Phase 8c-8f: Extract portal, stratum_client, mint_health, client into tollgate_core

New component modules:
- tollgate_core_portal.c/h: template rendering, usage calc, captive URI detection
- tollgate_core_stratum_client.c/h: Stratum V1 JSON protocol parsing, message building
- tollgate_core_mint_health.c/h: mint health state tracking, recovery threshold logic
- tollgate_core_client.c/h: discovery/session/usage JSON parsing, renewal check, price calc

Main shims updated to delegate pure logic to component:
- captive_portal.c: uses tollgate_core_portal_render(), format_usage(), is_captive_uri()
- stratum_client.c: uses tollgate_core_stratum_parse_notify/build_*()
- mint_health.c: uses tollgate_core_mint_health_update/is_reachable/mark_unreachable()
- tollgate_client.c: uses tollgate_core_client_parse_*/should_renew/calc_price_per_min()

4 new unit tests (test_portal, test_stratum_client, test_mint_health_core, test_client_core)
All 25 unit tests pass. ESP-IDF build passes (68% partition free).

1 files changed, 189 insertions, 0 deletions

diff --git a/tests/unit/test_client_core.c b/tests/unit/test_client_core.c
new file mode 100644
index 0000000..7cc6cc7
--- /dev/null
+++ b/tests/unit/test_client_core.c
@@ -0,0 +1,189 @@
+#include "test_framework.h"
+#include "../../components/tollgate_core/src/tollgate_core_client.h"
+#include <cjson/cJSON.h>
+#include <string.h>
+#include <stdio.h>
+
+int main(void)
+{
+    printf("=== test_client_core ===\n");
+
+    printf("\n--- parse_discovery valid ---\n");
+    {
+        const char *json = "{\"kind\":10021,\"content\":\"discovery\","
+                           "\"tags\":["
+                           "[\"metric\",\"milliseconds\"],"
+                           "[\"step_size\",\"60000\"],"
+                           "[\"price_per_step\",\"21\",\"21\",\"sha256\",\"https://test.mint\"]"
+                           "]}";
+        tollgate_discovery_t disc = {0};
+        bool ok = tollgate_core_client_parse_discovery(json, &disc);
+        ASSERT(ok, "parse_discovery returns true");
+        ASSERT(disc.is_tollgate, "is_tollgate set");
+        ASSERT_EQ_INT(21, disc.price_per_step, "price_per_step");
+        ASSERT_EQ_INT(60000, disc.step_size_ms, "step_size_ms");
+        ASSERT(strcmp(disc.metric, "milliseconds") == 0, "metric");
+        ASSERT(strcmp(disc.mint_url, "https://test.mint") == 0, "mint_url");
+    }
+
+    printf("\n--- parse_discovery wrong kind ---\n");
+    {
+        const char *json = "{\"kind\":9999}";
+        tollgate_discovery_t disc = {0};
+        bool ok = tollgate_core_client_parse_discovery(json, &disc);
+        ASSERT(!ok, "wrong kind returns false");
+    }
+
+    printf("\n--- parse_discovery mining payment ---\n");
+    {
+        const char *json = "{\"kind\":10021,\"content\":\"\","
+                           "\"tags\":["
+                           "[\"metric\",\"milliseconds\"],"
+                           "[\"step_size\",\"60000\"],"
+                           "[\"price_per_step\",\"0\",\"mining\",\"3333\",\"extra\"]"
+                           "]}";
+        tollgate_discovery_t disc = {0};
+        bool ok = tollgate_core_client_parse_discovery(json, &disc);
+        ASSERT(ok, "parse_discovery mining returns true");
+        ASSERT(disc.mining_available, "mining_available set");
+        ASSERT_EQ_INT(3333, (int)disc.mining_port, "mining_port");
+    }
+
+    printf("\n--- parse_discovery empty tags ---\n");
+    {
+        const char *json = "{\"kind\":10021,\"tags\":[]}";
+        tollgate_discovery_t disc = {0};
+        bool ok = tollgate_core_client_parse_discovery(json, &disc);
+        ASSERT(ok, "empty tags returns true");
+        ASSERT(disc.is_tollgate, "is_tollgate set");
+    }
+
+    printf("\n--- parse_discovery no tags ---\n");
+    {
+        const char *json = "{\"kind\":10021}";
+        tollgate_discovery_t disc = {0};
+        bool ok = tollgate_core_client_parse_discovery(json, &disc);
+        ASSERT(ok, "no tags returns true");
+    }
+
+    printf("\n--- parse_discovery invalid JSON ---\n");
+    {
+        tollgate_discovery_t disc = {0};
+        bool ok = tollgate_core_client_parse_discovery("not json", &disc);
+        ASSERT(!ok, "invalid JSON returns false");
+    }
+
+    printf("\n--- parse_session valid ---\n");
+    {
+        const char *json = "{\"kind\":1022,\"content\":\"session\","
+                           "\"tags\":[[\"allotment\",\"120000\"]]}";
+        int64_t allotment = 0;
+        bool ok = tollgate_core_client_parse_session(json, &allotment);
+        ASSERT(ok, "parse_session returns true");
+        ASSERT_EQ_UINT64(120000, (unsigned long long)allotment, "allotment_ms");
+    }
+
+    printf("\n--- parse_session wrong kind ---\n");
+    {
+        const char *json = "{\"kind\":10021}";
+        int64_t allotment = 0;
+        bool ok = tollgate_core_client_parse_session(json, &allotment);
+        ASSERT(!ok, "wrong kind returns false");
+    }
+
+    printf("\n--- parse_session no allotment tag ---\n");
+    {
+        const char *json = "{\"kind\":1022,\"tags\":[]}";
+        int64_t allotment = 999;
+        bool ok = tollgate_core_client_parse_session(json, &allotment);
+        ASSERT(ok, "returns true");
+        ASSERT_EQ_UINT64(999, (unsigned long long)allotment, "allotment unchanged when no tag");
+    }
+
+    printf("\n--- parse_usage valid ---\n");
+    {
+        int64_t remaining = 0, total = 0;
+        bool ok = tollgate_core_client_parse_usage("45000/60000", &remaining, &total);
+        ASSERT(ok, "parse_usage returns true");
+        ASSERT_EQ_UINT64(45000, (unsigned long long)remaining, "remaining");
+        ASSERT_EQ_UINT64(60000, (unsigned long long)total, "total");
+    }
+
+    printf("\n--- parse_usage no slash ---\n");
+    {
+        int64_t remaining = 0, total = 0;
+        bool ok = tollgate_core_client_parse_usage("45000", &remaining, &total);
+        ASSERT(!ok, "no slash returns false");
+    }
+
+    printf("\n--- parse_usage zero values ---\n");
+    {
+        int64_t remaining = 0, total = 0;
+        bool ok = tollgate_core_client_parse_usage("0/0", &remaining, &total);
+        ASSERT(ok, "parse_usage zero values");
+        ASSERT_EQ_UINT64(0, (unsigned long long)remaining, "remaining is 0");
+        ASSERT_EQ_UINT64(0, (unsigned long long)total, "total is 0");
+    }
+
+    printf("\n--- should_renew ---\n");
+    {
+        ASSERT(tollgate_core_client_should_renew(1000, 60000, 20),
+               "1.6% remaining → should renew");
+        ASSERT(tollgate_core_client_should_renew(0, 60000, 20),
+               "0% remaining → should renew");
+        ASSERT(!tollgate_core_client_should_renew(30000, 60000, 20),
+               "50% remaining → should not renew");
+        ASSERT(!tollgate_core_client_should_renew(60000, 60000, 20),
+               "100% remaining → should not renew");
+        ASSERT(tollgate_core_client_should_renew(11999, 60000, 20),
+               "19.99% → should renew");
+        ASSERT(tollgate_core_client_should_renew(12000, 60000, 20),
+               "20% exactly at threshold → should renew");
+    }
+
+    printf("\n--- should_renew default threshold ---\n");
+    {
+        ASSERT(tollgate_core_client_should_renew(1000, 60000, 0),
+               "threshold=0 defaults to 20%");
+        ASSERT(tollgate_core_client_should_renew(1000, 60000, -1),
+               "negative threshold defaults to 20%");
+    }
+
+    printf("\n--- should_renew edge cases ---\n");
+    {
+        ASSERT(!tollgate_core_client_should_renew(-1, 60000, 20),
+               "negative remaining → false");
+        ASSERT(!tollgate_core_client_should_renew(1000, 0, 20),
+               "zero allotment → false");
+    }
+
+    printf("\n--- calc_price_per_min ---\n");
+    {
+        ASSERT_EQ_INT(21, tollgate_core_client_calc_price_per_min(21, 60000),
+                      "21 sats/60s = 21 sats/min");
+        ASSERT_EQ_INT(42, tollgate_core_client_calc_price_per_min(21, 30000),
+                      "21 sats/30s = 42 sats/min");
+        ASSERT_EQ_INT(21000, tollgate_core_client_calc_price_per_min(21, 60),
+                      "21 sats/60ms effective");
+    }
+
+    printf("\n--- calc_price_per_min zero step ---\n");
+    {
+        int result = tollgate_core_client_calc_price_per_min(21, 0);
+        ASSERT(result > 0, "zero step_size_ms doesn't crash");
+    }
+
+    printf("\n--- calc_steps ---\n");
+    {
+        ASSERT_EQ_INT(21, tollgate_core_client_calc_steps(1, 21, 21),
+                      "1 step * 21 = 21");
+        ASSERT_EQ_INT(42, tollgate_core_client_calc_steps(2, 21, 21),
+                      "2 steps * 21 = 42");
+        ASSERT_EQ_INT(21, tollgate_core_client_calc_steps(0, 21, 21),
+                      "0 steps defaults to 1");
+        ASSERT_EQ_INT(21, tollgate_core_client_calc_steps(-1, 21, 21),
+                      "negative steps defaults to 1");
+    }
+
+    TEST_SUMMARY();
+}