fix(ai-proxy-multi): inconsistent resolved nodes for healthcheck

[Revolyssup]

Cause of defect
ai-proxy-multi executes resolve_endpoint once before creating health checker:

apisix/apisix/plugins/ai-proxy-multi.lua

Line 279 in 18884bc

local node = resolve_endpoint(instance)

, resolve_endpoint was executed again when obtaining the health status of the instance:

apisix/apisix/plugins/ai-proxy-multi.lua

Line 224 in 18884bc

local node = resolve_endpoint(ins)

When the results of two dns resolutions change (which is common when domain name resolution contains multiple IPs), the following error will be reported:

2025/08/21 09:38:13 [warn] 154#154: *381457 [lua] ai-proxy-multi.lua:345: fetch_health_instances(): failed to get health check target status, addr: 192.168.117.8:80, host: httpbin.local, err: target not found, client: 192.168.117.1, server: _, request: "POST /anything HTTP/1.1", host: "127.0.0.1:9080", request_id: "d2daae4e3eb88ecff5b3419c2cb38c02”

Repair suggestions
Refer to the parse_domain_in_route function currently in APISIX:

apisix/apisix/init.lua

Lines 242 to 267 in 3260931

	local function parse_domain_in_route(route)
	local nodes = route.value.upstream.nodes
	local new_nodes, err = upstream_util.parse_domain_for_nodes(nodes)
	if not new_nodes then
	return nil, err
	end
	local up_conf = route.dns_value and route.dns_value.upstream
	local ok = upstream_util.compare_upstream_node(up_conf, new_nodes)
	if ok then
	return route
	end
	-- don't modify the modifiedIndex to avoid plugin cache miss because of DNS resolve result
	-- has changed
	route.dns_value = core.table.deepcopy(route.value)
	route.dns_value.upstream.nodes = new_nodes
	if not route.dns_value._nodes_ver then
	route.dns_value._nodes_ver = 0
	end
	route.dns_value._nodes_ver = route.dns_value._nodes_ver + 1
	core.log.info("parse route which contain domain: ",
	core.json.delay_encode(route, true))
	return route
	end

Record the result of dns resolution in the instance table as _dns_value, and maintain the _nodes_ver variable.
At the same time, when _nodes_ver changes, the health checker needs to be rebuilt.

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)