feat(mcp-server): server instructions + report-only status tool guidance

When a user asks to view cluster status (e.g. "看看机器情况"), the LLM saw
non-OK values in the MCP response (a node UNAVAIL, a job PEND/EXIT) and
treated them as incidents — proposing unsolicited diagnostic/repair actions
and referencing "known bugs". The user only wanted a factual status report.

Mitigation at the MCP layer:
- Add server instructions (returned to the client in the initialize
  handshake) stating that the status tools return operational snapshots,
  that UNAVAIL/PEND/EXIT/UNKWN are normal state, and that the model must
  not speculate or propose actions unless the user explicitly asks.
- Append report-only guidance to the scheduler_list_nodes / list_jobs /
  cluster_metrics descriptions.

Verified: initialize response carries the 857-char instructions; tools/list
shows the updated descriptions.

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

src/frontend/mcp-server/cmd/main.go

@@ -10,6 +10,23 @@ import (
 	"mcp-server/internal"
 )
 
+// serverInstructions are returned to MCP clients (LLMs like Claude Code) in
+// the initialize handshake and are the standard way to steer how the model
+// uses the server. The key guidance: the status tools return operational
+// snapshots, not incident triggers — a node reporting UNAVAIL or a job in
+// PEND/EXIT/UNKWN is normal state. Without this, the model treats every
+// non-"OK" value as a problem and floods the user with unsolicited
+// diagnostic advice when they only asked to view status.
+const serverInstructions = "XCE scheduler agent — cluster status, not an incident console.\n\n" +
+	"Status tools (scheduler_list_nodes, scheduler_list_jobs, scheduler_get_job, scheduler_cluster_metrics) " +
+	"return informational snapshots. A node showing UNAVAIL/offline, or a job in PEND/EXIT/UNKWN/TRANSIENT, is " +
+	"normal operational state, not an error condition.\n\n" +
+	"When the user asks to view or check status, report the data factually and concisely. Do NOT speculate about " +
+	"root causes, do NOT reference \"known bugs\", and do NOT propose diagnostic or repair actions (checking logs, " +
+	"restarting daemons, opening tickets, ssh'ing to nodes, etc.) unless the user explicitly asks for help or " +
+	"remediation. If you believe action may be warranted, say so in at most one line and let the user decide.\n\n" +
+	"Write tools (scheduler_submit/hold/release/cancel) are destructive and require the user's explicit intent."
+
 func main() {
 	baseURL := os.Getenv("XCE_API_URL")
 	token := os.Getenv("XCE_API_KEY")
@@ -32,6 +49,7 @@ func main() {
 		"0.2.0",
 		mcps.WithResourceCapabilities(true, true),
 		mcps.WithLogging(),
+		mcps.WithInstructions(serverInstructions),
 	)
 
 	// Read-only tools are annotated as such so the MCP client does not prompt
@@ -39,7 +57,7 @@ func main() {
 
 	// ── scheduler_list_jobs ──
 	s.AddTool(mcp.NewTool("scheduler_list_jobs",
-		mcp.WithDescription("List jobs in the cluster. Supports filtering by queue, owner, status, and pagination."),
+		mcp.WithDescription("List jobs in the cluster. Supports filtering by queue, owner, status, and pagination. Status snapshot: report results as-is; job states (PEND/RUN/EXIT/DONE/etc.) are informational, not errors to investigate unprompted."),
 		mcp.WithString("queue", mcp.Description("Filter by queue name")),
 		mcp.WithString("owner", mcp.Description("Filter by job owner username")),
 		mcp.WithString("status", mcp.Description("Filter by status: pending|running|succeeded|failed|cancelled|suspended|unknown")),
@@ -69,7 +87,7 @@ func main() {
 
 	// ── scheduler_list_nodes ──
 	s.AddTool(mcp.NewTool("scheduler_list_nodes",
-		mcp.WithDescription("List all compute nodes with their resource usage and status."),
+		mcp.WithDescription("List all compute nodes with their resource usage and status. Status snapshot: report node states (OK/UNAVAIL/etc.) as-is — a non-OK node is informational, not an error; do not offer diagnostic/repair suggestions unless the user asks."),
 		mcp.WithReadOnlyHintAnnotation(true),
 		mcp.WithDestructiveHintAnnotation(false),
 	), app.HandleListNodes)
@@ -89,7 +107,7 @@ func main() {
 
 	// ── scheduler_cluster_metrics ──
 	s.AddTool(mcp.NewTool("scheduler_cluster_metrics",
-		mcp.WithDescription("Get a snapshot of overall cluster resource usage and utilization."),
+		mcp.WithDescription("Get a snapshot of overall cluster resource usage and utilization. Status snapshot: report as-is; do not speculate about causes or propose actions unless the user asks."),
 		mcp.WithReadOnlyHintAnnotation(true),
 		mcp.WithDestructiveHintAnnotation(false),
 	), app.HandleClusterMetrics)