feat(firmware): add OTA updater library skeleton with version comparison

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

firmware/lib/ota_updater/ota_updater.cpp

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+// firmware/lib/ota_updater/ota_updater.cpp
+#include "ota_updater.h"
+#include <stdio.h>
+#include <string.h>
+
+// ── version comparison ─────────────────────────────────────────────────────
+
+bool ota_version_newer(const char* current, const char* remote) {
+    int ca = 0, cb = 0, cc = 0;
+    int ra = 0, rb = 0, rc = 0;
+    if (sscanf(current, "%d.%d.%d", &ca, &cb, &cc) != 3) return false;
+    if (sscanf(remote,  "%d.%d.%d", &ra, &rb, &rc) != 3) return false;
+    if (ra != ca) return ra > ca;
+    if (rb != cb) return rb > cb;
+    return rc > cc;
+}
+
+// ── signature verification ─────────────────────────────────────────────────
+// (real implementation added in Task 7)
+bool ota_verify_signature_with_key(const uint8_t hash32[32], const uint8_t sig64[64],
+                                    const uint8_t pubkey65[65]) {
+    (void)hash32; (void)sig64; (void)pubkey65;
+    return false; // placeholder — filled in Task 7
+}
+
+// ── device-only code ───────────────────────────────────────────────────────
+#ifndef NATIVE_TEST
+
+#include "ota_pubkey.h"
+#include "version.h"
+
+bool ota_verify_signature(const uint8_t hash32[32], const uint8_t sig64[64]) {
+    return ota_verify_signature_with_key(hash32, sig64, kOtaPublicKey);
+}
+
+static const char* s_server_base   = nullptr;
+static const char* s_device_id     = nullptr;
+static const char* s_hmac_secret   = nullptr;
+static uint32_t    s_interval_ms   = 21600000UL; // 6 h default
+static uint32_t    s_last_check_ms = 0;
+
+void ota_updater_init(const char* server_base, const char* device_id,
+                      const char* hmac_secret, uint32_t check_interval_ms) {
+    s_server_base   = server_base;
+    s_device_id     = device_id;
+    s_hmac_secret   = hmac_secret;
+    s_interval_ms   = check_interval_ms;
+    s_last_check_ms = 0; // force first check on next call
+}
+
+bool ota_updater_check_and_apply() { return false; } // filled in Task 8
+
+#endif // NATIVE_TEST

firmware/lib/ota_updater/ota_updater.h

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+// firmware/lib/ota_updater/ota_updater.h
+#pragma once
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
+
+// One-time init. Call from setup() after WiFi is ready.
+// server_base: e.g. "http://logs.research.bike:8000"
+// check_interval_ms: milliseconds between polls (e.g. 6*3600*1000 = 21600000)
+void ota_updater_init(const char* server_base,
+                      const char* device_id,
+                      const char* hmac_secret,
+                      uint32_t    check_interval_ms);
+
+// Polls server; downloads, verifies, and flashes if newer version available.
+// Returns true if update was applied (device reboots before returning false path).
+// Safe to call from any task; blocks during download.
+bool ota_updater_check_and_apply();
+
+// Exposed for unit testing — pass an arbitrary 65-byte uncompressed P-256 pubkey.
+bool ota_version_newer(const char* current, const char* remote);
+bool ota_verify_signature_with_key(const uint8_t hash32[32], const uint8_t sig64[64],
+                                    const uint8_t pubkey65[65]);
+
+// Production wrapper — uses the compiled-in kOtaPublicKey from ota_pubkey.h.
+// Not callable from native tests (requires ota_pubkey.h / device build).
+bool ota_verify_signature(const uint8_t hash32[32], const uint8_t sig64[64]);

firmware/test/test_ota/test_version.cpp

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+// firmware/test/test_ota/test_version.cpp
+#include <unity.h>
+
+// Pull in the function under test — include .cpp directly for native builds
+// so we don't need a separate compilation unit per test.
+#define NATIVE_TEST
+#include "../../lib/ota_updater/ota_updater.cpp"
+
+void setUp() {}
+void tearDown() {}
+
+void test_remote_newer_patch() {
+    TEST_ASSERT_TRUE(ota_version_newer("1.0.0", "1.0.1"));
+}
+void test_remote_newer_minor() {
+    TEST_ASSERT_TRUE(ota_version_newer("1.0.9", "1.1.0"));
+}
+void test_remote_newer_major() {
+    TEST_ASSERT_TRUE(ota_version_newer("0.9.9", "1.0.0"));
+}
+void test_same_version() {
+    TEST_ASSERT_FALSE(ota_version_newer("1.2.3", "1.2.3"));
+}
+void test_remote_older() {
+    TEST_ASSERT_FALSE(ota_version_newer("1.2.3", "1.2.2"));
+}
+void test_malformed_current() {
+    TEST_ASSERT_FALSE(ota_version_newer("bad", "1.0.0"));
+}
+void test_malformed_remote() {
+    TEST_ASSERT_FALSE(ota_version_newer("1.0.0", "bad"));
+}
+
+int main() {
+    UNITY_BEGIN();
+    RUN_TEST(test_remote_newer_patch);
+    RUN_TEST(test_remote_newer_minor);
+    RUN_TEST(test_remote_newer_major);
+    RUN_TEST(test_same_version);
+    RUN_TEST(test_remote_older);
+    RUN_TEST(test_malformed_current);
+    RUN_TEST(test_malformed_remote);
+    return UNITY_END();
+}