diff --git a/npm/build.sh b/npm/build.sh
index 281a5758..f730e103 100755
--- a/npm/build.sh
+++ b/npm/build.sh
@@ -202,10 +202,10 @@ esac
 
 # --- optional test -----------------------------------------------------------
 # Runs the same smoke test that CI runs (see .github/workflows/main-wasm.yml).
+# Run in a subshell so the cd does not leak into the --pack step below, which
+# relies on the script's working directory being unchanged.
 if [ $OPT_TEST -eq 1 ]; then
-  cd "$SCRIPT_DIR"
-  npm run test
-  npm run test:tcl
+  ( cd "$SCRIPT_DIR" && npm run test && npm run test:tcl )
 fi
 
 # --- optional pack -----------------------------------------------------------
diff --git a/npm/examples/all-tcl.js b/npm/examples/all-tcl.js
index 20ec5c12..7fd14ff2 100644
--- a/npm/examples/all-tcl.js
+++ b/npm/examples/all-tcl.js
@@ -9,6 +9,7 @@ import { run as runGds }     from './gds-tcl.js';
 import { run as runDrc }     from './drc-tcl.js';
 import { run as runCif }     from './cif-tcl.js';
 import { run as runPcell }   from './pcell.js';
+import { reportError }       from './helpers-tcl.js';
 
 const PAD = 9;
 
@@ -20,6 +21,9 @@ async function test(name, fn) {
     return true;
   } catch (e) {
     console.log(`FAIL  ${e.message ?? e}`);
+    // Full stack to stderr so CI shows the wasm-function offsets, while the
+    // one-line summary above stays readable.  Other tests still run.
+    reportError(e);
     return false;
   }
 }
diff --git a/npm/examples/all.js b/npm/examples/all.js
index 8bc4985d..44699150 100644
--- a/npm/examples/all.js
+++ b/npm/examples/all.js
@@ -5,6 +5,7 @@ import { run as runExtract } from './extract.js';
 import { run as runGds }     from './gds.js';
 import { run as runDrc }     from './drc.js';
 import { run as runCif }     from './cif.js';
+import { reportError }       from './helpers.js';
 
 const PAD = 9;
 
@@ -16,6 +17,9 @@ async function test(name, fn) {
     return true;
   } catch (e) {
     console.log(`FAIL  ${e.message ?? e}`);
+    // Full stack to stderr so CI shows the wasm-function offsets, while the
+    // one-line summary above stays readable.  Other tests still run.
+    reportError(e);
     return false;
   }
 }
diff --git a/npm/examples/cif-tcl.js b/npm/examples/cif-tcl.js
index 3a6dbc62..212addbe 100644
--- a/npm/examples/cif-tcl.js
+++ b/npm/examples/cif-tcl.js
@@ -1,6 +1,6 @@
 // cif-tcl.js — CIF export via the TCL variant.
 import { createMagic, vfsRead, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT } from './helpers-tcl.js';
+         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT, reportError } from './helpers-tcl.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -22,7 +22,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH, outputDi
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { outPath, bytes } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { outPath, bytes } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\ncif: ${outPath} (${bytes} bytes)`);
   console.log('Done.');
 }
diff --git a/npm/examples/cif.js b/npm/examples/cif.js
index b24653b9..c41cb449 100644
--- a/npm/examples/cif.js
+++ b/npm/examples/cif.js
@@ -2,7 +2,7 @@
 //
 // Usage:  node examples/cif.js [magFile [tech [outputDir]]]
 import { createMagic, vfsRead, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT } from './helpers.js';
+         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT, reportError } from './helpers.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -24,7 +24,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH, outputDi
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { outPath, bytes } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { outPath, bytes } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\ncif: ${outPath} (${bytes} bytes)`);
   console.log('Done.');
 }
diff --git a/npm/examples/drc-tcl.js b/npm/examples/drc-tcl.js
index 2651af32..20258bd5 100644
--- a/npm/examples/drc-tcl.js
+++ b/npm/examples/drc-tcl.js
@@ -1,6 +1,6 @@
 // drc-tcl.js — DRC check via the TCL variant.
 import { createMagic, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG } from './helpers-tcl.js';
+         DEFAULT_TECH, DEFAULT_MAG, reportError } from './helpers-tcl.js';
 import { fileURLToPath } from 'node:url';
 
 export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH } = {}) {
@@ -22,7 +22,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH } = {}) {
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { violations } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { violations } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\nDRC violations: ${violations ?? '(count not found in output)'}`);
   console.log('Done.');
 }
diff --git a/npm/examples/drc.js b/npm/examples/drc.js
index 204f461d..52480fe2 100644
--- a/npm/examples/drc.js
+++ b/npm/examples/drc.js
@@ -2,7 +2,7 @@
 //
 // Usage:  node examples/drc.js [magFile [tech]]
 import { createMagic, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG } from './helpers.js';
+         DEFAULT_TECH, DEFAULT_MAG, reportError } from './helpers.js';
 import { fileURLToPath } from 'node:url';
 
 export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH } = {}) {
@@ -25,7 +25,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH } = {}) {
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { violations } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { violations } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\nDRC violations: ${violations ?? '(count not found in output)'}`);
   console.log('Done.');
 }
diff --git a/npm/examples/extract-tcl.js b/npm/examples/extract-tcl.js
index 193fb2ce..c307bdaf 100644
--- a/npm/examples/extract-tcl.js
+++ b/npm/examples/extract-tcl.js
@@ -1,6 +1,6 @@
 // extract-tcl.js — RC extraction via the TCL variant.
 import { createMagic, vfsWrite, vfsRead, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT } from './helpers-tcl.js';
+         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT, reportError } from './helpers-tcl.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -32,7 +32,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH, outputDi
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { ext, spice } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { ext, spice } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\next:   ${ext}`);
   if (spice) console.log(`spice: ${spice}`);
   console.log('Done.');
diff --git a/npm/examples/extract.js b/npm/examples/extract.js
index f2af0adf..2a6e18e2 100644
--- a/npm/examples/extract.js
+++ b/npm/examples/extract.js
@@ -2,7 +2,7 @@
 //
 // Usage:  node examples/extract.js [magFile [tech [outputDir]]]
 import { createMagic, vfsWrite, vfsRead, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT } from './helpers.js';
+         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT, reportError } from './helpers.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -34,7 +34,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH, outputDi
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { ext, spice } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { ext, spice } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\next:   ${ext}`);
   if (spice) console.log(`spice: ${spice}`);
   console.log('Done.');
diff --git a/npm/examples/gds-tcl.js b/npm/examples/gds-tcl.js
index 98bec535..5e219624 100644
--- a/npm/examples/gds-tcl.js
+++ b/npm/examples/gds-tcl.js
@@ -1,6 +1,6 @@
 // gds-tcl.js — GDS export via the TCL variant.
 import { createMagic, vfsRead, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT } from './helpers-tcl.js';
+         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT, reportError } from './helpers-tcl.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -22,7 +22,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH, outputDi
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { outPath, bytes } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { outPath, bytes } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\ngds: ${outPath} (${bytes} bytes)`);
   console.log('Done.');
 }
diff --git a/npm/examples/gds.js b/npm/examples/gds.js
index c07cba76..8f4ae974 100644
--- a/npm/examples/gds.js
+++ b/npm/examples/gds.js
@@ -2,7 +2,7 @@
 //
 // Usage:  node examples/gds.js [magFile [tech [outputDir]]]
 import { createMagic, vfsRead, loadCell, loadScript,
-         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT } from './helpers.js';
+         DEFAULT_TECH, DEFAULT_MAG, DEFAULT_OUT, reportError } from './helpers.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -24,7 +24,7 @@ export async function run({ magFile = DEFAULT_MAG, tech = DEFAULT_TECH, outputDi
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const { outPath, bytes } = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const { outPath, bytes } = await run().catch(e => { reportError(e); process.exit(1); });
   console.log(`\ngds: ${outPath} (${bytes} bytes)`);
   console.log('Done.');
 }
diff --git a/npm/examples/helpers-tcl.js b/npm/examples/helpers-tcl.js
index 35c12398..b4f25e4c 100644
--- a/npm/examples/helpers-tcl.js
+++ b/npm/examples/helpers-tcl.js
@@ -43,7 +43,14 @@ export class MagicWasm {
     const path = '/tmp/_magic_script.tcl';
     this.FS.mkdirTree('/tmp');
     this.FS.writeFile(path, text);
-    this._sourceFile(path);
+    try {
+      this._sourceFile(path);
+    } catch (e) {
+      // A WASM trap during Tcl evaluation otherwise gives no hint of the
+      // source; flag it before the error propagates.
+      console.error('[magic-tcl] script evaluation failed');
+      throw e;
+    }
   }
   // Evaluate a Tcl expression directly (needed for proc definitions in PCell).
   runTcl(text) {
@@ -74,3 +81,11 @@ export function loadScript(name, tech, cell) {
     .replaceAll('__TECH__', tech)
     .replaceAll('__CELL__', cell);
 }
+
+// Print a failure with enough detail to be actionable in CI.  WASM aborts
+// surface as a RuntimeError whose .message is terse while .stack carries the
+// wasm-function offsets that emsymbolizer maps back to C source — so always
+// prefer the stack.
+export function reportError(e) {
+  console.error(e?.stack ?? String(e?.message ?? e));
+}
diff --git a/npm/examples/helpers.js b/npm/examples/helpers.js
index 9092fb6c..1f0cadfb 100644
--- a/npm/examples/helpers.js
+++ b/npm/examples/helpers.js
@@ -38,11 +38,28 @@ export class MagicWasm {
   runScript(text) {
     for (const line of text.split('\n')) {
       const l = line.trim();
-      if (l && !l.startsWith('#')) this._run(l);
+      if (l && !l.startsWith('#')) {
+        try {
+          this._run(l);
+        } catch (e) {
+          // Name the command that aborted before the error propagates — a
+          // WASM trap otherwise gives no hint which step failed.
+          console.error(`[magic] command failed: ${l}`);
+          throw e;
+        }
+      }
     }
   }
 }
 
+// Print a failure with enough detail to be actionable in CI.  WASM aborts
+// surface as a RuntimeError whose .message is terse ("memory access out of
+// bounds") while .stack carries the wasm-function offsets that emsymbolizer
+// maps back to C source — so always prefer the stack.
+export function reportError(e) {
+  console.error(e?.stack ?? String(e?.message ?? e));
+}
+
 // Creates a fresh Magic WASM instance and calls init().
 // onPrint / onPrintErr default to console.log/error with a [magic] prefix.
 // All output lines are also collected into the returned `lines` array.
diff --git a/npm/examples/pcell.js b/npm/examples/pcell.js
index b31066fd..2d7b899d 100644
--- a/npm/examples/pcell.js
+++ b/npm/examples/pcell.js
@@ -4,7 +4,7 @@
 // and verifies that both GDS outputs are non-empty.
 //
 // Usage:  node examples/pcell.js
-import { createMagic, vfsRead, loadScript, DEFAULT_TECH, DEFAULT_OUT } from './helpers-tcl.js';
+import { createMagic, vfsRead, loadScript, DEFAULT_TECH, DEFAULT_OUT, reportError } from './helpers-tcl.js';
 import { writeFileSync, mkdirSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import { resolve } from 'node:path';
@@ -32,7 +32,7 @@ export async function run({ tech = DEFAULT_TECH, outputDir = DEFAULT_OUT } = {})
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const results = await run().catch(e => { console.error(e.message ?? e); process.exit(1); });
+  const results = await run().catch(e => { reportError(e); process.exit(1); });
   for (const [name, { outPath, bytes }] of Object.entries(results))
     console.log(`  ${name}.gds: ${outPath} (${bytes} bytes)`);
   console.log('Done.');