Initial JS runtime and Arborix Implementation

ext/js/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "arborix-runtime",
+  "version": "0.1.0",
+  "description": "Arborix portable bundle runtime — JavaScript reference implementation",
+  "type": "module",
+  "main": "src/bundle.js",
+  "bin": {
+    "arborix-run": "src/cli.js"
+  },
+  "scripts": {
+    "test": "node --test test/*.test.js",
+    "inspect": "node src/cli.js inspect",
+    "run": "node src/cli.js run"
+  },
+  "keywords": ["arborix", "tree-calculus", "trie", "runtime"],
+  "license": "MIT"
+}

ext/js/src/bundle.js

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+/**
+ * bundle.js — Parse an Arborix portable bundle binary into a JavaScript object.
+ *
+ * Format (v1):
+ *   Header (32 bytes):
+ *     Magic        8B  "ARBORIX\0"
+ *     Major        2B  u16 BE  (must be 1)
+ *     Minor        2B  u16 BE
+ *     SectionCount 4B  u32 BE
+ *     Flags        8B  u64 BE
+ *     DirOffset    8B  u64 BE
+ *   Section Directory (SectionCount × 60 bytes):
+ *     Type          4B  u32 BE
+ *     Version       2B  u16 BE
+ *     Flags         2B  u16 BE  (bit 0 = critical)
+ *     Compression   2B  u16 BE
+ *     DigestAlgo    2B  u16 BE
+ *     Offset        8B  u64 BE
+ *     Length        8B  u64 BE
+ *     SHA256Digest 32B raw
+ */
+
+import { createHash } from "node:crypto";
+
+// ── Constants ───────────────────────────────────────────────────────────────
+
+const MAGIC = Buffer.from([0x41, 0x52, 0x42, 0x4f, 0x52, 0x49, 0x58, 0x00]); // "ARBORIX\0"
+const HEADER_LENGTH = 32;
+const SECTION_ENTRY_LENGTH = 60;
+const SECTION_MANIFEST = 1;
+const SECTION_NODES = 2;
+const FLAG_CRITICAL = 0x0001;
+const COMPRESSION_NONE = 0;
+const DIGEST_SHA256 = 1;
+const MAJOR_VERSION = 1;
+const MINOR_VERSION = 0;
+
+// ── Helpers ─────────────────────────────────────────────────────────────────
+
+function readU16BE(buf, offset) {
+  return buf.readUint16BE(offset);
+}
+function readU32BE(buf, offset) {
+  return buf.readUint32BE(offset);
+}
+function readU64BE(buf, offset) {
+  return buf.readBigUInt64BE(offset);
+}
+
+function sha256(data) {
+  return createHash("sha256").update(data).digest();
+}
+
+// ── Public API ──────────────────────────────────────────────────────────────
+
+/**
+ * Parse a bundle Buffer into a Bundle object.
+ *
+ * Returns { version, sectionCount, sections } where sections maps
+ * section type numbers to parsed section info (offset, length, data).
+ */
+export function parseBundle(buffer) {
+  if (buffer.length < HEADER_LENGTH) {
+    throw new Error("bundle too short for header");
+  }
+
+  // Check magic
+  if (!buffer.slice(0, 8).equals(MAGIC)) {
+    throw new Error("invalid magic: expected ARBORIX\\0");
+  }
+
+  // Parse header
+  const major = readU16BE(buffer, 8);
+  const minor = readU16BE(buffer, 10);
+  const sectionCount = readU32BE(buffer, 12);
+
+  if (major !== MAJOR_VERSION) {
+    throw new Error(
+      `unsupported bundle major version: ${major} (expected ${MAJOR_VERSION})`
+    );
+  }
+
+  const dirOffset = Number(readU64BE(buffer, 24));
+
+  // Parse section directory
+  const dirStart = dirOffset;
+  const dirEnd = dirStart + sectionCount * SECTION_ENTRY_LENGTH;
+
+  if (buffer.length < dirEnd) {
+    throw new Error("bundle truncated in section directory");
+  }
+
+  const entries = [];
+  for (let i = 0; i < sectionCount; i++) {
+    const off = dirStart + i * SECTION_ENTRY_LENGTH;
+    const entry = {
+      type: readU32BE(buffer, off),
+      version: readU16BE(buffer, off + 4),
+      flags: readU16BE(buffer, off + 6),
+      compression: readU16BE(buffer, off + 8),
+      digestAlgorithm: readU16BE(buffer, off + 10),
+      offset: Number(readU64BE(buffer, off + 12)),
+      length: Number(readU64BE(buffer, off + 20)),
+      digest: buffer.slice(off + 28, off + 28 + 32),
+    };
+    entries.push(entry);
+  }
+
+  // Validate sections
+  for (const entry of entries) {
+    const isCritical = (entry.flags & FLAG_CRITICAL) !== 0;
+    const isKnown =
+      entry.type === SECTION_MANIFEST || entry.type === SECTION_NODES;
+    if (isCritical && !isKnown) {
+      throw new Error(`unknown critical section type: ${entry.type}`);
+    }
+    if (entry.compression !== COMPRESSION_NONE) {
+      throw new Error(
+        `unsupported compression codec in section ${entry.type}`
+      );
+    }
+    if (entry.digestAlgorithm !== DIGEST_SHA256) {
+      throw new Error(
+        `unsupported digest algorithm in section ${entry.type}`
+      );
+    }
+  }
+
+  // Verify section digests and extract data
+  const sections = new Map();
+  for (const entry of entries) {
+    if (entry.offset < 0 || entry.length < 0) {
+      throw new Error(`section ${entry.type} has negative offset/length`);
+    }
+    if (buffer.length < entry.offset + entry.length) {
+      throw new Error(
+        `section ${entry.type} extends beyond bundle end`
+      );
+    }
+
+    const data = buffer.slice(entry.offset, entry.offset + entry.length);
+
+    // Verify digest
+    const computed = sha256(data);
+    if (!computed.equals(entry.digest)) {
+      throw new Error(
+        `section digest mismatch for section type ${entry.type}`
+      );
+    }
+
+    sections.set(entry.type, {
+      ...entry,
+      data,
+    });
+  }
+
+  // Check required sections
+  if (!sections.has(SECTION_MANIFEST)) {
+    throw new Error("missing required section: manifest");
+  }
+  if (!sections.has(SECTION_NODES)) {
+    throw new Error("missing required section: nodes");
+  }
+
+  return {
+    version: `${major}.${minor}`,
+    sectionCount,
+    sections,
+  };
+}
+
+/**
+ * Convenience: parse and return just the manifest JSON.
+ */
+export function parseManifest(buffer) {
+  const bundle = parseBundle(buffer);
+  const manifestEntry = bundle.sections.get(SECTION_MANIFEST);
+  return JSON.parse(manifestEntry.data.toString("utf-8"));
+}
+
+/**
+ * Convenience: parse and return the node section binary.
+ */
+export function parseNodeSection(buffer) {
+  const bundle = parseBundle(buffer);
+  const nodesEntry = bundle.sections.get(SECTION_NODES);
+  return nodesEntry.data;
+}

ext/js/src/cli.js

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+#!/usr/bin/env node
+/**
+ * cli.js — Minimal CLI for inspecting and running Arborix bundles.
+ *
+ * Usage:
+ *   node cli.js inspect <bundle>
+ *   node cli.js run <bundle> [exportName] [input]
+ */
+
+import { readFileSync } from "node:fs";
+import { parseBundle, parseManifest } from "./bundle.js";
+import { parseNodeSection as parseNodeSectionMerkle } from "./merkle.js";
+import {
+  validateManifest,
+  selectExport,
+  printManifestInfo,
+} from "./manifest.js";
+import { parseNodeSection as parseNodeSectionBundle } from "./bundle.js";
+import {
+  verifyNodeHashes,
+  verifyClosure,
+  verifyRootClosure,
+} from "./merkle.js";
+import { isTree, apply, triage, isFork, isStem } from "./tree.js";
+import { decodeResult, formatTree } from "./codecs.js";
+
+// ── Commands ────────────────────────────────────────────────────────────────
+
+function cmdInspect(bundlePath) {
+  const buffer = readFileSync(bundlePath);
+  try {
+    const manifest = parseManifest(buffer);
+    validateManifest(manifest);
+
+    const nodeSectionBytes = parseNodeSectionBundle(buffer);
+    const { nodeMap } = parseNodeSectionMerkle(nodeSectionBytes);
+
+    console.log(`Bundle: ${bundlePath}`);
+    console.log("");
+
+    printManifestInfo(manifest, "  ");
+
+    console.log(`  Nodes: ${nodeMap.size}`);
+
+    // Verify hashes
+    const { verified: hashesOk, mismatches } = verifyNodeHashes(nodeMap);
+    console.log(`  Hash verification: ${hashesOk ? "OK" : "FAIL"}`);
+    for (const m of mismatches) {
+      console.log(`    MISMATCH ${m.type} ${m.hash.substring(0, 16)}... expected ${m.expected.substring(0, 16)}...`);
+    }
+
+    // Verify closure
+    const { complete: closureOk, missing } = verifyClosure(nodeMap);
+    console.log(`  Closure verification: ${closureOk ? "OK" : "FAIL"}`);
+    for (const m of missing) {
+      console.log(`    MISSING ${m.parent.substring(0, 16)}... → ${m.child.substring(0, 16)}...`);
+    }
+
+    // Verify root closure for each export
+    for (const exp of manifest.exports || []) {
+      const { complete, missingRoots } = verifyRootClosure(
+        nodeMap,
+        exp.root
+      );
+      if (!complete) {
+        console.log(
+          `  Root closure for "${exp.name}": FAIL — missing: ${missingRoots
+            .map((r) => r.substring(0, 16) + "...")
+            .join(", ")}`
+        );
+      }
+    }
+
+    console.log("");
+    console.log("Inspection complete.");
+  } catch (e) {
+    console.error(`Error: ${e.message}`);
+    process.exit(1);
+  }
+}
+
+function cmdRun(bundlePath, exportName, inputArg) {
+  const buffer = readFileSync(bundlePath);
+  let result;
+  try {
+    const manifest = parseManifest(buffer);
+    validateManifest(manifest);
+
+    const selectedExport = selectExport(manifest, exportName);
+
+    const nodeSectionBytes = parseNodeSectionBundle(buffer);
+    const { nodeMap } = parseNodeSectionMerkle(nodeSectionBytes);
+
+    // Verify hashes
+    const { verified, mismatches } = verifyNodeHashes(nodeMap);
+    if (!verified) {
+      console.error(
+        `Node hash mismatch:\n  ${mismatches
+          .map((m) => `  ${m.type}: ${m.hash} (expected ${m.expected})`)
+          .join("\n")}`
+      );
+      process.exit(1);
+    }
+
+    // Reconstruct the tree for the selected export
+    const root = buildTreeFromNodeMap(nodeMap, selectedExport.root);
+    if (!isTree(root)) {
+      console.error("Reconstructed root is not a valid tree value");
+      process.exit(1);
+    }
+
+    // Apply input if provided
+    let term = root;
+    if (inputArg !== undefined) {
+      // TODO: parse input (string/number) into a tree
+      // For now, just run the term as-is
+    }
+
+    // Reduce with fuel limit
+    const finalTerm = reduce(term, 1_000_000);
+
+    // Print result as tree calculus form
+    console.log(formatTree(finalTerm));
+  } catch (e) {
+    console.error(`Error: ${e.message}`);
+    process.exit(1);
+  }
+}
+
+// ── Tree reconstruction ─────────────────────────────────────────────────────
+
+/**
+ * Reconstruct a tree from a node map.
+ *
+ * Node map: Map<hexHash, { type, childHash?, leftHash?, rightHash? }>
+ *
+ * Returns the tree representation: [] for Leaf, [child] for Stem, [right, left] for Fork.
+ * Uses memoization to avoid re-processing nodes.
+ */
+export function buildTreeFromNodeMap(nodeMap, hash, memo = new Map()) {
+  if (memo.has(hash)) return memo.get(hash);
+
+  const node = nodeMap.get(hash);
+  if (!node) {
+    throw new Error(`missing node in bundle: ${hash}`);
+  }
+
+  let tree;
+  switch (node.type) {
+    case "leaf":
+      tree = [];
+      break;
+    case "stem":
+      tree = [buildTreeFromNodeMap(nodeMap, node.childHash, memo)];
+      break;
+    case "fork":
+      tree = [
+        buildTreeFromNodeMap(nodeMap, node.rightHash, memo),
+        buildTreeFromNodeMap(nodeMap, node.leftHash, memo),
+      ];
+      break;
+    default:
+      throw new Error(`unknown node type: ${node.type}`);
+  }
+
+  memo.set(hash, tree);
+  return tree;
+}
+
+// ── Reduction ───────────────────────────────────────────────────────────────
+
+/**
+ * Reduce a term to normal form with a fuel limit.
+ * Uses the stack-based approach from the TS evaluator.
+ */
+export function reduce(term, fuel) {
+  const stack = [term];
+  let remaining = fuel;
+
+  while (stack.length >= 2 && remaining-- > 0) {
+    // Pop right (top), then left
+    const b = stack.pop(); // right
+    const a = stack.pop(); // left
+
+    if (stack.length >= 2) {
+      // Push a back for potential further reduction
+      stack.push(a);
+    }
+
+    const result = apply(a, b);
+
+    if (isTree(result)) {
+      // If result is a value, push it. But if it's a Fork/Stem,
+      // we need to push its components for further reduction.
+      if (isFork(result)) {
+        // Push right first (so it's popped second), then left
+        stack.push(result[1]); // left
+        stack.push(result[0]); // right
+      } else if (isStem(result)) {
+        stack.push(result[0]); // child
+      } else {
+        stack.push(result); // Leaf
+      }
+    } else {
+      // Not a tree — push as-is (shouldn't happen after buildTree)
+      stack.push(result);
+    }
+  }
+
+  if (remaining <= 0) {
+    throw new Error("reduction step limit exceeded");
+  }
+
+  if (stack.length === 1) {
+    return stack[0];
+  }
+  return stack[0]; // fallback
+}
+
+// ── Main ────────────────────────────────────────────────────────────────────
+
+const args = process.argv.slice(2);
+const command = args[0];
+
+switch (command) {
+  case "inspect": {
+    if (args.length < 2) {
+      console.error("Usage: node cli.js inspect <bundle>");
+      process.exit(1);
+    }
+    cmdInspect(args[1]);
+    break;
+  }
+  case "run": {
+    if (args.length < 2) {
+      console.error("Usage: node cli.js run <bundle> [exportName] [input]");
+      process.exit(1);
+    }
+    cmdRun(args[1], args[2], args[3]);
+    break;
+  }
+  default:
+    console.log("Arborix JS Runtime");
+    console.log("");
+    console.log("Usage:");
+    console.log("  node cli.js inspect <bundle>");
+    console.log("  node cli.js run <bundle> [exportName] [input]");
+    break;
+}

ext/js/src/codecs.js

@@ -0,0 +1,135 @@
+/**
+ * codecs.js — Minimal codecs for decoding tree results.
+ *
+ * Implements: decodeResult (from Research.hs)
+ *   - Leaf → "t"
+ *   - Numbers: toNumber
+ *   - Strings: toString
+ *   - Lists: toList
+ *   - Fallback: raw tree format
+ */
+
+// ── toNumber ────────────────────────────────────────────────────────────────
+
+/**
+ * Decode a tree as a binary number (big-endian).
+ * Leaf = 0, Fork(Leaf, rest) = 2*n, Fork(Stem Leaf, rest) = 2*n+1.
+ */
+export function toNumber(t) {
+  if (!Array.isArray(t)) return null;
+  if (t.length === 0) return 0; // Leaf = 0
+  if (t.length !== 2) return null; // must be Fork
+
+  const [right, left] = t;
+  // Fork structure: [right, left]
+  // left child determines bit: Leaf = 0, Stem(Leaf) = 1
+  let bit;
+  if (Array.isArray(left) && left.length === 0) {
+    bit = 0; // Leaf
+  } else if (Array.isArray(left) && left.length === 1) {
+    const child = left[0];
+    if (Array.isArray(child) && child.length === 0) {
+      bit = 1; // Stem(Leaf) = 1
+    } else {
+      return null; // Stem of something other than Leaf
+    }
+  } else {
+    return null;
+  }
+
+  const rest = toNumber(right);
+  if (rest === null) return null;
+
+  return bit + 2 * rest;
+}
+
+// ── toString ────────────────────────────────────────────────────────────────
+
+/**
+ * Decode a tree as a list of numbers (characters).
+ * Fork(x, rest) = x : list.
+ */
+export function toList(t) {
+  if (!Array.isArray(t)) return null;
+  if (t.length === 0) return []; // Leaf = empty list
+  if (t.length !== 2) return null; // must be Fork
+
+  const [right, left] = t;
+  const rest = toList(right);
+  if (rest === null) return null;
+
+  return [left, ...rest];
+}
+
+/**
+ * Decode a tree as a string.
+ */
+export function toString(t) {
+  const list = toList(t);
+  if (list === null) return null;
+  try {
+    return list.map((ch) => String.fromCharCode(ch)).join("");
+  } catch {
+    return null;
+  }
+}
+
+// ── decodeResult ────────────────────────────────────────────────────────────
+
+/**
+ * Decode a tree result using multiple strategies:
+ *   1. Leaf → "t"
+ *   2. String (if all chars are printable)
+ *   3. Number
+ *   4. List
+ *   5. Raw tree format
+ */
+export function decodeResult(t) {
+  if (!Array.isArray(t)) {
+    return String(t);
+  }
+
+  // Leaf
+  if (t.length === 0) {
+    return "t";
+  }
+
+  // Try string first (list of char codes)
+  const list = toList(t);
+  if (list !== null && list.length > 0) {
+    const str = list.map((n) => {
+      if (n < 32 || n > 126) return null;
+      return String.fromCharCode(n);
+    }).join("");
+    if (str) return `"${str}"`;
+  }
+
+  // Try number
+  const num = toNumber(t);
+  if (num !== null) {
+    return String(num);
+  }
+
+  // Try list (elements are trees)
+  if (t.length === 2) {
+    const elements = toList(t);
+    if (elements !== null) {
+      const decoded = elements.map((e) => decodeResult(e));
+      return `[${decoded.join(", ")}]`;
+    }
+  }
+
+  // Raw tree format
+  return formatTree(t);
+}
+
+/**
+ * Format a tree as a parenthesized expression.
+ */
+export function formatTree(t) {
+  if (!Array.isArray(t)) return String(t);
+  if (t.length === 0) return "Leaf";
+  if (t.length === 1) return `Stem(${formatTree(t[0])})`;
+  if (t.length === 2) return `Fork(${formatTree(t[1])}, ${formatTree(t[0])})`;
+  return `[${t.map(formatTree).join(", ")}]`;
+}

ext/js/src/manifest.js

@@ -0,0 +1,167 @@
+/**
+ * manifest.js — Minimal manifest parsing and export lookup.
+ *
+ * The manifest is a JSON object with fields:
+ *   schema, bundleType, tree, runtime, closure, roots, exports,
+ *   imports, sections, metadata
+ *
+ * We parse only what we need for runtime entrypoint selection.
+ */
+
+/**
+ * Validate the manifest against the runtime profile requirements.
+ * Throws on violation.
+ */
+export function validateManifest(manifest) {
+  if (manifest.schema !== "arborix.bundle.manifest.v1") {
+    throw new Error(
+      `unsupported manifest schema: ${manifest.schema}`
+    );
+  }
+  if (manifest.bundleType !== "tree-calculus-executable-object") {
+    throw new Error(
+      `unsupported bundle type: ${manifest.bundleType}`
+    );
+  }
+
+  const tree = manifest.tree;
+  if (tree.calculus !== "tree-calculus.v1") {
+    throw new Error(`unsupported calculus: ${tree.calculus}`);
+  }
+  if (tree.nodeHash.algorithm !== "sha256") {
+    throw new Error(
+      `unsupported node hash algorithm: ${tree.nodeHash.algorithm}`
+    );
+  }
+  if (tree.nodeHash.domain !== "tricu.merkle.node.v1" && tree.nodeHash.domain !== "arborix.merkle.node.v1") {
+    throw new Error(
+      `unsupported node hash domain: ${tree.nodeHash.domain}`
+    );
+  }
+  if (tree.nodePayload !== "arborix.merkle.payload.v1") {
+    throw new Error(`unsupported node payload: ${tree.nodePayload}`);
+  }
+
+  const runtime = manifest.runtime;
+  if (runtime.semantics !== "tree-calculus.v1") {
+    throw new Error(`unsupported runtime semantics: ${runtime.semantics}`);
+  }
+  if (runtime.abi !== "arborix.abi.tree.v1") {
+    throw new Error(`unsupported runtime ABI: ${runtime.abi}`);
+  }
+  if (runtime.capabilities && runtime.capabilities.length > 0) {
+    throw new Error(
+      `host/runtime capabilities not supported: ${runtime.capabilities.join(", ")}`
+    );
+  }
+
+  if (manifest.closure !== "complete") {
+    throw new Error("bundle v1 requires closure = complete");
+  }
+  if (manifest.imports && manifest.imports.length > 0) {
+    throw new Error("bundle v1 requires an empty imports list");
+  }
+  if (!manifest.roots || manifest.roots.length === 0) {
+    throw new Error("manifest has no roots");
+  }
+  if (!manifest.exports || manifest.exports.length === 0) {
+    throw new Error("manifest has no exports");
+  }
+
+  for (const exp of manifest.exports) {
+    if (!exp.name) {
+      throw new Error("manifest export has empty name");
+    }
+    if (!exp.root) {
+      throw new Error("manifest export has empty root");
+    }
+  }
+}
+
+/**
+ * Select an export hash given a requested name.
+ *
+ * Selection strategy:
+ *   1. Explicit export name
+ *   2. Export named "main"
+ *   3. Single export (auto-select)
+ *   4. Error if multiple exports and no "main"
+ */
+export function selectExport(manifest, requestedName) {
+  const exports = manifest.exports || [];
+
+  // Strategy 1: explicit name
+  if (requestedName) {
+    const found = exports.find((e) => e.name === requestedName);
+    if (found) {
+      return found;
+    }
+    throw new Error(
+      `requested export "${requestedName}" not found. Available: ${exports.map((e) => e.name).join(", ")}`
+    );
+  }
+
+  // Strategy 2: prefer "main"
+  const mainExport = exports.find((e) => e.name === "main");
+  if (mainExport) {
+    return mainExport;
+  }
+
+  // Strategy 3: single export
+  if (exports.length === 1) {
+    return exports[0];
+  }
+
+  // Strategy 4: multiple exports, require explicit
+  throw new Error(
+    `multiple exports available but none named "main": ${exports.map((e) => e.name).join(", ")}. Specify an export name.`
+  );
+}
+
+/**
+ * Get all root hashes from the manifest.
+ */
+export function getRootHashes(manifest) {
+  return (manifest.roots || []).map((r) => r.hash);
+}
+
+/**
+ * Get all export names.
+ */
+export function getExportNames(manifest) {
+  return (manifest.exports || []).map((e) => e.name);
+}
+
+/**
+ * Print manifest summary info.
+ */
+export function printManifestInfo(manifest, indent = "") {
+  const tree = manifest.tree;
+  const runtime = manifest.runtime;
+
+  console.log(`${indent}Schema:          ${manifest.schema}`);
+  console.log(`${indent}Bundle type:     ${manifest.bundleType}`);
+  console.log(`${indent}Closure:         ${manifest.closure}`);
+  console.log(`${indent}Tree calculus:   ${tree.calculus}`);
+  console.log(`${indent}Hash algo:       ${tree.nodeHash.algorithm}`);
+  console.log(`${indent}Hash domain:     ${tree.nodeHash.domain}`);
+  console.log(`${indent}Runtime:         ${runtime.semantics}`);
+  console.log(`${indent}ABI:             ${runtime.abi}`);
+  console.log(`${indent}Evaluation:      ${runtime.evaluation || "N/A"}`);
+  console.log("");
+  console.log(`${indent}Roots (${getRootHashes(manifest).length}):`);
+  for (const root of getRootHashes(manifest)) {
+    console.log(`${indent}  ${root.substring(0, 16)}...`);
+  }
+  console.log("");
+  console.log(`${indent}Exports (${getExportNames(manifest).length}):`);
+  for (const name of getExportNames(manifest)) {
+    console.log(`${indent}  ${name}`);
+  }
+
+  const meta = manifest.metadata;
+  if (meta && meta.createdBy) {
+    console.log("");
+    console.log(`${indent}Created by:      ${meta.createdBy}`);
+  }
+}

ext/js/src/merkle.js

@@ -0,0 +1,276 @@
+/**
+ * merkle.js — Node payload decoding and hash verification.
+ *
+ * Node payload format:
+ *   Leaf: 0x00
+ *   Stem: 0x01 || child_hash (32 bytes raw)
+ *   Fork: 0x02 || left_hash (32 bytes raw) || right_hash (32 bytes raw)
+ *
+ * Hash computation:
+ *   hash = SHA256( "tricu.merkle.node.v1" || 0x00 || node_payload )
+ */
+
+import { createHash } from "node:crypto";
+
+// ── Constants ───────────────────────────────────────────────────────────────
+
+const DOMAIN_TAG = "tricu.merkle.node.v1";
+const HASH_LENGTH = 32; // raw hash bytes
+const HEX_LENGTH = 64;  // hex-encoded hash length
+
+// ── Helpers ─────────────────────────────────────────────────────────────────
+
+function rawToHex(buf) {
+  if (buf.length !== HASH_LENGTH) {
+    throw new Error(`raw hash must be ${HASH_LENGTH} bytes, got ${buf.length}`);
+  }
+  return buf.toString("hex");
+}
+
+function hexToRaw(hex) {
+  const buf = Buffer.from(hex, "hex");
+  if (buf.length !== HASH_LENGTH) {
+    throw new Error(`hex hash must decode to ${HASH_LENGTH} bytes`);
+  }
+  return buf;
+}
+
+function sha256(data) {
+  return createHash("sha256").update(data).digest();
+}
+
+function nodeHash(prefix, payload) {
+  return sha256(Buffer.concat([Buffer.from(prefix), Buffer.from([0x00]), payload]));
+}
+
+// ── Node payload types ──────────────────────────────────────────────────────
+
+/**
+ * Deserialize a node payload into { type, childHash, leftHash, rightHash }.
+ *
+ * type: "leaf" | "stem" | "fork"
+ * childHash: hex string (for stem)
+ * leftHash: hex string (for fork)
+ * rightHash: hex string (for fork)
+ */
+export function deserializePayload(payload) {
+  if (payload.length === 0) {
+    throw new Error("empty payload");
+  }
+
+  const type = payload.readUInt8(0);
+
+  switch (type) {
+    case 0x00:
+      if (payload.length !== 1) {
+        throw new Error(
+          `invalid leaf payload: expected 1 byte, got ${payload.length}`
+        );
+      }
+      return { type: "leaf" };
+
+    case 0x01:
+      if (payload.length !== 1 + HASH_LENGTH) {
+        throw new Error(
+          `invalid stem payload: expected ${1 + HASH_LENGTH} bytes, got ${payload.length}`
+        );
+      }
+      return {
+        type: "stem",
+        childHash: rawToHex(payload.slice(1, 1 + HASH_LENGTH)),
+      };
+
+    case 0x02:
+      if (payload.length !== 1 + 2 * HASH_LENGTH) {
+        throw new Error(
+          `invalid fork payload: expected ${1 + 2 * HASH_LENGTH} bytes, got ${payload.length}`
+        );
+      }
+      return {
+        type: "fork",
+        leftHash: rawToHex(payload.slice(1, 1 + HASH_LENGTH)),
+        rightHash: rawToHex(payload.slice(1 + HASH_LENGTH, 1 + 2 * HASH_LENGTH)),
+      };
+
+    default:
+      throw new Error(
+        `invalid merkle node payload: unknown type 0x${type.toString(16)}`
+      );
+  }
+}
+
+/**
+ * Compute the canonical payload bytes for a given tree node structure.
+ */
+export function serializeNode(node) {
+  switch (node.type) {
+    case "leaf":
+      return Buffer.from([0x00]);
+    case "stem":
+      return Buffer.concat([Buffer.from([0x01]), hexToRaw(node.childHash)]);
+    case "fork":
+      return Buffer.concat([
+        Buffer.from([0x02]),
+        hexToRaw(node.leftHash),
+        hexToRaw(node.rightHash),
+      ]);
+  }
+}
+
+/**
+ * Compute the Merkle hash of a node from its type and parameters.
+ */
+export function computeNodeHash(node) {
+  const payload = serializeNode(node);
+  const hash = nodeHash(DOMAIN_TAG, payload);
+  return hash.toString("hex");
+}
+
+// ── Node section parsing ────────────────────────────────────────────────────
+
+/**
+ * Parse the node section binary into a Map<hexHash, { type, payload, node }>.
+ *
+ * Node section format:
+ *   nodeCount (8B u64 BE)
+ *   entries[]:
+ *     hash (32B raw)
+ *     payloadLen (4B u32 BE)
+ *     payload (payloadLen bytes)
+ */
+export function parseNodeSection(data) {
+  if (data.length < 8) {
+    throw new Error("node section too short for count");
+  }
+
+  const nodeCount = Number(data.readBigUInt64BE(0));
+  let offset = 8;
+
+  const nodeMap = new Map();
+  const errors = [];
+
+  for (let i = 0; i < nodeCount; i++) {
+    // Read hash
+    if (offset + HASH_LENGTH > data.length) {
+      errors.push(`node ${i}: not enough bytes for hash`);
+      break;
+    }
+    const hash = rawToHex(data.slice(offset, offset + HASH_LENGTH));
+    offset += HASH_LENGTH;
+
+    // Read payload length
+    if (offset + 4 > data.length) {
+      errors.push(`node ${i} (${hash}): not enough bytes for payload length`);
+      break;
+    }
+    const payloadLen = data.readUint32BE(offset);
+    offset += 4;
+
+    // Read payload
+    if (offset + payloadLen > data.length) {
+      errors.push(`node ${i} (${hash}): payload extends beyond section end`);
+      break;
+    }
+    const payload = data.slice(offset, offset + payloadLen);
+    offset += payloadLen;
+
+    // Deserialize payload
+    let node;
+    try {
+      node = deserializePayload(payload);
+    } catch (e) {
+      errors.push(`node ${i} (${hash}): ${e.message}`);
+      continue;
+    }
+
+    nodeMap.set(hash, {
+      hash,
+      payload,
+      ...node,
+    });
+  }
+
+  if (errors.length > 0) {
+    throw new Error(
+      `node section parse errors:\n  ${errors.join("\n  ")}`
+    );
+  }
+
+  return { nodeMap, count: nodeCount };
+}
+
+// ── Verification ────────────────────────────────────────────────────────────
+
+/**
+ * Verify all node hashes match their payloads.
+ * Returns { verified, mismatches }
+ */
+export function verifyNodeHashes(nodeMap) {
+  const mismatches = [];
+
+  for (const [hash, node] of nodeMap) {
+    const expected = computeNodeHash(node);
+    if (hash !== expected) {
+      mismatches.push({
+        hash,
+        expected,
+        type: node.type,
+      });
+    }
+  }
+
+  return { verified: mismatches.length === 0, mismatches };
+}
+
+/**
+ * Verify that all child references exist in the node map (closure).
+ * Returns { complete, missing } where missing is an array of { parent, child }.
+ */
+export function verifyClosure(nodeMap) {
+  const missing = [];
+
+  for (const [hash, node] of nodeMap) {
+    if (node.type === "stem") {
+      if (!nodeMap.has(node.childHash)) {
+        missing.push({ parent: hash, child: node.childHash });
+      }
+    } else if (node.type === "fork") {
+      if (!nodeMap.has(node.leftHash)) {
+        missing.push({ parent: hash, child: node.leftHash });
+      }
+      if (!nodeMap.has(node.rightHash)) {
+        missing.push({ parent: hash, child: node.rightHash });
+      }
+    }
+  }
+
+  return { complete: missing.length === 0, missing };
+}
+
+/**
+ * Verify closure for a specific root hash (transitive reachability).
+ * Returns { complete, missingRoots }.
+ */
+export function verifyRootClosure(nodeMap, rootHash) {
+  const visited = new Set();
+  const missingRoots = [];
+
+  function visit(hash) {
+    if (visited.has(hash)) return;
+    if (!nodeMap.has(hash)) {
+      missingRoots.push(hash);
+      return;
+    }
+    visited.add(hash);
+    const node = nodeMap.get(hash);
+    if (node.type === "stem") {
+      visit(node.childHash);
+    } else if (node.type === "fork") {
+      visit(node.leftHash);
+      visit(node.rightHash);
+    }
+  }
+
+  visit(rootHash);
+  return { complete: missingRoots.length === 0, missingRoots };
+}

ext/js/src/tree.js

@@ -0,0 +1,125 @@
+/**
+ * tree.js — Runtime tree representation.
+ *
+ * The JS tree uses a simple array representation matching the
+ * TypeScript reference evaluator:
+ *
+ *   Leaf  = []
+ *   Stem  = [child]          (array length === 1)
+ *   Fork  = [right, left]    (array length === 2)
+ *
+ * This is a "flattened stack" representation: when reduced, terms
+ * become arrays and the evaluator pops three elements at a time.
+ */
+
+/**
+ * Check if a value is a Leaf (empty array).
+ */
+export function isLeaf(t) {
+  return Array.isArray(t) && t.length === 0;
+}
+
+/**
+ * Check if a value is a Stem (single element array).
+ */
+export function isStem(t) {
+  return Array.isArray(t) && t.length === 1;
+}
+
+/**
+ * Check if a value is a Fork (two element array).
+ */
+export function isFork(t) {
+  return Array.isArray(t) && t.length === 2;
+}
+
+/**
+ * Check if a value is a valid tree calculus value (Leaf, Stem, or Fork).
+ */
+export function isTree(t) {
+  return isLeaf(t) || isStem(t) || isFork(t);
+}
+
+/**
+ * Triage a tree: classify it as Leaf/Stem/Fork.
+ * The tree must be in normal form (no reducible redexes).
+ *
+ * Returns { kind: "leaf"|"stem"|"fork", ...rest }
+ */
+export function triage(t) {
+  if (!Array.isArray(t)) {
+    throw new Error("not a tree (not an array)");
+  }
+  if (t.length === 0) return { kind: "leaf" };
+  if (t.length === 1) return { kind: "stem", child: t[0] };
+  if (t.length === 2) return { kind: "fork", right: t[0], left: t[1] };
+  throw new Error(`not a value/binary tree: length ${t.length}`);
+}
+
+/**
+ * Apply the Tree Calculus apply rules.
+ *
+ * apply(a, b) computes the application of term a to term b.
+ *
+ * Rules:
+ *   apply(Fork(Leaf, a), _)       = a
+ *   apply(Fork(Stem(a), b), c)    = apply(apply(a, c), apply(b, c))
+ *   apply(Fork(Fork, _, _), Leaf) = left of inner Fork
+ *   apply(Fork(Fork, _, _), Stem) = right of inner Fork
+ *   apply(Fork(Fork, _, _), Fork) = apply(apply(c, u), v)  where c=Fork(u,v)
+ *   apply(Leaf, b)               = Stem(b)
+ *   apply(Stem(a), b)            = Fork(a, b)
+ *
+ * For Fork, the inner structure is [right, left], so:
+ *   a = right, b = left
+ */
+export function apply(a, b) {
+  // apply(Fork(Leaf, a), _) = a
+  // Fork = [right, left] = [Leaf, a] → left child is Leaf
+  if (isFork(a) && isLeaf(a[1])) {
+    return a[0]; // return right child
+  }
+
+  // apply(Fork(Stem(a), b), c)
+  if (isFork(a) && isStem(a[1])) {
+    const stemChild = a[1][0]; // left child of fork
+    const right = a[0]; // right child of fork
+    const innerA = stemChild;
+    const innerB = right;
+    const appliedA = apply(innerA, b);
+    const appliedB = apply(innerB, b);
+    return apply(appliedA, appliedB);
+  }
+
+  // apply(Fork(Fork, _, _), Leaf)
+  if (isFork(a) && isFork(a[1]) && isLeaf(b)) {
+    return a[1][0]; // right child of inner fork (which is left child)
+  }
+
+  // apply(Fork(Fork, _, _), Stem)
+  if (isFork(a) && isFork(a[1]) && isStem(b)) {
+    return a[1][1]; // left child of inner fork
+  }
+
+  // apply(Fork(Fork, _, _), Fork)
+  if (isFork(a) && isFork(a[1]) && isFork(b)) {
+    // b = Fork(u, v) = [v, u]
+    const u = b[0];
+    const v = b[1];
+    // apply(apply(c, u), v) where c = inner fork
+    const applied = apply(apply(a[1], u), v);
+    return applied;
+  }
+
+  // apply(Leaf, b) = Stem(b)
+  if (isLeaf(a)) {
+    return [b];
+  }
+
+  // apply(Stem(a), b) = Fork(a, b)
+  if (isStem(a)) {
+    return [b, a[0]]; // [right, left]
+  }
+
+  throw new Error("apply: undefined reduction for terms");
+}

ext/js/test/bundle.test.js

@@ -0,0 +1,67 @@
+import { readFileSync } from "node:fs";
+import { strictEqual, ok, throws } from "node:assert";
+import { describe, it } from "node:test";
+import {
+  parseBundle,
+  parseManifest,
+} from "../src/bundle.js";
+import {
+  parseNodeSection as bundleParseNodeSection,
+} from "../src/bundle.js";
+import {
+  verifyNodeHashes,
+  parseNodeSection as parseNodes,
+} from "../src/merkle.js";
+
+const fixtureDir = "test/fixtures";
+
+describe("bundle parsing", () => {
+  it("valid bundle parses header and sections", () => {
+    const bundle = parseBundle(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    strictEqual(bundle.version, "1.0");
+    strictEqual(bundle.sectionCount, 2);
+    ok(bundle.sections.has(1)); // manifest
+    ok(bundle.sections.has(2)); // nodes
+  });
+
+  it("parseManifest returns valid JSON", () => {
+    const manifest = parseManifest(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    strictEqual(manifest.schema, "arborix.bundle.manifest.v1");
+    strictEqual(manifest.bundleType, "tree-calculus-executable-object");
+    strictEqual(manifest.closure, "complete");
+    strictEqual(manifest.tree.calculus, "tree-calculus.v1");
+    strictEqual(manifest.tree.nodeHash.algorithm, "sha256");
+    strictEqual(manifest.runtime.semantics, "tree-calculus.v1");
+    strictEqual(manifest.runtime.abi, "arborix.abi.tree.v1");
+  });
+});
+
+describe("hash verification", () => {
+  it("valid bundle nodes verify", () => {
+    const data = bundleParseNodeSection(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    const { verified } = verifyNodeHashes(nodeMap);
+    ok(verified, "all node hashes should verify");
+  });
+});
+
+describe("errors", () => {
+  it("bad magic fails", () => {
+    const buf = Buffer.alloc(32, 0);
+    buf.write("WRONGMAG", 0, 8);
+    throws(() => parseBundle(buf), /invalid magic/);
+  });
+
+  it("unsupported version fails", () => {
+    const buf = Buffer.alloc(32, 0);
+    buf.write("ARBORIX\0", 0, 8);
+    buf.writeUInt16BE(2, 8); // major version 2
+    throws(() => parseBundle(buf), /unsupported bundle major version/);
+  });
+});

ext/js/test/merkle.test.js

@@ -0,0 +1,148 @@
+import { readFileSync } from "node:fs";
+import { strictEqual, ok } from "node:assert";
+import { describe, it } from "node:test";
+import { parseNodeSection } from "../src/bundle.js";
+import {
+  verifyNodeHashes,
+  verifyClosure,
+  verifyRootClosure,
+  deserializePayload,
+  computeNodeHash,
+} from "../src/merkle.js";
+
+describe("merkle — deserializePayload", () => {
+  it("Leaf (0x00)", () => {
+    const result = deserializePayload(Buffer.from([0x00]));
+    strictEqual(result.type, "leaf");
+  });
+
+  it("Stem (0x01 + 32 bytes)", () => {
+    const childHash = Buffer.alloc(32, 0xab);
+    const payload = Buffer.concat([Buffer.from([0x01]), childHash]);
+    const result = deserializePayload(payload);
+    strictEqual(result.type, "stem");
+    strictEqual(result.childHash, "ab".repeat(32));
+  });
+
+  it("Fork (0x02 + 64 bytes)", () => {
+    const left = Buffer.alloc(32, 0x01);
+    const right = Buffer.alloc(32, 0x02);
+    const payload = Buffer.concat([Buffer.from([0x02]), left, right]);
+    const result = deserializePayload(payload);
+    strictEqual(result.type, "fork");
+    strictEqual(result.leftHash, "01".repeat(32));
+    strictEqual(result.rightHash, "02".repeat(32));
+  });
+
+  it("Leaf with extra bytes fails", () => {
+    throws(() => deserializePayload(Buffer.from([0x00, 0x00])), /invalid leaf/);
+  });
+
+  it("Unknown type fails", () => {
+    throws(() => deserializePayload(Buffer.from([0xff])), /unknown type/);
+  });
+});
+
+describe("merkle — computeNodeHash", () => {
+  it("Leaf hash is correct length", () => {
+    const leaf = { type: "leaf" };
+    const hash = computeNodeHash(leaf);
+    strictEqual(hash.length, 64);
+  });
+});
+
+describe("merkle — node section parsing", () => {
+  const fixtureDir = "test/fixtures";
+
+  it("parses id.tri.bundle with correct node count", () => {
+    const data = parseNodeSection(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    strictEqual(nodeMap.size, 4);
+  });
+
+  it("parses true.tri.bundle with correct node count", () => {
+    const data = parseNodeSection(
+      readFileSync(`${fixtureDir}/true.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    strictEqual(nodeMap.size, 2);
+  });
+});
+
+describe("merkle — hash verification", () => {
+  const fixtureDir = "test/fixtures";
+
+  it("id.tri.bundle nodes all verify", () => {
+    const data = parseNodeSection(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    const { verified, mismatches } = verifyNodeHashes(nodeMap);
+    ok(verified, "id.tri.bundle node hashes should verify");
+    strictEqual(mismatches.length, 0);
+  });
+
+  it("corrupted node payload fails hash verification", () => {
+    const data = parseNodeSection(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    // Find a stem node to corrupt
+    let stemKey = null;
+    for (const [key, node] of nodeMap) {
+      if (node.type === "stem") { stemKey = key; break; }
+    }
+    ok(stemKey, "should find a stem node to corrupt");
+    const stem = nodeMap.get(stemKey);
+    // Corrupt the child hash so serializeNode produces a different payload
+    const corrupted = {
+      ...stem,
+      childHash: "00".repeat(32),
+      payload: Buffer.concat([Buffer.from([0x01]), Buffer.alloc(32, 0x00)]),
+    };
+    nodeMap.set(stemKey, corrupted);
+    const { verified, mismatches } = verifyNodeHashes(nodeMap);
+    ok(!verified, "corrupted stem should fail hash verification");
+    ok(mismatches.length > 0, "should have mismatches");
+  });
+});
+
+describe("merkle — closure verification", () => {
+  const fixtureDir = "test/fixtures";
+
+  it("id.tri.bundle has complete closure", () => {
+    const data = parseNodeSection(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    const { complete, missing } = verifyClosure(nodeMap);
+    ok(complete, "id.tri.bundle should have complete closure");
+    strictEqual(missing.length, 0);
+  });
+
+  it("verifyRootClosure checks transitive reachability", () => {
+    const data = parseNodeSection(
+      readFileSync(`${fixtureDir}/id.tri.bundle`)
+    );
+    const { nodeMap } = parseNodes(data);
+    const rootHash = "039cc9aacf5be78ec1975713e6ad154a36988e3f3df18589b0d0c801d0825d78";
+    const { complete, missingRoots } = verifyRootClosure(nodeMap, rootHash);
+    ok(complete, "root should be reachable");
+    strictEqual(missingRoots.length, 0);
+  });
+});
+
+// Helper import
+import { parseNodeSection as parseNodes } from "../src/merkle.js";
+
+// Helper for throws
+function throws(fn, expected) {
+  try {
+    fn();
+    return false;
+  } catch (e) {
+    return expected.test(e.message);
+  }
+}

ext/js/test/reduce.test.js

@@ -0,0 +1,80 @@
+import { strictEqual, ok } from "node:assert";
+import { describe, it } from "node:test";
+import { apply, isLeaf, isStem, isFork } from "../src/tree.js";
+import { reduce } from "../src/cli.js";
+
+describe("tree — basic types", () => {
+  it("Leaf is empty array", () => {
+    ok(isLeaf([]));
+    ok(!isStem([]));
+    ok(!isFork([]));
+  });
+
+  it("Stem is single-element array", () => {
+    ok(isStem([[]]));
+    ok(!isLeaf([[]]));
+  });
+
+  it("Fork is two-element array", () => {
+    ok(isFork([[], []]));
+    ok(!isLeaf([[], []]));
+  });
+});
+
+describe("tree — apply rules", () => {
+  // Leaf = [], Stem = [child], Fork = [right, left]
+
+  it("apply(Leaf, b) = Stem(b)", () => {
+    const b = []; // Leaf
+    const result = apply([], b);
+    ok(isStem(result), "Stem(b) should be a Stem");
+    strictEqual(result[0], b);
+  });
+
+  it("apply(Stem(a), b) = Fork(a, b)", () => {
+    const a = []; // Leaf
+    const b = []; // Leaf
+    const result = apply([a], b);
+    ok(isFork(result), "Fork(a, b) should be a Fork");
+    // Fork = [right, left] = [b, a]
+    strictEqual(result[0], b);
+    strictEqual(result[1], a);
+  });
+
+  it("apply(Fork(Leaf, a), _) = a", () => {
+    // Fork(Leaf, a) = [a, Leaf]
+    const a = []; // Leaf
+    const result = apply([a, []], []);
+    strictEqual(result, a);
+    ok(isLeaf(result));
+  });
+});
+
+describe("tree — reduction", () => {
+  it("reduces Leaf to Leaf", () => {
+    const result = reduce([], 100);
+    ok(isLeaf(result));
+  });
+
+  it("reduces Stem Leaf to Stem Leaf", () => {
+    const result = reduce([[]], 100);
+    ok(isStem(result));
+    ok(isLeaf(result[0]));
+  });
+
+  it("reduces Fork Leaf Leaf to Fork Leaf Leaf", () => {
+    const result = reduce([[], []], 100);
+    ok(isFork(result));
+    ok(isLeaf(result[0]));
+    ok(isLeaf(result[1]));
+  });
+
+  it("S combinator applied to Leaf reduces", () => {
+    // S = t (t (t t)) t = Fork (Fork (Fork Leaf Leaf) Leaf) Leaf
+    // In array form: [[[], []], [], []]
+    const s = [[], [[[], []], []]];
+    const leaf = [];
+    const result = reduce([s, leaf], 100);
+    ok(Array.isArray(result), "S Leaf should reduce to an array");
+  });
+});

ext/js/test/run-bundle.test.js

@@ -0,0 +1,84 @@
+import { readFileSync } from "node:fs";
+import { strictEqual, ok, throws } from "node:assert";
+import { describe, it } from "node:test";
+import { parseManifest } from "../src/bundle.js";
+import { parseNodeSection as bundleParseNodeSection } from "../src/bundle.js";
+import { validateManifest, selectExport } from "../src/manifest.js";
+import { verifyNodeHashes, parseNodeSection as parseNodes } from "../src/merkle.js";
+import { buildTreeFromNodeMap } from "../src/cli.js";
+
+const fixtureDir = "test/fixtures";
+
+describe("run bundle — id.tri.bundle", () => {
+  const bundle = readFileSync(`${fixtureDir}/id.tri.bundle`);
+  const manifest = parseManifest(bundle);
+  const nodeSectionData = bundleParseNodeSection(bundle);
+  const { nodeMap } = parseNodes(nodeSectionData);
+
+  it("manifest validates", () => {
+    validateManifest(manifest);
+  });
+
+  it("node hashes verify", () => {
+    const { verified } = verifyNodeHashes(nodeMap);
+    ok(verified);
+  });
+
+  it("export 'id' is selectable", () => {
+    const exp = selectExport(manifest, "id");
+    strictEqual(exp.name, "id");
+  });
+
+  it("tree reconstructs as a Fork", () => {
+    const exp = selectExport(manifest, "id");
+    const tree = buildTreeFromNodeMap(nodeMap, exp.root);
+    ok(Array.isArray(tree));
+    // id = t (t t) = Fork (Stem Leaf) Leaf... 
+    // In Haskell: id = S = t (t (t t)) t
+    // This is Fork (Fork (Fork Leaf Leaf) Leaf) Leaf
+    // In array form: [[[], []], [], []]
+    ok(tree.length >= 2, "tree should be a Fork (length >= 2)");
+  });
+});
+
+describe("run bundle — true.tri.bundle", () => {
+  const bundle = readFileSync(`${fixtureDir}/true.tri.bundle`);
+  const manifest = parseManifest(bundle);
+  const nodeSectionData = bundleParseNodeSection(bundle);
+  const { nodeMap } = parseNodes(nodeSectionData);
+
+  it("manifest validates", () => {
+    validateManifest(manifest);
+  });
+
+  it("export 'const' is selectable", () => {
+    const exp = selectExport(manifest, "const");
+    strictEqual(exp.name, "const");
+  });
+
+  it("tree reconstructs", () => {
+    const exp = selectExport(manifest, "const");
+    const tree = buildTreeFromNodeMap(nodeMap, exp.root);
+    ok(Array.isArray(tree));
+  });
+});
+
+describe("run bundle — missing export", () => {
+  const bundle = readFileSync(`${fixtureDir}/id.tri.bundle`);
+  const manifest = parseManifest(bundle);
+
+  it("nonexistent export fails clearly", () => {
+    throws(() => selectExport(manifest, "nonexistent"), /not found/);
+  });
+});
+
+describe("run bundle — auto-select", () => {
+  // true.tri.bundle has only one export, should auto-select
+  const bundle = readFileSync(`${fixtureDir}/true.tri.bundle`);
+  const manifest = parseManifest(bundle);
+
+  it("single export auto-selects", () => {
+    const exp = selectExport(manifest, undefined);
+    ok(exp, "should auto-select the only export");
+  });
+});