diff --git a/frontend/src/__tests__/chipbus-twochip-integration.test.ts b/frontend/src/__tests__/chipbus-twochip-integration.test.ts
new file mode 100644
index 00000000..9255f51f
--- /dev/null
+++ b/frontend/src/__tests__/chipbus-twochip-integration.test.ts
@@ -0,0 +1,104 @@
+/**
+ * Multi-chip digital bus — Phase 0 LIVE proof with REAL compiled WASM chips.
+ *
+ * This is the "2 chips exchange a real byte" milestone (03-phases.md, D-008),
+ * end-to-end through the actual ChipRuntime + PinManager + the chipbus net-key
+ * resolver — not a unit stub. Two chips compiled from C with wasi-sdk:
+ *   - bus-driver: drives 0xA5 onto D0..D7 at setup (OUTPUT_HIGH/LOW).
+ *   - bus-reader: polls D0..D7 on a 1ms timer, mirrors onto OUT0..OUT7.
+ * Wired chip-to-chip (D0..D7 straight across), no board. With the chipbus flag
+ * the two chips' Dn pins resolve to ONE shared net key, so the reader observes
+ * the driver's byte and reproduces 0xA5 on OUT.
+ *
+ * Sources: test/test_custom_chips/sdk/examples/{bus-driver,bus-reader}.c.
+ * Fixtures (.wasm) are committed alongside this test; regenerate with:
+ *   clang --target=wasm32-unknown-wasip1 -O2 -nostartfiles -Wl,--import-memory \
+ *     -Wl,--export-table -Wl,--no-entry -Wl,--export=chip_setup \
+ *     -Wl,--allow-undefined -I test/test_custom_chips/sdk/include <src.c> -o <out.wasm>
+ * (same flags as test_intel/scripts/compile-chip.sh).
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { readFileSync, existsSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { PinManager } from '../simulation/PinManager';
+import { ChipInstance } from '../simulation/customChips/ChipRuntime';
+import {
+  resolveChipNetKey,
+  setChipBusEnabledForTest,
+  resetChipNetIndexForTest,
+  type ChipNetState,
+} from '../simulation/customChips/chipNets';
+import { syntheticChipPin } from '../simulation/customChips/syntheticPins';
+
+const driverWasmPath = fileURLToPath(new URL('./fixtures/chipbus/bus-driver.wasm', import.meta.url));
+const readerWasmPath = fileURLToPath(new URL('./fixtures/chipbus/bus-reader.wasm', import.meta.url));
+const haveFixtures = existsSync(driverWasmPath) && existsSync(readerWasmPath);
+
+const chip = (id: string) => ({ id, metadataId: 'custom-chip' });
+const wire = (aId: string, aPin: string, bId: string, bPin: string) => ({
+  start: { componentId: aId, pinName: aPin },
+  end: { componentId: bId, pinName: bPin },
+});
+const range = (n: number) => Array.from({ length: n }, (_, i) => i);
+
+// The data bus: driver.D0..D7 wired straight across to reader.D0..D7, no board.
+const STATE: ChipNetState = {
+  wires: range(8).map((i) => wire('driver', `D${i}`, 'reader', `D${i}`)),
+  components: [chip('driver'), chip('reader')],
+  boards: [],
+};
+
+// Mirror what traceDetailed hands CustomChipPart's `wires` map: a chip-to-chip
+// net resolves to the shared net key; an unwired chip pin (the reader's OUTn)
+// falls back to its own synthetic key (rule 3).
+function pinKey(chipId: string, pin: string): number {
+  return resolveChipNetKey(STATE, chipId, pin) ?? syntheticChipPin(chipId, pin);
+}
+
+describe.skipIf(!haveFixtures)('chipbus Phase 0 — two REAL chips exchange a byte', () => {
+  beforeAll(() => {
+    setChipBusEnabledForTest(true);
+    resetChipNetIndexForTest();
+  });
+  afterAll(() => {
+    setChipBusEnabledForTest(null);
+    resetChipNetIndexForTest();
+  });
+
+  it('reader reproduces the driver byte 0xA5 over the shared chip-to-chip bus', async () => {
+    const driverWasm = new Uint8Array(readFileSync(driverWasmPath));
+    const readerWasm = new Uint8Array(readFileSync(readerWasmPath));
+
+    // The bus pins resolve to ONE shared key for both chips (root cause A fix).
+    expect(pinKey('driver', 'D0')).toBe(pinKey('reader', 'D0'));
+
+    const pm = new PinManager();
+
+    const driverWires = new Map<string, number>(
+      range(8).map((i) => [`D${i}`, pinKey('driver', `D${i}`)] as [string, number]),
+    );
+    const readerWires = new Map<string, number>([
+      ...range(8).map((i) => [`D${i}`, pinKey('reader', `D${i}`)] as [string, number]),
+      ...range(8).map((i) => [`OUT${i}`, pinKey('reader', `OUT${i}`)] as [string, number]),
+    ]);
+
+    const driver = await ChipInstance.create({ wasm: driverWasm, pinManager: pm, wires: driverWires });
+    driver.start(); // chip_setup drives 0xA5 onto the shared D0..D7 net keys.
+
+    const reader = await ChipInstance.create({ wasm: readerWasm, pinManager: pm, wires: readerWires });
+    reader.start();
+
+    // Fire the reader's 1ms polling timer (advance sim time well past it).
+    reader.tickTimers(5_000_000n);
+
+    // Reconstruct the byte the reader mirrored onto OUT0..OUT7.
+    let out = 0;
+    for (const i of range(8)) {
+      if (pm.getPinState(pinKey('reader', `OUT${i}`))) out |= 1 << i;
+    }
+    expect(out).toBe(0xa5);
+
+    driver.dispose();
+    reader.dispose();
+  });
+});
diff --git a/frontend/src/__tests__/fixtures/chipbus/bus-driver.wasm b/frontend/src/__tests__/fixtures/chipbus/bus-driver.wasm
new file mode 100644
index 00000000..8fe492d3
Binary files /dev/null and b/frontend/src/__tests__/fixtures/chipbus/bus-driver.wasm differ
diff --git a/frontend/src/__tests__/fixtures/chipbus/bus-reader.wasm b/frontend/src/__tests__/fixtures/chipbus/bus-reader.wasm
new file mode 100644
index 00000000..7b31fc38
Binary files /dev/null and b/frontend/src/__tests__/fixtures/chipbus/bus-reader.wasm differ
diff --git a/test/test_custom_chips/sdk/examples/bus-driver.c b/test/test_custom_chips/sdk/examples/bus-driver.c
new file mode 100644
index 00000000..c01d727a
--- /dev/null
+++ b/test/test_custom_chips/sdk/examples/bus-driver.c
@@ -0,0 +1,20 @@
+/*
+ * bus-driver — Phase 0 chip-to-chip bus proof (project/multichip-bus/ in the
+ * velxio-prod repo). Drives a fixed byte 0xA5 onto an 8-bit data bus D0..D7 at
+ * setup. No board involved; the only consumer is another custom chip
+ * (bus-reader) wired straight across. Proves a shared chip-to-chip net key lets
+ * one chip's write reach another chip's read.
+ */
+#include "velxio-chip.h"
+
+void chip_setup(void) {
+  const int byte = 0xA5; /* 1010 0101 */
+  char name[4] = {'D', '0', 0, 0};
+  for (int i = 0; i < 8; i++) {
+    name[1] = (char)('0' + i);
+    int bit = (byte >> i) & 1;
+    /* OUTPUT_HIGH/LOW drives the level at registration time, so the byte is
+     * present on the shared net immediately — no timer needed. */
+    vx_pin_register(name, bit ? VX_OUTPUT_HIGH : VX_OUTPUT_LOW);
+  }
+}
diff --git a/test/test_custom_chips/sdk/examples/bus-driver.chip.json b/test/test_custom_chips/sdk/examples/bus-driver.chip.json
new file mode 100644
index 00000000..0287d56e
--- /dev/null
+++ b/test/test_custom_chips/sdk/examples/bus-driver.chip.json
@@ -0,0 +1,9 @@
+{
+  "schema": "velxio-chip/v1",
+  "name": "Bus Driver (0xA5)",
+  "author": "Velxio",
+  "license": "MIT",
+  "description": "Drives the constant byte 0xA5 onto an 8-bit data bus D0..D7. Phase 0 chip-to-chip bus proof.",
+  "pins": ["D0", "D1", "D2", "D3", "D4", "D5", "D6", "D7"],
+  "attributes": []
+}
diff --git a/test/test_custom_chips/sdk/examples/bus-reader.c b/test/test_custom_chips/sdk/examples/bus-reader.c
new file mode 100644
index 00000000..b9e10303
--- /dev/null
+++ b/test/test_custom_chips/sdk/examples/bus-reader.c
@@ -0,0 +1,34 @@
+/*
+ * bus-reader — Phase 0 chip-to-chip bus proof (project/multichip-bus/ in the
+ * velxio-prod repo). Reads the 8-bit data bus D0..D7 and mirrors it onto
+ * OUT0..OUT7 (which would drive 8 LEDs in the app). Polls on a 1 ms timer so it
+ * is order-independent w.r.t. the driver's setup. If chip-to-chip keying works,
+ * OUT == whatever the driver put on the bus (0xA5).
+ */
+#include "velxio-chip.h"
+
+static vx_pin D[8];
+static vx_pin OUT[8];
+
+static void poll(void* ud) {
+  (void)ud;
+  for (int i = 0; i < 8; i++) {
+    int v = vx_pin_read(D[i]);
+    vx_pin_write(OUT[i], v);
+  }
+}
+
+void chip_setup(void) {
+  char dn[4] = {'D', '0', 0, 0};
+  for (int i = 0; i < 8; i++) {
+    dn[1] = (char)('0' + i);
+    D[i] = vx_pin_register(dn, VX_INPUT);
+  }
+  char on[5] = {'O', 'U', 'T', '0', 0};
+  for (int i = 0; i < 8; i++) {
+    on[3] = (char)('0' + i);
+    OUT[i] = vx_pin_register(on, VX_OUTPUT_LOW);
+  }
+  vx_timer t = vx_timer_create(poll, (void*)0);
+  vx_timer_start(t, 1000000ULL, true); /* 1 ms, repeating */
+}
diff --git a/test/test_custom_chips/sdk/examples/bus-reader.chip.json b/test/test_custom_chips/sdk/examples/bus-reader.chip.json
new file mode 100644
index 00000000..54124cfd
--- /dev/null
+++ b/test/test_custom_chips/sdk/examples/bus-reader.chip.json
@@ -0,0 +1,9 @@
+{
+  "schema": "velxio-chip/v1",
+  "name": "Bus Reader (8 LEDs)",
+  "author": "Velxio",
+  "license": "MIT",
+  "description": "Reads an 8-bit data bus D0..D7 and mirrors it onto OUT0..OUT7. Phase 0 chip-to-chip bus proof.",
+  "pins": ["D0", "D1", "D2", "D3", "D4", "D5", "D6", "D7", "OUT0", "OUT1", "OUT2", "OUT3", "OUT4", "OUT5", "OUT6", "OUT7"],
+  "attributes": []
+}