fix(schema): compose portable stack-safe base64 constraints

Replace the lookahead-based pattern with separate allOf/not JSON Schema rules for quartet length, alphabet, padding and canonical pad bits. Share the runtime predicates with HAR and padded base64 parsing.

Validate converted advertised leaves with the MCP SDK validator, preserve permissive versus canonical semantics, and exercise every pattern near the 32 MiB encoded-input budget in all JavaScript modes.

src/browser/history/HarCapture.ts

@@ -2,7 +2,7 @@ import { createHash } from "node:crypto";
 import { LosslessNumber } from "lossless-json";
 import { parseCaptureJson } from "./CaptureJson.js";
 import type { JsonValue } from "../../domain/jsonValue.js";
-import { CANONICAL_BASE64_PATTERN } from "../../domain/stringPatterns.js";
+import { isCanonicalBase64 } from "../../domain/stringPatterns.js";
 import {
   WEB_NETWORK_CAPTURE_LIMITS,
   type WebNetworkCapture,
@@ -265,7 +265,7 @@ const integerLexeme = (literal: string): boolean => {
 
 const decodeHarBase64 = (value: string, pointer: string): Buffer => {
   const compact = value.replace(/[\t\n\r ]/g, "");
-  if (compact.length % 4 !== 0 || !CANONICAL_BASE64_PATTERN.test(compact))
+  if (!isCanonicalBase64(compact))
     throw new CaptureFormatError(
       "format",
       "HAR content declares base64 but its text is not valid canonical base64 (ASCII whitespace is allowed).",

src/domain/go/goBinary.ts

@@ -1,7 +1,7 @@
 import { z } from "zod";
 import { digestSchema } from "../digests.js";
 import { localPathStringSchema } from "../localPath.js";
-import { CANONICAL_BASE64_PATTERN } from "../stringPatterns.js";
+import { canonicalBase64Schema } from "../stringPatterns.js";
 
 const sourceRangeSchema = z.strictObject({
   offset: z.number().int().nonnegative(),
@@ -25,9 +25,7 @@ export const goModuleMetadataSchema = z.strictObject({
   dependencies: z.array(goModuleSchema),
   settings: z.array(z.strictObject({ key: z.string(), value: z.string() })),
   unparsed_lines: z.array(z.string()),
-  unparsed_line_bytes_base64: z.array(
-    z.string().regex(CANONICAL_BASE64_PATTERN),
-  ),
+  unparsed_line_bytes_base64: z.array(canonicalBase64Schema),
   complete: z.boolean(),
 });
 
@@ -43,9 +41,9 @@ export const goBuildInfoSchema = z.strictObject({
   header_offset: z.number().int().nonnegative(),
   encoding: z.enum(["inline", "pointer"]),
   go_version: z.string().nullable(),
-  go_version_bytes_base64: z.string().regex(CANONICAL_BASE64_PATTERN),
+  go_version_bytes_base64: canonicalBase64Schema,
   module_text: z.string().nullable(),
-  module_bytes_base64: z.string().regex(CANONICAL_BASE64_PATTERN),
+  module_bytes_base64: canonicalBase64Schema,
   version_location: sourceRangeSchema,
   module_location: sourceRangeSchema,
   module: goModuleMetadataSchema,

src/domain/native/binaryLayout.ts

@@ -2,13 +2,13 @@ import { z } from "zod";
 import { canBorrowParsedJsonSnapshot } from "../immutableJson.js";
 
 import { localPathStringSchema } from "../localPath.js";
-import { CANONICAL_BASE64_PATTERN } from "../stringPatterns.js";
+import { canonicalBase64Schema } from "../stringPatterns.js";
 
 const unsignedHex = z.string().regex(/^0x(?:0|[1-9a-f][0-9a-f]{0,15})$/);
 const index = z.number().int().nonnegative();
 const scalar = z.union([z.string(), z.number().int()]);
 const range = z.strictObject({ offset: unsignedHex, bytes: unsignedHex });
-const canonicalBase64 = z.string().regex(CANONICAL_BASE64_PATTERN);
+const canonicalBase64 = canonicalBase64Schema;
 const name = z.strictObject({
   display: z.string(),
   bytes_base64: canonicalBase64.nullable(),

src/domain/native/recordedCrash.ts

@@ -2,13 +2,13 @@ import { z } from "zod";
 
 import type { BinaryArchitecture } from "../binaryTargetTypes.js";
 import { localPathStringSchema } from "../localPath.js";
-import { CANONICAL_BASE64_PATTERN } from "../stringPatterns.js";
+import { canonicalBase64Schema } from "../stringPatterns.js";
 import { recordedNoteCoverageIssues } from "./recordedCrashNoteCoverage.js";
 
 const hex = z.string().regex(/^0x(?:0|[1-9a-f][0-9a-f]{0,15})$/);
 const index = z.number().int().nonnegative();
 const signed32 = z.number().int().min(-2147483648).max(2147483647);
-const base64 = z.string().regex(CANONICAL_BASE64_PATTERN);
+const base64 = canonicalBase64Schema;
 const range = z.strictObject({ offset: hex, bytes: hex });
 const diagnostics = z.strictObject({
   stdout: z.string(),

src/domain/paddedBase64.ts

@@ -1,9 +1,8 @@
-import { PADDED_BASE64_PATTERN } from "./stringPatterns.js";
+import { isPaddedBase64 } from "./stringPatterns.js";
 
 /** Validate padded syntax without imposing canonical zero pad bits. */
 export const paddedBase64ByteLength = (value: string): number | undefined => {
-  if (value.length % 4 !== 0 || !PADDED_BASE64_PATTERN.test(value))
-    return undefined;
+  if (!isPaddedBase64(value)) return undefined;
   const padding = value.endsWith("==") ? 2 : value.endsWith("=") ? 1 : 0;
   return (value.length / 4) * 3 - padding;
 };

src/domain/stringPatterns.test.ts

@@ -1,10 +1,16 @@
 import { expect, it } from "vitest";
+import { z } from "zod";
 
 import {
-  CANONICAL_BASE64_PATTERN,
+  BASE64_QUARTET_LENGTH_PATTERN,
+  INVALID_BASE64_CHARACTER_PATTERN,
+  INVALID_BASE64_PADDING_PATTERN,
+  INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN,
   IDENTIFIER_PATTERN,
-  PADDED_BASE64_PATTERN,
   STABLE_IDENTIFIER_PATTERN,
+  canonicalBase64Schema,
+  isCanonicalBase64,
+  isPaddedBase64,
 } from "./stringPatterns.js";
 
 it("preserves identifier grammars under Unicode and Unicode-set compilation", () => {
@@ -43,7 +49,7 @@ it("preserves identifier grammars under Unicode and Unicode-set compilation", ()
   }
 });
 
-it("preserves canonical base64 padding and pad-bit validation", () => {
+it("preserves canonical and permissive padded base64 validation", () => {
   const previous =
     /^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/][AQgw]==|[A-Za-z0-9+/]{2}[AEIMQUYcgkosw048]=)?$/;
   const samples = [
@@ -71,28 +77,62 @@ it("preserves canonical base64 padding and pad-bit validation", () => {
   for (const first of alphabet)
     for (const second of alphabet)
       samples.push(`${first}${second}==`, `A${first}${second}=`);
-  for (const flag of ["u", "v"]) {
-    const projected = new RegExp(CANONICAL_BASE64_PATTERN.source, flag);
-    for (const sample of samples)
-      expect(projected.test(sample), JSON.stringify({ flag, sample })).toBe(
-        previous.test(sample),
-      );
+  for (const sample of samples) {
+    expect(isCanonicalBase64(sample), JSON.stringify({ sample })).toBe(
+      previous.test(sample),
+    );
+    expect(isPaddedBase64(sample), JSON.stringify({ sample })).toBe(
+      sample.length % 4 === 0 && /^[A-Za-z0-9+/]*(?:==|=)?$/.test(sample),
+    );
   }
 });
 
-it("validates large canonical base64 under JSON Schema Unicode modes", () => {
-  // Near the 32 MiB capture input budget: a quartet expansion alone still
-  // overflows at this size, especially in Unicode-set client validators.
+it("advertises every portable base64 constraint and keeps large inputs stack-safe", () => {
+  const jsonSchema = z.toJSONSchema(canonicalBase64Schema, {
+    target: "draft-2020-12",
+  });
+  expect(jsonSchema).toMatchObject({
+    allOf: expect.arrayContaining([
+      { pattern: BASE64_QUARTET_LENGTH_PATTERN.source },
+      { not: { pattern: INVALID_BASE64_CHARACTER_PATTERN.source } },
+      { not: { pattern: INVALID_BASE64_PADDING_PATTERN.source } },
+      { not: { pattern: INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source } },
+    ]),
+  });
+
   const body = Buffer.alloc(24 * 1024 * 1024 - 3, 0x81);
   const encoded = body.toString("base64");
   for (const flag of ["", "u", "v"]) {
-    const pattern = new RegExp(CANONICAL_BASE64_PATTERN.source, flag);
-    expect(pattern.test(encoded), flag).toBe(true);
-    expect(pattern.test(`${encoded.slice(0, -1)}!`), flag).toBe(false);
-    expect(pattern.test(`${encoded.slice(0, -3)}R==`), flag).toBe(false);
-    expect(pattern.test(`${encoded}A`), flag).toBe(false);
-    const padded = new RegExp(PADDED_BASE64_PATTERN.source, flag);
-    expect(padded.test(encoded), flag).toBe(true);
-    expect(padded.test(`${encoded.slice(0, -1)}!`), flag).toBe(false);
+    expect(
+      new RegExp(BASE64_QUARTET_LENGTH_PATTERN.source, flag).test(encoded),
+      flag,
+    ).toBe(true);
+    expect(
+      new RegExp(INVALID_BASE64_CHARACTER_PATTERN.source, flag).test(encoded),
+      flag,
+    ).toBe(false);
+    expect(
+      new RegExp(INVALID_BASE64_PADDING_PATTERN.source, flag).test(encoded),
+      flag,
+    ).toBe(false);
+    expect(
+      new RegExp(INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source, flag).test(
+        encoded,
+      ),
+      flag,
+    ).toBe(false);
+    expect(
+      new RegExp(INVALID_BASE64_CHARACTER_PATTERN.source, flag).test(
+        `${encoded.slice(0, -1)}!`,
+      ),
+      flag,
+    ).toBe(true);
+    expect(
+      new RegExp(INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source, flag).test(
+        `${encoded.slice(0, -3)}R==`,
+      ),
+      flag,
+    ).toBe(true);
   }
+  expect(isCanonicalBase64(encoded)).toBe(true);
 });

src/domain/stringPatterns.ts

@@ -1,20 +1,44 @@
+import { z } from "zod";
+
 /** Portable ASCII identifier starting with a letter. */
 export const IDENTIFIER_PATTERN = /^[A-Za-z][A-Za-z0-9._\x2d]*$/u;
 
 /** Stable evidence identifier, also admitting namespace and path separators. */
 export const STABLE_IDENTIFIER_PATTERN = /^[A-Za-z][A-Za-z0-9._:\x2f\x2d]*$/u;
 
-// Repeated alphabet quartets exhaust V8's regexp stack on large bodies,
-// including under JSON Schema's Unicode-set mode. Check alphabet and terminal
-// padding separately, leaving an unconstrained fixed-width loop for length.
-const PADDED_BASE64_PREFIX = String.raw`^(?!.*[^A-Za-z0-9+\x2f=])(?!.*=[^=])(?!.*===)`;
+// These rules are separate JSON Schema constraints. A single RE2-compatible
+// regex for alphabet and quartet validity requires a repeated alphabet group;
+// V8's Unicode-set engine overflows its regexp stack on that group near the
+// provider's 32 MiB encoded-input budget. Wildcard quartets and literal bad
+// token probes stay stack-safe at that size and compose exactly with `allOf`.
+export const BASE64_QUARTET_LENGTH_PATTERN = /^(?:....)*$/;
+export const INVALID_BASE64_CHARACTER_PATTERN = /[^A-Za-z0-9+\x2f=]/;
+export const INVALID_BASE64_PADDING_PATTERN = /(?:=[^=]|===)/;
+export const INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN =
+  /(?:[^AQgw]==$|[BCDFGHJKLNOPRSTVWXZabdefhijlmnpqrtuvxyz1235679+\x2f]=$)/;
 
-/** Padded base64 syntax, allowing nonzero pad bits and the empty encoding. */
-export const PADDED_BASE64_PATTERN = new RegExp(
-  `${PADDED_BASE64_PREFIX}(?:....)*$`,
-);
+export const isPaddedBase64 = (value: string): boolean =>
+  value.length % 4 === 0 &&
+  !INVALID_BASE64_CHARACTER_PATTERN.test(value) &&
+  !INVALID_BASE64_PADDING_PATTERN.test(value);
 
-/** Canonical padded base64, including zero pad bits and the empty encoding. */
-export const CANONICAL_BASE64_PATTERN = new RegExp(
-  `${PADDED_BASE64_PREFIX}(?!.*[^AQgw]==$)(?!.*[^AEIMQUYcgkosw048=]=$)(?:....)*$`,
-);
+export const isCanonicalBase64 = (value: string): boolean =>
+  isPaddedBase64(value) &&
+  !INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.test(value);
+
+const paddedBase64SchemaRules = [
+  { pattern: BASE64_QUARTET_LENGTH_PATTERN.source },
+  { not: { pattern: INVALID_BASE64_CHARACTER_PATTERN.source } },
+  { not: { pattern: INVALID_BASE64_PADDING_PATTERN.source } },
+];
+
+/** Canonical padded base64 with zero pad bits, including the empty encoding. */
+export const canonicalBase64Schema = z
+  .string()
+  .refine(isCanonicalBase64, "Expected canonical padded base64")
+  .meta({
+    allOf: [
+      ...paddedBase64SchemaRules,
+      { not: { pattern: INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source } },
+    ],
+  });

tests/boundary/mcp/advertisedPatternsVMode.test.ts

@@ -1,7 +1,14 @@
 import { Client, InMemoryTransport } from "@modelcontextprotocol/client";
+import { AjvJsonSchemaValidator } from "@modelcontextprotocol/client/validators/ajv";
 import { expect, it, onTestFinished } from "vitest";
 
 import { createServer } from "../../../src/server/createServer.js";
+import {
+  BASE64_QUARTET_LENGTH_PATTERN,
+  INVALID_BASE64_CHARACTER_PATTERN,
+  INVALID_BASE64_PADDING_PATTERN,
+  INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN,
+} from "../../../src/domain/stringPatterns.js";
 import { createTestBinarySession } from "../../fixtures/binarySession.js";
 
 interface AdvertisedPattern {
@@ -10,6 +17,33 @@ interface AdvertisedPattern {
   readonly pattern: string;
 }
 
+const collectCanonicalBase64Leaves = (
+  value: unknown,
+  leaves: Record<string, unknown>[],
+): void => {
+  if (value === null || typeof value !== "object") return;
+  if (Array.isArray(value)) {
+    value.forEach((entry) => collectCanonicalBase64Leaves(entry, leaves));
+    return;
+  }
+  const record = value as Record<string, unknown>;
+  const allOf = record.allOf;
+  if (
+    Array.isArray(allOf) &&
+    allOf.some(
+      (entry) =>
+        entry !== null &&
+        typeof entry === "object" &&
+        "pattern" in entry &&
+        entry.pattern === BASE64_QUARTET_LENGTH_PATTERN.source,
+    )
+  )
+    leaves.push(record);
+  Object.values(record).forEach((entry) =>
+    collectCanonicalBase64Leaves(entry, leaves),
+  );
+};
+
 const collectPatterns = (
   value: unknown,
   where: string,
@@ -48,12 +82,29 @@ it("advertises portable NUL escapes and patterns that compile in all JS modes",
 
   const advertised = (await client.listTools()).tools;
   const patterns: AdvertisedPattern[] = [];
+  const canonicalBase64Leaves: Record<string, unknown>[] = [];
   for (const tool of advertised) {
     collectPatterns(tool.inputSchema, "inputSchema", tool.name, patterns);
+    collectCanonicalBase64Leaves(tool.inputSchema, canonicalBase64Leaves);
     if (tool.outputSchema !== undefined)
       collectPatterns(tool.outputSchema, "outputSchema", tool.name, patterns);
+    if (tool.outputSchema !== undefined)
+      collectCanonicalBase64Leaves(tool.outputSchema, canonicalBase64Leaves);
   }
 
+  for (const pattern of [
+    BASE64_QUARTET_LENGTH_PATTERN,
+    INVALID_BASE64_CHARACTER_PATTERN,
+    INVALID_BASE64_PADDING_PATTERN,
+    INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN,
+  ])
+    expect(
+      patterns.some(({ pattern: advertisedPattern }) =>
+        advertisedPattern.includes(pattern.source),
+      ),
+      pattern.source,
+    ).toBe(true);
+
   // Annex B and `u` mode accept an unescaped `-`, `/` or `[` inside a character
   // class, so REA's own schema validation cannot observe the defect. `v` mode
   // rejects them, and a client that compiles advertised patterns rejects the
@@ -87,4 +138,19 @@ it("advertises portable NUL escapes and patterns that compile in all JS modes",
     ),
   ).toEqual([]);
   expect(patterns.some(({ pattern }) => pattern.includes("\\x00"))).toBe(true);
+
+  expect(canonicalBase64Leaves.length).toBeGreaterThan(0);
+  const sdkValidator = new AjvJsonSchemaValidator();
+  const validators = canonicalBase64Leaves.map((schema) =>
+    sdkValidator.getValidator(schema),
+  );
+  for (const value of ["", "AA==", "AQID", "AB==", "AAA", "AA$=", "AA\n=="])
+    expect(
+      validators.map((validate) => validate(value).valid),
+      JSON.stringify(value),
+    ).toEqual(
+      canonicalBase64Leaves.map(
+        () => value === "" || value === "AA==" || value === "AQID",
+      ),
+    );
 });