBeGreaterThan(0);
+      }
+    }
+    // Empty cells become a space
+    expect(tableBlock.rows[0][1].text).toBe(" "); // empty header
+    expect(tableBlock.rows[2][1].text).toBe(" "); // empty data cell
+  });
 });

packages/adapter-slack/src/cards.ts

@@ -400,13 +400,13 @@ function convertTableToBlocks(
   // First row is headers, subsequent rows are data
   const headerRow = element.headers.map((header) => ({
     type: "raw_text" as const,
-    text: convertEmoji(header),
+    text: convertEmoji(header) || " ",
   }));
 
   const dataRows = element.rows.map((row) =>
     row.map((cell) => ({
       type: "raw_text" as const,
-      text: convertEmoji(cell),
+      text: convertEmoji(cell) || " ",
     }))
   );
 

packages/adapter-slack/src/markdown.test.ts

@@ -214,6 +214,23 @@ describe("SlackMarkdownConverter", () => {
       expect(blocks?.[1].type).toBe("section");
       expect(blocks?.[1].text.text).toContain("```");
     });
+
+    it("should replace empty table cells with a space to satisfy Slack API", () => {
+      const ast = converter.toAst(
+        "| Kind | Label |\n|------|-------|\n| FORM | Form Submission |\n| and more... | |"
+      );
+      const blocks = converter.toBlocksWithTable(ast);
+      const tableBlock = blocks?.[0];
+      expect(tableBlock?.type).toBe("table");
+      // Every cell must have non-empty text (Slack rejects empty strings)
+      for (const row of tableBlock?.rows ?? []) {
+        for (const cell of row) {
+          expect(cell.text.length).toBeGreaterThan(0);
+        }
+      }
+      // The empty cell should be a space
+      expect(tableBlock?.rows[2][1].text).toBe(" ");
+    });
   });
 
   describe("nested lists", () => {

packages/adapter-slack/src/markdown.ts

@@ -254,7 +254,7 @@ function mdastTableToSlackBlock(
   for (const row of node.children) {
     const cells = getNodeChildren(row).map((cell) => ({
       type: "raw_text" as const,
-      text: getNodeChildren(cell).map(cellConverter).join(""),
+      text: getNodeChildren(cell).map(cellConverter).join("") || " ",
     }));
     rows.push(cells);
   }