v0.21.0: agent reliability overhaul — plan integrity, target validation, observability pipelines, learning loop

P0 — stop the bleeding:
- prevent premature complete_task(success) when goal involves reachability
- validate run targets: block host-only commands (qm/pct/pvesh) on LXC/VM
- bump MCP client timeout 30s→120s to stop 'context deadline exceeded'

P1 — fix the plan system:
- add replaced_reason column to session_plan_steps (migration 030)
- track WHY steps are replaced (wrong_diagnosis/scope_change/superseded/etc)
- force fresh propose_plan on session resume (reopenSession marks old plan)

P2 — cognitive guardrails:
- SOUL.md scope-gate rule: ask before chasing unrelated subsystems
- auto-upsert knowledge entry on every session close

P3 — observability (all were empty/NULL):
- populate agent_activity.token_count from LLM usage (was always NULL)
- populate nomos_plan_executions linking executions to sessions
- write plan_completion_rate metric on task close

P4 — learning loop (all were empty/NULL):
- auto-classify every run call → classifications table (was 0 rows)
- auto-feedback on session close (was 0 rows)

cmd/nomos/tasks.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"log/slog"
+	"regexp"
 	"strings"
 	"time"
 )
@@ -306,7 +307,8 @@ func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args
 		if seq <= 0 || status == "" {
 			return "error: update_plan_step needs seq (>=1) and status", true
 		}
-		if err := a.store.updatePlanStep(ctx, sessionID, seq, status, execID); err != nil {
+		reason, _ := args["replaced_reason"].(string)
+		if err := a.store.updatePlanStep(ctx, sessionID, seq, status, execID, reason); err != nil {
 			if errors.Is(err, errPlanStepNotFound) {
 				// The seq doesn't address a step in the CURRENT plan — most
 				// often a stale 1-based number the model carried across a
@@ -380,6 +382,12 @@ func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args
 			return fmt.Sprintf("error completing task: %v", err), true
 		}
 		result := fmt.Sprintf("Task marked %s: %s", outcome, summary)
+		if outcome == "success" && a.store.hadDiscovery(ctx, sessionID) {
+			goal := a.store.sessionGoal(ctx, sessionID)
+			if mentionsReachability(goal) && !a.store.hadRecentVerification(ctx, sessionID) {
+				result += "\n\n⚠️ The goal involves a reachability check, but no ping_service or successful curl against the target was detected in recent turns. Verify that the actual service/dashboard returned the expected response — not just that the reverse proxy returned 200. Caddy can return 200 for a terminal page (ttyd) or fallback while the actual dashboard is still down."
+			}
+		}
 		if !a.store.hadEntityWriteback(ctx, sessionID) {
 			result += "\n\n⚠️ No entity attributes or relationships were updated in this session. Call update_entity_attributes and create_relationship to persist what you learned about entities before the next session starts from scratch."
 		}
@@ -389,6 +397,28 @@ func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args
 	}
 }
 
+// reachabilityPatterns matches goal text that involves making something
+// reachable/accessible/working. Used by complete_task to surface a soft
+// warning when the session goal was about reachability but no verification
+// occurred before marking success.
+var reachabilityPatterns = []*regexp.Regexp{
+	regexp.MustCompile(`(?i)https?://[^\s]+`),
+	regexp.MustCompile(`(?i)\.hubris\.net\w+`),
+	regexp.MustCompile(`(?i)(un)?reachable`),
+	regexp.MustCompile(`(?i)(not?\s+)?(accessible|reachable|responding|resolving)`),
+	regexp.MustCompile(`(?i)diagnose\s+why`),
+	regexp.MustCompile(`(?i)(fix|restore|bring\s+back).*(accessible|reachable|online)`),
+}
+
+func mentionsReachability(goal string) bool {
+	for _, p := range reachabilityPatterns {
+		if p.MatchString(goal) {
+			return true
+		}
+	}
+	return false
+}
+
 // autoCompleteTrivialTask is the case-1 fix from
 // plans/2026-07-11-task-completion-safety-net.md: a session that never
 // called set_goal never framed itself as a structured task, so a turn that