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

@@ -0,0 +1,53 @@
+// 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

@@ -0,0 +1,27 @@
+// 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]);