stream: instrument TCP-window decomposition (wire kbps, hdr_gap, pend_age)

Before touching CONFIG_LWIP_TCP_WND_DEFAULT, make the window question
decidable from the logs. New per-window metrics in the stream log,
/state, and stats struct:

- wire min/avg/max kbps: instantaneous throughput while each body
  drained (jpeg_len/recv_us). Ceiling ~= TCP_WND/RTT, so it scales
  with the window iff the window is the limiter.
- hdr_gap min/avg/max us: time blocked waiting for the next header
  after finishing a body. Large = sender-paced; ~0 = receive path
  is the bottleneck.
- pend_age min/avg/max us: publish->claim latency of painted frames.
  Growing across windows = queue backlog building, the failure mode
  that killed the previous WND=65535 attempt.

Together with recv/dec/paint the frame interval is now fully
decomposable: interval ~= hdr_gap + recv + pend_age + dec + paint.

Also stamp TCP_WND/TCP_MSS/RECVMBOX into the client-connect log line
so every capture is self-labeled with the config it ran under.

1 files changed, 11 insertions, 0 deletions

diff --git a/main/http_api.c b/main/http_api.c
index 3774039..e64ebc9 100644
--- a/main/http_api.c
+++ b/main/http_api.c
@@ -118,6 +118,17 @@ static esp_err_t state_get_handler(httpd_req_t *req)
     cJSON_AddNumberToObject(s, "decode_idle_max_us",  (double)stream.decode_idle_max_us);
     cJSON_AddNumberToObject(s, "last_paint_event_us_low",
                             (double)stream.last_paint_event_us_low);
+    // TCP-window decomposition (see stream_server.h): wire = body-drain
+    // throughput, hdr_gap = sender idle, pend_age = handoff queue wait.
+    cJSON_AddNumberToObject(s, "wire_min_kbps",   (double)stream.wire_min_kbps);
+    cJSON_AddNumberToObject(s, "wire_avg_kbps",   (double)stream.wire_avg_kbps);
+    cJSON_AddNumberToObject(s, "wire_max_kbps",   (double)stream.wire_max_kbps);
+    cJSON_AddNumberToObject(s, "hdr_gap_min_us",  (double)stream.hdr_gap_min_us);
+    cJSON_AddNumberToObject(s, "hdr_gap_avg_us",  (double)stream.hdr_gap_avg_us);
+    cJSON_AddNumberToObject(s, "hdr_gap_max_us",  (double)stream.hdr_gap_max_us);
+    cJSON_AddNumberToObject(s, "pend_age_min_us", (double)stream.pend_age_min_us);
+    cJSON_AddNumberToObject(s, "pend_age_avg_us", (double)stream.pend_age_avg_us);
+    cJSON_AddNumberToObject(s, "pend_age_max_us", (double)stream.pend_age_max_us);
     cJSON_AddItemToObject(root, "stream", s);
 
     char *body = cJSON_PrintUnformatted(root);