feat: add agent loop and context builder

Agent loop runs on Core 1: pops inbound messages, builds system
prompt from bootstrap files + memory, calls Claude API, saves
session, pushes response to outbound queue. PSRAM-allocated buffers.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

main/agent/context_builder.c

@@ -0,0 +1,97 @@
+#include "context_builder.h"
+#include "mimi_config.h"
+#include "memory/memory_store.h"
+
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+#include "esp_log.h"
+#include "cJSON.h"
+
+static const char *TAG = "context";
+
+static size_t append_file(char *buf, size_t size, size_t offset, const char *path, const char *header)
+{
+    FILE *f = fopen(path, "r");
+    if (!f) return offset;
+
+    if (header && offset < size - 1) {
+        offset += snprintf(buf + offset, size - offset, "\n## %s\n\n", header);
+    }
+
+    size_t n = fread(buf + offset, 1, size - offset - 1, f);
+    offset += n;
+    buf[offset] = '\0';
+    fclose(f);
+    return offset;
+}
+
+esp_err_t context_build_system_prompt(char *buf, size_t size)
+{
+    size_t off = 0;
+
+    /* Identity header */
+    time_t now;
+    time(&now);
+    struct tm tm;
+    localtime_r(&now, &tm);
+    char time_str[64];
+    strftime(time_str, sizeof(time_str), "%Y-%m-%d %H:%M (%A)", &tm);
+
+    off += snprintf(buf + off, size - off,
+        "# MimiClaw\n\n"
+        "You are MimiClaw, a personal AI assistant running on an ESP32-S3 device.\n"
+        "You communicate through Telegram and WebSocket.\n\n"
+        "## Current Time\n%s\n\n"
+        "Be helpful, accurate, and concise.\n",
+        time_str);
+
+    /* Bootstrap files */
+    off = append_file(buf, size, off, MIMI_SOUL_FILE, "Personality");
+    off = append_file(buf, size, off, MIMI_USER_FILE, "User Info");
+
+    /* Long-term memory */
+    char mem_buf[4096];
+    if (memory_read_long_term(mem_buf, sizeof(mem_buf)) == ESP_OK && mem_buf[0]) {
+        off += snprintf(buf + off, size - off, "\n## Long-term Memory\n\n%s\n", mem_buf);
+    }
+
+    /* Recent daily notes (last 3 days) */
+    char recent_buf[4096];
+    if (memory_read_recent(recent_buf, sizeof(recent_buf), 3) == ESP_OK && recent_buf[0]) {
+        off += snprintf(buf + off, size - off, "\n## Recent Notes\n\n%s\n", recent_buf);
+    }
+
+    ESP_LOGI(TAG, "System prompt built: %d bytes", (int)off);
+    return ESP_OK;
+}
+
+esp_err_t context_build_messages(const char *history_json, const char *user_message,
+                                 char *buf, size_t size)
+{
+    /* Parse existing history */
+    cJSON *history = cJSON_Parse(history_json);
+    if (!history) {
+        history = cJSON_CreateArray();
+    }
+
+    /* Append current user message */
+    cJSON *user_msg = cJSON_CreateObject();
+    cJSON_AddStringToObject(user_msg, "role", "user");
+    cJSON_AddStringToObject(user_msg, "content", user_message);
+    cJSON_AddItemToArray(history, user_msg);
+
+    /* Serialize */
+    char *json_str = cJSON_PrintUnformatted(history);
+    cJSON_Delete(history);
+
+    if (json_str) {
+        strncpy(buf, json_str, size - 1);
+        buf[size - 1] = '\0';
+        free(json_str);
+    } else {
+        snprintf(buf, size, "[{\"role\":\"user\",\"content\":\"%s\"}]", user_message);
+    }
+
+    return ESP_OK;
+}