15 files changed, 675 insertions, 694 deletions

diff --git a/src/content-function.js b/src/content-function.js
index 8c7c4e2e..16b18641 100644
--- a/src/content-function.js
+++ b/src/content-function.js
@@ -1,14 +1,9 @@
 import {inspect as nodeInspect} from 'node:util';
 
+import {decorateError} from '#aggregate';
 import {colors, ENABLE_COLOR} from '#cli';
 import {Template} from '#html';
-
-import {
-  annotateFunction,
-  decorateError,
-  empty,
-  setIntersection,
-} from '#sugar';
+import {annotateFunction, empty, setIntersection} from '#sugar';
 
 function inspect(value, opts = {}) {
   return nodeInspect(value, {colors: ENABLE_COLOR, ...opts});
diff --git a/src/content/dependencies/generatePageLayout.js b/src/content/dependencies/generatePageLayout.js
index 0d2ce557..76d07c40 100644
--- a/src/content/dependencies/generatePageLayout.js
+++ b/src/content/dependencies/generatePageLayout.js
@@ -1,4 +1,5 @@
-import {empty, openAggregate} from '#sugar';
+import {openAggregate} from '#aggregate';
+import {empty} from '#sugar';
 
 function sidebarSlots(side) {
   return {
diff --git a/src/content/dependencies/index.js b/src/content/dependencies/index.js
index 28755f7b..a5009804 100644
--- a/src/content/dependencies/index.js
+++ b/src/content/dependencies/index.js
@@ -6,13 +6,10 @@ import {fileURLToPath} from 'node:url';
 import chokidar from 'chokidar';
 import {ESLint} from 'eslint';
 
+import {showAggregate as _showAggregate} from '#aggregate';
 import {colors, logWarn} from '#cli';
 import contentFunction, {ContentFunctionSpecError} from '#content-function';
-
-import {
-  annotateFunction,
-  showAggregate as _showAggregate
-} from '#sugar';
+import {annotateFunction} from '#sugar';
 
 function cachebust(filePath) {
   if (filePath in cachebust.cache) {
diff --git a/src/data/checks.js b/src/data/checks.js
index 25e94aa9..ad86087b 100644
--- a/src/data/checks.js
+++ b/src/data/checks.js
@@ -4,19 +4,18 @@ import {inspect as nodeInspect} from 'node:util';
 import {colors, ENABLE_COLOR} from '#cli';
 
 import CacheableObject from '#cacheable-object';
+import {compareArrays, empty} from '#sugar';
 import Thing from '#thing';
 import thingConstructors from '#things';
 import {commentaryRegexCaseSensitive} from '#wiki-data';
 
 import {
-  compareArrays,
   conditionallySuppressError,
   decorateErrorWithIndex,
-  empty,
   filterAggregate,
   openAggregate,
   withAggregate,
-} from '#sugar';
+} from '#aggregate';
 
 function inspect(value, opts = {}) {
   return nodeInspect(value, {colors: ENABLE_COLOR, ...opts});
diff --git a/src/data/composite.js b/src/data/composite.js
index 4f89d887..7a98c424 100644
--- a/src/data/composite.js
+++ b/src/data/composite.js
@@ -1,19 +1,12 @@
 import {inspect} from 'node:util';
 
+import {decorateErrorWithIndex, openAggregate, withAggregate}
+  from '#aggregate';
 import {colors} from '#cli';
-import {TupleMap} from '#wiki-data';
+import {empty, filterProperties, stitchArrays, typeAppearance, unique}
+  from '#sugar';
 import {a} from '#validators';
-
-import {
-  decorateErrorWithIndex,
-  empty,
-  filterProperties,
-  openAggregate,
-  stitchArrays,
-  typeAppearance,
-  unique,
-  withAggregate,
-} from '#sugar';
+import {TupleMap} from '#wiki-data';
 
 const globalCompositeCache = {};
 
diff --git a/src/data/language.js b/src/data/language.js
index 6f774f27..96d39d81 100644
--- a/src/data/language.js
+++ b/src/data/language.js
@@ -7,10 +7,10 @@ import chokidar from 'chokidar';
 import he from 'he'; // It stands for "HTML Entities", apparently. Cursed.
 import yaml from 'js-yaml';
 
+import {annotateError, annotateErrorWithFile, showAggregate, withAggregate}
+  from '#aggregate';
 import {externalLinkSpec} from '#external-links';
 import {colors, logWarn} from '#cli';
-import {annotateError, annotateErrorWithFile, showAggregate, withAggregate}
-  from '#sugar';
 import T from '#things';
 
 const {Language} = T;
diff --git a/src/data/things/index.js b/src/data/things/index.js
index 9a36eaae..3bf84091 100644
--- a/src/data/things/index.js
+++ b/src/data/things/index.js
@@ -1,10 +1,10 @@
 import * as path from 'node:path';
 import {fileURLToPath} from 'node:url';
 
+import {openAggregate, showAggregate} from '#aggregate';
 import {logError} from '#cli';
 import {compositeFrom} from '#composite';
 import * as serialize from '#serialize';
-import {openAggregate, showAggregate} from '#sugar';
 
 import Thing from '#thing';
 
diff --git a/src/data/things/language.js b/src/data/things/language.js
index 6bd5a78a..93ed40b6 100644
--- a/src/data/things/language.js
+++ b/src/data/things/language.js
@@ -1,8 +1,9 @@
 import { Temporal, toTemporalInstant } from '@js-temporal/polyfill';
 
+import {withAggregate} from '#aggregate';
 import CacheableObject from '#cacheable-object';
 import * as html from '#html';
-import {empty, withAggregate} from '#sugar';
+import {empty} from '#sugar';
 import {isLanguageCode} from '#validators';
 import Thing from '#thing';
 
diff --git a/src/data/validators.js b/src/data/validators.js
index 7eabe720..4fc2ac65 100644
--- a/src/data/validators.js
+++ b/src/data/validators.js
@@ -1,18 +1,11 @@
 import {inspect as nodeInspect} from 'node:util';
 
+import {openAggregate, withAggregate} from '#aggregate';
 import {colors, ENABLE_COLOR} from '#cli';
+import {cut, empty, matchMultiline, typeAppearance} from '#sugar';
 import {commentaryRegexCaseInsensitive, commentaryRegexCaseSensitiveOneShot}
   from '#wiki-data';
 
-import {
-  cut,
-  empty,
-  matchMultiline,
-  openAggregate,
-  typeAppearance,
-  withAggregate,
-} from '#sugar';
-
 function inspect(value) {
   return nodeInspect(value, {colors: ENABLE_COLOR});
 }
diff --git a/src/data/yaml.js b/src/data/yaml.js
index 7a0643e8..100e07b9 100644
--- a/src/data/yaml.js
+++ b/src/data/yaml.js
@@ -10,23 +10,20 @@ import yaml from 'js-yaml';
 import {colors, ENABLE_COLOR, logInfo, logWarn} from '#cli';
 import {reportDuplicateDirectories, filterReferenceErrors}
   from '#data-checks';
+import {atOffset, empty, filterProperties, typeAppearance, withEntries}
+  from '#sugar';
 import Thing from '#thing';
 import thingConstructors from '#things';
 import {sortByName} from '#wiki-data';
 
 import {
   annotateErrorWithFile,
-  atOffset,
   decorateErrorWithIndex,
   decorateErrorWithAnnotation,
-  empty,
-  filterProperties,
   openAggregate,
   showAggregate,
-  typeAppearance,
   withAggregate,
-  withEntries,
-} from '#sugar';
+} from '#aggregate';
 
 function inspect(value, opts = {}) {
   return nodeInspect(value, {colors: ENABLE_COLOR, ...opts});
diff --git a/src/listing-spec.js b/src/listing-spec.js
index 9433ee68..73fbee6d 100644
--- a/src/listing-spec.js
+++ b/src/listing-spec.js
@@ -1,4 +1,5 @@
-import {empty, showAggregate} from '#sugar';
+import {showAggregate} from '#aggregate';
+import {empty} from '#sugar';
 
 const listingSpec = [];
 
diff --git a/src/upd8.js b/src/upd8.js
index 04c0ce2e..13c625a3 100755
--- a/src/upd8.js
+++ b/src/upd8.js
@@ -38,6 +38,7 @@ import {fileURLToPath} from 'node:url';
 
 import wrap from 'word-wrap';
 
+import {showAggregate} from '#aggregate';
 import CacheableObject from '#cacheable-object';
 import {displayCompositeCacheAnalysis} from '#composite';
 import {filterReferenceErrors, reportDuplicateDirectories}
@@ -46,7 +47,7 @@ import {bindFind, getAllFindSpecs} from '#find';
 import {processLanguageFile, watchLanguageFile, internalDefaultStringsFile}
   from '#language';
 import {isMain, traverse} from '#node-utils';
-import {empty, showAggregate, withEntries} from '#sugar';
+import {empty, withEntries} from '#sugar';
 import {generateURLs, urlSpec} from '#urls';
 import {sortByName} from '#wiki-data';
 import {linkWikiDataArrays, loadAndProcessDataDocuments, sortWikiDataArrays}
diff --git a/src/util/aggregate.js b/src/util/aggregate.js
new file mode 100644
index 00000000..c5d4198f
--- /dev/null
+++ b/src/util/aggregate.js
@@ -0,0 +1,646 @@
+import {colors} from './cli.js';
+import {empty, typeAppearance} from './sugar.js';
+
+// Utility function for providing useful interfaces to the JS AggregateError
+// class.
+//
+// Generally, this works by returning a set of interfaces which operate on
+// functions: wrap() takes a function and returns a new function which passes
+// its arguments through and appends any resulting error to the internal error
+// list; call() simplifies this process by wrapping the provided function and
+// then calling it immediately. Once the process for which errors should be
+// aggregated is complete, close() constructs and throws an AggregateError
+// object containing all caught errors (or doesn't throw anything if there were
+// no errors).
+export function openAggregate({
+  // Constructor to use, defaulting to the builtin AggregateError class.
+  // Anything passed here should probably extend from that! May be used for
+  // letting callers programatically distinguish between multiple aggregate
+  // errors.
+  //
+  // This should be provided using the aggregateThrows utility function.
+  [openAggregate.errorClassSymbol]: errorClass = AggregateError,
+
+  // Optional human-readable message to describe the aggregate error, if
+  // constructed.
+  message = '',
+
+  // Optional flag to indicate that this layer of the aggregate error isn't
+  // generally useful outside of developer debugging purposes - it will be
+  // skipped by default when using showAggregate, showing contained errors
+  // inline with other children of this aggregate's parent.
+  //
+  // If set to 'single', it'll be hidden only if there's a single error in the
+  // aggregate (so it's not grouping multiple errors together).
+  translucent = false,
+
+  // Value to return when a provided function throws an error. If this is a
+  // function, it will be called with the arguments given to the function.
+  // (This is primarily useful when wrapping a function and then providing it
+  // to another utility, e.g. array.map().)
+  returnOnFail = null,
+} = {}) {
+  const errors = [];
+
+  const aggregate = {};
+
+  aggregate.wrap =
+    (fn) =>
+    (...args) => {
+      try {
+        return fn(...args);
+      } catch (error) {
+        errors.push(error);
+        return typeof returnOnFail === 'function'
+          ? returnOnFail(...args)
+          : returnOnFail;
+      }
+    };
+
+  aggregate.wrapAsync =
+    (fn) =>
+    (...args) => {
+      return fn(...args).then(
+        (value) => value,
+        (error) => {
+          errors.push(error);
+          return typeof returnOnFail === 'function'
+            ? returnOnFail(...args)
+            : returnOnFail;
+        }
+      );
+    };
+
+  aggregate.push = (error) => {
+    errors.push(error);
+  };
+
+  aggregate.call = (fn, ...args) => {
+    return aggregate.wrap(fn)(...args);
+  };
+
+  aggregate.callAsync = (fn, ...args) => {
+    return aggregate.wrapAsync(fn)(...args);
+  };
+
+  aggregate.nest = (...args) => {
+    return aggregate.call(() => withAggregate(...args));
+  };
+
+  aggregate.nestAsync = (...args) => {
+    return aggregate.callAsync(() => withAggregateAsync(...args));
+  };
+
+  aggregate.map = (...args) => {
+    const parent = aggregate;
+    const {result, aggregate: child} = mapAggregate(...args);
+    parent.call(child.close);
+    return result;
+  };
+
+  aggregate.mapAsync = async (...args) => {
+    const parent = aggregate;
+    const {result, aggregate: child} = await mapAggregateAsync(...args);
+    parent.call(child.close);
+    return result;
+  };
+
+  aggregate.filter = (...args) => {
+    const parent = aggregate;
+    const {result, aggregate: child} = filterAggregate(...args);
+    parent.call(child.close);
+    return result;
+  };
+
+  aggregate.throws = aggregateThrows;
+
+  aggregate.close = () => {
+    if (errors.length) {
+      const error = Reflect.construct(errorClass, [errors, message]);
+
+      if (translucent) {
+        error[Symbol.for('hsmusic.aggregate.translucent')] = translucent;
+      }
+
+      throw error;
+    }
+  };
+
+  return aggregate;
+}
+
+openAggregate.errorClassSymbol = Symbol('error class');
+
+// Utility function for providing {errorClass} parameter to aggregate functions.
+export function aggregateThrows(errorClass) {
+  return {[openAggregate.errorClassSymbol]: errorClass};
+}
+
+// Helper function for allowing both (fn, aggregateOpts) and (aggregateOpts, fn)
+// in aggregate utilities.
+function _reorganizeAggregateArguments(arg1, arg2) {
+  if (typeof arg1 === 'function') {
+    return {fn: arg1, opts: arg2 ?? {}};
+  } else if (typeof arg2 === 'function') {
+    return {fn: arg2, opts: arg1 ?? {}};
+  } else {
+    throw new Error(`Expected a function`);
+  }
+}
+
+// Performs an ordinary array map with the given function, collating into a
+// results array (with errored inputs filtered out) and an error aggregate.
+//
+// Optionally, override returnOnFail to disable filtering and map errored inputs
+// to a particular output.
+//
+// Note the aggregate property is the result of openAggregate(), still unclosed;
+// use aggregate.close() to throw the error. (This aggregate may be passed to a
+// parent aggregate: `parent.call(aggregate.close)`!)
+export function mapAggregate(array, arg1, arg2) {
+  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
+  return _mapAggregate('sync', null, array, fn, opts);
+}
+
+export function mapAggregateAsync(array, arg1, arg2) {
+  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
+  const {promiseAll = Promise.all.bind(Promise), ...remainingOpts} = opts;
+  return _mapAggregate('async', promiseAll, array, fn, remainingOpts);
+}
+
+// Helper function for mapAggregate which holds code common between sync and
+// async versions.
+export function _mapAggregate(mode, promiseAll, array, fn, aggregateOpts) {
+  const failureSymbol = Symbol();
+
+  const aggregate = openAggregate({
+    returnOnFail: failureSymbol,
+    ...aggregateOpts,
+  });
+
+  if (mode === 'sync') {
+    const result = array
+      .map(aggregate.wrap(fn))
+      .filter((value) => value !== failureSymbol);
+    return {result, aggregate};
+  } else {
+    return promiseAll(array.map(aggregate.wrapAsync(fn)))
+      .then((values) => {
+        const result = values.filter((value) => value !== failureSymbol);
+        return {result, aggregate};
+      });
+  }
+}
+
+// Performs an ordinary array filter with the given function, collating into a
+// results array (with errored inputs filtered out) and an error aggregate.
+//
+// Optionally, override returnOnFail to disable filtering errors and map errored
+// inputs to a particular output.
+//
+// As with mapAggregate, the returned aggregate property is not yet closed.
+export function filterAggregate(array, arg1, arg2) {
+  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
+  return _filterAggregate('sync', null, array, fn, opts);
+}
+
+export async function filterAggregateAsync(array, arg1, arg2) {
+  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
+  const {promiseAll = Promise.all.bind(Promise), ...remainingOpts} = opts;
+  return _filterAggregate('async', promiseAll, array, fn, remainingOpts);
+}
+
+// Helper function for filterAggregate which holds code common between sync and
+// async versions.
+function _filterAggregate(mode, promiseAll, array, fn, aggregateOpts) {
+  const failureSymbol = Symbol();
+
+  const aggregate = openAggregate({
+    returnOnFail: failureSymbol,
+    ...aggregateOpts,
+  });
+
+  function filterFunction(value) {
+    // Filter out results which match the failureSymbol, i.e. errored
+    // inputs.
+    if (value === failureSymbol) return false;
+
+    // Always keep results which match the overridden returnOnFail
+    // value, if provided.
+    if (value === aggregateOpts.returnOnFail) return true;
+
+    // Otherwise, filter according to the returned value of the wrapped
+    // function.
+    return value.output;
+  }
+
+  function mapFunction(value) {
+    // Then turn the results back into their corresponding input, or, if
+    // provided, the overridden returnOnFail value.
+    return value === aggregateOpts.returnOnFail ? value : value.input;
+  }
+
+  if (mode === 'sync') {
+    const result = array
+      .map(aggregate.wrap((input, index, array) => {
+        const output = fn(input, index, array);
+        return {input, output};
+      }))
+      .filter(filterFunction)
+      .map(mapFunction);
+
+    return {result, aggregate};
+  } else {
+    return promiseAll(
+      array.map(aggregate.wrapAsync(async (input, index, array) => {
+        const output = await fn(input, index, array);
+        return {input, output};
+      }))
+    ).then((values) => {
+      const result = values.filter(filterFunction).map(mapFunction);
+
+      return {result, aggregate};
+    });
+  }
+}
+
+// Totally sugar function for opening an aggregate, running the provided
+// function with it, then closing the function and returning the result (if
+// there's no throw).
+export function withAggregate(arg1, arg2) {
+  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
+  return _withAggregate('sync', opts, fn);
+}
+
+export function withAggregateAsync(arg1, arg2) {
+  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
+  return _withAggregate('async', opts, fn);
+}
+
+export function _withAggregate(mode, aggregateOpts, fn) {
+  const aggregate = openAggregate(aggregateOpts);
+
+  if (mode === 'sync') {
+    const result = fn(aggregate);
+    aggregate.close();
+    return result;
+  } else {
+    return fn(aggregate).then((result) => {
+      aggregate.close();
+      return result;
+    });
+  }
+}
+
+export const unhelpfulTraceLines = [
+  /sugar/,
+  /node:/,
+  /<anonymous>/,
+];
+
+export function getUsefulTraceLine(trace, {helpful, unhelpful}) {
+  if (!trace) return '';
+
+  for (const traceLine of trace.split('\n')) {
+    if (!traceLine.trim().startsWith('at')) {
+      continue;
+    }
+
+    if (!empty(unhelpful)) {
+      if (unhelpful.some(regex => regex.test(traceLine))) {
+        continue;
+      }
+    }
+
+    if (!empty(helpful)) {
+      for (const regex of helpful) {
+        const match = traceLine.match(regex);
+
+        if (match) {
+          return match[1] ?? traceLine;
+        }
+      }
+
+      continue;
+    }
+
+    return traceLine;
+  }
+
+  return '';
+}
+
+export function showAggregate(topError, {
+  pathToFileURL = f => f,
+  showTraces = true,
+  showTranslucent = showTraces,
+  print = true,
+} = {}) {
+  const getTranslucency = error =>
+    error[Symbol.for('hsmusic.aggregate.translucent')] ?? false;
+
+  const determineCauseHelper = cause => {
+    if (!cause) {
+      return null;
+    }
+
+    const translucency = getTranslucency(cause);
+
+    if (!translucency) {
+      return cause;
+    }
+
+    if (translucency === 'single') {
+      if (cause.errors?.length === 1) {
+        return determineCauseHelper(cause.errors[0]);
+      } else {
+        return cause;
+      }
+    }
+
+    return determineCauseHelper(cause.cause);
+  };
+
+  const determineCause = error =>
+    (showTranslucent
+      ? error.cause ?? null
+      : determineCauseHelper(error.cause));
+
+  const determineErrorsHelper = error => {
+    const translucency = getTranslucency(error);
+
+    if (!translucency) {
+      return [error];
+    }
+
+    if (translucency === 'single' && error.errors?.length >= 2) {
+      return [error];
+    }
+
+    const errors = [];
+
+    if (error.cause) {
+      errors.push(...determineErrorsHelper(error.cause));
+    }
+
+    if (error.errors) {
+      errors.push(...error.errors.flatMap(determineErrorsHelper));
+    }
+
+    return errors;
+  };
+
+  const determineErrors = error =>
+    (showTranslucent
+      ? error.errors ?? null
+      : error.errors?.flatMap(determineErrorsHelper) ?? null);
+
+  const flattenErrorStructure = (error, level = 0) => {
+    const cause = determineCause(error);
+    const errors = determineErrors(error);
+
+    return {
+      level,
+
+      kind: error.constructor.name,
+      message: error.message,
+
+      trace:
+        (error[Symbol.for(`hsmusic.aggregate.traceFrom`)]
+          ? error[Symbol.for(`hsmusic.aggregate.traceFrom`)].stack
+          : error.stack),
+
+      cause:
+        (cause
+          ? flattenErrorStructure(cause, level + 1)
+          : null),
+
+      errors:
+        (errors
+          ? errors.map(error => flattenErrorStructure(error, level + 1))
+          : null),
+
+      options: {
+        alwaysTrace:
+          error[Symbol.for(`hsmusic.aggregate.alwaysTrace`)],
+
+        helpfulTraceLines:
+          error[Symbol.for(`hsmusic.aggregate.helpfulTraceLines`)],
+
+        unhelpfulTraceLines:
+          error[Symbol.for(`hsmusic.aggregate.unhelpfulTraceLines`)],
+      }
+    };
+  };
+
+  const recursive = ({
+    level,
+    kind,
+    message,
+    trace,
+    cause,
+    errors,
+    options: {
+      alwaysTrace,
+      helpfulTraceLines: ownHelpfulTraceLines,
+      unhelpfulTraceLines: ownUnhelpfulTraceLines,
+    },
+  }, index, apparentSiblings) => {
+    const subApparentSiblings =
+      (cause && errors
+        ? [cause, ...errors]
+     : cause
+        ? [cause]
+     : errors
+        ? errors
+        : []);
+
+    const anythingHasErrorsThisLayer =
+      apparentSiblings.some(({errors}) => !empty(errors));
+
+    const messagePart =
+      message || `(no message)`;
+
+    const kindPart =
+      kind || `unnamed kind`;
+
+    let headerPart =
+      (showTraces
+        ? `[${kindPart}] ${messagePart}`
+     : errors
+        ? `[${messagePart}]`
+     : anythingHasErrorsThisLayer
+        ? ` ${messagePart}`
+        : messagePart);
+
+    if (showTraces || alwaysTrace) {
+      const traceLine =
+        getUsefulTraceLine(trace, {
+          unhelpful:
+            (ownUnhelpfulTraceLines
+              ? unhelpfulTraceLines.concat(ownUnhelpfulTraceLines)
+              : unhelpfulTraceLines),
+
+          helpful:
+            (ownHelpfulTraceLines
+              ? ownHelpfulTraceLines
+              : null),
+        });
+
+      const tracePart =
+        (traceLine
+          ? '- ' +
+            traceLine
+              .trim()
+              .replace(/file:\/\/.*\.js/, (match) => pathToFileURL(match))
+          : '(no stack trace)');
+
+      headerPart += ` ${colors.dim(tracePart)}`;
+    }
+
+    const head1 = level % 2 === 0 ? '\u21aa' : colors.dim('\u21aa');
+    const bar1 = ' ';
+
+    const causePart =
+      (cause
+        ? recursive(cause, 0, subApparentSiblings)
+            .split('\n')
+            .map((line, i) => i === 0 ? ` ${head1} ${line}` : ` ${bar1} ${line}`)
+            .join('\n')
+        : '');
+
+    const head2 = level % 2 === 0 ? '\u257f' : colors.dim('\u257f');
+    const bar2 = level % 2 === 0 ? '\u2502' : colors.dim('\u254e');
+
+    const errorsPart =
+      (errors
+        ? errors
+            .map((error, index) => recursive(error, index + 1, subApparentSiblings))
+            .flatMap(str => str.split('\n'))
+            .map((line, i) => i === 0 ? ` ${head2} ${line}` : ` ${bar2} ${line}`)
+            .join('\n')
+        : '');
+
+    return [headerPart, errorsPart, causePart].filter(Boolean).join('\n');
+  };
+
+  const structure = flattenErrorStructure(topError);
+  const message = recursive(structure, 0, [structure]);
+
+  if (print) {
+    console.error(message);
+  } else {
+    return message;
+  }
+}
+
+export function annotateError(error, ...callbacks) {
+  for (const callback of callbacks) {
+    error = callback(error) ?? error;
+  }
+
+  return error;
+}
+
+export function annotateErrorWithIndex(error, index) {
+  return Object.assign(error, {
+    [Symbol.for('hsmusic.annotateError.indexInSourceArray')]:
+      index,
+
+    message:
+      `(${colors.yellow(`#${index + 1}`)}) ` +
+      error.message,
+  });
+}
+
+export function annotateErrorWithFile(error, file) {
+  return Object.assign(error, {
+    [Symbol.for('hsmusic.annotateError.file')]:
+      file,
+
+    message:
+      error.message +
+      (error.message.includes('\n') ? '\n' : ' ') +
+      `(file: ${colors.bright(colors.blue(file))})`,
+  });
+}
+
+export function asyncAdaptiveDecorateError(fn, callback) {
+  if (typeof callback !== 'function') {
+    throw new Error(`Expected callback to be a function, got ${typeAppearance(callback)}`);
+  }
+
+  const syncDecorated = function (...args) {
+    try {
+      return fn(...args);
+    } catch (caughtError) {
+      throw callback(caughtError, ...args);
+    }
+  };
+
+  const asyncDecorated = async function(...args) {
+    try {
+      return await fn(...args);
+    } catch (caughtError) {
+      throw callback(caughtError, ...args);
+    }
+  };
+
+  syncDecorated.async = asyncDecorated;
+
+  return syncDecorated;
+}
+
+export function decorateError(fn, callback) {
+  return asyncAdaptiveDecorateError(fn, callback);
+}
+
+export function asyncDecorateError(fn, callback) {
+  return asyncAdaptiveDecorateError(fn, callback).async;
+}
+
+export function decorateErrorWithAnnotation(fn, ...annotationCallbacks) {
+  return asyncAdaptiveDecorateError(fn,
+    (caughtError, ...args) =>
+      annotateError(caughtError,
+        ...annotationCallbacks
+          .map(callback => error => callback(error, ...args))));
+}
+
+export function decorateErrorWithIndex(fn) {
+  return decorateErrorWithAnnotation(fn,
+    (caughtError, _value, index) =>
+      annotateErrorWithIndex(caughtError, index));
+}
+
+export function decorateErrorWithCause(fn, cause) {
+  return asyncAdaptiveDecorateError(fn,
+    (caughtError) =>
+      Object.assign(caughtError, {cause}));
+}
+
+export function asyncDecorateErrorWithAnnotation(fn, ...annotationCallbacks) {
+  return decorateErrorWithAnnotation(fn, ...annotationCallbacks).async;
+}
+
+export function asyncDecorateErrorWithIndex(fn) {
+  return decorateErrorWithIndex(fn).async;
+}
+
+export function asyncDecorateErrorWithCause(fn, cause) {
+  return decorateErrorWithCause(fn, cause).async;
+}
+
+export function conditionallySuppressError(conditionFn, callbackFn) {
+  return (...args) => {
+    try {
+      return callbackFn(...args);
+    } catch (error) {
+      if (conditionFn(error, ...args) === true) {
+        return;
+      }
+
+      throw error;
+    }
+  };
+}
diff --git a/src/util/html.js b/src/util/html.js
index ddc0277a..49816990 100644
--- a/src/util/html.js
+++ b/src/util/html.js
@@ -2,8 +2,9 @@
 
 import {inspect} from 'node:util';
 
+import {withAggregate} from '#aggregate';
 import {colors} from '#cli';
-import {empty, typeAppearance, unique, withAggregate} from '#sugar';
+import {empty, typeAppearance, unique} from '#sugar';
 import * as commonValidators from '#validators';
 
 const {
diff --git a/src/util/sugar.js b/src/util/sugar.js
index 2a028f30..70749d8a 100644
--- a/src/util/sugar.js
+++ b/src/util/sugar.js
@@ -406,650 +406,6 @@ export function bindOpts(fn, bind) {
 
 bindOpts.bindIndex = Symbol();
 
-// Utility function for providing useful interfaces to the JS AggregateError
-// class.
-//
-// Generally, this works by returning a set of interfaces which operate on
-// functions: wrap() takes a function and returns a new function which passes
-// its arguments through and appends any resulting error to the internal error
-// list; call() simplifies this process by wrapping the provided function and
-// then calling it immediately. Once the process for which errors should be
-// aggregated is complete, close() constructs and throws an AggregateError
-// object containing all caught errors (or doesn't throw anything if there were
-// no errors).
-export function openAggregate({
-  // Constructor to use, defaulting to the builtin AggregateError class.
-  // Anything passed here should probably extend from that! May be used for
-  // letting callers programatically distinguish between multiple aggregate
-  // errors.
-  //
-  // This should be provided using the aggregateThrows utility function.
-  [openAggregate.errorClassSymbol]: errorClass = AggregateError,
-
-  // Optional human-readable message to describe the aggregate error, if
-  // constructed.
-  message = '',
-
-  // Optional flag to indicate that this layer of the aggregate error isn't
-  // generally useful outside of developer debugging purposes - it will be
-  // skipped by default when using showAggregate, showing contained errors
-  // inline with other children of this aggregate's parent.
-  //
-  // If set to 'single', it'll be hidden only if there's a single error in the
-  // aggregate (so it's not grouping multiple errors together).
-  translucent = false,
-
-  // Value to return when a provided function throws an error. If this is a
-  // function, it will be called with the arguments given to the function.
-  // (This is primarily useful when wrapping a function and then providing it
-  // to another utility, e.g. array.map().)
-  returnOnFail = null,
-} = {}) {
-  const errors = [];
-
-  const aggregate = {};
-
-  aggregate.wrap =
-    (fn) =>
-    (...args) => {
-      try {
-        return fn(...args);
-      } catch (error) {
-        errors.push(error);
-        return typeof returnOnFail === 'function'
-          ? returnOnFail(...args)
-          : returnOnFail;
-      }
-    };
-
-  aggregate.wrapAsync =
-    (fn) =>
-    (...args) => {
-      return fn(...args).then(
-        (value) => value,
-        (error) => {
-          errors.push(error);
-          return typeof returnOnFail === 'function'
-            ? returnOnFail(...args)
-            : returnOnFail;
-        }
-      );
-    };
-
-  aggregate.push = (error) => {
-    errors.push(error);
-  };
-
-  aggregate.call = (fn, ...args) => {
-    return aggregate.wrap(fn)(...args);
-  };
-
-  aggregate.callAsync = (fn, ...args) => {
-    return aggregate.wrapAsync(fn)(...args);
-  };
-
-  aggregate.nest = (...args) => {
-    return aggregate.call(() => withAggregate(...args));
-  };
-
-  aggregate.nestAsync = (...args) => {
-    return aggregate.callAsync(() => withAggregateAsync(...args));
-  };
-
-  aggregate.map = (...args) => {
-    const parent = aggregate;
-    const {result, aggregate: child} = mapAggregate(...args);
-    parent.call(child.close);
-    return result;
-  };
-
-  aggregate.mapAsync = async (...args) => {
-    const parent = aggregate;
-    const {result, aggregate: child} = await mapAggregateAsync(...args);
-    parent.call(child.close);
-    return result;
-  };
-
-  aggregate.filter = (...args) => {
-    const parent = aggregate;
-    const {result, aggregate: child} = filterAggregate(...args);
-    parent.call(child.close);
-    return result;
-  };
-
-  aggregate.throws = aggregateThrows;
-
-  aggregate.close = () => {
-    if (errors.length) {
-      const error = Reflect.construct(errorClass, [errors, message]);
-
-      if (translucent) {
-        error[Symbol.for('hsmusic.aggregate.translucent')] = translucent;
-      }
-
-      throw error;
-    }
-  };
-
-  return aggregate;
-}
-
-openAggregate.errorClassSymbol = Symbol('error class');
-
-// Utility function for providing {errorClass} parameter to aggregate functions.
-export function aggregateThrows(errorClass) {
-  return {[openAggregate.errorClassSymbol]: errorClass};
-}
-
-// Helper function for allowing both (fn, aggregateOpts) and (aggregateOpts, fn)
-// in aggregate utilities.
-function _reorganizeAggregateArguments(arg1, arg2) {
-  if (typeof arg1 === 'function') {
-    return {fn: arg1, opts: arg2 ?? {}};
-  } else if (typeof arg2 === 'function') {
-    return {fn: arg2, opts: arg1 ?? {}};
-  } else {
-    throw new Error(`Expected a function`);
-  }
-}
-
-// Performs an ordinary array map with the given function, collating into a
-// results array (with errored inputs filtered out) and an error aggregate.
-//
-// Optionally, override returnOnFail to disable filtering and map errored inputs
-// to a particular output.
-//
-// Note the aggregate property is the result of openAggregate(), still unclosed;
-// use aggregate.close() to throw the error. (This aggregate may be passed to a
-// parent aggregate: `parent.call(aggregate.close)`!)
-export function mapAggregate(array, arg1, arg2) {
-  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
-  return _mapAggregate('sync', null, array, fn, opts);
-}
-
-export function mapAggregateAsync(array, arg1, arg2) {
-  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
-  const {promiseAll = Promise.all.bind(Promise), ...remainingOpts} = opts;
-  return _mapAggregate('async', promiseAll, array, fn, remainingOpts);
-}
-
-// Helper function for mapAggregate which holds code common between sync and
-// async versions.
-export function _mapAggregate(mode, promiseAll, array, fn, aggregateOpts) {
-  const failureSymbol = Symbol();
-
-  const aggregate = openAggregate({
-    returnOnFail: failureSymbol,
-    ...aggregateOpts,
-  });
-
-  if (mode === 'sync') {
-    const result = array
-      .map(aggregate.wrap(fn))
-      .filter((value) => value !== failureSymbol);
-    return {result, aggregate};
-  } else {
-    return promiseAll(array.map(aggregate.wrapAsync(fn)))
-      .then((values) => {
-        const result = values.filter((value) => value !== failureSymbol);
-        return {result, aggregate};
-      });
-  }
-}
-
-// Performs an ordinary array filter with the given function, collating into a
-// results array (with errored inputs filtered out) and an error aggregate.
-//
-// Optionally, override returnOnFail to disable filtering errors and map errored
-// inputs to a particular output.
-//
-// As with mapAggregate, the returned aggregate property is not yet closed.
-export function filterAggregate(array, arg1, arg2) {
-  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
-  return _filterAggregate('sync', null, array, fn, opts);
-}
-
-export async function filterAggregateAsync(array, arg1, arg2) {
-  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
-  const {promiseAll = Promise.all.bind(Promise), ...remainingOpts} = opts;
-  return _filterAggregate('async', promiseAll, array, fn, remainingOpts);
-}
-
-// Helper function for filterAggregate which holds code common between sync and
-// async versions.
-function _filterAggregate(mode, promiseAll, array, fn, aggregateOpts) {
-  const failureSymbol = Symbol();
-
-  const aggregate = openAggregate({
-    returnOnFail: failureSymbol,
-    ...aggregateOpts,
-  });
-
-  function filterFunction(value) {
-    // Filter out results which match the failureSymbol, i.e. errored
-    // inputs.
-    if (value === failureSymbol) return false;
-
-    // Always keep results which match the overridden returnOnFail
-    // value, if provided.
-    if (value === aggregateOpts.returnOnFail) return true;
-
-    // Otherwise, filter according to the returned value of the wrapped
-    // function.
-    return value.output;
-  }
-
-  function mapFunction(value) {
-    // Then turn the results back into their corresponding input, or, if
-    // provided, the overridden returnOnFail value.
-    return value === aggregateOpts.returnOnFail ? value : value.input;
-  }
-
-  if (mode === 'sync') {
-    const result = array
-      .map(aggregate.wrap((input, index, array) => {
-        const output = fn(input, index, array);
-        return {input, output};
-      }))
-      .filter(filterFunction)
-      .map(mapFunction);
-
-    return {result, aggregate};
-  } else {
-    return promiseAll(
-      array.map(aggregate.wrapAsync(async (input, index, array) => {
-        const output = await fn(input, index, array);
-        return {input, output};
-      }))
-    ).then((values) => {
-      const result = values.filter(filterFunction).map(mapFunction);
-
-      return {result, aggregate};
-    });
-  }
-}
-
-// Totally sugar function for opening an aggregate, running the provided
-// function with it, then closing the function and returning the result (if
-// there's no throw).
-export function withAggregate(arg1, arg2) {
-  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
-  return _withAggregate('sync', opts, fn);
-}
-
-export function withAggregateAsync(arg1, arg2) {
-  const {fn, opts} = _reorganizeAggregateArguments(arg1, arg2);
-  return _withAggregate('async', opts, fn);
-}
-
-export function _withAggregate(mode, aggregateOpts, fn) {
-  const aggregate = openAggregate(aggregateOpts);
-
-  if (mode === 'sync') {
-    const result = fn(aggregate);
-    aggregate.close();
-    return result;
-  } else {
-    return fn(aggregate).then((result) => {
-      aggregate.close();
-      return result;
-    });
-  }
-}
-
-export const unhelpfulTraceLines = [
-  /sugar/,
-  /node:/,
-  /<anonymous>/,
-];
-
-export function getUsefulTraceLine(trace, {helpful, unhelpful}) {
-  if (!trace) return '';
-
-  for (const traceLine of trace.split('\n')) {
-    if (!traceLine.trim().startsWith('at')) {
-      continue;
-    }
-
-    if (!empty(unhelpful)) {
-      if (unhelpful.some(regex => regex.test(traceLine))) {
-        continue;
-      }
-    }
-
-    if (!empty(helpful)) {
-      for (const regex of helpful) {
-        const match = traceLine.match(regex);
-
-        if (match) {
-          return match[1] ?? traceLine;
-        }
-      }
-
-      continue;
-    }
-
-    return traceLine;
-  }
-
-  return '';
-}
-
-export function showAggregate(topError, {
-  pathToFileURL = f => f,
-  showTraces = true,
-  showTranslucent = showTraces,
-  print = true,
-} = {}) {
-  const getTranslucency = error =>
-    error[Symbol.for('hsmusic.aggregate.translucent')] ?? false;
-
-  const determineCauseHelper = cause => {
-    if (!cause) {
-      return null;
-    }
-
-    const translucency = getTranslucency(cause);
-
-    if (!translucency) {
-      return cause;
-    }
-
-    if (translucency === 'single') {
-      if (cause.errors?.length === 1) {
-        return determineCauseHelper(cause.errors[0]);
-      } else {
-        return cause;
-      }
-    }
-
-    return determineCauseHelper(cause.cause);
-  };
-
-  const determineCause = error =>
-    (showTranslucent
-      ? error.cause ?? null
-      : determineCauseHelper(error.cause));
-
-  const determineErrorsHelper = error => {
-    const translucency = getTranslucency(error);
-
-    if (!translucency) {
-      return [error];
-    }
-
-    if (translucency === 'single' && error.errors?.length >= 2) {
-      return [error];
-    }
-
-    const errors = [];
-
-    if (error.cause) {
-      errors.push(...determineErrorsHelper(error.cause));
-    }
-
-    if (error.errors) {
-      errors.push(...error.errors.flatMap(determineErrorsHelper));
-    }
-
-    return errors;
-  };
-
-  const determineErrors = error =>
-    (showTranslucent
-      ? error.errors ?? null
-      : error.errors?.flatMap(determineErrorsHelper) ?? null);
-
-  const flattenErrorStructure = (error, level = 0) => {
-    const cause = determineCause(error);
-    const errors = determineErrors(error);
-
-    return {
-      level,
-
-      kind: error.constructor.name,
-      message: error.message,
-
-      trace:
-        (error[Symbol.for(`hsmusic.aggregate.traceFrom`)]
-          ? error[Symbol.for(`hsmusic.aggregate.traceFrom`)].stack
-          : error.stack),
-
-      cause:
-        (cause
-          ? flattenErrorStructure(cause, level + 1)
-          : null),
-
-      errors:
-        (errors
-          ? errors.map(error => flattenErrorStructure(error, level + 1))
-          : null),
-
-      options: {
-        alwaysTrace:
-          error[Symbol.for(`hsmusic.aggregate.alwaysTrace`)],
-
-        helpfulTraceLines:
-          error[Symbol.for(`hsmusic.aggregate.helpfulTraceLines`)],
-
-        unhelpfulTraceLines:
-          error[Symbol.for(`hsmusic.aggregate.unhelpfulTraceLines`)],
-      }
-    };
-  };
-
-  const recursive = ({
-    level,
-    kind,
-    message,
-    trace,
-    cause,
-    errors,
-    options: {
-      alwaysTrace,
-      helpfulTraceLines: ownHelpfulTraceLines,
-      unhelpfulTraceLines: ownUnhelpfulTraceLines,
-    },
-  }, index, apparentSiblings) => {
-    const subApparentSiblings =
-      (cause && errors
-        ? [cause, ...errors]
-     : cause
-        ? [cause]
-     : errors
-        ? errors
-        : []);
-
-    const anythingHasErrorsThisLayer =
-      apparentSiblings.some(({errors}) => !empty(errors));
-
-    const messagePart =
-      message || `(no message)`;
-
-    const kindPart =
-      kind || `unnamed kind`;
-
-    let headerPart =
-      (showTraces
-        ? `[${kindPart}] ${messagePart}`
-     : errors
-        ? `[${messagePart}]`
-     : anythingHasErrorsThisLayer
-        ? ` ${messagePart}`
-        : messagePart);
-
-    if (showTraces || alwaysTrace) {
-      const traceLine =
-        getUsefulTraceLine(trace, {
-          unhelpful:
-            (ownUnhelpfulTraceLines
-              ? unhelpfulTraceLines.concat(ownUnhelpfulTraceLines)
-              : unhelpfulTraceLines),
-
-          helpful:
-            (ownHelpfulTraceLines
-              ? ownHelpfulTraceLines
-              : null),
-        });
-
-      const tracePart =
-        (traceLine
-          ? '- ' +
-            traceLine
-              .trim()
-              .replace(/file:\/\/.*\.js/, (match) => pathToFileURL(match))
-          : '(no stack trace)');
-
-      headerPart += ` ${colors.dim(tracePart)}`;
-    }
-
-    const head1 = level % 2 === 0 ? '\u21aa' : colors.dim('\u21aa');
-    const bar1 = ' ';
-
-    const causePart =
-      (cause
-        ? recursive(cause, 0, subApparentSiblings)
-            .split('\n')
-            .map((line, i) => i === 0 ? ` ${head1} ${line}` : ` ${bar1} ${line}`)
-            .join('\n')
-        : '');
-
-    const head2 = level % 2 === 0 ? '\u257f' : colors.dim('\u257f');
-    const bar2 = level % 2 === 0 ? '\u2502' : colors.dim('\u254e');
-
-    const errorsPart =
-      (errors
-        ? errors
-            .map((error, index) => recursive(error, index + 1, subApparentSiblings))
-            .flatMap(str => str.split('\n'))
-            .map((line, i) => i === 0 ? ` ${head2} ${line}` : ` ${bar2} ${line}`)
-            .join('\n')
-        : '');
-
-    return [headerPart, errorsPart, causePart].filter(Boolean).join('\n');
-  };
-
-  const structure = flattenErrorStructure(topError);
-  const message = recursive(structure, 0, [structure]);
-
-  if (print) {
-    console.error(message);
-  } else {
-    return message;
-  }
-}
-
-export function annotateError(error, ...callbacks) {
-  for (const callback of callbacks) {
-    error = callback(error) ?? error;
-  }
-
-  return error;
-}
-
-export function annotateErrorWithIndex(error, index) {
-  return Object.assign(error, {
-    [Symbol.for('hsmusic.annotateError.indexInSourceArray')]:
-      index,
-
-    message:
-      `(${colors.yellow(`#${index + 1}`)}) ` +
-      error.message,
-  });
-}
-
-export function annotateErrorWithFile(error, file) {
-  return Object.assign(error, {
-    [Symbol.for('hsmusic.annotateError.file')]:
-      file,
-
-    message:
-      error.message +
-      (error.message.includes('\n') ? '\n' : ' ') +
-      `(file: ${colors.bright(colors.blue(file))})`,
-  });
-}
-
-export function asyncAdaptiveDecorateError(fn, callback) {
-  if (typeof callback !== 'function') {
-    throw new Error(`Expected callback to be a function, got ${typeAppearance(callback)}`);
-  }
-
-  const syncDecorated = function (...args) {
-    try {
-      return fn(...args);
-    } catch (caughtError) {
-      throw callback(caughtError, ...args);
-    }
-  };
-
-  const asyncDecorated = async function(...args) {
-    try {
-      return await fn(...args);
-    } catch (caughtError) {
-      throw callback(caughtError, ...args);
-    }
-  };
-
-  syncDecorated.async = asyncDecorated;
-
-  return syncDecorated;
-}
-
-export function decorateError(fn, callback) {
-  return asyncAdaptiveDecorateError(fn, callback);
-}
-
-export function asyncDecorateError(fn, callback) {
-  return asyncAdaptiveDecorateError(fn, callback).async;
-}
-
-export function decorateErrorWithAnnotation(fn, ...annotationCallbacks) {
-  return asyncAdaptiveDecorateError(fn,
-    (caughtError, ...args) =>
-      annotateError(caughtError,
-        ...annotationCallbacks
-          .map(callback => error => callback(error, ...args))));
-}
-
-export function decorateErrorWithIndex(fn) {
-  return decorateErrorWithAnnotation(fn,
-    (caughtError, _value, index) =>
-      annotateErrorWithIndex(caughtError, index));
-}
-
-export function decorateErrorWithCause(fn, cause) {
-  return asyncAdaptiveDecorateError(fn,
-    (caughtError) =>
-      Object.assign(caughtError, {cause}));
-}
-
-export function asyncDecorateErrorWithAnnotation(fn, ...annotationCallbacks) {
-  return decorateErrorWithAnnotation(fn, ...annotationCallbacks).async;
-}
-
-export function asyncDecorateErrorWithIndex(fn) {
-  return decorateErrorWithIndex(fn).async;
-}
-
-export function asyncDecorateErrorWithCause(fn, cause) {
-  return decorateErrorWithCause(fn, cause).async;
-}
-
-export function conditionallySuppressError(conditionFn, callbackFn) {
-  return (...args) => {
-    try {
-      return callbackFn(...args);
-    } catch (error) {
-      if (conditionFn(error, ...args) === true) {
-        return;
-      }
-
-      throw error;
-    }
-  };
-}
-
 // Delicious function annotations, such as:
 //
 //   (*bound) soWeAreBackInTheMine