fix: query Horizon inside the container and flag lost core connection

- Fetch Horizon via curl inside the container (127.0.0.1:8000) instead of
  the host port 31401; the host->bridge forwarding hung until the 5 s
  timeout and made each cycle take ~6 s instead of ~1 s
- Report an error when Horizon's core_latest_ledger is 0 (no connection
  to stellar-core) instead of a false "Synced" with a negative lag
- Compute the ingest lag against stellar-core's own ledger
- "History Oldest" now shows history_elder_ledger; the latest ledger is
  listed separately as "History Latest"

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -45,7 +45,7 @@ Single self-contained script (`pi-stat`). Logic is split into helper functions a
 
 - **Docker SDK** — container CPU/RAM stats; all commands run inside the auto-detected container (`mainnet` → `testnet2` → `testnet`, first running one) via `exec_run`
 - **Stellar Core HTTP API** — `exec_json()` runs `stellar-core http-command <cmd>` inside the container
-- **Horizon API** — `http://localhost:31401`
+- **Horizon API** — `curl http://127.0.0.1:8000/` run inside the container via `exec_json()`, not via the host port `31401` (host→bridge forwarding can hang until timeout if Docker's host firewall rules are broken)
 - **PostgreSQL** — `psql` inside the container; used for peer DB counts and pubkey→IP mapping
 - **ZFS CLI** — `zpool`/`zfs` commands on the host for disk health (`z01pool`); if `zpool` is not found (`HAS_ZFS = False`), falls back to `shutil.disk_usage()` — works on Linux without ZFS, WSL2, and Windows
 - **ip-api.com** — batch geolocation (Country, City), cached in `_geo_cache`; only fetched with `-g`

pi-stat

@@ -38,7 +38,7 @@ except ImportError:
 # --- Configuration ---
 HAS_ZFS              = shutil.which("zpool") is not None
 CANDIDATE_CONTAINERS = ["mainnet", "testnet2", "testnet"]
-HORIZON_URL          = "http://localhost:31401"
+HORIZON_URL          = "http://127.0.0.1:8000"  # queried from inside the container, not via the host port
 CFG_PATH             = os.path.join(os.path.dirname(os.path.realpath(__file__)), "stellar-core.cfg")
 DEFAULT_REFRESH      = 5
 REFRESH_WARN_RATIO   = 0.8  # warn if a cycle takes >= 80% of the refresh interval
@@ -262,12 +262,12 @@ def run_cycle(client, peers_extended, geo_enabled, show_ip, interactive=False, e
         if raw:
             core_info = raw.get("info")
 
+    # Query Horizon via curl inside the container: independent of the host's
+    # port forwarding (31401), which can hang until timeout if Docker's
+    # firewall rules on the host are broken.
     hz_data = None
-    try:
-        with urlopen(HORIZON_URL + "/", timeout=5) as resp:
-            hz_data = json.loads(resp.read())
-    except Exception:
-        pass
+    if container:
+        hz_data = exec_json(container, ["curl", "-s", "-m", "5", HORIZON_URL + "/"])
 
     # =============================================================
     # 1. CONTAINER STATUS
@@ -373,23 +373,36 @@ def run_cycle(client, peers_extended, geo_enabled, show_ip, interactive=False, e
     hdr("🌅 API Status (Horizon)")
 
     if hz_data is None:
-        err(f"Horizon API not reachable ({HORIZON_URL})")
+        err(f"Horizon API not reachable ({HORIZON_URL} in container '{container_name}')")
     else:
         core_blk  = hz_data.get("core_latest_ledger",    0)
         hist_blk  = hz_data.get("history_latest_ledger", 0)
+        elder_blk = hz_data.get("history_elder_ledger",  0)
         ings_blk  = hz_data.get("ingest_latest_ledger",  0)
-        lag       = core_blk - ings_blk
         closed_at = hz_data.get("history_latest_ledger_closed_at", "?")
 
-        if lag <= 2:
+        # Reference ledger for the ingest lag: stellar-core's own ledger if we
+        # have it, otherwise what Horizon reports for core. core_latest_ledger
+        # is 0 when Horizon has lost its connection to stellar-core; computing
+        # the lag against 0 would give a negative value and a false "Synced".
+        ref_blk = block if core_info is not None else core_blk
+        lag     = (ref_blk - ings_blk) if ref_blk else None
+
+        if not core_blk:
+            err("Status: Horizon has no connection to stellar-core (core_latest_ledger = 0)")
+            if lag is not None and lag > 2:
+                warn(f"Ingest {lag} ledger behind core")
+        elif lag <= 2:
             ok(f"Status: Synced (Ingest lag: {lag} ledger)")
         else:
             warn(f"Status: Lagging (Ingest {lag} ledger behind core)")
         core_diff = (block - core_blk) if (core_info is not None and core_blk) else None
         core_diff_str = f"  (Δ {core_diff:+d} vs Core)" if core_diff is not None else ""
-        print(f"     Core Latest Ledger:   {core_blk}{core_diff_str}")
+        core_blk_str  = str(core_blk) if core_blk else "— (not connected)"
+        print(f"     Core Latest Ledger:   {core_blk_str}{core_diff_str}")
         print(f"     Ingest Latest Ledger: {ings_blk}  (last closed: {closed_at})")
-        print(f"     History Oldest:       {hist_blk}")
+        print(f"     History Latest:       {hist_blk}")
+        print(f"     History Oldest:       {elder_blk}")
 
     # =============================================================
     # 5. NODE METRICS (stellar-core)