diff --git a/.changeset/2002-cli-self-healing-runtime-build.md b/.changeset/2002-cli-self-healing-runtime-build.md
new file mode 100644
index 000000000..3e2f35507
--- /dev/null
+++ b/.changeset/2002-cli-self-healing-runtime-build.md
@@ -0,0 +1,6 @@
+---
+type: Changed
+pr: 2036
+---
+
+**The GSD CLI now self-heals a missing runtime build.** The compiled `gsd-core/bin/lib/*.cjs` modules are gitignored build artifacts (ADR-457) that ship prebuilt in the npm tarball but are absent on a Claude Code plugin-marketplace / git-clone install, which never runs `npm run build:lib`. Previously every command died at load with `Cannot find module './lib/cli-exit.cjs'`. The `gsd-tools` entrypoint now detects the missing output and compiles it once, on demand (lock-guarded so parallel invocations don't race), then proceeds — a single no-op check on the already-built npm path. When TypeScript is genuinely unavailable it prints an actionable `npm install && npm run build:lib` message instead of crashing.
diff --git a/docs/how-to/install-on-your-runtime.md b/docs/how-to/install-on-your-runtime.md
index d24c1203f..051b94828 100644
--- a/docs/how-to/install-on-your-runtime.md
+++ b/docs/how-to/install-on-your-runtime.md
@@ -102,6 +102,8 @@ The `gsd-tools` binary (installed as part of the `@opengsd/gsd-core` npm package
 
 Node.js (`node`) must also be available on your `PATH`. The plugin's always-on guard hooks (wired in `hooks/hooks.json`) are invoked as `node "${CLAUDE_PLUGIN_ROOT}/hooks/<script>"`. Some Claude Code distributions ship as a standalone binary and do not expose a `node` executable on `PATH`; in those environments the plugin's hooks will not run. Verify with `node --version` before relying on the plugin hooks.
 
+**Runtime build (self-healing).** The runtime CLI's compiled modules under `gsd-core/bin/lib/*.cjs` are build artifacts (ADR-457): they are compiled from `src/*.cts` by `npm run build:lib` and shipped prebuilt in the npm tarball. A plugin-marketplace or git-clone install materializes the repository tree directly and never runs that build step, so those files are initially absent. The CLI heals this automatically: the first `gsd-tools` invocation detects the missing output and compiles it once (using the bundled `typescript` devDependency), then proceeds normally. You may see a one-time `gsd: runtime library not built — compiling once…` notice on stderr; subsequent commands are unaffected. If auto-build cannot run (for example `node_modules` was pruned to production-only and `typescript` is unavailable), the CLI prints an actionable message telling you to run `npm install && npm run build:lib` in the plugin directory.
+
 #### Claude plugin marketplace discovery (ZCODE and compatible runtimes)
 
 GSD Core also ships a `.claude-plugin/marketplace.json` marketplace manifest (sibling to `plugin.json`). Runtimes that implement the Claude plugin marketplace contract — such as ZCODE — can discover and install GSD Core from a custom marketplace source without a manual clone:
diff --git a/gsd-core/bin/ensure-runtime-build.cjs b/gsd-core/bin/ensure-runtime-build.cjs
new file mode 100644
index 000000000..6d9fb9727
--- /dev/null
+++ b/gsd-core/bin/ensure-runtime-build.cjs
@@ -0,0 +1,246 @@
+'use strict';
+
+/**
+ * Self-healing runtime build (#2002).
+ *
+ * The GSD runtime CLI (gsd-tools.cjs) require()s ~150 compiled modules from
+ * ./lib/*.cjs. Per ADR-457 ("build-at-publish") those are build artifacts:
+ * compiled from src/*.cts by `npm run build:lib` (tsc -p tsconfig.build.json),
+ * gitignored, and shipped prebuilt in the npm tarball via the prepack /
+ * prepublishOnly lifecycle scripts.
+ *
+ * The Claude Code plugin-marketplace channel does NOT go through `npm publish`
+ * or bin/install.js. Claude Code materializes the git tag tree into its plugin
+ * cache and at most runs `npm install --ignore-scripts`, so neither `prepare`
+ * nor `build:lib` ever fires. The compiled ./lib/*.cjs therefore never exist on
+ * that path and every CLI command dies at module load with
+ * `Cannot find module './lib/cli-exit.cjs'`.
+ *
+ * This module heals that: before gsd-tools.cjs require()s ./lib, if the compiled
+ * output is absent it invokes tsc once — lock-guarded so the many parallel
+ * gsd-tools shell-outs a workflow performs do not race the build — then lets the
+ * requires proceed. On the npm path the artifacts already exist, so the common
+ * case is a single fs.existsSync check and a no-op.
+ *
+ * Deliberately depends on nothing under ./lib (that tree is precisely what may
+ * be missing) — only on Node built-ins.
+ */
+
+const fs = require('fs');
+const path = require('path');
+const { spawnSync } = require('child_process');
+
+// The first module gsd-tools.cjs require()s, and a gitignored build artifact
+// (so it is absent on a raw git-tag checkout even though ~11 other bin/lib/*.cjs
+// are git-tracked). tsconfig.build.json sets noEmitOnError:true, so tsc is
+// all-or-nothing: if this file exists, the whole tree was emitted.
+const SENTINEL = 'cli-exit.cjs';
+
+/** Directory holding the compiled ./lib/*.cjs, relative to this file. */
+function defaultLibDir() {
+  return path.join(__dirname, 'lib');
+}
+
+/**
+ * Package root (holds tsconfig.build.json + node_modules). This file lives at
+ * <root>/gsd-core/bin/ensure-runtime-build.cjs, so the root is two levels up —
+ * true for both the dev repo layout and the marketplace plugin-cache checkout
+ * (…/<version>/gsd-core/bin/ensure-runtime-build.cjs).
+ */
+function defaultPackageRoot() {
+  return path.resolve(__dirname, '..', '..');
+}
+
+/**
+ * Resolve the tsc entry SCRIPT (not the .bin/tsc shim). We run it as
+ * `node <tsc.js>` so behaviour is identical on POSIX and Windows and does not
+ * depend on a shell or on the .cmd shim. Returns null when TypeScript is not
+ * installed under packageRoot.
+ */
+function resolveTscScript(packageRoot) {
+  try {
+    return require.resolve('typescript/bin/tsc', { paths: [packageRoot] });
+  } catch {
+    return null;
+  }
+}
+
+function isBuilt(libDir) {
+  return fs.existsSync(path.join(libDir, SENTINEL));
+}
+
+/** Synchronous sleep with no dependencies, portable across platforms. */
+function sleepSync(ms) {
+  Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0, Math.max(0, ms));
+}
+
+/**
+ * Raised when the runtime library is missing and cannot be auto-built. The
+ * message is user-facing and actionable; callers print `.message` (not a stack).
+ */
+class RuntimeBuildError extends Error {
+  constructor(message) {
+    super(message);
+    this.name = 'RuntimeBuildError';
+    this.code = 'GSD_RUNTIME_BUILD_FAILED';
+  }
+}
+
+/**
+ * Ensure the compiled ./lib/*.cjs exist, building them once if absent.
+ *
+ * Idempotent and safe to call concurrently from many processes. When another
+ * process holds the build lock, this one waits for the build to finish rather
+ * than launching a competing tsc.
+ *
+ * @param {object} [opts]
+ * @param {string} [opts.libDir]        Override the compiled-output directory.
+ * @param {string} [opts.packageRoot]   Override the tsconfig/node_modules root.
+ * @param {string|null} [opts.tscScript] Override tsc resolution (null = "absent").
+ * @param {function} [opts.spawn]       Override spawnSync (for tests).
+ * @param {function} [opts.log]         Override the progress logger.
+ * @param {number} [opts.waitTimeoutMs] Max wait for a peer build (default 120s).
+ * @param {number} [opts.pollMs]        Poll interval while waiting (default 100ms).
+ * @param {function} [opts.onPoll]      Test hook invoked before each wait-poll.
+ * @returns {{built: true, healed: boolean, waited?: boolean}}
+ * @throws {RuntimeBuildError} when the library is absent and cannot be built.
+ */
+function ensureRuntimeBuild(opts = {}) {
+  const libDir = opts.libDir || defaultLibDir();
+  const packageRoot = opts.packageRoot || defaultPackageRoot();
+  const spawn = opts.spawn || spawnSync;
+  const log = opts.log || ((m) => process.stderr.write(m + '\n'));
+  const waitTimeoutMs = opts.waitTimeoutMs != null ? opts.waitTimeoutMs : 120000;
+  const pollMs = opts.pollMs != null ? opts.pollMs : 100;
+
+  // Fast path: already built (the npm-registry install and every subsequent run).
+  if (isBuilt(libDir)) return { built: true, healed: false };
+
+  const tsconfig = path.join(packageRoot, 'tsconfig.build.json');
+  if (!fs.existsSync(tsconfig)) {
+    throw new RuntimeBuildError(
+      'GSD runtime library is not built and cannot be auto-built: ' +
+        `${tsconfig} not found. Run \`npm run build:lib\` in the gsd-core package.`,
+    );
+  }
+
+  const tscScript =
+    opts.tscScript !== undefined ? opts.tscScript : resolveTscScript(packageRoot);
+  if (!tscScript) {
+    throw new RuntimeBuildError(
+      `GSD runtime library is not built (missing ${path.join(libDir, SENTINEL)}) ` +
+        'and TypeScript is unavailable to build it. Run ' +
+        `\`npm install && npm run build:lib\` in the gsd-core package (${packageRoot}).`,
+    );
+  }
+
+  // libDir may not exist yet on a totally fresh tree; create it so the lock and
+  // tsc output have a home.
+  fs.mkdirSync(libDir, { recursive: true });
+  const lockDir = path.join(libDir, '.build.lock');
+
+  let haveLock = acquireLock(lockDir);
+  if (!haveLock) {
+    // A peer process is building. Wait for the sentinel rather than racing tsc.
+    const deadline = Date.now() + waitTimeoutMs;
+    while (!isBuilt(libDir)) {
+      if (typeof opts.onPoll === 'function') opts.onPoll();
+      if (isBuilt(libDir)) break;
+      if (Date.now() > deadline) break; // peer wedged/crashed — take over below
+      sleepSync(pollMs);
+    }
+    if (isBuilt(libDir)) return { built: true, healed: true, waited: true };
+    // Peer never finished; try to take over the (stale) lock.
+    haveLock = acquireLock(lockDir);
+    if (!haveLock && !isBuilt(libDir)) {
+      throw new RuntimeBuildError(
+        `GSD runtime build did not complete within ${waitTimeoutMs}ms and the ` +
+          `build lock (${lockDir}) is held by another process. Remove it and run ` +
+          '`npm run build:lib` if this persists.',
+      );
+    }
+    if (isBuilt(libDir)) return { built: true, healed: true, waited: true };
+  }
+
+  try {
+    log('gsd: runtime library not built — compiling once (tsc -p tsconfig.build.json)…');
+    // Heal only runs when the build is genuinely absent/broken, so force a full
+    // emit: a stale incremental cache from a partial build would make tsc report
+    // success without re-emitting the (still-missing) sentinel.
+    forceFullEmit(packageRoot, tsconfig);
+    const res = spawn(process.execPath, [tscScript, '-p', tsconfig], {
+      cwd: packageRoot,
+      stdio: ['ignore', 'pipe', 'pipe'],
+      encoding: 'utf8',
+    });
+    if (!res || res.status !== 0) {
+      const detail = ((res && (res.stderr || res.stdout)) || '').toString().trim();
+      throw new RuntimeBuildError(
+        `GSD runtime build failed (tsc exit ${res ? res.status : 'unknown'}). ` +
+          `Run \`npm run build:lib\` in ${packageRoot} to see the error.` +
+          (detail ? `\n${detail}` : ''),
+      );
+    }
+  } finally {
+    releaseLock(lockDir);
+  }
+
+  if (!isBuilt(libDir)) {
+    throw new RuntimeBuildError(
+      `GSD runtime build ran but ${path.join(libDir, SENTINEL)} is still missing. ` +
+        `Run \`npm run build:lib\` in ${packageRoot}.`,
+    );
+  }
+  return { built: true, healed: true };
+}
+
+/**
+ * Delete tsc's incremental build cache so the heal re-emits every module. The
+ * cache path defaults to tsconfig.build.tsbuildinfo (per tsconfig.build.json)
+ * but is read from the config when overridden. Best-effort: a missing or
+ * unreadable config just falls back to the default and a missing cache is fine.
+ */
+function forceFullEmit(packageRoot, tsconfigPath) {
+  let rel = 'tsconfig.build.tsbuildinfo';
+  try {
+    const cfg = JSON.parse(fs.readFileSync(tsconfigPath, 'utf8'));
+    if (cfg && cfg.compilerOptions && cfg.compilerOptions.tsBuildInfoFile) {
+      rel = cfg.compilerOptions.tsBuildInfoFile;
+    }
+  } catch {
+    /* unreadable/JSONC config — use the default cache path */
+  }
+  try {
+    fs.rmSync(path.resolve(packageRoot, rel), { force: true });
+  } catch {
+    /* best effort */
+  }
+}
+
+/** Atomically acquire the build lock. Returns true on success. */
+function acquireLock(lockDir) {
+  try {
+    fs.mkdirSync(lockDir); // atomic — throws EEXIST if a peer holds it
+    return true;
+  } catch (e) {
+    if (e && e.code === 'EEXIST') return false;
+    throw e;
+  }
+}
+
+/** Best-effort lock release. */
+function releaseLock(lockDir) {
+  try {
+    fs.rmSync(lockDir, { recursive: true, force: true });
+  } catch {
+    /* best effort — a leftover lock is recovered by the wait-then-takeover path */
+  }
+}
+
+module.exports = {
+  ensureRuntimeBuild,
+  resolveTscScript,
+  isBuilt,
+  RuntimeBuildError,
+  SENTINEL,
+};
diff --git a/gsd-core/bin/gsd-tools.cjs b/gsd-core/bin/gsd-tools.cjs
index 474dec90c..c3cec6716 100755
--- a/gsd-core/bin/gsd-tools.cjs
+++ b/gsd-core/bin/gsd-tools.cjs
@@ -195,6 +195,24 @@
 
 const fs = require('fs');
 const path = require('path');
+
+// #2002 — self-healing runtime build. The compiled ./lib/*.cjs modules this
+// entrypoint require()s below are gitignored build artifacts (ADR-457), shipped
+// prebuilt in the npm tarball. The Claude Code plugin-marketplace channel never
+// runs `npm run build:lib` or bin/install.js, so on that path they can be
+// absent and every command dies at module load. Compile them once (lock-guarded,
+// idempotent, a no-op when already built) before the ./lib requires run.
+const { ensureRuntimeBuild } = require('./ensure-runtime-build.cjs');
+try {
+  ensureRuntimeBuild();
+} catch (bootErr) {
+  process.stderr.write((bootErr && bootErr.message ? bootErr.message : String(bootErr)) + '\n');
+  // Fatal bootstrap failure before the CLI's ExitError/runMain machinery (which
+  // lives in ./lib) is available to load, so a direct exit is the only option.
+  // eslint-disable-next-line n/no-process-exit
+  process.exit(1);
+}
+
 const { ExitError, runMain } = require('./lib/cli-exit.cjs');
 const io = require('./lib/io.cjs');
 const { error, ERROR_REASON, setJsonErrorMode, output } = io;
diff --git a/tests/ensure-runtime-build.test.cjs b/tests/ensure-runtime-build.test.cjs
new file mode 100644
index 000000000..2716ea39c
--- /dev/null
+++ b/tests/ensure-runtime-build.test.cjs
@@ -0,0 +1,340 @@
+'use strict';
+
+/**
+ * Tests for gsd-core/bin/ensure-runtime-build.cjs — the self-healing runtime
+ * build that compiles the gitignored ./lib/*.cjs artifacts on demand when the
+ * CLI is run from a channel (Claude Code plugin marketplace) that never ran
+ * `npm run build:lib`. See #2002.
+ *
+ * The unit tests inject `spawn` so no real tsc runs; the final integration test
+ * drives the REAL module against a real (tiny) tsc build in a temp package to
+ * prove the end-to-end heal. IO failures are injected by monkeypatching the fs
+ * method (root-independent, OS-independent), never via chmod.
+ */
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const { execFileSync } = require('node:child_process');
+const { createTempDir, cleanup } = require('./helpers.cjs');
+
+const {
+  ensureRuntimeBuild,
+  resolveTscScript,
+  isBuilt,
+  RuntimeBuildError,
+  SENTINEL,
+} = require('../gsd-core/bin/ensure-runtime-build.cjs');
+
+const REPO_ROOT = path.resolve(__dirname, '..');
+
+/** Fresh isolated package dir (auto-cleaned) with a libDir and optional tsconfig. */
+function makeEnv(t, { withTsconfig = true, prebuilt = false } = {}) {
+  const dir = createTempDir('gsd-erb-');
+  t.after(() => cleanup(dir));
+  const libDir = path.join(dir, 'gsd-core', 'bin', 'lib');
+  fs.mkdirSync(libDir, { recursive: true });
+  if (withTsconfig) fs.writeFileSync(path.join(dir, 'tsconfig.build.json'), '{}');
+  if (prebuilt) fs.writeFileSync(path.join(libDir, SENTINEL), '// built\n');
+  return { dir, packageRoot: dir, libDir };
+}
+
+/** A spawn stub that "builds" by writing the sentinel, then reports success. */
+function buildingSpawn(libDir, calls) {
+  return (cmd, args, options) => {
+    calls.push({ cmd, args, options });
+    fs.writeFileSync(path.join(libDir, SENTINEL), '// built by stub\n');
+    return { status: 0, stdout: '', stderr: '' };
+  };
+}
+
+const silent = () => {};
+
+test('fast path: already-built lib is a no-op, never spawns tsc', (t) => {
+  const { libDir, packageRoot } = makeEnv(t, { prebuilt: true });
+  const calls = [];
+  const res = ensureRuntimeBuild({
+    libDir,
+    packageRoot,
+    spawn: (...a) => { calls.push(a); return { status: 0 }; },
+    log: silent,
+  });
+  assert.deepEqual(res, { built: true, healed: false });
+  assert.equal(calls.length, 0, 'must not spawn when already built');
+});
+
+test('heal path: missing lib is compiled once with the correct tsc invocation', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  const calls = [];
+  const res = ensureRuntimeBuild({
+    libDir,
+    packageRoot,
+    tscScript: '/fake/typescript/bin/tsc',
+    spawn: buildingSpawn(libDir, calls),
+    log: silent,
+  });
+  assert.equal(res.built, true);
+  assert.equal(res.healed, true);
+  assert.equal(calls.length, 1, 'compiles exactly once');
+  const { cmd, args, options } = calls[0];
+  assert.equal(cmd, process.execPath, 'runs `node <tsc>` (portable, no shell/.cmd)');
+  assert.deepEqual(args, [
+    '/fake/typescript/bin/tsc',
+    '-p',
+    path.join(packageRoot, 'tsconfig.build.json'),
+  ]);
+  assert.equal(options.cwd, packageRoot);
+  assert.ok(isBuilt(libDir), 'sentinel exists after heal');
+});
+
+test('missing tsconfig.build.json throws an actionable RuntimeBuildError', (t) => {
+  const { libDir, packageRoot } = makeEnv(t, { withTsconfig: false });
+  assert.throws(
+    () => ensureRuntimeBuild({ libDir, packageRoot, tscScript: '/fake/tsc', log: silent }),
+    (err) => {
+      assert.ok(err instanceof RuntimeBuildError);
+      assert.match(err.message, /tsconfig\.build\.json not found/);
+      assert.match(err.message, /npm run build:lib/);
+      return true;
+    },
+  );
+});
+
+test('absent TypeScript throws with install guidance and does not spawn', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  const calls = [];
+  assert.throws(
+    () => ensureRuntimeBuild({
+      libDir,
+      packageRoot,
+      tscScript: null, // TypeScript not resolvable
+      spawn: (...a) => { calls.push(a); return { status: 0 }; },
+      log: silent,
+    }),
+    (err) => {
+      assert.ok(err instanceof RuntimeBuildError);
+      assert.match(err.message, /TypeScript is unavailable/);
+      assert.match(err.message, /npm install && npm run build:lib/);
+      return true;
+    },
+  );
+  assert.equal(calls.length, 0, 'never spawns when tsc is absent');
+});
+
+test('non-zero tsc exit surfaces the exit code and captured output', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  assert.throws(
+    () => ensureRuntimeBuild({
+      libDir,
+      packageRoot,
+      tscScript: '/fake/tsc',
+      spawn: () => ({ status: 2, stdout: '', stderr: 'src/x.cts(1,1): error TS1005' }),
+      log: silent,
+    }),
+    (err) => {
+      assert.ok(err instanceof RuntimeBuildError);
+      assert.match(err.message, /tsc exit 2/);
+      assert.match(err.message, /error TS1005/);
+      return true;
+    },
+  );
+});
+
+test('tsc reports success but sentinel is still missing → throws', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  assert.throws(
+    () => ensureRuntimeBuild({
+      libDir,
+      packageRoot,
+      tscScript: '/fake/tsc',
+      spawn: () => ({ status: 0 }), // "succeeds" but writes nothing
+      log: silent,
+    }),
+    (err) => {
+      assert.ok(err instanceof RuntimeBuildError);
+      assert.match(err.message, /still missing/);
+      return true;
+    },
+  );
+});
+
+test('the build lock releases after a successful heal', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  ensureRuntimeBuild({
+    libDir,
+    packageRoot,
+    tscScript: '/fake/tsc',
+    spawn: buildingSpawn(libDir, []),
+    log: silent,
+  });
+  assert.ok(!fs.existsSync(path.join(libDir, '.build.lock')), 'lock removed in finally');
+});
+
+test('lock contention: waits for a peer build instead of racing tsc', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  fs.mkdirSync(path.join(libDir, '.build.lock')); // a peer "holds" the lock
+  const calls = [];
+  const res = ensureRuntimeBuild({
+    libDir,
+    packageRoot,
+    tscScript: '/fake/tsc',
+    spawn: (...a) => { calls.push(a); return { status: 0 }; },
+    log: silent,
+    pollMs: 1,
+    waitTimeoutMs: 1000,
+    // Peer finishes the build between polls.
+    onPoll: () => fs.writeFileSync(path.join(libDir, SENTINEL), '// peer built\n'),
+  });
+  assert.equal(res.healed, true);
+  assert.equal(res.waited, true);
+  assert.equal(calls.length, 0, 'never launches a competing tsc');
+});
+
+test('lock takeover: a crashed peer (stale lock) is taken over and the build runs', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  const lockDir = path.join(libDir, '.build.lock');
+  fs.mkdirSync(lockDir);
+  const calls = [];
+  const res = ensureRuntimeBuild({
+    libDir,
+    packageRoot,
+    tscScript: '/fake/tsc',
+    spawn: buildingSpawn(libDir, calls),
+    log: silent,
+    pollMs: 1,
+    waitTimeoutMs: 0, // give up waiting immediately
+    // Peer vanished without finishing — free the stale lock so we can take over.
+    // eslint-disable-next-line local/no-raw-rmsync-in-tests -- simulating a peer releasing its lock, not temp-dir teardown
+    onPoll: () => fs.rmSync(lockDir, { recursive: true, force: true }),
+  });
+  assert.equal(res.healed, true);
+  assert.equal(calls.length, 1, 'takes over and builds once');
+});
+
+test('lock never frees before timeout → throws a lock-held RuntimeBuildError', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  fs.mkdirSync(path.join(libDir, '.build.lock')); // stuck peer, never released
+  assert.throws(
+    () => ensureRuntimeBuild({
+      libDir,
+      packageRoot,
+      tscScript: '/fake/tsc',
+      spawn: buildingSpawn(libDir, []),
+      log: silent,
+      pollMs: 1,
+      waitTimeoutMs: 0,
+    }),
+    (err) => {
+      assert.ok(err instanceof RuntimeBuildError);
+      assert.match(err.message, /did not complete within 0ms/);
+      return true;
+    },
+  );
+});
+
+test('IO fault on lock acquisition propagates (injected via fs monkeypatch, not chmod)', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  const lockDir = path.join(libDir, '.build.lock');
+  const orig = fs.mkdirSync;
+  fs.mkdirSync = (target, opts) => {
+    if (target === lockDir) {
+      const e = new Error('injected EPERM');
+      e.code = 'EPERM';
+      throw e;
+    }
+    return orig(target, opts);
+  };
+  try {
+    assert.throws(
+      () => ensureRuntimeBuild({
+        libDir,
+        packageRoot,
+        tscScript: '/fake/tsc',
+        spawn: buildingSpawn(libDir, []),
+        log: silent,
+      }),
+      (err) => {
+        // Non-EEXIST lock errors must NOT be swallowed as "peer holds lock".
+        assert.equal(err.code, 'EPERM');
+        return true;
+      },
+    );
+  } finally {
+    fs.mkdirSync = orig;
+  }
+});
+
+test('heal clears a stale tsc incremental cache before compiling (forces full emit)', (t) => {
+  const { libDir, packageRoot } = makeEnv(t);
+  const buildInfo = path.join(packageRoot, 'tsconfig.build.tsbuildinfo');
+  fs.writeFileSync(buildInfo, '{"stale":true}'); // leftover from a partial build
+  ensureRuntimeBuild({
+    libDir,
+    packageRoot,
+    tscScript: '/fake/tsc',
+    spawn: buildingSpawn(libDir, []),
+    log: silent,
+  });
+  assert.ok(!fs.existsSync(buildInfo), 'stale .tsbuildinfo removed so tsc re-emits');
+});
+
+test('resolveTscScript finds the real TypeScript under the repo root', () => {
+  const tsc = resolveTscScript(REPO_ROOT);
+  assert.ok(tsc && tsc.includes('typescript'), 'resolves the installed typescript/bin/tsc');
+  assert.ok(fs.existsSync(tsc), 'resolved tsc script exists on disk');
+});
+
+test('integration: real tsc heals a missing lib end-to-end (subprocess)', (t) => {
+  // Build a tiny package that mirrors the real layout: a src/*.cts that tsc
+  // compiles to gsd-core/bin/lib/cli-exit.cjs. Then invoke the REAL module from
+  // a subprocess with lib absent and assert it self-heals and the require works.
+  const dir = createTempDir('gsd-erb-int-');
+  t.after(() => cleanup(dir));
+  fs.mkdirSync(path.join(dir, 'src'), { recursive: true });
+  fs.mkdirSync(path.join(dir, 'gsd-core', 'bin', 'lib'), { recursive: true });
+  fs.writeFileSync(
+    path.join(dir, 'tsconfig.build.json'),
+    JSON.stringify({
+      compilerOptions: {
+        rootDir: 'src',
+        outDir: 'gsd-core/bin/lib',
+        module: 'nodenext',
+        moduleResolution: 'nodenext',
+        target: 'ES2022',
+        noEmitOnError: true,
+      },
+      include: ['src/**/*.cts'],
+    }),
+  );
+  fs.writeFileSync(
+    path.join(dir, 'src', 'cli-exit.cts'),
+    'export const runMain = (): string => "ok";\n',
+  );
+
+  // Resolve the REAL tsc and pass it explicitly, rather than symlinking
+  // node_modules into the temp package — directory-symlink creation is a
+  // privileged operation on Windows and would fail on CI runners. resolveTscScript
+  // itself is covered by its own unit test; here we just need a real tsc to run.
+  const realTsc = resolveTscScript(REPO_ROOT);
+  assert.ok(realTsc, 'real typescript resolvable for the integration build');
+  const driver = path.join(dir, 'driver.cjs');
+  fs.writeFileSync(
+    driver,
+    `const { ensureRuntimeBuild } = require(${JSON.stringify(
+      path.join(REPO_ROOT, 'gsd-core', 'bin', 'ensure-runtime-build.cjs'),
+    )});\n` +
+      `const libDir = ${JSON.stringify(path.join(dir, 'gsd-core', 'bin', 'lib'))};\n` +
+      `const packageRoot = ${JSON.stringify(dir)};\n` +
+      `const tscScript = ${JSON.stringify(realTsc)};\n` +
+      'const r = ensureRuntimeBuild({ libDir, packageRoot, tscScript, log: () => {} });\n' +
+      'const { runMain } = require(require("path").join(libDir, "cli-exit.cjs"));\n' +
+      'process.stdout.write(JSON.stringify({ healed: r.healed, run: runMain() }));\n',
+  );
+
+  assert.ok(!isBuilt(path.join(dir, 'gsd-core', 'bin', 'lib')), 'lib starts empty');
+  const out = execFileSync(process.execPath, [driver], { encoding: 'utf8', cwd: dir });
+  const parsed = JSON.parse(out);
+  assert.equal(parsed.healed, true, 'self-healed the missing build');
+  assert.equal(parsed.run, 'ok', 'the freshly-compiled cli-exit.cjs loads and runs');
+});
diff --git a/tests/fixtures/golden-install-parity/antigravity.json b/tests/fixtures/golden-install-parity/antigravity.json
index 0789647ed..a3010ad28 100644
--- a/tests/fixtures/golden-install-parity/antigravity.json
+++ b/tests/fixtures/golden-install-parity/antigravity.json
@@ -37,7 +37,8 @@
   "agents/gsd-verifier.md": "224e8df2d8fd1d95",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e839e52071d5baa1",
+  "gsd-core/bin/ensure-runtime-build.cjs": "ea841e2865248e74",
+  "gsd-core/bin/gsd-tools.cjs": "747defe620cb8ae6",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/augment.json b/tests/fixtures/golden-install-parity/augment.json
index 709d168ea..a1f17b717 100644
--- a/tests/fixtures/golden-install-parity/augment.json
+++ b/tests/fixtures/golden-install-parity/augment.json
@@ -107,7 +107,8 @@
   "commands/gsd-workstreams.md": "52ab9c585d3a00f3",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/claude.json b/tests/fixtures/golden-install-parity/claude.json
index fe2c991b9..ca5de7ff1 100644
--- a/tests/fixtures/golden-install-parity/claude.json
+++ b/tests/fixtures/golden-install-parity/claude.json
@@ -36,7 +36,8 @@
   "agents/gsd-verifier.md": "2271174b5aa20e31",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/cline.json b/tests/fixtures/golden-install-parity/cline.json
index 29676a00f..bb39ffde8 100644
--- a/tests/fixtures/golden-install-parity/cline.json
+++ b/tests/fixtures/golden-install-parity/cline.json
@@ -40,7 +40,8 @@
   "agents/gsd-verifier.md": "75912e9cadd83eb3",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "476aa24e8c4f03cf",
+  "gsd-core/bin/gsd-tools.cjs": "13640341aa311ae3",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/codebuddy.json b/tests/fixtures/golden-install-parity/codebuddy.json
index bcfa031ea..965a083e0 100644
--- a/tests/fixtures/golden-install-parity/codebuddy.json
+++ b/tests/fixtures/golden-install-parity/codebuddy.json
@@ -107,7 +107,8 @@
   "commands/gsd-workstreams.md": "884b6c8d648422c7",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/codex.json b/tests/fixtures/golden-install-parity/codex.json
index b9c054582..f1bc28c60 100644
--- a/tests/fixtures/golden-install-parity/codex.json
+++ b/tests/fixtures/golden-install-parity/codex.json
@@ -72,7 +72,8 @@
   "config.toml": "a34316b9ac61a620",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/copilot.json b/tests/fixtures/golden-install-parity/copilot.json
index 1587338a1..5565c2ab6 100644
--- a/tests/fixtures/golden-install-parity/copilot.json
+++ b/tests/fixtures/golden-install-parity/copilot.json
@@ -38,7 +38,8 @@
   "copilot-instructions.md": "1fb04111759f1645",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e839e52071d5baa1",
+  "gsd-core/bin/ensure-runtime-build.cjs": "ea841e2865248e74",
+  "gsd-core/bin/gsd-tools.cjs": "747defe620cb8ae6",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/cursor.json b/tests/fixtures/golden-install-parity/cursor.json
index 8703f0963..01e84ef0e 100644
--- a/tests/fixtures/golden-install-parity/cursor.json
+++ b/tests/fixtures/golden-install-parity/cursor.json
@@ -107,7 +107,8 @@
   "commands/gsd-workstreams.md": "112660ceb663c750",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e839e52071d5baa1",
+  "gsd-core/bin/ensure-runtime-build.cjs": "2525f1ae8b086828",
+  "gsd-core/bin/gsd-tools.cjs": "887e2cb9ebdb609d",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/hermes.json b/tests/fixtures/golden-install-parity/hermes.json
index 44bbdba23..2d0d8be59 100644
--- a/tests/fixtures/golden-install-parity/hermes.json
+++ b/tests/fixtures/golden-install-parity/hermes.json
@@ -37,7 +37,8 @@
   "agents/gsd-verifier.md": "82d3e9015ed04017",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "3a3409215044af9f",
+  "gsd-core/bin/gsd-tools.cjs": "cbdd5da1b973c6ae",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/kilo.json b/tests/fixtures/golden-install-parity/kilo.json
index 302dc5bb1..9d80d3939 100644
--- a/tests/fixtures/golden-install-parity/kilo.json
+++ b/tests/fixtures/golden-install-parity/kilo.json
@@ -107,7 +107,8 @@
   "command/gsd-workstreams.md": "5e57eed1881c3891",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/kimi.json b/tests/fixtures/golden-install-parity/kimi.json
index b289f7ae0..a57b5f545 100644
--- a/tests/fixtures/golden-install-parity/kimi.json
+++ b/tests/fixtures/golden-install-parity/kimi.json
@@ -73,7 +73,8 @@
   "agents/subagents/gsd-verifier.yaml": "2d2bd6b37626f382",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/opencode.json b/tests/fixtures/golden-install-parity/opencode.json
index de87b3b82..0b80baba8 100644
--- a/tests/fixtures/golden-install-parity/opencode.json
+++ b/tests/fixtures/golden-install-parity/opencode.json
@@ -107,7 +107,8 @@
   "command/gsd-workstreams.md": "5e57eed1881c3891",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
+  "gsd-core/bin/gsd-tools.cjs": "770e0b1c1f08ef47",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/qwen.json b/tests/fixtures/golden-install-parity/qwen.json
index f81102328..7f7d47367 100644
--- a/tests/fixtures/golden-install-parity/qwen.json
+++ b/tests/fixtures/golden-install-parity/qwen.json
@@ -37,7 +37,8 @@
   "agents/gsd-verifier.md": "45c450b6d7cc5f0d",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e504d3b82da834ae",
+  "gsd-core/bin/ensure-runtime-build.cjs": "6e98d76e955e35a2",
+  "gsd-core/bin/gsd-tools.cjs": "1118403709188168",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/trae.json b/tests/fixtures/golden-install-parity/trae.json
index 89e5f358f..9f94c2697 100644
--- a/tests/fixtures/golden-install-parity/trae.json
+++ b/tests/fixtures/golden-install-parity/trae.json
@@ -37,7 +37,8 @@
   "agents/gsd-verifier.md": "99e95e235aacffbf",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e839e52071d5baa1",
+  "gsd-core/bin/ensure-runtime-build.cjs": "de4627dff103d527",
+  "gsd-core/bin/gsd-tools.cjs": "fa4db2ce1f77ef99",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",
diff --git a/tests/fixtures/golden-install-parity/windsurf.json b/tests/fixtures/golden-install-parity/windsurf.json
index 32a327a0a..c53cf5a10 100644
--- a/tests/fixtures/golden-install-parity/windsurf.json
+++ b/tests/fixtures/golden-install-parity/windsurf.json
@@ -37,7 +37,8 @@
   "agents/gsd-verifier.md": "a07b00b9c5b7b338",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
-  "gsd-core/bin/gsd-tools.cjs": "e839e52071d5baa1",
+  "gsd-core/bin/ensure-runtime-build.cjs": "5636ca0b726871b2",
+  "gsd-core/bin/gsd-tools.cjs": "92e0f7b7eb55af51",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "c55b99e5d82f69fb",