diff --git a/scripts/hooks/lib/shell-scan.js b/scripts/hooks/lib/shell-scan.js
index b887e2789..94a23a32a 100644
--- a/scripts/hooks/lib/shell-scan.js
+++ b/scripts/hooks/lib/shell-scan.js
@@ -18,13 +18,15 @@ function continuationEnd(input, index) {
   return index;
 }
 
-// Delimiters undergo quote removal, not command expansion. Keeping this small
-// reader shared with substitution matching prevents body punctuation becoming
-// shell syntax while locating the enclosing execution region.
-function heredocDelimiter(input, start, budget) {
-  if (!input.startsWith('<<', start) || input[start + 2] === '<') return null;
-  const operator = input[start + 2] === '-' ? '<<-' : '<<';
-  let i = start + operator.length;
+// Skip to the end of a comment. The returned index is the newline or EOF.
+function skipComment(input, start, budget) {
+  let i = start;
+  while (i < input.length && input[i] !== '\n') { budget.spend(); i++; }
+  return i;
+}
+
+function skipDelimiterBlanks(input, start, budget) {
+  let i = start;
   while (i < input.length) {
     budget.spend();
     if (input[i] === ' ' || input[i] === '\t' || input[i] === '\r') { i++; continue; }
@@ -32,37 +34,55 @@ function heredocDelimiter(input, start, budget) {
     if (continued === i) break;
     i = continued;
   }
-  let value = '';
-  let quote = null;
-  let began = false;
-  let quoted = false;
+  return i;
+}
+
+// A backslash in the delimiter word. Returns the index of the last consumed
+// character; a continuation is removed without starting the word.
+function delimiterEscape(input, i, word) {
+  const continued = continuationEnd(input, i);
+  if (continued !== i) return continued - 1;
+  word.began = true; word.quoted = true;
+  const next = input[i + 1];
+  if (next === undefined) { word.value += '\\'; return i; }
+  if (word.quote === '"' && !'"$`\\'.includes(next)) word.value += '\\';
+  word.value += next;
+  return i + 1;
+}
+
+function readDelimiterWord(input, start, budget) {
+  const word = { value: '', quote: null, began: false, quoted: false, end: start };
+  let i = start;
   for (; i < input.length; i++) {
     budget.spend();
     const c = input[i];
-    if (quote === "'") {
-      if (c === "'") quote = null;
-      else value += c;
+    if (word.quote === "'") {
+      if (c === "'") word.quote = null;
+      else word.value += c;
       continue;
     }
-    if (c === '\\') {
-      const continued = continuationEnd(input, i);
-      if (continued !== i) { i = continued - 1; continue; }
-      began = true; quoted = true;
-      const next = input[i + 1];
-      if (next === undefined) { value += c; continue; }
-      if (quote === '"' && !'"$`\\'.includes(next)) value += '\\';
-      value += next; i++; continue;
-    }
-    if (quote === '"') {
-      if (c === '"') quote = null;
-      else value += c;
+    if (c === '\\') { i = delimiterEscape(input, i, word); continue; }
+    if (word.quote === '"') {
+      if (c === '"') word.quote = null;
+      else word.value += c;
       continue;
     }
-    if (c === "'" || c === '"') { quote = c; began = true; quoted = true; continue; }
-    if (/[\s;|&()<>]/.test(c) || (!began && c === '#')) break;
-    began = true; value += c;
+    if (c === "'" || c === '"') { word.quote = c; word.began = true; word.quoted = true; continue; }
+    if (/[\s;|&()<>]/.test(c) || (!word.began && c === '#')) break;
+    word.began = true; word.value += c;
   }
-  return began ? { operator, word: { value, quoted }, end: i } : null;
+  word.end = i;
+  return word;
+}
+
+// Delimiters undergo quote removal, not command expansion. Keeping this small
+// reader shared with substitution matching prevents body punctuation becoming
+// shell syntax while locating the enclosing execution region.
+function heredocDelimiter(input, start, budget) {
+  if (!input.startsWith('<<', start) || input[start + 2] === '<') return null;
+  const operator = input[start + 2] === '-' ? '<<-' : '<<';
+  const word = readDelimiterWord(input, skipDelimiterBlanks(input, start + operator.length, budget), budget);
+  return word.began ? { operator, word: { value: word.value, quoted: word.quoted }, end: word.end } : null;
 }
 
 function heredocLine(input, start, joinContinuations, budget) {
@@ -129,90 +149,141 @@ function legacyRegion(input, start, budget) {
   return { text: decoded.join(''), end: i < input.length ? i + 1 : i };
 }
 
+// --- $(...) region state ---
+// Each helper below takes the innermost frame and the index of the current
+// character. Those that consume input return the index of the last consumed
+// character, or undefined when the character was not theirs to handle.
+
+function regionFrame() {
+  return { quote: null, depth: 1, cases: [], word: '', quotedWord: false, commandStart: true, heredocs: [] };
+}
+
+function endRegionWord(state) {
+  if (!state.word) return;
+  const phase = state.cases[state.cases.length - 1];
+  if (!state.quotedWord && state.word === 'esac' && (state.commandStart || phase === 'pattern')) state.cases.pop();
+  else if (!state.quotedWord && state.word === 'case' && state.commandStart) state.cases.push('subject');
+  else if (phase === 'subject') state.cases[state.cases.length - 1] = 'in';
+  else if (!state.quotedWord && state.word === 'in' && phase === 'in') state.cases[state.cases.length - 1] = 'pattern';
+  state.commandStart = false;
+  state.word = ''; state.quotedWord = false;
+}
+
+// Inside '...' or $'...': only the closing quote matters, and an ANSI-C escape
+// protects the next character.
+function regionQuotedEnd(state, input, i) {
+  const c = input[i];
+  if (state.quote === "$'" && c === '\\' && i + 1 < input.length) return i + 1;
+  if (c === "'") state.quote = null;
+  return i;
+}
+
+// Escapes and nested substitutions apply inside double quotes as well.
+function regionSubstitution(state, stack, input, i, budget) {
+  const c = input[i];
+  if (c === '\\') { state.word += input[i + 1] || ''; state.quotedWord = true; return i + 1; }
+  if (c === '$' && input[i + 1] === '(') {
+    state.word += '$()'; state.quotedWord = true; stack.push(regionFrame()); return i + 1;
+  }
+  if (c === '`') {
+    const region = legacyRegion(input, i, budget);
+    state.word += '`'; state.quotedWord = true; return region.end - 1;
+  }
+  return undefined;
+}
+
+function openRegionQuote(state, input, i) {
+  const c = input[i];
+  if (c === '$' && input[i + 1] === "'") {
+    state.quote = "$'"; state.word += "$'"; state.quotedWord = true; return i + 1;
+  }
+  if (c === '"' || c === "'") { state.quote = c; state.word += c; state.quotedWord = true; return i; }
+  return undefined;
+}
+
+// A here-string or heredoc operator ends the current word. A heredoc
+// delimiter queues its body for the next newline.
+function regionHeredocOperator(state, input, i, budget) {
+  if (input[i] !== '<') return undefined;
+  if (input.startsWith('<<<', i)) { endRegionWord(state); return i + 2; }
+  if (input[i + 1] === '<' && input[i + 2] !== '<') {
+    endRegionWord(state);
+    const delimiter = heredocDelimiter(input, i, budget);
+    if (delimiter) { state.heredocs.push(delimiter); return delimiter.end - 1; }
+  }
+  return undefined;
+}
+
+function regionHeredocBodies(state, input, i, budget) {
+  endRegionWord(state);
+  let next = i + 1;
+  for (const redirect of state.heredocs) next = heredocBody(input, next, redirect, budget).end;
+  state.heredocs.length = 0;
+  state.commandStart = true;
+  return next - 1;
+}
+
+// A case pattern's closing ')' is not the end of $(...). Only literal
+// keyword positions affect this state; quoted or echo operands do not.
+function casePhaseStep(state, input, i) {
+  const c = input[i];
+  const phase = state.cases[state.cases.length - 1];
+  if (c === ')' && phase === 'pattern') {
+    state.cases[state.cases.length - 1] = 'body'; state.commandStart = true; return i;
+  }
+  if (c === '(' && phase === 'pattern') return i;
+  if (c === ';' && input[i + 1] === ';' && phase === 'body') {
+    state.cases[state.cases.length - 1] = 'pattern'; state.commandStart = true; return i + 1;
+  }
+  return undefined;
+}
+
+// Tracks parenthesis depth; true once the outermost region has closed.
+function closeRegionParen(stack, state, c) {
+  if (/[;|&\n]/.test(c)) state.commandStart = true;
+  if (c === '(') state.depth++;
+  if (c !== ')') return false;
+  state.depth--;
+  if (state.depth !== 0) return false;
+  stack.pop();
+  return stack.length === 0;
+}
+
 // Locate a nested execution region without evaluating any supplied text.
 // Balanced substitutions have independent quote state; malformed regions extend
 // to EOF and remain conservatively inspectable instead of silently disappearing.
 function executionRegion(input, start, budget) {
   if (input[start] === '`') return legacyRegion(input, start, budget);
   const from = start + 2;
-  const frame = () => ({ quote: null, depth: 1, cases: [], word: '', quotedWord: false, commandStart: true, heredocs: [] });
-  const stack = [frame()];
-  function endWord(state) {
-    if (!state.word) return;
-    const phase = state.cases[state.cases.length - 1];
-    if (!state.quotedWord && state.word === 'esac' && (state.commandStart || phase === 'pattern')) state.cases.pop();
-    else if (!state.quotedWord && state.word === 'case' && state.commandStart) state.cases.push('subject');
-    else if (phase === 'subject') state.cases[state.cases.length - 1] = 'in';
-    else if (!state.quotedWord && state.word === 'in' && phase === 'in') state.cases[state.cases.length - 1] = 'pattern';
-    state.commandStart = false;
-    state.word = ''; state.quotedWord = false;
-  }
+  const stack = [regionFrame()];
   for (let i = from; i < input.length; i++) {
     budget.spend();
     const state = stack[stack.length - 1];
     const c = input[i];
-    if (state.quote === "'" || state.quote === "$'") {
-      if (state.quote === "$'" && c === '\\' && i + 1 < input.length) { i++; continue; }
-      if (c === "'") state.quote = null;
-      continue;
-    }
-    if (c === '\\') { state.word += input[i + 1] || ''; state.quotedWord = true; i++; continue; }
-    if (c === '$' && input[i + 1] === '(') {
-      state.word += '$()'; state.quotedWord = true; stack.push(frame()); i++; continue;
-    }
-    if (c === '`') {
-      const region = legacyRegion(input, i, budget);
-      state.word += '`'; state.quotedWord = true; i = region.end - 1; continue;
-    }
+    if (state.quote === "'" || state.quote === "$'") { i = regionQuotedEnd(state, input, i); continue; }
+    const substituted = regionSubstitution(state, stack, input, i, budget);
+    if (substituted !== undefined) { i = substituted; continue; }
     if (state.quote === '"') {
       if (c === '"') state.quote = null;
       continue;
     }
-    if (c === '$' && input[i + 1] === "'") {
-      state.quote = "$'"; state.word += "$'"; state.quotedWord = true; i++; continue;
-    }
-    if (c === '"' || c === "'") { state.quote = c; state.word += c; state.quotedWord = true; continue; }
+    const opened = openRegionQuote(state, input, i);
+    if (opened !== undefined) { i = opened; continue; }
     if (c === '#' && /[\s;|&()]/.test(input[i - 1] || ' ')) {
-      while (i < input.length && input[i] !== '\n') { budget.spend(); i++; }
-      i--; // Process the newline, including any pending heredoc bodies.
+      // Stop before the newline so pending heredoc bodies are still processed.
+      i = skipComment(input, i, budget) - 1;
       continue;
     }
-    if (c === '<' && input.startsWith('<<<', i)) { endWord(state); i += 2; continue; }
-    if (c === '<' && input[i + 1] === '<' && input[i + 2] !== '<') {
-      endWord(state);
-      const delimiter = heredocDelimiter(input, i, budget);
-      if (delimiter) { state.heredocs.push(delimiter); i = delimiter.end - 1; continue; }
-    }
-    if (c === '\n' && state.heredocs.length) {
-      endWord(state);
-      let next = i + 1;
-      for (const redirect of state.heredocs) next = heredocBody(input, next, redirect, budget).end;
-      state.heredocs.length = 0;
-      state.commandStart = true; i = next - 1; continue;
-    }
-    if (/[\s;|&()]/.test(c)) endWord(state);
+    const redirected = regionHeredocOperator(state, input, i, budget);
+    if (redirected !== undefined) { i = redirected; continue; }
+    if (c === '\n' && state.heredocs.length) { i = regionHeredocBodies(state, input, i, budget); continue; }
+    if (/[\s;|&()]/.test(c)) endRegionWord(state);
     else state.word += c;
-    const phase = state.cases[state.cases.length - 1];
-    // A case pattern's closing ')' is not the end of $(...). Only literal
-    // keyword positions affect this state; quoted or echo operands do not.
-    if (c === ')' && phase === 'pattern') {
-      state.cases[state.cases.length - 1] = 'body'; state.commandStart = true; continue;
-    }
-    if (c === '(' && phase === 'pattern') continue;
-    if (c === ';' && input[i + 1] === ';' && phase === 'body') {
-      state.cases[state.cases.length - 1] = 'pattern'; state.commandStart = true; i++; continue;
-    }
-    if (/[;|&\n]/.test(c)) state.commandStart = true;
-    if (c === '(') state.depth++;
-    if (c === ')') {
-      state.depth--;
-      if (state.depth === 0) {
-        stack.pop();
-        if (stack.length === 0) {
-          budget.spend(i - from + 1);
-          return { text: input.slice(from, i), end: i + 1 };
-        }
-      }
+    const stepped = casePhaseStep(state, input, i);
+    if (stepped !== undefined) { i = stepped; continue; }
+    if (closeRegionParen(stack, state, c)) {
+      budget.spend(i - from + 1);
+      return { text: input.slice(from, i), end: i + 1 };
     }
   }
   budget.spend(input.length - from + 1);
@@ -243,164 +314,226 @@ function scanExpansions(input, budget) {
   return nested;
 }
 
-function scanShell(input, budget) {
-  const commands = [];
-  const nested = [];
-  const pendingHeredocs = [];
+// --- Top-level scan state ---
+// scan.i is the read position; every helper advances it past what it consumed.
+
+const COMPOUND_KEYWORDS = ['if', 'then', 'elif', 'else', 'while', 'until', 'do', 'case', 'for', 'select', 'function'];
+
+function newCommand(scan, pipeFrom) {
+  return { words: [], redirects: [], pipeFrom, nested: [], scope: scan.scope };
+}
+
+function createScan(input, budget) {
   const rootScope = { parent: null, isolated: false, conditional: false };
-  let scope = rootScope;
-  const command = pipeFrom => ({ words: [], redirects: [], pipeFrom, nested: [], scope });
-  let current = command(null);
-  let word = null;
-  let quote = null;
-  let pendingRedirect = null;
-  let i = 0;
-  function begin() {
-    if (!word) word = { value: '', start: i, end: i, quoted: false, literal: true, dynamic: false };
+  const scan = {
+    input, budget, commands: [], nested: [], pendingHeredocs: [], rootScope,
+    scope: rootScope, current: null, word: null, quote: null, pendingRedirect: null, i: 0
+  };
+  scan.current = newCommand(scan, null);
+  return scan;
+}
+
+function beginWord(scan) {
+  if (!scan.word) scan.word = { value: '', start: scan.i, end: scan.i, quoted: false, literal: true, dynamic: false };
+}
+
+function flushWord(scan) {
+  const { word, current } = scan;
+  if (!word) return;
+  word.end = scan.i;
+  word.raw = scan.input.slice(word.start, scan.i);
+  if (scan.pendingRedirect) {
+    const redirect = { operator: scan.pendingRedirect, word, body: '' };
+    current.redirects.push(redirect);
+    if (scan.pendingRedirect === '<<' || scan.pendingRedirect === '<<-') scan.pendingHeredocs.push({ redirect, owner: current });
+    scan.pendingRedirect = null;
+  } else current.words.push(word);
+  scan.word = null;
+}
+
+function flushCommand(scan, pipe = false, background = false) {
+  flushWord(scan);
+  const previous = scan.current;
+  previous.pipeTo = pipe;
+  previous.background = background;
+  if (previous.closedScope && (pipe || background)) {
+    previous.closedScope.isolated = true;
+    previous.closedScope.pipelineLast = false;
   }
-  function flushWord() {
-    if (!word) return;
-    word.end = i;
-    word.raw = input.slice(word.start, i);
-    if (pendingRedirect) {
-      const redirect = { operator: pendingRedirect, word, body: '' };
-      current.redirects.push(redirect);
-      if (pendingRedirect === '<<' || pendingRedirect === '<<-') pendingHeredocs.push({ redirect, owner: current });
-      pendingRedirect = null;
-    } else current.words.push(word);
-    word = null;
-  }
-  function flushCommand(pipe = false, background = false) {
-    flushWord();
-    const previous = current;
-    previous.pipeTo = pipe;
-    previous.background = background;
-    if (previous.closedScope && (pipe || background)) {
-      previous.closedScope.isolated = true;
-      previous.closedScope.pipelineLast = false;
+  const first = previous.words[0];
+  if (first && !first.quoted && COMPOUND_KEYWORDS.includes(first.value)) scan.scope.conditional = true;
+  if (previous.words.length || previous.redirects.length) scan.commands.push(previous);
+  scan.current = newCommand(scan, pipe ? previous : null);
+  scan.pendingRedirect = null;
+}
+
+function consumeHeredocs(scan) {
+  for (const { redirect, owner } of scan.pendingHeredocs) {
+    const region = heredocBody(scan.input, scan.i, redirect, scan.budget);
+    redirect.body = region.body;
+    scan.i = region.end;
+    if (!redirect.word.quoted) {
+      const regions = scanExpansions(redirect.body, scan.budget);
+      for (const text of regions) { scan.budget.spend(); scan.nested.push(text); owner.nested.push(text); }
     }
-    const first = previous.words[0];
-    if (first && !first.quoted && ['if', 'then', 'elif', 'else', 'while', 'until', 'do', 'case', 'for', 'select', 'function'].includes(first.value)) scope.conditional = true;
-    if (previous.words.length || previous.redirects.length) commands.push(previous);
-    current = command(pipe ? previous : null);
-    pendingRedirect = null;
   }
-  function consumeHeredocs() {
-    for (const { redirect, owner } of pendingHeredocs) {
-      const region = heredocBody(input, i, redirect, budget);
-      redirect.body = region.body;
-      i = region.end;
-      if (!redirect.word.quoted) {
-        const regions = scanExpansions(redirect.body, budget);
-        for (const text of regions) { budget.spend(); nested.push(text); owner.nested.push(text); }
-      }
-    }
-    pendingHeredocs.length = 0;
+  scan.pendingHeredocs.length = 0;
+}
+
+// Inside '...' or $'...'.
+function scanQuotedChar(scan) {
+  const c = scan.input[scan.i];
+  if (scan.quote === "$'" && c === '\\' && scan.i + 1 < scan.input.length) {
+    const next = scan.input[scan.i + 1];
+    // Preserve boundaries without claiming general ANSI-C escape expansion.
+    scan.word.value += next === "'" || next === '\\' ? next : c + next;
+    scan.i += 2;
+    return;
   }
-  while (i < input.length) {
+  if (c === "'") scan.quote = null;
+  else scan.word.value += c;
+  scan.i++;
+}
+
+function scanDoubleQuotedChar(scan, c) {
+  if (c === '"') scan.quote = null;
+  else scan.word.value += c;
+  scan.i++;
+}
+
+function scanEscape(scan) {
+  beginWord(scan); scan.word.quoted = true;
+  const next = scan.input[scan.i + 1];
+  if (next === undefined) { scan.word.value += '\\'; scan.i++; return; }
+  if (scan.quote === '"' && !'"$`\\'.includes(next)) scan.word.value += '\\';
+  scan.word.value += next; scan.i += 2;
+}
+
+function scanSubstitution(scan) {
+  beginWord(scan); scan.word.literal = false; scan.word.dynamic = true;
+  const region = executionRegion(scan.input, scan.i, scan.budget);
+  scan.nested.push(region.text); scan.current.nested.push(region.text);
+  scan.word.value += '\u0000'; scan.i = region.end;
+}
+
+// Parameter expansions remain opaque values. Escaped/single/ANSI-C
+// quoted dollars have already been consumed as data before this point.
+function markParameterExpansion(scan, c) {
+  if (c === '$' && /[A-Za-z0-9_@*#?$!{-]/.test(scan.input[scan.i + 1] || '')) {
+    beginWord(scan); scan.word.dynamic = true;
+  }
+}
+
+function openQuote(scan, c) {
+  if (c === '$' && scan.input[scan.i + 1] === "'") {
+    // ANSI-C escaped quotes do not close the word; its contents never expand.
+    // Numeric/control escapes and generated names remain outside this grammar.
+    beginWord(scan); scan.word.quoted = true; scan.quote = "$'"; scan.i += 2;
+    return true;
+  }
+  if (c === '"' || c === "'") { beginWord(scan); scan.word.quoted = true; scan.quote = c; scan.i++; return true; }
+  return false;
+}
+
+function isBraceKeyword(scan, c) {
+  return (c === '{' || c === '}') && !scan.word && scan.current.words.length === 0 && /[\s;&|]/.test(scan.input[scan.i + 1] || ' ');
+}
+
+function markFunctionDefinition(scan) {
+  flushWord(scan);
+  // A function definition does not execute its body. Function grammar
+  // is unsupported: keep pre-definition alternatives instead of using
+  // flattened body mutations to certify a later command as safe.
+  const words = scan.current.words;
+  if (words.length === 1 && !words[0].quoted && /^[A-Za-z_][A-Za-z0-9_]*$/.test(words[0].value)) scan.scope.conditional = true;
+}
+
+function openScope(scan, c, incomingPipe) {
+  scan.scope = { parent: scan.scope, isolated: c === '(' || incomingPipe, conditional: false, pipelineLast: c === '{' && incomingPipe };
+  scan.current.scope = scan.scope;
+}
+
+function closeScope(scan) {
+  const closedScope = scan.scope;
+  scan.scope = closedScope.parent;
+  scan.current.scope = scan.scope;
+  scan.current.closedScope = closedScope;
+  // Ordered metadata only; there is no executable argv in this event.
+  scan.commands.push({ ...newCommand(scan, null), scopeExit: closedScope });
+}
+
+function scanOperator(scan, c, braceKeyword) {
+  const doubled = (c === '&' || c === '|') && scan.input[scan.i + 1] === c;
+  const pipe = c === '|' && !doubled;
+  const background = c === '&' && !doubled;
+  if (doubled) scan.scope.conditional = true;
+  const incomingPipe = Boolean(scan.current.pipeFrom);
+  if (c === '(') markFunctionDefinition(scan);
+  flushCommand(scan, pipe, background);
+  if (c === '(' || (braceKeyword && c === '{')) openScope(scan, c, incomingPipe);
+  else if ((c === ')' || (braceKeyword && c === '}')) && scan.scope.parent) closeScope(scan);
+  scan.i += doubled ? 2 : 1;
+  if (c === '\n') consumeHeredocs(scan);
+}
+
+// An immediately adjacent numeric word is a descriptor, not an argv word.
+function dropDescriptorWord(scan) {
+  if (scan.word && /^\d+$/.test(scan.word.value)) scan.word = null;
+}
+
+function queueHeredoc(scan, delimiter) {
+  dropDescriptorWord(scan);
+  flushWord(scan);
+  const redirect = { operator: delimiter.operator, word: delimiter.word, body: '' };
+  scan.current.redirects.push(redirect);
+  scan.pendingHeredocs.push({ redirect, owner: scan.current });
+  scan.i = delimiter.end;
+  scan.pendingRedirect = null;
+}
+
+function redirectOperator(input, i, c) {
+  let operator = c;
+  if (input[i + 1] === c) operator += c;
+  if (operator === '<<' && input[i + 2] === '<') operator = '<<<';
+  else if (operator === '<<' && input[i + 2] === '-') operator = '<<-';
+  else if (input[i + 1] === '&') operator += '&';
+  return operator;
+}
+
+function scanRedirect(scan, c) {
+  const { input } = scan;
+  if (c === '<' && input[scan.i + 1] === '<' && input[scan.i + 2] !== '<') {
+    const delimiter = heredocDelimiter(input, scan.i, scan.budget);
+    if (delimiter) { queueHeredoc(scan, delimiter); return; }
+  }
+  dropDescriptorWord(scan);
+  flushWord(scan);
+  scan.pendingRedirect = redirectOperator(input, scan.i, c);
+  scan.i += scan.pendingRedirect.length;
+}
+
+function scanShell(input, budget) {
+  const scan = createScan(input, budget);
+  while (scan.i < input.length) {
     budget.spend();
-    const c = input[i];
-    if (quote === "'" || quote === "$'") {
-      if (quote === "$'" && c === '\\' && i + 1 < input.length) {
-        const next = input[i + 1];
-        // Preserve boundaries without claiming general ANSI-C escape expansion.
-        word.value += next === "'" || next === '\\' ? next : c + next;
-        i += 2; continue;
-      }
-      if (c === "'") quote = null;
-      else word.value += c;
-      i++; continue;
-    }
-    const continued = continuationEnd(input, i);
-    if (continued !== i) { i = continued; continue; }
-    if (c === '\\') {
-      begin(); word.quoted = true;
-      const next = input[i + 1];
-      if (next === undefined) { word.value += c; i++; continue; }
-      if (quote === '"' && !'"$`\\'.includes(next)) word.value += '\\';
-      word.value += next; i += 2; continue;
-    }
-    if (hasExpansion(input, i, quote === null)) {
-      begin(); word.literal = false; word.dynamic = true;
-      const region = executionRegion(input, i, budget);
-      nested.push(region.text); current.nested.push(region.text); word.value += '\u0000'; i = region.end; continue;
-    }
-    // Parameter expansions remain opaque values. Escaped/single/ANSI-C
-    // quoted dollars have already been consumed as data above.
-    if (c === '$' && /[A-Za-z0-9_@*#?$!{-]/.test(input[i + 1] || '')) {
-      begin(); word.dynamic = true;
-    }
-    if (quote === '"') {
-      if (c === '"') quote = null;
-      else word.value += c;
-      i++; continue;
-    }
-    if (c === '$' && input[i + 1] === "'") {
-      // ANSI-C escaped quotes do not close the word; its contents never expand.
-      // Numeric/control escapes and generated names remain outside this grammar.
-      begin(); word.quoted = true; quote = "$'"; i += 2; continue;
-    }
-    if (c === '"' || c === "'") { begin(); word.quoted = true; quote = c; i++; continue; }
-    if (c === '#' && !word) {
-      while (i < input.length && input[i] !== '\n') { budget.spend(); i++; }
-      continue;
-    }
-    const braceKeyword = (c === '{' || c === '}') && !word && current.words.length === 0 && /[\s;&|]/.test(input[i + 1] || ' ');
-    if (c === '\n' || c === ';' || c === '&' || c === '|' || c === '(' || c === ')' || braceKeyword) {
-      const pipe = c === '|' && input[i + 1] !== '|';
-      const background = c === '&' && input[i + 1] !== '&';
-      if ((c === '&' || c === '|') && input[i + 1] === c) scope.conditional = true;
-      const incomingPipe = Boolean(current.pipeFrom);
-      if (c === '(') {
-        flushWord();
-        // A function definition does not execute its body. Function grammar
-        // is unsupported: keep pre-definition alternatives instead of using
-        // flattened body mutations to certify a later command as safe.
-        if (current.words.length === 1 && !current.words[0].quoted &&
-            /^[A-Za-z_][A-Za-z0-9_]*$/.test(current.words[0].value)) scope.conditional = true;
-      }
-      flushCommand(pipe, background);
-      if (c === '(' || (braceKeyword && c === '{')) {
-        scope = { parent: scope, isolated: c === '(' || incomingPipe, conditional: false, pipelineLast: c === '{' && incomingPipe };
-        current.scope = scope;
-      } else if ((c === ')' || (braceKeyword && c === '}')) && scope.parent) {
-        const closedScope = scope;
-        scope = scope.parent;
-        current.scope = scope;
-        current.closedScope = closedScope;
-        // Ordered metadata only; there is no executable argv in this event.
-        commands.push({ ...command(null), scopeExit: closedScope });
-      }
-      i += (c === '&' || c === '|') && input[i + 1] === c ? 2 : 1;
-      if (c === '\n') consumeHeredocs();
-      continue;
-    }
-    if (c === '<' && input[i + 1] === '<' && input[i + 2] !== '<') {
-      const delimiter = heredocDelimiter(input, i, budget);
-      if (delimiter) {
-        if (word && /^\d+$/.test(word.value)) word = null;
-        flushWord();
-        const redirect = { operator: delimiter.operator, word: delimiter.word, body: '' };
-        current.redirects.push(redirect); pendingHeredocs.push({ redirect, owner: current });
-        i = delimiter.end; pendingRedirect = null; continue;
-      }
-    }
-    if (c === '<' || c === '>') {
-      // An immediately adjacent numeric word is a descriptor, not an argv word.
-      if (word && /^\d+$/.test(word.value)) word = null;
-      flushWord();
-      let operator = c;
-      if (input[i + 1] === c) operator += c;
-      if (operator === '<<' && input[i + 2] === '<') operator = '<<<';
-      else if (operator === '<<' && input[i + 2] === '-') operator = '<<-';
-      else if (input[i + 1] === '&') operator += '&';
-      pendingRedirect = operator; i += operator.length; continue;
-    }
-    if (/\s/.test(c)) { flushWord(); i++; continue; }
-    begin(); word.value += c; i++;
+    if (scan.quote === "'" || scan.quote === "$'") { scanQuotedChar(scan); continue; }
+    const continued = continuationEnd(input, scan.i);
+    if (continued !== scan.i) { scan.i = continued; continue; }
+    const c = input[scan.i];
+    if (c === '\\') { scanEscape(scan); continue; }
+    if (hasExpansion(input, scan.i, scan.quote === null)) { scanSubstitution(scan); continue; }
+    markParameterExpansion(scan, c);
+    if (scan.quote === '"') { scanDoubleQuotedChar(scan, c); continue; }
+    if (openQuote(scan, c)) continue;
+    if (c === '#' && !scan.word) { scan.i = skipComment(input, scan.i, budget); continue; }
+    const braceKeyword = isBraceKeyword(scan, c);
+    if (braceKeyword || '\n;&|()'.includes(c)) { scanOperator(scan, c, braceKeyword); continue; }
+    if (c === '<' || c === '>') { scanRedirect(scan, c); continue; }
+    if (/\s/.test(c)) { flushWord(scan); scan.i++; continue; }
+    beginWord(scan); scan.word.value += c; scan.i++;
   }
-  flushCommand();
-  return { commands, nested, rootScope };
+  flushCommand(scan);
+  return { commands: scan.commands, nested: scan.nested, rootScope: scan.rootScope };
 }
 
 module.exports = { createBudget, scanShell, scanExpansions };