Treat here-strings as inline arguments, never heredoc openers

Author: TheGreatAxios

src/permission/permission.test.ts

@@ -176,6 +176,23 @@ describe("splitChainedCommand", () => {
     expect(splitChainedCommand(cmd)).toHaveLength(2);
   });
 
+  test("does not treat a here-string (<<<) as a heredoc opener", () => {
+    expect(splitChainedCommand('cat <<< "word" && echo hi')).toEqual([
+      'cat <<< "word"',
+      "echo hi",
+    ]);
+    expect(splitChainedCommand("cmd <<<EOF")).toEqual(["cmd <<<EOF"]);
+    expect(splitChainedCommand("<<< EOF && echo done")).toEqual([
+      "<<< EOF",
+      "echo done",
+    ]);
+  });
+
+  test("still treats <<- as a heredoc opener", () => {
+    const cmd = "cat <<-EOF\nbody\nEOF";
+    expect(splitChainedCommand(cmd)).toHaveLength(1);
+  });
+
   test("treats shell line continuation (backslash + newline) as glue, not a chain split", () => {
     // Common pattern from agents emitting readable multi-line shell calls.
     expect(splitChainedCommand("cd foo && \\\nbun test")).toEqual([
@@ -3962,6 +3979,11 @@ describe("stripCommentLines", () => {
     expect(stripCommentLines(command)).toBe(command);
   });
 
+  test("a here-string never swallows a later line into a heredoc body", () => {
+    const command = 'cat <<< "word"\n# a real comment';
+    expect(stripCommentLines(command)).toBe('cat <<< "word"\n');
+  });
+
   test("leaves a real command with a trailing inline comment untouched", () => {
     expect(stripCommentLines("ls -la # list files")).toBe(
       "ls -la # list files",

src/shell/command-segments.ts

@@ -152,6 +152,15 @@ export function parseHeredocOpener(
   i: number,
 ): { marker: string; lineEnd: number } | null {
   if (command[i] !== "<" || command[i + 1] !== "<") return null;
+  // `<<<` is a here-string, not a heredoc: its word is an inline argument,
+  // so there is no marker line to wait for.
+  if (command[i + 2] === "<") return null;
+  // A `<<` opener cannot start in the middle of a `<` run: when the scan
+  // reaches the second `<` of a `<<<` here-string, the character ahead is no
+  // longer `<`, so only this backward guard stops it from parsing the
+  // here-string word as a heredoc marker and swallowing the rest of the
+  // command as body.
+  if (command[i - 1] === "<") return null;
   let j = i + 2;
   if (command[j] === "-") j++; // <<- strips leading tabs
   // Skip whitespace between << and the marker word.

src/tui/command-display.test.ts

@@ -61,6 +61,18 @@ test("heredoc bodies are not enumerated as segments", () => {
   ]);
 });
 
+test("a here-string never opens a pending heredoc", () => {
+  expect(groupChainSegmentsForDisplay('cat <<< "word" && echo hi')).toEqual([
+    'cat <<< "word"',
+    "echo hi",
+  ]);
+  expect(groupChainSegmentsForDisplay("cmd <<<EOF")).toEqual(["cmd <<<EOF"]);
+  expect(verbatimCommandLines('cat <<< "word"\n# a real comment')).toEqual([
+    { text: 'cat <<< "word"', isComment: false },
+    { text: "# a real comment", isComment: true },
+  ]);
+});
+
 test("top-level newlines become verbatim lines; quoted newlines stay marked inline", () => {
   expect(verbatimCommandLines('echo "a\nb"\necho two')).toEqual([
     { text: 'echo "a↵b"', isComment: false },

src/tui/command-display.ts

@@ -5,6 +5,9 @@ import { sliceTailToWidth, sliceToWidth, stringWidth } from "./view/height.js";
 function parseHeredocMarker(command: string, i: number): string | null {
   if (command[i] !== "<" || command[i + 1] !== "<" || command[i + 2] === "<")
     return null;
+  // Same `<`-run rule as parseHeredocOpener: the second `<` of a `<<<`
+  // here-string must not parse the here-string word as a heredoc marker.
+  if (command[i - 1] === "<") return null;
   let j = i + 2;
   if (command[j] === "-") j++;
   while (command[j] === " " || command[j] === "\t") j++;