diff --git a/test/js/improv-frame.test.mjs b/test/js/improv-frame.test.mjs
index 5444094..a6df1a6 100644
--- a/test/js/improv-frame.test.mjs
+++ b/test/js/improv-frame.test.mjs
@@ -12,6 +12,7 @@ import {
     encodeApplyOpFrames,
     APPLY_OP_CHUNK_MAX,
     IMPROV_CMD_APPLY_OP,
+    IMPROV_CMD_SET_TX_POWER,
     IMPROV_FRAME_TYPE_RPC,
     IMPROV_MAGIC,
 } from "../../docs/install/improv-frame.js";
@@ -80,3 +81,138 @@ test("APPLY_OP always emits at least one frame (so `last` always sends)", () =>
     assert.equal(frames.length, 1);
     assert.equal(frames[0][9 + 2], 1, "last=1 on the lone frame");
 });
+
+// ---------------------------------------------------------------------------
+// PR regression: IMPROV_CMD_SET_DEVICE_MODEL (0xFE) removed from improv-frame.js
+// ---------------------------------------------------------------------------
+
+test("IMPROV_CMD_SET_DEVICE_MODEL is NOT exported (removed in this PR)", async () => {
+    // The SET_DEVICE_MODEL RPC (0xFE) was a dedicated vendor command; it has been
+    // removed — the device model is now just one `set` op in the APPLY_OP stream.
+    // Verify the export no longer exists so callers can't accidentally reference it.
+    const mod = await import("../../docs/install/improv-frame.js");
+    assert.equal(
+        mod.IMPROV_CMD_SET_DEVICE_MODEL,
+        undefined,
+        "IMPROV_CMD_SET_DEVICE_MODEL must not be exported",
+    );
+    // 0xFE must not appear as a value for any named export either
+    const values = Object.values(mod).filter(v => typeof v === "number");
+    assert.ok(!values.includes(0xFE), "0xFE must not be exported as any constant");
+});
+
+// ---------------------------------------------------------------------------
+// IMPROV_CMD_SET_TX_POWER — still exported, value and wire format
+// ---------------------------------------------------------------------------
+
+test("IMPROV_CMD_SET_TX_POWER equals 0xFD", () => {
+    assert.equal(IMPROV_CMD_SET_TX_POWER, 0xFD);
+});
+
+test("SET_TX_POWER frame layout: [cmd][1][dBm] three-byte payload", () => {
+    // The orchestrator sends: buildImprovFrame(IMPROV_FRAME_TYPE_RPC,
+    //   new Uint8Array([IMPROV_CMD_SET_TX_POWER, 1, dBm & 0xFF]))
+    const dBm = 8;
+    const payload = new Uint8Array([IMPROV_CMD_SET_TX_POWER, 0x01, dBm]);
+    const frame = buildImprovFrame(IMPROV_FRAME_TYPE_RPC, payload);
+    assert.equal(frame[7], IMPROV_FRAME_TYPE_RPC, "type byte");
+    assert.equal(frame[8], 3, "payload length = 3");
+    assert.equal(frame[9], IMPROV_CMD_SET_TX_POWER, "payload[0] = 0xFD");
+    assert.equal(frame[10], 0x01, "payload[1] = length-of-value = 1");
+    assert.equal(frame[11], dBm, "payload[2] = dBm value");
+    assert.equal(frame.length, 13, "total frame length");
+});
+
+test("golden vector: SET_TX_POWER(8 dBm) frame bytes", () => {
+    // Hand-verified: IMPROV_MAGIC + version(1) + type(3) + length(3) +
+    //   [0xFD, 0x01, 0x08] + checksum(0xEA).
+    // Checksum = (0x49+0x4d+0x50+0x52+0x4f+0x56+0x01+0x03+0x03+0xFD+0x01+0x08) mod 256
+    //          = 746 mod 256 = 234 = 0xEA.
+    const frame = buildImprovFrame(
+        IMPROV_FRAME_TYPE_RPC,
+        new Uint8Array([IMPROV_CMD_SET_TX_POWER, 0x01, 8]),
+    );
+    assert.equal(hex(frame), "49 4d 50 52 4f 56 01 03 03 fd 01 08 ea");
+});
+
+test("SET_TX_POWER frame: dBm=0 (lift cap) encodes correctly", () => {
+    const frame = buildImprovFrame(
+        IMPROV_FRAME_TYPE_RPC,
+        new Uint8Array([IMPROV_CMD_SET_TX_POWER, 0x01, 0]),
+    );
+    assert.equal(frame[11], 0, "dBm=0 lifts the cap");
+    assert.equal(frame.length, 13);
+});
+
+test("SET_TX_POWER frame: dBm=21 (max) encodes correctly", () => {
+    const frame = buildImprovFrame(
+        IMPROV_FRAME_TYPE_RPC,
+        new Uint8Array([IMPROV_CMD_SET_TX_POWER, 0x01, 21]),
+    );
+    assert.equal(frame[11], 21);
+});
+
+// ---------------------------------------------------------------------------
+// buildImprovFrame edge cases
+// ---------------------------------------------------------------------------
+
+test("buildImprovFrame throws if payload exceeds 255 bytes", () => {
+    const oversized = new Uint8Array(256);
+    assert.throws(
+        () => buildImprovFrame(IMPROV_FRAME_TYPE_RPC, oversized),
+        /255/,
+        "must mention the 255 limit in the error",
+    );
+});
+
+test("buildImprovFrame accepts payload of exactly 255 bytes", () => {
+    const maxPayload = new Uint8Array(255).fill(0x01);
+    const frame = buildImprovFrame(IMPROV_FRAME_TYPE_RPC, maxPayload);
+    assert.equal(frame[8], 255, "length byte = 255");
+    assert.equal(frame.length, 6 + 1 + 1 + 1 + 255 + 1, "total frame size");
+});
+
+// ---------------------------------------------------------------------------
+// encodeApplyOpFrames boundary cases
+// ---------------------------------------------------------------------------
+
+test("exactly APPLY_OP_CHUNK_MAX bytes of JSON stays in one frame", () => {
+    // Craft an op whose JSON is exactly APPLY_OP_CHUNK_MAX bytes.
+    // {"op":"set","module":"X","control":"c","value":"<padding>"}
+    const prefix = '{"op":"set","module":"X","control":"c","value":"';
+    const suffix = '"}';
+    const pad = APPLY_OP_CHUNK_MAX - prefix.length - suffix.length;
+    // Guard: if pad < 0 the test premise is broken.
+    assert.ok(pad >= 0, "prefix+suffix fits within APPLY_OP_CHUNK_MAX");
+    const value = "A".repeat(pad);
+    const op = { op: "set", module: "X", control: "c", value };
+    const json = JSON.stringify(op);
+    assert.equal(new TextEncoder().encode(json).length, APPLY_OP_CHUNK_MAX, "JSON is exactly the chunk max");
+    const frames = encodeApplyOpFrames(op);
+    assert.equal(frames.length, 1, "fits in one frame");
+    assert.equal(frames[0][9 + 2], 1, "last=1");
+});
+
+test("APPLY_OP_CHUNK_MAX + 1 bytes of JSON produces exactly two frames", () => {
+    // Build an op whose JSON exceeds the chunk max by exactly one byte.
+    const prefix = '{"op":"set","module":"X","control":"c","value":"';
+    const suffix = '"}';
+    const pad = APPLY_OP_CHUNK_MAX - prefix.length - suffix.length + 1;
+    assert.ok(pad >= 0, "prefix+suffix fits within APPLY_OP_CHUNK_MAX+1");
+    const value = "A".repeat(pad);
+    const op = { op: "set", module: "X", control: "c", value };
+    const jsonLen = new TextEncoder().encode(JSON.stringify(op)).length;
+    assert.equal(jsonLen, APPLY_OP_CHUNK_MAX + 1);
+    const frames = encodeApplyOpFrames(op);
+    assert.equal(frames.length, 2);
+    assert.equal(frames[0][9 + 1], 0, "frame 0: seq=0");
+    assert.equal(frames[0][9 + 2], 0, "frame 0: not last");
+    assert.equal(frames[1][9 + 1], 1, "frame 1: seq=1");
+    assert.equal(frames[1][9 + 2], 1, "frame 1: last=1");
+    // The two chunks reassemble to the original JSON exactly.
+    const enc = new TextEncoder().encode(JSON.stringify(op));
+    const chunk0 = enc.subarray(0, APPLY_OP_CHUNK_MAX);
+    const chunk1 = enc.subarray(APPLY_OP_CHUNK_MAX);
+    assert.deepEqual(Array.from(frames[0].subarray(9 + 3, 9 + frames[0][8])), Array.from(chunk0));
+    assert.deepEqual(Array.from(frames[1].subarray(9 + 3, 9 + frames[1][8])), Array.from(chunk1));
+});