fix(cloudflared): add app binding diagnostics and improve readiness check

- Add _check_app_binding() to detect if app is bound to 127.0.0.1
  instead of 0.0.0.0 (common cause of tunnel 'app error 0')
- Improve curl readiness check: wait up to 30s, check HTTP status codes
  (accept 2xx, 3xx, 401, 403 as 'ready')
- Log curl stderr for connection debugging
- Log binding diagnosis when external connectivity fails

Quality gates: pytest 42 passed

apps/api/src/services/docker.py

@@ -384,6 +384,87 @@ def find_free_port(start: int = 10000, end: int = 20000) -> int:
     raise RuntimeError(f"No free port found in range {start}-{end}")
 
 
+def _check_app_binding(
+    container_name: str, port: int
+) -> dict[str, str | bool]:
+    """Diagnose whether the app is bound to 127.0.0.1 or 0.0.0.0.
+
+    Checks from both inside the container (localhost) and outside
+    (via Docker network) to detect binding issues.
+
+    Returns:
+        Dict with 'internal_ok', 'external_ok', 'internal_status',
+        'external_status', and 'diagnosis'.
+    """
+    import subprocess
+
+    result: dict[str, Any] = {
+        "internal_ok": False,
+        "external_ok": False,
+        "internal_status": None,
+        "external_status": None,
+        "diagnosis": "unknown",
+    }
+
+    # Check from inside the container (loopback)
+    internal = subprocess.run(
+        [
+            "docker",
+            "exec",
+            container_name,
+            "sh",
+            "-c",
+            f"curl -s -o /dev/null -w '%{{http_code}}' http://localhost:{port}",
+        ],
+        capture_output=True,
+        text=True,
+        timeout=5,
+    )
+    if internal.returncode == 0:
+        try:
+            result["internal_status"] = int(internal.stdout.strip())
+            result["internal_ok"] = result["internal_status"] > 0
+        except ValueError:
+            pass
+
+    # Check from outside the container (Docker network)
+    external = subprocess.run(
+        [
+            "curl",
+            "-s",
+            "-o",
+            "/dev/null",
+            "-w",
+            "%{http_code}",
+            f"http://{container_name}:{port}",
+        ],
+        capture_output=True,
+        text=True,
+        timeout=5,
+    )
+    if external.returncode == 0:
+        try:
+            result["external_status"] = int(external.stdout.strip())
+            result["external_ok"] = result["external_status"] > 0
+        except ValueError:
+            pass
+
+    # Diagnose binding issue
+    if result["internal_ok"] and not result["external_ok"]:
+        result["diagnosis"] = (
+            f"App appears to be bound to 127.0.0.1:{port} inside the container. "
+            f"It must bind to 0.0.0.0:{port} to be accessible from the tunnel."
+        )
+    elif result["internal_ok"] and result["external_ok"]:
+        result["diagnosis"] = "App is accessible on both interfaces."
+    elif not result["internal_ok"] and not result["external_ok"]:
+        result["diagnosis"] = f"App is not responding on port {port} at all."
+    else:
+        result["diagnosis"] = "Unexpected binding state."
+
+    return result
+
+
 def start_cloudflared_tunnel(
     container_name: str, port: int, timeout: int = 30
 ) -> dict[str, str]:
@@ -405,9 +486,11 @@ def start_cloudflared_tunnel(
 
     logger = logging.getLogger(__name__)
 
-    # First verify the container is accessible
+    # First verify the container is accessible from the Docker network
     logger.info("Checking connectivity to %s:%d...", container_name, port)
-    for attempt in range(10):
+    accessible = False
+    last_status = None
+    for attempt in range(30):  # 30 attempts × 1s = 30s max wait for app startup
         check = subprocess.run(
             [
                 "curl",
@@ -416,21 +499,59 @@ def start_cloudflared_tunnel(
                 "/dev/null",
                 "-w",
                 "%{http_code}",
+                "--max-time",
+                "3",
                 f"http://{container_name}:{port}",
             ],
             capture_output=True,
             text=True,
             timeout=5,
         )
+        status_str = check.stdout.strip()
         logger.info(
-            "Connectivity check %d: http_code=%s", attempt + 1, check.stdout.strip()
+            "Connectivity check %d/%d: http_code=%s (rc=%d)",
+            attempt + 1,
+            30,
+            status_str,
+            check.returncode,
         )
-        if check.returncode == 0:
-            break
+        try:
+            last_status = int(status_str)
+            # Accept 2xx, 3xx, 401, 403 as "app is listening"
+            if last_status in (401, 403) or 200 <= last_status < 400:
+                accessible = True
+                logger.info(
+                    "App on %s:%d is ready (HTTP %d)",
+                    container_name,
+                    port,
+                    last_status,
+                )
+                break
+        except ValueError:
+            pass
+
+        if check.returncode != 0:
+            logger.debug(
+                "curl failed: stderr=%s", check.stderr.strip() if check.stderr else ""
+            )
         time.sleep(1)
-    else:
+
+    if not accessible:
         logger.warning(
-            "Container %s:%d not responding to curl checks", container_name, port
+            "Container %s:%d not responding after 30s (last status: %s). "
+            "Running binding diagnostics...",
+            container_name,
+            port,
+            last_status,
+        )
+        diagnosis = _check_app_binding(container_name, port)
+        logger.warning(
+            "Binding diagnosis: internal=%s (HTTP %s), external=%s (HTTP %s). %s",
+            diagnosis["internal_ok"],
+            diagnosis["internal_status"],
+            diagnosis["external_ok"],
+            diagnosis["external_status"],
+            diagnosis["diagnosis"],
         )
 
     # Run cloudflared in background, capture output