checker: add JoinRelative helper for service-relative owner names

Drains in-flight requests within a 10s timeout and stops the load-average
sampler before returning. Callers needing custom signal handling can still
opt out via Handler() and run their own http.Server.

README.md

@@ -30,6 +30,53 @@ go get git.happydns.org/checker-sdk-go/checker
 See [checker-dummy](https://git.happydns.org/checker-dummy) for a
 fully working, documented template.
 
+## Extending the server
+
+`checker.Server` exposes the standard SDK routes (`/health`, `/collect`,
+and, depending on the provider's optional interfaces, `/definition`,
+`/evaluate`, `/report`). Plugins that need to serve auxiliary endpoints
+(debug pages, webhooks, custom UI assets, …) can register them on the
+same mux:
+
+```go
+srv := checker.NewServer(provider)
+
+srv.HandleFunc("GET /debug/state", func(w http.ResponseWriter, r *http.Request) {
+    // …
+})
+
+// Opt a custom route into the in-flight / load-average signal
+// reported on /health:
+srv.Handle("POST /webhook", srv.TrackWork(myWebhookHandler))
+
+log.Fatal(srv.ListenAndServe(":8080"))
+```
+
+Patterns that collide with built-in routes panic at registration:
+pick non-overlapping paths. Custom handlers are not wrapped by the
+load-tracking middleware unless you opt in via `TrackWork`.
+
+## Standalone human UI (`/check`)
+
+Providers that implement `CheckerInteractive` get a built-in human-facing
+web form on `/check`, usable outside of happyDomain:
+
+```go
+type CheckerInteractive interface {
+    RenderForm() []CheckerOptionField
+    ParseForm(r *http.Request) (CheckerOptions, error)
+}
+```
+
+- `GET /check` renders a form derived from `RenderForm()`.
+- `POST /check` calls `ParseForm` to obtain `CheckerOptions`, runs the
+  standard `Collect` → `Evaluate` → `GetHTMLReport` / `ExtractMetrics`
+  pipeline, and returns a consolidated HTML page.
+
+`ParseForm` is where the checker replaces what happyDomain would normally
+auto-fill (zone records, service payload, …), typically by issuing its
+own DNS queries from the human-supplied inputs.
+
 ## License
 
 Apache License 2.0. See [LICENSE](LICENSE) and [NOTICE](NOTICE).

checker/names.go

@@ -0,0 +1,37 @@
+// Copyright 2020-2026 The happyDomain Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package checker
+
+import "strings"
+
+// JoinRelative treats name as relative to origin, as happyDomain encodes
+// service-embedded record owners and subdomains. An empty or "@" name
+// resolves to the origin itself; an empty origin returns the trimmed name
+// unchanged. A name already suffixed by origin is returned as-is so that
+// absolute encodings round-trip safely. Trailing dots are stripped.
+func JoinRelative(name, origin string) string {
+	origin = strings.TrimSuffix(origin, ".")
+	name = strings.TrimSuffix(name, ".")
+	if origin == "" {
+		return name
+	}
+	if name == "" || name == "@" {
+		return origin
+	}
+	if name == origin || strings.HasSuffix(name, "."+origin) {
+		return name
+	}
+	return name + "." + origin
+}

checker/registry_test.go

@@ -74,7 +74,7 @@ func TestRegisterExternalizableChecker_AppendsEndpointOnce(t *testing.T) {
 	}
 
 	// Second registration of the same definition pointer must NOT append a
-	// second "endpoint" AdminOpt — the duplicate check has to fire before
+	// second "endpoint" AdminOpt, the duplicate check has to fire before
 	// the append, otherwise we silently mutate the live definition.
 	RegisterExternalizableChecker(c)
 	if n := len(c.Options.AdminOpts); n != 1 {

checker/server/healthcheck.go

@@ -0,0 +1,81 @@
+// Copyright 2020-2026 The happyDomain Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"net"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// healthcheckMode is registered on the default flag set so any consumer that
+// calls flag.Parse() before ListenAndServe (the standard pattern in our
+// checker mains) gets the behaviour for free. When set, ListenAndServe
+// performs a short-lived HTTP probe against /health on the configured listen
+// address and exits 0/1 instead of starting the server. This lets the same
+// binary act as its own Docker HEALTHCHECK probe for scratch images, where
+// no shell, curl or wget is available.
+var healthcheckMode = flag.Bool(
+	"healthcheck",
+	false,
+	"probe /health on the server's listen address and exit 0 if healthy, 1 "+
+		"otherwise (intended as a Docker HEALTHCHECK for scratch-based images)",
+)
+
+// runHealthcheck performs a GET against http://<addr>/health with a short
+// timeout. Returns nil on a 2xx response, an error otherwise. A bind address
+// like ":8080" or "0.0.0.0:8080" is rewritten to dial the loopback interface
+// so the probe targets the local process.
+func runHealthcheck(addr string) error {
+	host, port, err := net.SplitHostPort(normalizeHealthcheckAddr(addr))
+	if err != nil {
+		return fmt.Errorf("invalid listen addr %q: %w", addr, err)
+	}
+	if host == "" || host == "0.0.0.0" || host == "::" {
+		host = "127.0.0.1"
+	}
+	url := fmt.Sprintf("http://%s/health", net.JoinHostPort(host, port))
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return err
+	}
+	client := &http.Client{Timeout: 2 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode/100 != 2 {
+		return fmt.Errorf("unhealthy: HTTP %d", resp.StatusCode)
+	}
+	return nil
+}
+
+func normalizeHealthcheckAddr(a string) string {
+	if strings.HasPrefix(a, ":") {
+		return "127.0.0.1" + a
+	}
+	if strings.HasPrefix(a, "[::]:") {
+		return "[::1]:" + strings.TrimPrefix(a, "[::]:")
+	}
+	return a
+}

checker/server/healthcheck_test.go

@@ -0,0 +1,72 @@
+// Copyright 2020-2026 The happyDomain Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestRunHealthcheck_OK(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/health", func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+
+	addr := strings.TrimPrefix(srv.URL, "http://")
+	if err := runHealthcheck(addr); err != nil {
+		t.Fatalf("runHealthcheck(%s) returned error: %v", addr, err)
+	}
+}
+
+func TestRunHealthcheck_NonOK(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/health", func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusServiceUnavailable)
+	})
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+
+	addr := strings.TrimPrefix(srv.URL, "http://")
+	if err := runHealthcheck(addr); err == nil {
+		t.Fatalf("runHealthcheck against 503 returned nil; want error")
+	}
+}
+
+func TestRunHealthcheck_Unreachable(t *testing.T) {
+	// Reserved-for-documentation port on loopback that nothing should bind.
+	if err := runHealthcheck("127.0.0.1:1"); err == nil {
+		t.Fatalf("runHealthcheck against unreachable port returned nil; want error")
+	}
+}
+
+func TestNormalizeHealthcheckAddr(t *testing.T) {
+	cases := map[string]string{
+		":8080":          "127.0.0.1:8080",
+		"127.0.0.1:8080": "127.0.0.1:8080",
+		"0.0.0.0:8080":   "0.0.0.0:8080",
+		"[::1]:8080":     "[::1]:8080",
+		"[::]:8080":      "[::1]:8080",
+	}
+	for in, want := range cases {
+		if got := normalizeHealthcheckAddr(in); got != want {
+			t.Errorf("normalizeHealthcheckAddr(%q) = %q, want %q", in, got, want)
+		}
+	}
+}

checker/server/interactive.go

@@ -0,0 +1,453 @@
+// Copyright 2020-2026 The happyDomain Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"html/template"
+	"log"
+	"maps"
+	"net/http"
+	"time"
+
+	"git.happydns.org/checker-sdk-go/checker"
+)
+
+// Interactive is an optional interface that observation providers
+// can implement to expose a human-facing web form usable standalone,
+// outside of a happyDomain host. Detect support with a type assertion:
+// _, ok := provider.(server.Interactive).
+//
+// When the provider implements it, Server binds GET and POST on /check.
+// GET renders an HTML form built from RenderForm(). POST calls ParseForm
+// to obtain the checker.CheckerOptions, then runs the standard pipeline
+// (Collect, Evaluate, GetHTMLReport, ExtractMetrics) and renders a
+// consolidated result page.
+//
+// Unlike /evaluate, which relies on happyDomain to fill AutoFill-backed
+// options from execution context, an Interactive implementation is
+// responsible for resolving whatever it needs from the human inputs
+// (typically via direct DNS queries) before Collect runs.
+type Interactive interface {
+	// RenderForm returns the fields the human must fill in to bootstrap
+	// a check. Typically a minimal set (domain name, nameserver to
+	// query, …) that ParseForm expands into the full CheckerOptions
+	// that Collect expects.
+	RenderForm() []checker.CheckerOptionField
+
+	// ParseForm reads the submitted form and returns the CheckerOptions
+	// ready to feed Collect. It is the checker's responsibility to do
+	// whatever lookups or resolutions are needed to populate fields
+	// that would normally be auto-filled by happyDomain. Returning an
+	// error causes the SDK to re-render the form with the error
+	// displayed.
+	ParseForm(r *http.Request) (checker.CheckerOptions, error)
+}
+
+// Siblings is an optional interface an interactive ObservationProvider
+// can co-implement to declare sibling providers whose Collect the SDK
+// runs in-process during /check. Their results are exposed as
+// RelatedObservations on ObservationGetter and ReportContext, mirroring
+// the cross-checker lineage a happyDomain host resolves.
+//
+// For each sibling the SDK seeds options from the primary and, when the
+// primary implements DiscoveryPublisher, writes its entries into any
+// sibling option tagged AutoFill == checker.AutoFillDiscoveryEntries.
+// Sibling errors are logged and skipped so the primary result still
+// reaches the user.
+type Siblings interface {
+	RelatedProviders() []checker.ObservationProvider
+}
+
+// checkResult holds everything the result page needs to render.
+type checkResult struct {
+	Title      string
+	States     []checker.CheckState
+	Metrics    []checker.CheckMetric
+	ReportHTML string
+	CollectErr string
+	ReportErr  string
+	MetricsErr string
+}
+
+type checkFormPage struct {
+	Title  string
+	Fields []checker.CheckerOptionField
+	Error  string
+}
+
+func (s *Server) handleCheckForm(w http.ResponseWriter, r *http.Request) {
+	s.renderCheckForm(w, s.interactive.RenderForm(), "")
+}
+
+func (s *Server) handleCheckSubmit(w http.ResponseWriter, r *http.Request) {
+	fields := s.interactive.RenderForm()
+	if err := r.ParseForm(); err != nil {
+		s.renderCheckForm(w, fields, fmt.Sprintf("invalid form: %v", err))
+		return
+	}
+
+	opts, err := s.interactive.ParseForm(r)
+	if err != nil {
+		s.renderCheckForm(w, fields, err.Error())
+		return
+	}
+
+	result := &checkResult{Title: s.checkPageTitle()}
+
+	data, err := s.provider.Collect(r.Context(), opts)
+	if err != nil {
+		result.CollectErr = err.Error()
+		s.renderCheckResult(w, result)
+		return
+	}
+
+	raw, err := json.Marshal(data)
+	if err != nil {
+		result.CollectErr = fmt.Sprintf("failed to marshal collected data: %v", err)
+		s.renderCheckResult(w, result)
+		return
+	}
+
+	related := s.collectRelatedObservations(r.Context(), opts, data)
+
+	if s.definition != nil {
+		obs := &mapObservationGetter{
+			data: map[checker.ObservationKey]json.RawMessage{
+				s.provider.Key(): raw,
+			},
+			related: related,
+		}
+		result.States = s.evaluateRules(r.Context(), obs, opts, nil)
+	}
+
+	ctx := checker.NewReportContext(raw, related, result.States)
+
+	if reporter, ok := s.provider.(checker.CheckerHTMLReporter); ok {
+		html, rerr := reporter.GetHTMLReport(ctx)
+		if rerr != nil {
+			result.ReportErr = rerr.Error()
+		} else {
+			result.ReportHTML = html
+		}
+	}
+
+	if reporter, ok := s.provider.(checker.CheckerMetricsReporter); ok {
+		metrics, merr := reporter.ExtractMetrics(ctx, time.Now())
+		if merr != nil {
+			result.MetricsErr = merr.Error()
+		} else {
+			result.Metrics = metrics
+		}
+	}
+
+	s.renderCheckResult(w, result)
+}
+
+// collectRelatedObservations runs sibling providers declared via Siblings
+// and returns their results keyed by the sibling's observation key.
+// Sibling errors are logged and skipped.
+func (s *Server) collectRelatedObservations(ctx context.Context, opts checker.CheckerOptions, data any) map[checker.ObservationKey][]checker.RelatedObservation {
+	irp, ok := s.provider.(Siblings)
+	if !ok {
+		return nil
+	}
+	siblings := irp.RelatedProviders()
+	if len(siblings) == 0 {
+		return nil
+	}
+
+	var entries []checker.DiscoveryEntry
+	if dp, ok := s.provider.(checker.DiscoveryPublisher); ok {
+		e, err := dp.DiscoverEntries(data)
+		if err != nil {
+			log.Printf("interactive: DiscoverEntries failed: %v", err)
+		} else {
+			entries = e
+		}
+	}
+
+	related := make(map[checker.ObservationKey][]checker.RelatedObservation, len(siblings))
+	for _, sp := range siblings {
+		sOpts := cloneOptions(opts)
+		siblingID := ""
+		if dp, ok := sp.(checker.CheckerDefinitionProvider); ok {
+			if def := dp.Definition(); def != nil {
+				siblingID = def.ID
+				if len(entries) > 0 {
+					fillDiscoveryEntryOption(sOpts, def, entries)
+				}
+			}
+		}
+		sData, err := sp.Collect(ctx, sOpts)
+		if err != nil {
+			log.Printf("interactive: sibling %q Collect failed: %v", sp.Key(), err)
+			continue
+		}
+		raw, err := json.Marshal(sData)
+		if err != nil {
+			log.Printf("interactive: sibling %q marshal failed: %v", sp.Key(), err)
+			continue
+		}
+		related[sp.Key()] = append(related[sp.Key()], checker.RelatedObservation{
+			CheckerID:   siblingID,
+			Key:         sp.Key(),
+			Data:        raw,
+			CollectedAt: time.Now(),
+		})
+	}
+	return related
+}
+
+func cloneOptions(opts checker.CheckerOptions) checker.CheckerOptions {
+	out := make(checker.CheckerOptions, len(opts))
+	maps.Copy(out, opts)
+	return out
+}
+
+// fillDiscoveryEntryOption mirrors the host's AutoFill wiring: it writes
+// entries into every option in def tagged AutoFill == checker.AutoFillDiscoveryEntries.
+func fillDiscoveryEntryOption(opts checker.CheckerOptions, def *checker.CheckerDefinition, entries []checker.DiscoveryEntry) {
+	scopes := [][]checker.CheckerOptionDocumentation{
+		def.Options.AdminOpts,
+		def.Options.UserOpts,
+		def.Options.DomainOpts,
+		def.Options.ServiceOpts,
+		def.Options.RunOpts,
+	}
+	for _, scope := range scopes {
+		for _, f := range scope {
+			if f.AutoFill == checker.AutoFillDiscoveryEntries {
+				opts[f.Id] = entries
+			}
+		}
+	}
+}
+
+func (s *Server) checkPageTitle() string {
+	if s.definition != nil && s.definition.Name != "" {
+		return s.definition.Name
+	}
+	return "Checker"
+}
+
+func renderHTML(w http.ResponseWriter, status int, tpl *template.Template, data any) {
+	var buf bytes.Buffer
+	if err := tpl.Execute(&buf, data); err != nil {
+		log.Printf("render %s: %v", tpl.Name(), err)
+		http.Error(w, "failed to render page", http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.WriteHeader(status)
+	w.Write(buf.Bytes())
+}
+
+func (s *Server) renderCheckForm(w http.ResponseWriter, fields []checker.CheckerOptionField, errMsg string) {
+	status := http.StatusOK
+	if errMsg != "" {
+		status = http.StatusBadRequest
+	}
+	renderHTML(w, status, checkFormTemplate, checkFormPage{
+		Title:  s.checkPageTitle(),
+		Fields: fields,
+		Error:  errMsg,
+	})
+}
+
+func (s *Server) renderCheckResult(w http.ResponseWriter, result *checkResult) {
+	renderHTML(w, http.StatusOK, checkResultTemplate, result)
+}
+
+func statusClass(s checker.Status) string {
+	switch s {
+	case checker.StatusOK:
+		return "ok"
+	case checker.StatusInfo:
+		return "info"
+	case checker.StatusWarn:
+		return "warn"
+	case checker.StatusCrit:
+		return "crit"
+	case checker.StatusError:
+		return "error"
+	default:
+		return "unknown"
+	}
+}
+
+// defaultString avoids printing the literal "<nil>" for unset defaults.
+func defaultString(v any) string {
+	if v == nil {
+		return ""
+	}
+	switch t := v.(type) {
+	case string:
+		return t
+	case bool:
+		if t {
+			return "true"
+		}
+		return ""
+	default:
+		return fmt.Sprintf("%v", v)
+	}
+}
+
+func defaultBool(v any) bool {
+	b, _ := v.(bool)
+	return b
+}
+
+var templateFuncs = template.FuncMap{
+	"statusClass":   statusClass,
+	"statusString":  checker.Status.String,
+	"defaultString": defaultString,
+	"defaultBool":   defaultBool,
+}
+
+const baseCSS = `
+body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif; max-width: 960px; margin: 2rem auto; padding: 0 1rem; color: #222; }
+h1, h2 { border-bottom: 1px solid #eee; padding-bottom: 0.3rem; }
+form { display: grid; gap: 1rem; }
+label { display: block; font-weight: 600; margin-bottom: 0.25rem; }
+.required::after { content: " *"; color: #c00; }
+.desc { font-weight: normal; color: #666; font-size: 0.9rem; display: block; margin-top: 0.1rem; }
+input[type=text], input[type=password], input[type=number], select, textarea {
+  width: 100%; padding: 0.5rem; border: 1px solid #bbb; border-radius: 4px; box-sizing: border-box; font: inherit;
+}
+textarea { min-height: 6rem; }
+button { padding: 0.6rem 1.2rem; background: #0b63c5; color: #fff; border: 0; border-radius: 4px; font: inherit; cursor: pointer; }
+button:hover { background: #084c98; }
+.err { background: #fee; border: 1px solid #fbb; color: #900; padding: 0.6rem 0.8rem; border-radius: 4px; margin: 1rem 0; }
+table { border-collapse: collapse; width: 100%; margin: 0.5rem 0 1.5rem; }
+th, td { text-align: left; padding: 0.5rem 0.6rem; border-bottom: 1px solid #eee; vertical-align: top; }
+th { background: #f7f7f7; }
+.badge { display: inline-block; padding: 0.15rem 0.5rem; border-radius: 3px; font-size: 0.8rem; font-weight: 600; color: #fff; }
+.badge.ok { background: #2a9d3c; }
+.badge.info { background: #3277cc; }
+.badge.warn { background: #d08a00; }
+.badge.crit { background: #c0392b; }
+.badge.error { background: #7a1f1f; }
+.badge.unknown { background: #777; }
+iframe.report { width: 100%; min-height: 480px; border: 1px solid #ccc; border-radius: 4px; }
+.actions { margin-top: 1.5rem; }
+.actions a { color: #0b63c5; text-decoration: none; }
+.actions a:hover { text-decoration: underline; }
+`
+
+var checkFormTemplate = template.Must(template.New("form").Funcs(templateFuncs).Parse(`<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>{{.Title}} – Check</title>
+<style>` + baseCSS + `</style>
+</head>
+<body>
+<h1>{{.Title}}</h1>
+{{if .Error}}<div class="err">{{.Error}}</div>{{end}}
+<form method="POST" action="/check">
+{{range .Fields}}{{if not .Hide}}
+<div>
+  <label for="{{.Id}}" class="{{if .Required}}required{{end}}">{{if .Label}}{{.Label}}{{else}}{{.Id}}{{end}}
+    {{if .Description}}<span class="desc">{{.Description}}</span>{{end}}
+  </label>
+  {{if .Choices}}
+    <select id="{{.Id}}" name="{{.Id}}"{{if .Required}} required{{end}}>
+      {{$def := defaultString .Default}}
+      {{range .Choices}}<option value="{{.}}"{{if eq . $def}} selected{{end}}>{{.}}</option>{{end}}
+    </select>
+  {{else if eq .Type "bool"}}
+    <input type="checkbox" id="{{.Id}}" name="{{.Id}}" value="true"{{if defaultBool .Default}} checked{{end}}>
+  {{else if .Textarea}}
+    <textarea id="{{.Id}}" name="{{.Id}}" placeholder="{{.Placeholder}}"{{if .Required}} required{{end}}>{{defaultString .Default}}</textarea>
+  {{else if eq .Type "number"}}
+    <input type="number" step="any" id="{{.Id}}" name="{{.Id}}" placeholder="{{.Placeholder}}" value="{{defaultString .Default}}"{{if .Required}} required{{end}}>
+  {{else if eq .Type "uint"}}
+    <input type="number" min="0" step="1" id="{{.Id}}" name="{{.Id}}" placeholder="{{.Placeholder}}" value="{{defaultString .Default}}"{{if .Required}} required{{end}}>
+  {{else if .Secret}}
+    <input type="password" id="{{.Id}}" name="{{.Id}}" placeholder="{{.Placeholder}}"{{if .Required}} required{{end}}>
+  {{else}}
+    <input type="text" id="{{.Id}}" name="{{.Id}}" placeholder="{{.Placeholder}}" value="{{defaultString .Default}}"{{if .Required}} required{{end}}>
+  {{end}}
+</div>
+{{end}}{{end}}
+<div><button type="submit">Run check</button></div>
+</form>
+</body>
+</html>`))
+
+var checkResultTemplate = template.Must(template.New("result").Funcs(templateFuncs).Parse(`<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>{{.Title}} – Result</title>
+<style>` + baseCSS + `</style>
+</head>
+<body>
+<h1>{{.Title}}</h1>
+
+{{if .CollectErr}}<div class="err"><strong>Collect failed:</strong> {{.CollectErr}}</div>{{end}}
+
+{{if .States}}
+<h2>Check states</h2>
+<table>
+  <thead><tr><th>Status</th><th>Rule</th><th>Code</th><th>Subject</th><th>Message</th></tr></thead>
+  <tbody>
+  {{range .States}}
+    <tr>
+      <td><span class="badge {{statusClass .Status}}">{{statusString .Status}}</span></td>
+      <td>{{.RuleName}}</td>
+      <td>{{.Code}}</td>
+      <td>{{.Subject}}</td>
+      <td>{{.Message}}</td>
+    </tr>
+  {{end}}
+  </tbody>
+</table>
+{{end}}
+
+{{if .Metrics}}
+<h2>Metrics</h2>
+<table>
+  <thead><tr><th>Name</th><th>Value</th><th>Unit</th><th>Labels</th></tr></thead>
+  <tbody>
+  {{range .Metrics}}
+    <tr>
+      <td>{{.Name}}</td>
+      <td>{{.Value}}</td>
+      <td>{{.Unit}}</td>
+      <td>{{range $k, $v := .Labels}}{{$k}}={{$v}} {{end}}</td>
+    </tr>
+  {{end}}
+  </tbody>
+</table>
+{{end}}
+
+{{if .MetricsErr}}<div class="err"><strong>Metrics error:</strong> {{.MetricsErr}}</div>{{end}}
+
+{{if .ReportHTML}}
+<h2>Report</h2>
+<iframe class="report" sandbox srcdoc="{{.ReportHTML}}"></iframe>
+{{end}}
+
+{{if .ReportErr}}<div class="err"><strong>Report error:</strong> {{.ReportErr}}</div>{{end}}
+
+<div class="actions"><a href="/check">← Run another check</a></div>
+</body>
+</html>`))

checker/server/interactive_test.go

@@ -0,0 +1,439 @@
+// Copyright 2020-2026 The happyDomain Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	"git.happydns.org/checker-sdk-go/checker"
+)
+
+// interactiveProvider embeds testProvider and adds Interactive.
+type interactiveProvider struct {
+	*testProvider
+	fields   []checker.CheckerOptionField
+	parseFn  func(r *http.Request) (checker.CheckerOptions, error)
+	parseErr error
+}
+
+func (p *interactiveProvider) RenderForm() []checker.CheckerOptionField {
+	return p.fields
+}
+
+func (p *interactiveProvider) ParseForm(r *http.Request) (checker.CheckerOptions, error) {
+	if p.parseErr != nil {
+		return nil, p.parseErr
+	}
+	if p.parseFn != nil {
+		return p.parseFn(r)
+	}
+	return checker.CheckerOptions{"domain": r.FormValue("domain")}, nil
+}
+
+func postForm(handler http.Handler, path string, values url.Values) *httptest.ResponseRecorder {
+	req := httptest.NewRequest("POST", path, strings.NewReader(values.Encode()))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	rec := httptest.NewRecorder()
+	handler.ServeHTTP(rec, req)
+	return rec
+}
+
+// minimalProvider implements only ObservationProvider.
+type minimalProvider struct{ key checker.ObservationKey }
+
+func (m *minimalProvider) Key() checker.ObservationKey { return m.key }
+func (m *minimalProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	return nil, nil
+}
+
+func TestCheck_NotRegistered_WhenProviderLacksInterface(t *testing.T) {
+	p := &minimalProvider{key: "test"}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := doRequest(srv.Handler(), "GET", "/check", nil, nil)
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("GET /check without Interactive = %d, want 404", rec.Code)
+	}
+}
+
+func TestCheck_Form_Renders(t *testing.T) {
+	p := &interactiveProvider{
+		testProvider: &testProvider{key: "test"},
+		fields: []checker.CheckerOptionField{
+			{Id: "domain", Type: "string", Label: "Domain name", Required: true, Placeholder: "example.com"},
+			{Id: "verbose", Type: "bool", Label: "Verbose", Default: true},
+			{Id: "flavor", Type: "string", Choices: []string{"a", "b"}, Default: "b"},
+			{Id: "hidden", Type: "string", Hide: true},
+		},
+	}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := doRequest(srv.Handler(), "GET", "/check", nil, nil)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("GET /check = %d, want 200", rec.Code)
+	}
+	body := rec.Body.String()
+	for _, want := range []string{
+		`name="domain"`,
+		`placeholder="example.com"`,
+		`Domain name`,
+		`type="checkbox"`,
+		`name="verbose"`,
+		` checked`,
+		`<select id="flavor"`,
+		`<option value="b" selected>`,
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("form body missing %q", want)
+		}
+	}
+	if strings.Contains(body, `name="hidden"`) {
+		t.Errorf("hidden field should not be rendered")
+	}
+}
+
+func TestCheck_Submit_Success(t *testing.T) {
+	definition := &checker.CheckerDefinition{
+		ID:   "test",
+		Name: "Test Checker",
+		Rules: []checker.CheckRule{
+			&dummyRule{name: "rule1", desc: "first rule"},
+		},
+	}
+	p := &interactiveProvider{
+		testProvider: &testProvider{key: "test", definition: definition},
+		fields:       []checker.CheckerOptionField{{Id: "domain", Type: "string"}},
+	}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {"example.com"}})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /check = %d, want 200", rec.Code)
+	}
+	body := rec.Body.String()
+	for _, want := range []string{
+		`Test Checker`,
+		`Check states`,
+		`rule1`,
+		`rule1 passed`,
+		`badge ok`,
+		`Metrics`,
+		`m1`,
+		`Report`,
+		`<iframe`,
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("result body missing %q", want)
+		}
+	}
+}
+
+func TestCheck_Submit_ParseError_RerendersForm(t *testing.T) {
+	p := &interactiveProvider{
+		testProvider: &testProvider{key: "test"},
+		fields:       []checker.CheckerOptionField{{Id: "domain", Type: "string"}},
+		parseErr:     errors.New("domain is required"),
+	}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {""}})
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("POST /check with bad input = %d, want 400", rec.Code)
+	}
+	body := rec.Body.String()
+	if !strings.Contains(body, "domain is required") {
+		t.Errorf("body missing error message, got: %s", body)
+	}
+	if !strings.Contains(body, `name="domain"`) {
+		t.Errorf("form not re-rendered on error")
+	}
+}
+
+func TestCheck_Submit_CollectError(t *testing.T) {
+	p := &interactiveProvider{
+		testProvider: &testProvider{
+			key: "test",
+			collectFn: func(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+				return nil, errors.New("boom")
+			},
+		},
+		fields: []checker.CheckerOptionField{{Id: "domain", Type: "string"}},
+	}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {"x"}})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /check = %d, want 200 (collect failure still renders a page)", rec.Code)
+	}
+	body := rec.Body.String()
+	if !strings.Contains(body, "Collect failed") || !strings.Contains(body, "boom") {
+		t.Errorf("body missing Collect error, got: %s", body)
+	}
+	if strings.Contains(body, "Check states") {
+		t.Errorf("states section should not render when Collect failed")
+	}
+}
+
+func TestCheck_NoReporters(t *testing.T) {
+	// Provider implements Interactive and has a definition (so
+	// /evaluate-like logic runs) but no HTMLReporter / MetricsReporter.
+	bare := &bareInteractiveProvider{
+		key: "test",
+		def: &checker.CheckerDefinition{
+			ID:    "test",
+			Rules: []checker.CheckRule{&dummyRule{name: "r", desc: "r"}},
+		},
+	}
+	srv := New(bare)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {"x"}})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /check = %d, want 200", rec.Code)
+	}
+	body := rec.Body.String()
+	if !strings.Contains(body, "Check states") {
+		t.Errorf("body missing states section")
+	}
+	if strings.Contains(body, "<iframe") {
+		t.Errorf("body should not contain iframe when no HTML reporter")
+	}
+	if strings.Contains(body, "<h2>Metrics</h2>") {
+		t.Errorf("body should not contain metrics section when no metrics reporter")
+	}
+}
+
+// bareInteractiveProvider implements only the required interfaces
+// (ObservationProvider, CheckerDefinitionProvider, Interactive),
+// no reporters.
+type bareInteractiveProvider struct {
+	key checker.ObservationKey
+	def *checker.CheckerDefinition
+}
+
+func (b *bareInteractiveProvider) Key() checker.ObservationKey { return b.key }
+func (b *bareInteractiveProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	return map[string]string{"ok": "1"}, nil
+}
+func (b *bareInteractiveProvider) Definition() *checker.CheckerDefinition { return b.def }
+func (b *bareInteractiveProvider) RenderForm() []checker.CheckerOptionField {
+	return []checker.CheckerOptionField{{Id: "domain", Type: "string"}}
+}
+func (b *bareInteractiveProvider) ParseForm(r *http.Request) (checker.CheckerOptions, error) {
+	return checker.CheckerOptions{"domain": r.FormValue("domain")}, nil
+}
+
+type siblingProvider struct {
+	key        checker.ObservationKey
+	id         string
+	entriesOpt string
+	gotOpts    checker.CheckerOptions
+	payload    any
+}
+
+func (s *siblingProvider) Key() checker.ObservationKey { return s.key }
+func (s *siblingProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	s.gotOpts = opts
+	return s.payload, nil
+}
+func (s *siblingProvider) Definition() *checker.CheckerDefinition {
+	return &checker.CheckerDefinition{
+		ID: s.id,
+		Options: checker.CheckerOptionsDocumentation{
+			RunOpts: []checker.CheckerOptionDocumentation{
+				{Id: s.entriesOpt, Type: "array", AutoFill: checker.AutoFillDiscoveryEntries},
+			},
+		},
+	}
+}
+
+type primaryWithSibling struct {
+	key     checker.ObservationKey
+	def     *checker.CheckerDefinition
+	entries []checker.DiscoveryEntry
+	sibling checker.ObservationProvider
+}
+
+func (p *primaryWithSibling) Key() checker.ObservationKey { return p.key }
+func (p *primaryWithSibling) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	return map[string]string{"primary": "ok"}, nil
+}
+func (p *primaryWithSibling) Definition() *checker.CheckerDefinition { return p.def }
+func (p *primaryWithSibling) RenderForm() []checker.CheckerOptionField {
+	return []checker.CheckerOptionField{{Id: "domain", Type: "string"}}
+}
+func (p *primaryWithSibling) ParseForm(r *http.Request) (checker.CheckerOptions, error) {
+	return checker.CheckerOptions{"domain": r.FormValue("domain")}, nil
+}
+func (p *primaryWithSibling) DiscoverEntries(data any) ([]checker.DiscoveryEntry, error) {
+	return p.entries, nil
+}
+func (p *primaryWithSibling) RelatedProviders() []checker.ObservationProvider {
+	return []checker.ObservationProvider{p.sibling}
+}
+
+type relatedAssertRule struct {
+	key checker.ObservationKey
+}
+
+func (r *relatedAssertRule) Name() string        { return "related_assert" }
+func (r *relatedAssertRule) Description() string { return "" }
+func (r *relatedAssertRule) Evaluate(ctx context.Context, obs checker.ObservationGetter, opts checker.CheckerOptions) []checker.CheckState {
+	related, err := obs.GetRelated(ctx, r.key)
+	if err != nil {
+		return []checker.CheckState{{Status: checker.StatusError, Message: err.Error()}}
+	}
+	if len(related) == 0 {
+		return []checker.CheckState{{Status: checker.StatusCrit, Message: "no related observation"}}
+	}
+	return []checker.CheckState{{Status: checker.StatusOK, Message: "saw related observation"}}
+}
+
+func TestCheck_Submit_RunsSiblingAndExposesRelated(t *testing.T) {
+	sibling := &siblingProvider{
+		key:        "sibling_key",
+		id:         "sibling",
+		entriesOpt: "endpoints",
+		payload:    map[string]string{"sibling": "ok"},
+	}
+	entry := checker.DiscoveryEntry{Type: "fake.v1", Ref: "r1"}
+	primary := &primaryWithSibling{
+		key: "primary_key",
+		def: &checker.CheckerDefinition{
+			ID:    "primary",
+			Rules: []checker.CheckRule{&relatedAssertRule{key: sibling.key}},
+		},
+		entries: []checker.DiscoveryEntry{entry},
+		sibling: sibling,
+	}
+
+	srv := New(primary)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {"example.com"}})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /check = %d, want 200", rec.Code)
+	}
+	body := rec.Body.String()
+	if !strings.Contains(body, "saw related observation") {
+		t.Errorf("rule did not see related observation; body:\n%s", body)
+	}
+
+	got, ok := sibling.gotOpts[sibling.entriesOpt].([]checker.DiscoveryEntry)
+	if !ok {
+		t.Fatalf("sibling opts missing %q or wrong type: %#v", sibling.entriesOpt, sibling.gotOpts[sibling.entriesOpt])
+	}
+	if len(got) != 1 || got[0].Ref != entry.Ref {
+		t.Errorf("sibling saw entries %v, want [%v]", got, entry)
+	}
+
+	if v, _ := sibling.gotOpts["domain"].(string); v != "example.com" {
+		t.Errorf("sibling did not receive primary domain opt, got %q", v)
+	}
+}
+
+// interactiveStatesPeekingProvider implements Interactive + HTMLReporter
+// and captures the ReportContext.States() seen at GetHTMLReport time.
+type interactiveStatesPeekingProvider struct {
+	key  checker.ObservationKey
+	def  *checker.CheckerDefinition
+	seen *[]checker.CheckState
+}
+
+func (p *interactiveStatesPeekingProvider) Key() checker.ObservationKey { return p.key }
+func (p *interactiveStatesPeekingProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	return map[string]string{"ok": "1"}, nil
+}
+func (p *interactiveStatesPeekingProvider) Definition() *checker.CheckerDefinition { return p.def }
+func (p *interactiveStatesPeekingProvider) RenderForm() []checker.CheckerOptionField {
+	return []checker.CheckerOptionField{{Id: "domain", Type: "string"}}
+}
+func (p *interactiveStatesPeekingProvider) ParseForm(r *http.Request) (checker.CheckerOptions, error) {
+	return checker.CheckerOptions{"domain": r.FormValue("domain")}, nil
+}
+func (p *interactiveStatesPeekingProvider) GetHTMLReport(ctx checker.ReportContext) (string, error) {
+	if p.seen != nil {
+		*p.seen = ctx.States()
+	}
+	return "<p>ok</p>", nil
+}
+
+// TestCheck_Submit_ThreadsStatesIntoReport verifies that CheckStates
+// produced by evaluateRules during POST /check are threaded into the
+// ReportContext handed to GetHTMLReport. Without this wiring, the /check
+// UI can show states in its own section but the embedded report would
+// have to re-derive severity/hints from Data.
+func TestCheck_Submit_ThreadsStatesIntoReport(t *testing.T) {
+	var seen []checker.CheckState
+	p := &interactiveStatesPeekingProvider{
+		key: "test",
+		def: &checker.CheckerDefinition{
+			ID:    "test",
+			Rules: []checker.CheckRule{&dummyRule{name: "rule1", desc: "first"}},
+		},
+		seen: &seen,
+	}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {"example.com"}})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /check = %d, want 200", rec.Code)
+	}
+	if len(seen) != 1 {
+		t.Fatalf("reporter saw %d states, want 1", len(seen))
+	}
+	if seen[0].RuleName != "rule1" {
+		t.Errorf("state RuleName = %q, want %q", seen[0].RuleName, "rule1")
+	}
+	if seen[0].Status != checker.StatusOK {
+		t.Errorf("state Status = %v, want %v", seen[0].Status, checker.StatusOK)
+	}
+}
+
+func TestCheck_Submit_NoSibling_LeavesRelatedEmpty(t *testing.T) {
+	p := &interactiveProvider{
+		testProvider: &testProvider{
+			key: "test",
+			definition: &checker.CheckerDefinition{
+				ID:    "test",
+				Rules: []checker.CheckRule{&relatedAssertRule{key: "other"}},
+			},
+		},
+		fields: []checker.CheckerOptionField{{Id: "domain", Type: "string"}},
+	}
+	srv := New(p)
+	defer srv.Close()
+
+	rec := postForm(srv.Handler(), "/check", url.Values{"domain": {"example.com"}})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /check = %d, want 200", rec.Code)
+	}
+	body := rec.Body.String()
+	if !strings.Contains(body, "no related observation") {
+		t.Errorf("rule should have seen no related observation; body:\n%s", body)
+	}
+}

checker/server/server.go

@@ -12,7 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package checker
+// Package server provides the HTTP server scaffolding used by standalone
+// checkers. It is separated from the core checker package so that plugin
+// and builtin builds, which never expose an HTTP endpoint, do not pay the
+// cost of net/http, html/template, and their transitive dependencies.
+package server
 
 import (
 	"context"
@@ -22,11 +26,16 @@ import (
 	"log"
 	"math"
 	"net/http"
+	"os"
+	"os/signal"
 	"runtime"
 	"strings"
 	"sync"
 	"sync/atomic"
+	"syscall"
 	"time"
+
+	"git.happydns.org/checker-sdk-go/checker"
 )
 
 // maxRequestBodySize is the maximum allowed size for incoming request bodies (1 MB).
@@ -37,6 +46,10 @@ const maxRequestBodySize = 1 << 20
 // 5 seconds matches the Unix kernel's loadavg cadence.
 const loadSampleInterval = 5 * time.Second
 
+// shutdownTimeout bounds how long ListenAndServe waits for in-flight
+// requests to drain after receiving SIGINT or SIGTERM.
+const shutdownTimeout = 10 * time.Second
+
 // EWMA smoothing factors for 1, 5, and 15-minute windows sampled every
 // loadSampleInterval. Derived as 1 - exp(-interval/window) so that the
 // steady-state response to a constant InFlight of N converges to N.
@@ -58,19 +71,21 @@ func updateLoadAvg(prev [3]float64, sample float64) [3]float64 {
 
 // Server is a generic HTTP server for external checkers.
 // It always exposes /health and /collect. If the provider implements
-// CheckerDefinitionProvider, it also exposes /definition and /evaluate.
-// If the provider implements CheckerHTMLReporter or CheckerMetricsReporter,
-// it also exposes /report.
+// checker.CheckerDefinitionProvider, it also exposes /definition and /evaluate.
+// If the provider implements checker.CheckerHTMLReporter or checker.CheckerMetricsReporter,
+// it also exposes /report. If the provider implements Interactive,
+// it also exposes /check (a human-facing web form).
 //
 // Security: Server does not perform any authentication or authorization.
 // It is intended to be run behind a reverse proxy or in a trusted network
 // where access control is handled externally (e.g. by the happyDomain server).
 type Server struct {
-	provider   ObservationProvider
-	definition *CheckerDefinition
-	mux        *http.ServeMux
+	provider    checker.ObservationProvider
+	definition  *checker.CheckerDefinition
+	interactive Interactive
+	mux         *http.ServeMux
 
-	// startTime is captured in NewServer and used to compute uptime.
+	// startTime is captured in New and used to compute uptime.
 	startTime time.Time
 
 	// inFlight counts work requests (/collect, /evaluate, /report) currently
@@ -95,13 +110,13 @@ type Server struct {
 	closeOnce sync.Once
 }
 
-// NewServer creates a new checker HTTP server backed by the given provider.
+// New creates a new checker HTTP server backed by the given provider.
 // Additional endpoints are registered based on optional interfaces the provider implements.
 //
-// NewServer also starts a background goroutine that samples the in-flight
+// New also starts a background goroutine that samples the in-flight
 // request count every loadSampleInterval to compute the load averages
 // reported on /health. Call Close to stop it.
-func NewServer(provider ObservationProvider) *Server {
+func New(provider checker.ObservationProvider) *Server {
 	ctx, cancel := context.WithCancel(context.Background())
 	s := &Server{
 		provider:      provider,
@@ -111,19 +126,27 @@ func NewServer(provider ObservationProvider) *Server {
 	}
 	s.mux = http.NewServeMux()
 	s.mux.HandleFunc("GET /health", s.handleHealth)
-	s.mux.Handle("POST /collect", s.trackWork(http.HandlerFunc(s.handleCollect)))
+	s.mux.Handle("POST /collect", s.TrackWork(http.HandlerFunc(s.handleCollect)))
 
-	if dp, ok := provider.(CheckerDefinitionProvider); ok {
-		s.definition = dp.Definition()
-		s.definition.BuildRulesInfo()
-		s.mux.HandleFunc("GET /definition", s.handleDefinition)
-		s.mux.Handle("POST /evaluate", s.trackWork(http.HandlerFunc(s.handleEvaluate)))
+	if dp, ok := provider.(checker.CheckerDefinitionProvider); ok {
+		if def := dp.Definition(); def != nil {
+			s.definition = def
+			s.definition.BuildRulesInfo()
+			s.mux.HandleFunc("GET /definition", s.handleDefinition)
+			s.mux.Handle("POST /evaluate", s.TrackWork(http.HandlerFunc(s.handleEvaluate)))
+		}
 	}
 
-	if _, ok := provider.(CheckerHTMLReporter); ok {
-		s.mux.Handle("POST /report", s.trackWork(http.HandlerFunc(s.handleReport)))
-	} else if _, ok := provider.(CheckerMetricsReporter); ok {
-		s.mux.Handle("POST /report", s.trackWork(http.HandlerFunc(s.handleReport)))
+	if _, ok := provider.(checker.CheckerHTMLReporter); ok {
+		s.mux.Handle("POST /report", s.TrackWork(http.HandlerFunc(s.handleReport)))
+	} else if _, ok := provider.(checker.CheckerMetricsReporter); ok {
+		s.mux.Handle("POST /report", s.TrackWork(http.HandlerFunc(s.handleReport)))
+	}
+
+	if ip, ok := provider.(Interactive); ok {
+		s.interactive = ip
+		s.mux.HandleFunc("GET /check", s.handleCheckForm)
+		s.mux.Handle("POST /check", s.TrackWork(http.HandlerFunc(s.handleCheckSubmit)))
 	}
 
 	go s.runSampler(ctx)
@@ -137,19 +160,82 @@ func (s *Server) Handler() http.Handler {
 	return requestLogger(s.mux)
 }
 
-// ListenAndServe starts the HTTP server on the given address.
+// Handle registers an auxiliary handler on the server's mux. Must be called
+// before ListenAndServe or Handler(). Custom handlers are not tracked by
+// TrackWork; wrap them explicitly if you want them counted in /health load.
+func (s *Server) Handle(pattern string, handler http.Handler) {
+	s.mux.Handle(pattern, handler)
+}
+
+// HandleFunc is the http.HandlerFunc-flavoured counterpart of Handle.
+func (s *Server) HandleFunc(pattern string, handler func(http.ResponseWriter, *http.Request)) {
+	s.mux.HandleFunc(pattern, handler)
+}
+
+// ListenAndServe starts the HTTP server on the given address and blocks
+// until the server stops.
 //
-// ListenAndServe does not stop the background load-average sampler on return;
-// call Close to stop it. This is not required for process-scoped usage but is
-// recommended for tests and embedded lifecycles.
+// ListenAndServe installs a SIGINT/SIGTERM handler that triggers a graceful
+// shutdown: new connections are refused and in-flight requests are given up
+// to shutdownTimeout to complete. The background load-average sampler is
+// stopped via Close before returning. Callers who need their own signal
+// handling or shutdown semantics should use Handler() and run their own
+// http.Server instead.
+//
+// If the consumer's flag.Parse() set the SDK-registered -healthcheck flag,
+// ListenAndServe never starts the server: it probes /health on addr and calls
+// os.Exit(0) on success or os.Exit(1) on failure. This is what lets a
+// scratch-based Docker image use the binary itself as its HEALTHCHECK probe.
 func (s *Server) ListenAndServe(addr string) error {
+	if *healthcheckMode {
+		if err := runHealthcheck(addr); err != nil {
+			fmt.Fprintln(os.Stderr, "healthcheck failed:", err)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	srv := &http.Server{Addr: addr, Handler: requestLogger(s.mux)}
+
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
+	defer signal.Stop(sigCh)
+
+	shutdownErr := make(chan error, 1)
+	go func() {
+		sig, ok := <-sigCh
+		if !ok {
+			shutdownErr <- nil
+			return
+		}
+		log.Printf("checker received %s, shutting down (timeout %s)", sig, shutdownTimeout)
+		ctx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
+		defer cancel()
+		shutdownErr <- srv.Shutdown(ctx)
+	}()
+
 	log.Printf("checker listening on %s", addr)
-	return http.ListenAndServe(addr, requestLogger(s.mux))
+	err := srv.ListenAndServe()
+	signal.Stop(sigCh)
+	close(sigCh)
+
+	if err == http.ErrServerClosed {
+		if sErr := <-shutdownErr; sErr != nil {
+			err = sErr
+		} else {
+			err = nil
+		}
+	}
+
+	if cErr := s.Close(); cErr != nil && err == nil {
+		err = cErr
+	}
+	return err
 }
 
 // Close stops the background load-average sampler goroutine. It is safe to
 // call multiple times; subsequent calls are no-ops. Close does not shut down
-// any underlying http.Server — callers own that lifecycle.
+// any underlying http.Server, callers own that lifecycle.
 func (s *Server) Close() error {
 	s.closeOnce.Do(func() {
 		s.cancelSampler()
@@ -158,10 +244,9 @@ func (s *Server) Close() error {
 	return nil
 }
 
-// trackWork wraps a handler with in-flight and total-request accounting.
-// It is applied only to "work" endpoints (/collect, /evaluate, /report) so
-// that /health polling traffic does not pollute the load signal.
-func (s *Server) trackWork(next http.Handler) http.Handler {
+// TrackWork wraps a handler with in-flight and total-request accounting,
+// opting custom routes into the load signal reported on /health.
+func (s *Server) TrackWork(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		s.inFlight.Add(1)
 		s.totalRequests.Add(1)
@@ -217,7 +302,7 @@ func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
 	for i := range load {
 		load[i] = math.Float64frombits(s.loadBits[i].Load())
 	}
-	writeJSON(w, http.StatusOK, HealthResponse{
+	writeJSON(w, http.StatusOK, checker.HealthResponse{
 		Status:        "ok",
 		Uptime:        time.Since(s.startTime).Seconds(),
 		NumCPU:        runtime.NumCPU(),
@@ -232,9 +317,9 @@ func (s *Server) handleDefinition(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) handleCollect(w http.ResponseWriter, r *http.Request) {
-	var req ExternalCollectRequest
+	var req checker.ExternalCollectRequest
 	if err := json.NewDecoder(io.LimitReader(r.Body, maxRequestBodySize)).Decode(&req); err != nil {
-		writeJSON(w, http.StatusBadRequest, ExternalCollectResponse{
+		writeJSON(w, http.StatusBadRequest, checker.ExternalCollectResponse{
 			Error: fmt.Sprintf("invalid request body: %v", err),
 		})
 		return
@@ -242,7 +327,7 @@ func (s *Server) handleCollect(w http.ResponseWriter, r *http.Request) {
 
 	data, err := s.provider.Collect(r.Context(), req.Options)
 	if err != nil {
-		writeJSON(w, http.StatusInternalServerError, ExternalCollectResponse{
+		writeJSON(w, http.StatusInternalServerError, checker.ExternalCollectResponse{
 			Error: err.Error(),
 		})
 		return
@@ -250,18 +335,18 @@ func (s *Server) handleCollect(w http.ResponseWriter, r *http.Request) {
 
 	raw, err := json.Marshal(data)
 	if err != nil {
-		writeJSON(w, http.StatusInternalServerError, ExternalCollectResponse{
+		writeJSON(w, http.StatusInternalServerError, checker.ExternalCollectResponse{
 			Error: fmt.Sprintf("failed to marshal result: %v", err),
 		})
 		return
 	}
 
-	resp := ExternalCollectResponse{Data: json.RawMessage(raw)}
+	resp := checker.ExternalCollectResponse{Data: json.RawMessage(raw)}
 
 	// Harvest discovery entries from the native Go value, before it goes
 	// out of scope. No re-parse; DiscoverEntries operates on the same
 	// object that was just marshaled above.
-	if dp, ok := s.provider.(DiscoveryPublisher); ok {
+	if dp, ok := s.provider.(checker.DiscoveryPublisher); ok {
 		entries, derr := dp.DiscoverEntries(data)
 		if derr != nil {
 			log.Printf("DiscoverEntries failed: %v", derr)
@@ -273,36 +358,47 @@ func (s *Server) handleCollect(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, resp)
 }
 
+// evaluateRules runs all definition rules against obs/opts, skipping any rule
+// whose name maps to false in enabledRules (nil means run all).
+func (s *Server) evaluateRules(ctx context.Context, obs checker.ObservationGetter, opts checker.CheckerOptions, enabledRules map[string]bool) []checker.CheckState {
+	var states []checker.CheckState
+	for _, rule := range s.definition.Rules {
+		if len(enabledRules) > 0 {
+			if enabled, ok := enabledRules[rule.Name()]; ok && !enabled {
+				continue
+			}
+		}
+		ruleStates := rule.Evaluate(ctx, obs, opts)
+		if len(ruleStates) == 0 {
+			ruleStates = []checker.CheckState{{
+				Status:  checker.StatusUnknown,
+				Message: fmt.Sprintf("rule %q returned no state", rule.Name()),
+			}}
+		}
+		for _, state := range ruleStates {
+			state.RuleName = rule.Name()
+			states = append(states, state)
+		}
+	}
+	return states
+}
+
 func (s *Server) handleEvaluate(w http.ResponseWriter, r *http.Request) {
-	var req ExternalEvaluateRequest
+	var req checker.ExternalEvaluateRequest
 	if err := json.NewDecoder(io.LimitReader(r.Body, maxRequestBodySize)).Decode(&req); err != nil {
-		writeJSON(w, http.StatusBadRequest, ExternalEvaluateResponse{
+		writeJSON(w, http.StatusBadRequest, checker.ExternalEvaluateResponse{
 			Error: fmt.Sprintf("invalid request body: %v", err),
 		})
 		return
 	}
 
 	obs := &mapObservationGetter{data: req.Observations}
-
-	var states []CheckState
-	for _, rule := range s.definition.Rules {
-		if len(req.EnabledRules) > 0 {
-			if enabled, ok := req.EnabledRules[rule.Name()]; ok && !enabled {
-				continue
-			}
-		}
-		state := rule.Evaluate(r.Context(), obs, req.Options)
-		if state.Code == "" {
-			state.Code = rule.Name()
-		}
-		states = append(states, state)
-	}
-
-	writeJSON(w, http.StatusOK, ExternalEvaluateResponse{States: states})
+	states := s.evaluateRules(r.Context(), obs, req.Options, req.EnabledRules)
+	writeJSON(w, http.StatusOK, checker.ExternalEvaluateResponse{States: states})
 }
 
 func (s *Server) handleReport(w http.ResponseWriter, r *http.Request) {
-	var req ExternalReportRequest
+	var req checker.ExternalReportRequest
 	if err := json.NewDecoder(io.LimitReader(r.Body, maxRequestBodySize)).Decode(&req); err != nil {
 		writeJSON(w, http.StatusBadRequest, map[string]string{
 			"error": fmt.Sprintf("invalid request body: %v", err),
@@ -313,13 +409,13 @@ func (s *Server) handleReport(w http.ResponseWriter, r *http.Request) {
 	accept := r.Header.Get("Accept")
 
 	if strings.Contains(accept, "text/html") {
-		reporter, ok := s.provider.(CheckerHTMLReporter)
+		reporter, ok := s.provider.(checker.CheckerHTMLReporter)
 		if !ok {
 			http.Error(w, "this checker does not support HTML reports", http.StatusNotImplemented)
 			return
 		}
 
-		html, err := reporter.GetHTMLReport(NewReportContext(req.Data, req.Related))
+		html, err := reporter.GetHTMLReport(checker.NewReportContext(req.Data, req.Related, req.States))
 		if err != nil {
 			http.Error(w, fmt.Sprintf("failed to generate HTML report: %v", err), http.StatusInternalServerError)
 			return
@@ -331,13 +427,13 @@ func (s *Server) handleReport(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Default: JSON metrics.
-	reporter, ok := s.provider.(CheckerMetricsReporter)
+	reporter, ok := s.provider.(checker.CheckerMetricsReporter)
 	if !ok {
 		http.Error(w, "this checker does not support metrics reports", http.StatusNotImplemented)
 		return
 	}
 
-	metrics, err := reporter.ExtractMetrics(NewReportContext(req.Data, req.Related), time.Now())
+	metrics, err := reporter.ExtractMetrics(checker.NewReportContext(req.Data, req.Related, req.States), time.Now())
 	if err != nil {
 		writeJSON(w, http.StatusInternalServerError, map[string]string{
 			"error": fmt.Sprintf("failed to extract metrics: %v", err),
@@ -348,12 +444,16 @@ func (s *Server) handleReport(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, metrics)
 }
 
-// mapObservationGetter implements ObservationGetter backed by a static map.
+// mapObservationGetter implements checker.ObservationGetter backed by static maps.
+// Both fields are optional: Get reads from data, GetRelated reads from
+// related. Leaving related nil preserves the pre-existing "no lineage"
+// behavior used by the remote /evaluate path.
 type mapObservationGetter struct {
-	data map[ObservationKey]json.RawMessage
+	data    map[checker.ObservationKey]json.RawMessage
+	related map[checker.ObservationKey][]checker.RelatedObservation
 }
 
-func (g *mapObservationGetter) Get(ctx context.Context, key ObservationKey, dest any) error {
+func (g *mapObservationGetter) Get(ctx context.Context, key checker.ObservationKey, dest any) error {
 	raw, ok := g.data[key]
 	if !ok {
 		return fmt.Errorf("observation %q not available", key)
@@ -361,13 +461,13 @@ func (g *mapObservationGetter) Get(ctx context.Context, key ObservationKey, dest
 	return json.Unmarshal(raw, dest)
 }
 
-// GetRelated always returns nil in the remote /evaluate path: the host that
-// invokes /evaluate does not (currently) carry cross-checker related data in
-// ExternalEvaluateRequest. Consumers that need related observations must run
-// evaluation locally with a host-side ObservationContext that resolves
-// lineage.
-func (g *mapObservationGetter) GetRelated(ctx context.Context, key ObservationKey) ([]RelatedObservation, error) {
-	return nil, nil
+// GetRelated returns the pre-resolved related observations for key, or nil
+// when none were seeded. The remote /evaluate path leaves related nil
+// because ExternalEvaluateRequest does not currently carry cross-checker
+// lineage; the interactive /check path can seed it from sibling providers
+// declared via Siblings.
+func (g *mapObservationGetter) GetRelated(ctx context.Context, key checker.ObservationKey) ([]checker.RelatedObservation, error) {
+	return g.related[key], nil
 }
 
 func writeJSON(w http.ResponseWriter, status int, v any) {

checker/server/server_test.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package checker
+package server
 
 import (
 	"bytes"
@@ -24,37 +24,39 @@ import (
 	"sync"
 	"testing"
 	"time"
+
+	"git.happydns.org/checker-sdk-go/checker"
 )
 
 // --- test doubles ---
 
 type testProvider struct {
-	key        ObservationKey
-	collectFn  func(ctx context.Context, opts CheckerOptions) (any, error)
-	definition *CheckerDefinition
+	key        checker.ObservationKey
+	collectFn  func(ctx context.Context, opts checker.CheckerOptions) (any, error)
+	definition *checker.CheckerDefinition
 	htmlFn     func(raw json.RawMessage) (string, error)
-	metricsFn  func(raw json.RawMessage, t time.Time) ([]CheckMetric, error)
+	metricsFn  func(raw json.RawMessage, t time.Time) ([]checker.CheckMetric, error)
 }
 
-func (p *testProvider) Key() ObservationKey { return p.key }
-func (p *testProvider) Collect(ctx context.Context, opts CheckerOptions) (any, error) {
+func (p *testProvider) Key() checker.ObservationKey { return p.key }
+func (p *testProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
 	if p.collectFn != nil {
 		return p.collectFn(ctx, opts)
 	}
 	return map[string]string{"result": "ok"}, nil
 }
-func (p *testProvider) Definition() *CheckerDefinition { return p.definition }
-func (p *testProvider) GetHTMLReport(ctx ReportContext) (string, error) {
+func (p *testProvider) Definition() *checker.CheckerDefinition { return p.definition }
+func (p *testProvider) GetHTMLReport(ctx checker.ReportContext) (string, error) {
 	if p.htmlFn != nil {
 		return p.htmlFn(ctx.Data())
 	}
 	return "<h1>report</h1>", nil
 }
-func (p *testProvider) ExtractMetrics(ctx ReportContext, t time.Time) ([]CheckMetric, error) {
+func (p *testProvider) ExtractMetrics(ctx checker.ReportContext, t time.Time) ([]checker.CheckMetric, error) {
 	if p.metricsFn != nil {
 		return p.metricsFn(ctx.Data(), t)
 	}
-	return []CheckMetric{{Name: "m1", Value: 1.0, Timestamp: t}}, nil
+	return []checker.CheckMetric{{Name: "m1", Value: 1.0, Timestamp: t}}, nil
 }
 
 // dummyRule is a minimal CheckRule for testing evaluate.
@@ -65,14 +67,37 @@ type dummyRule struct {
 
 func (r *dummyRule) Name() string        { return r.name }
 func (r *dummyRule) Description() string { return r.desc }
-func (r *dummyRule) Evaluate(ctx context.Context, obs ObservationGetter, opts CheckerOptions) CheckState {
-	return CheckState{Status: StatusOK, Message: r.name + " passed"}
+func (r *dummyRule) Evaluate(ctx context.Context, obs checker.ObservationGetter, opts checker.CheckerOptions) []checker.CheckState {
+	return []checker.CheckState{{Status: checker.StatusOK, Message: r.name + " passed"}}
+}
+
+// codedRule emits a CheckState with a pre-set Code, to verify the server
+// stamps RuleName without clobbering rule-provided codes.
+type codedRule struct {
+	name, code string
+}
+
+func (r *codedRule) Name() string        { return r.name }
+func (r *codedRule) Description() string { return "" }
+func (r *codedRule) Evaluate(ctx context.Context, obs checker.ObservationGetter, opts checker.CheckerOptions) []checker.CheckState {
+	return []checker.CheckState{{Status: checker.StatusWarn, Code: r.code, Message: "coded finding"}}
+}
+
+// stubProvider is a minimal ObservationProvider that does not implement
+// CheckerDefinitionProvider, used to verify conditional endpoint registration.
+type stubProvider struct {
+	key checker.ObservationKey
+}
+
+func (s stubProvider) Key() checker.ObservationKey { return s.key }
+func (s stubProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	return nil, nil
 }
 
 // --- helpers ---
 
 func newTestServer(p *testProvider) *Server {
-	return NewServer(p)
+	return New(p)
 }
 
 func doRequest(handler http.Handler, method, path string, body any, headers map[string]string) *httptest.ResponseRecorder {
@@ -95,14 +120,14 @@ func doRequest(handler http.Handler, method, path string, body any, headers map[
 // --- tests ---
 
 func TestServer_Health(t *testing.T) {
-	p := &testProvider{key: "test", definition: &CheckerDefinition{ID: "test", Rules: []CheckRule{}}}
+	p := &testProvider{key: "test", definition: &checker.CheckerDefinition{ID: "test", Rules: []checker.CheckRule{}}}
 	srv := newTestServer(p)
 	defer srv.Close()
 	rec := doRequest(srv.Handler(), "GET", "/health", nil, nil)
 	if rec.Code != http.StatusOK {
 		t.Fatalf("GET /health = %d, want %d", rec.Code, http.StatusOK)
 	}
-	var resp HealthResponse
+	var resp checker.HealthResponse
 	if err := json.NewDecoder(rec.Body).Decode(&resp); err != nil {
 		t.Fatalf("decode /health: %v", err)
 	}
@@ -131,8 +156,8 @@ func TestServer_Health_TracksInFlight(t *testing.T) {
 	var collectEntered sync.WaitGroup
 	p := &testProvider{
 		key:        "test",
-		definition: &CheckerDefinition{ID: "test", Rules: []CheckRule{}},
-		collectFn: func(ctx context.Context, opts CheckerOptions) (any, error) {
+		definition: &checker.CheckerDefinition{ID: "test", Rules: []checker.CheckRule{}},
+		collectFn: func(ctx context.Context, opts checker.CheckerOptions) (any, error) {
 			collectEntered.Done()
 			<-release
 			return map[string]string{"ok": "1"}, nil
@@ -149,7 +174,7 @@ func TestServer_Health_TracksInFlight(t *testing.T) {
 	for i := 0; i < n; i++ {
 		go func() {
 			defer clientsDone.Done()
-			doRequest(handler, "POST", "/collect", ExternalCollectRequest{Key: "test"}, nil)
+			doRequest(handler, "POST", "/collect", checker.ExternalCollectRequest{Key: "test"}, nil)
 		}()
 	}
 
@@ -158,7 +183,7 @@ func TestServer_Health_TracksInFlight(t *testing.T) {
 
 	// Record /health mid-flight. Also hammer it to verify /health polls
 	// do not inflate InFlight or TotalRequests.
-	var mid HealthResponse
+	var mid checker.HealthResponse
 	for i := 0; i < 5; i++ {
 		rec := doRequest(handler, "GET", "/health", nil, nil)
 		if rec.Code != http.StatusOK {
@@ -180,7 +205,7 @@ func TestServer_Health_TracksInFlight(t *testing.T) {
 	clientsDone.Wait()
 
 	rec := doRequest(handler, "GET", "/health", nil, nil)
-	var after HealthResponse
+	var after checker.HealthResponse
 	if err := json.NewDecoder(rec.Body).Decode(&after); err != nil {
 		t.Fatalf("decode /health: %v", err)
 	}
@@ -225,7 +250,7 @@ func TestUpdateLoadAvg(t *testing.T) {
 }
 
 func TestServer_Close_Idempotent(t *testing.T) {
-	p := &testProvider{key: "test", definition: &CheckerDefinition{ID: "test", Rules: []CheckRule{}}}
+	p := &testProvider{key: "test", definition: &checker.CheckerDefinition{ID: "test", Rules: []checker.CheckRule{}}}
 	srv := newTestServer(p)
 	done := make(chan error, 2)
 	go func() { done <- srv.Close() }()
@@ -245,20 +270,20 @@ func TestServer_Close_Idempotent(t *testing.T) {
 func TestServer_Collect_Success(t *testing.T) {
 	p := &testProvider{
 		key:        "test",
-		definition: &CheckerDefinition{ID: "test", Rules: []CheckRule{}},
-		collectFn: func(ctx context.Context, opts CheckerOptions) (any, error) {
+		definition: &checker.CheckerDefinition{ID: "test", Rules: []checker.CheckRule{}},
+		collectFn: func(ctx context.Context, opts checker.CheckerOptions) (any, error) {
 			return map[string]int{"count": 42}, nil
 		},
 	}
 	srv := newTestServer(p)
-	rec := doRequest(srv.Handler(), "POST", "/collect", ExternalCollectRequest{
+	rec := doRequest(srv.Handler(), "POST", "/collect", checker.ExternalCollectRequest{
 		Key:     "test",
-		Options: CheckerOptions{"a": "b"},
+		Options: checker.CheckerOptions{"a": "b"},
 	}, nil)
 	if rec.Code != http.StatusOK {
 		t.Fatalf("POST /collect = %d, want %d", rec.Code, http.StatusOK)
 	}
-	var resp ExternalCollectResponse
+	var resp checker.ExternalCollectResponse
 	json.NewDecoder(rec.Body).Decode(&resp)
 	if resp.Error != "" {
 		t.Errorf("POST /collect error = %q, want empty", resp.Error)
@@ -271,17 +296,17 @@ func TestServer_Collect_Success(t *testing.T) {
 func TestServer_Collect_ProviderError(t *testing.T) {
 	p := &testProvider{
 		key:        "test",
-		definition: &CheckerDefinition{ID: "test", Rules: []CheckRule{}},
-		collectFn: func(ctx context.Context, opts CheckerOptions) (any, error) {
+		definition: &checker.CheckerDefinition{ID: "test", Rules: []checker.CheckRule{}},
+		collectFn: func(ctx context.Context, opts checker.CheckerOptions) (any, error) {
 			return nil, errors.New("provider failed")
 		},
 	}
 	srv := newTestServer(p)
-	rec := doRequest(srv.Handler(), "POST", "/collect", ExternalCollectRequest{Key: "test"}, nil)
+	rec := doRequest(srv.Handler(), "POST", "/collect", checker.ExternalCollectRequest{Key: "test"}, nil)
 	if rec.Code != http.StatusInternalServerError {
 		t.Fatalf("POST /collect = %d, want %d", rec.Code, http.StatusInternalServerError)
 	}
-	var resp ExternalCollectResponse
+	var resp checker.ExternalCollectResponse
 	json.NewDecoder(rec.Body).Decode(&resp)
 	if resp.Error == "" {
 		t.Error("expected error in response, got empty")
@@ -289,7 +314,7 @@ func TestServer_Collect_ProviderError(t *testing.T) {
 }
 
 func TestServer_Collect_BadBody(t *testing.T) {
-	p := &testProvider{key: "test", definition: &CheckerDefinition{ID: "test", Rules: []CheckRule{}}}
+	p := &testProvider{key: "test", definition: &checker.CheckerDefinition{ID: "test", Rules: []checker.CheckRule{}}}
 	srv := newTestServer(p)
 	req := httptest.NewRequest("POST", "/collect", bytes.NewBufferString("{invalid"))
 	rec := httptest.NewRecorder()
@@ -300,10 +325,10 @@ func TestServer_Collect_BadBody(t *testing.T) {
 }
 
 func TestServer_Definition(t *testing.T) {
-	def := &CheckerDefinition{
+	def := &checker.CheckerDefinition{
 		ID:   "test-checker",
 		Name: "Test Checker",
-		Rules: []CheckRule{
+		Rules: []checker.CheckRule{
 			&dummyRule{name: "rule1", desc: "first rule"},
 		},
 	}
@@ -313,7 +338,7 @@ func TestServer_Definition(t *testing.T) {
 	if rec.Code != http.StatusOK {
 		t.Fatalf("GET /definition = %d, want %d", rec.Code, http.StatusOK)
 	}
-	var got CheckerDefinition
+	var got checker.CheckerDefinition
 	json.NewDecoder(rec.Body).Decode(&got)
 	if got.ID != "test-checker" {
 		t.Errorf("definition ID = %q, want \"test-checker\"", got.ID)
@@ -324,10 +349,10 @@ func TestServer_Definition(t *testing.T) {
 }
 
 func TestServer_Evaluate(t *testing.T) {
-	def := &CheckerDefinition{
+	def := &checker.CheckerDefinition{
 		ID:   "test-checker",
 		Name: "Test Checker",
-		Rules: []CheckRule{
+		Rules: []checker.CheckRule{
 			&dummyRule{name: "rule1", desc: "first rule"},
 			&dummyRule{name: "rule2", desc: "second rule"},
 		},
@@ -335,29 +360,32 @@ func TestServer_Evaluate(t *testing.T) {
 	p := &testProvider{key: "test", definition: def}
 	srv := newTestServer(p)
 
-	rec := doRequest(srv.Handler(), "POST", "/evaluate", ExternalEvaluateRequest{
-		Observations: map[ObservationKey]json.RawMessage{
+	rec := doRequest(srv.Handler(), "POST", "/evaluate", checker.ExternalEvaluateRequest{
+		Observations: map[checker.ObservationKey]json.RawMessage{
 			"test": json.RawMessage(`{"count":42}`),
 		},
-		Options: CheckerOptions{},
+		Options: checker.CheckerOptions{},
 	}, nil)
 	if rec.Code != http.StatusOK {
 		t.Fatalf("POST /evaluate = %d, want %d", rec.Code, http.StatusOK)
 	}
-	var resp ExternalEvaluateResponse
+	var resp checker.ExternalEvaluateResponse
 	json.NewDecoder(rec.Body).Decode(&resp)
 	if len(resp.States) != 2 {
 		t.Fatalf("evaluate states = %d, want 2", len(resp.States))
 	}
-	if resp.States[0].Code != "rule1" {
-		t.Errorf("evaluate state[0].Code = %q, want \"rule1\"", resp.States[0].Code)
+	if resp.States[0].RuleName != "rule1" {
+		t.Errorf("evaluate state[0].RuleName = %q, want \"rule1\"", resp.States[0].RuleName)
+	}
+	if resp.States[0].Code != "" {
+		t.Errorf("evaluate state[0].Code = %q, want empty (rule did not set one)", resp.States[0].Code)
 	}
 }
 
 func TestServer_Evaluate_DisabledRule(t *testing.T) {
-	def := &CheckerDefinition{
+	def := &checker.CheckerDefinition{
 		ID: "test-checker",
-		Rules: []CheckRule{
+		Rules: []checker.CheckRule{
 			&dummyRule{name: "rule1", desc: "first"},
 			&dummyRule{name: "rule2", desc: "second"},
 		},
@@ -365,8 +393,8 @@ func TestServer_Evaluate_DisabledRule(t *testing.T) {
 	p := &testProvider{key: "test", definition: def}
 	srv := newTestServer(p)
 
-	rec := doRequest(srv.Handler(), "POST", "/evaluate", ExternalEvaluateRequest{
-		Observations: map[ObservationKey]json.RawMessage{
+	rec := doRequest(srv.Handler(), "POST", "/evaluate", checker.ExternalEvaluateRequest{
+		Observations: map[checker.ObservationKey]json.RawMessage{
 			"test": json.RawMessage(`{}`),
 		},
 		EnabledRules: map[string]bool{"rule1": false},
@@ -374,26 +402,55 @@ func TestServer_Evaluate_DisabledRule(t *testing.T) {
 	if rec.Code != http.StatusOK {
 		t.Fatalf("POST /evaluate = %d, want %d", rec.Code, http.StatusOK)
 	}
-	var resp ExternalEvaluateResponse
+	var resp checker.ExternalEvaluateResponse
 	json.NewDecoder(rec.Body).Decode(&resp)
 	if len(resp.States) != 1 {
 		t.Fatalf("evaluate with disabled rule: states = %d, want 1", len(resp.States))
 	}
-	if resp.States[0].Code != "rule2" {
-		t.Errorf("remaining state code = %q, want \"rule2\"", resp.States[0].Code)
+	if resp.States[0].RuleName != "rule2" {
+		t.Errorf("remaining state rule name = %q, want \"rule2\"", resp.States[0].RuleName)
+	}
+}
+
+func TestServer_Evaluate_RulePreservesCode(t *testing.T) {
+	def := &checker.CheckerDefinition{
+		ID: "test-checker",
+		Rules: []checker.CheckRule{
+			&codedRule{name: "ruleA", code: "too_many_lookups"},
+		},
+	}
+	p := &testProvider{key: "test", definition: def}
+	srv := newTestServer(p)
+
+	rec := doRequest(srv.Handler(), "POST", "/evaluate", checker.ExternalEvaluateRequest{
+		Observations: map[checker.ObservationKey]json.RawMessage{"test": json.RawMessage(`{}`)},
+	}, nil)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /evaluate = %d, want %d", rec.Code, http.StatusOK)
+	}
+	var resp checker.ExternalEvaluateResponse
+	json.NewDecoder(rec.Body).Decode(&resp)
+	if len(resp.States) != 1 {
+		t.Fatalf("states = %d, want 1", len(resp.States))
+	}
+	if resp.States[0].RuleName != "ruleA" {
+		t.Errorf("state.RuleName = %q, want \"ruleA\"", resp.States[0].RuleName)
+	}
+	if resp.States[0].Code != "too_many_lookups" {
+		t.Errorf("state.Code = %q, want \"too_many_lookups\" (rule-set code must be preserved)", resp.States[0].Code)
 	}
 }
 
 func TestServer_Report_HTML(t *testing.T) {
 	p := &testProvider{
-		key: "test",
-		definition: &CheckerDefinition{ID: "test-checker", Rules: []CheckRule{}},
+		key:        "test",
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
 		htmlFn: func(raw json.RawMessage) (string, error) {
 			return "<p>hello</p>", nil
 		},
 	}
 	srv := newTestServer(p)
-	rec := doRequest(srv.Handler(), "POST", "/report", ExternalReportRequest{
+	rec := doRequest(srv.Handler(), "POST", "/report", checker.ExternalReportRequest{
 		Key:  "test",
 		Data: json.RawMessage(`{}`),
 	}, map[string]string{"Accept": "text/html"})
@@ -410,18 +467,18 @@ func TestServer_Report_HTML(t *testing.T) {
 
 func TestServer_Report_Metrics(t *testing.T) {
 	p := &testProvider{
-		key: "test",
-		definition: &CheckerDefinition{ID: "test-checker", Rules: []CheckRule{}},
+		key:        "test",
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
 	}
 	srv := newTestServer(p)
-	rec := doRequest(srv.Handler(), "POST", "/report", ExternalReportRequest{
+	rec := doRequest(srv.Handler(), "POST", "/report", checker.ExternalReportRequest{
 		Key:  "test",
 		Data: json.RawMessage(`{}`),
 	}, map[string]string{"Accept": "application/json"})
 	if rec.Code != http.StatusOK {
 		t.Fatalf("POST /report metrics = %d, want %d", rec.Code, http.StatusOK)
 	}
-	var metrics []CheckMetric
+	var metrics []checker.CheckMetric
 	json.NewDecoder(rec.Body).Decode(&metrics)
 	if len(metrics) != 1 {
 		t.Errorf("metrics count = %d, want 1", len(metrics))
@@ -432,25 +489,25 @@ func TestServer_Report_Metrics(t *testing.T) {
 // ExternalReportRequest.Related through to the provider's ReportContext,
 // the fix for the "remote checkers can't see related observations" gap.
 func TestServer_Report_Related(t *testing.T) {
-	var gotRelated []RelatedObservation
+	var gotRelated []checker.RelatedObservation
 	p := &testProvider{
-		key: "test",
-		definition: &CheckerDefinition{ID: "test-checker", Rules: []CheckRule{}},
+		key:        "test",
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
 	}
 	// Replace htmlFn with one that peeks at a related key. We can't do that
 	// directly through testProvider's htmlFn (which only sees raw), so
 	// bind to GetHTMLReport via an inline wrapper: use a per-test provider
 	// that captures the ReportContext before delegating to the template.
-	srv := NewServer(&relatedPeekingProvider{
+	srv := New(&relatedPeekingProvider{
 		base:   p,
 		target: &gotRelated,
 	})
 	defer srv.Close()
 
-	req := ExternalReportRequest{
+	req := checker.ExternalReportRequest{
 		Key:  "test",
 		Data: json.RawMessage(`{}`),
-		Related: map[ObservationKey][]RelatedObservation{
+		Related: map[checker.ObservationKey][]checker.RelatedObservation{
 			"tls_probes": {
 				{CheckerID: "tls", Key: "tls_probes", Data: json.RawMessage(`{"ok":true}`), Ref: "ep-1"},
 			},
@@ -472,23 +529,124 @@ func TestServer_Report_Related(t *testing.T) {
 // Related("tls_probes") slice observed at GetHTMLReport time into target.
 type relatedPeekingProvider struct {
 	base   *testProvider
-	target *[]RelatedObservation
+	target *[]checker.RelatedObservation
 }
 
-func (p *relatedPeekingProvider) Key() ObservationKey { return p.base.Key() }
-func (p *relatedPeekingProvider) Collect(ctx context.Context, opts CheckerOptions) (any, error) {
+func (p *relatedPeekingProvider) Key() checker.ObservationKey { return p.base.Key() }
+func (p *relatedPeekingProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
 	return p.base.Collect(ctx, opts)
 }
-func (p *relatedPeekingProvider) Definition() *CheckerDefinition { return p.base.definition }
-func (p *relatedPeekingProvider) GetHTMLReport(ctx ReportContext) (string, error) {
+func (p *relatedPeekingProvider) Definition() *checker.CheckerDefinition { return p.base.definition }
+func (p *relatedPeekingProvider) GetHTMLReport(ctx checker.ReportContext) (string, error) {
 	*p.target = ctx.Related("tls_probes")
 	return "<p>ok</p>", nil
 }
 
+// statesPeekingProvider captures the ReportContext's States slice at
+// GetHTMLReport / ExtractMetrics time.
+type statesPeekingProvider struct {
+	base       *testProvider
+	htmlSeen   *[]checker.CheckState
+	metricSeen *[]checker.CheckState
+}
+
+func (p *statesPeekingProvider) Key() checker.ObservationKey { return p.base.Key() }
+func (p *statesPeekingProvider) Collect(ctx context.Context, opts checker.CheckerOptions) (any, error) {
+	return p.base.Collect(ctx, opts)
+}
+func (p *statesPeekingProvider) Definition() *checker.CheckerDefinition { return p.base.definition }
+func (p *statesPeekingProvider) GetHTMLReport(ctx checker.ReportContext) (string, error) {
+	if p.htmlSeen != nil {
+		*p.htmlSeen = ctx.States()
+	}
+	return "<p>ok</p>", nil
+}
+func (p *statesPeekingProvider) ExtractMetrics(ctx checker.ReportContext, t time.Time) ([]checker.CheckMetric, error) {
+	if p.metricSeen != nil {
+		*p.metricSeen = ctx.States()
+	}
+	return []checker.CheckMetric{{Name: "m1", Value: 1.0, Timestamp: t}}, nil
+}
+
+// TestServer_Report_States_HTML verifies ExternalReportRequest.States is
+// threaded into the ReportContext seen by the HTML reporter.
+func TestServer_Report_States_HTML(t *testing.T) {
+	var seen []checker.CheckState
+	base := &testProvider{
+		key:        "test",
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
+	}
+	srv := New(&statesPeekingProvider{base: base, htmlSeen: &seen})
+	defer srv.Close()
+
+	states := []checker.CheckState{
+		{Status: checker.StatusCrit, Message: "broken", RuleName: "r1", Code: "bad", Subject: "host.example"},
+	}
+	req := checker.ExternalReportRequest{
+		Key:    "test",
+		Data:   json.RawMessage(`{}`),
+		States: states,
+	}
+	rec := doRequest(srv.Handler(), "POST", "/report", req, map[string]string{"Accept": "text/html"})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /report = %d, want 200", rec.Code)
+	}
+	if len(seen) != 1 || seen[0].RuleName != "r1" || seen[0].Code != "bad" || seen[0].Subject != "host.example" {
+		t.Errorf("reporter saw states = %+v, want single state {RuleName:r1, Code:bad, Subject:host.example}", seen)
+	}
+}
+
+// TestServer_Report_States_Metrics verifies the States passthrough on the
+// metrics path as well.
+func TestServer_Report_States_Metrics(t *testing.T) {
+	var seen []checker.CheckState
+	base := &testProvider{
+		key:        "test",
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
+	}
+	srv := New(&statesPeekingProvider{base: base, metricSeen: &seen})
+	defer srv.Close()
+
+	req := checker.ExternalReportRequest{
+		Key:    "test",
+		Data:   json.RawMessage(`{}`),
+		States: []checker.CheckState{{Status: checker.StatusWarn, RuleName: "r1"}},
+	}
+	rec := doRequest(srv.Handler(), "POST", "/report", req, map[string]string{"Accept": "application/json"})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /report = %d, want 200", rec.Code)
+	}
+	if len(seen) != 1 || seen[0].RuleName != "r1" {
+		t.Errorf("reporter saw states = %+v, want single state with RuleName=r1", seen)
+	}
+}
+
+// TestServer_Report_States_Absent verifies that omitting States in the
+// request yields a nil States() slice on the reporter side (graceful
+// degradation for hosts that don't thread evaluate→report yet).
+func TestServer_Report_States_Absent(t *testing.T) {
+	seen := []checker.CheckState{{Status: checker.StatusOK}} // non-nil sentinel
+	base := &testProvider{
+		key:        "test",
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
+	}
+	srv := New(&statesPeekingProvider{base: base, htmlSeen: &seen})
+	defer srv.Close()
+
+	req := checker.ExternalReportRequest{Key: "test", Data: json.RawMessage(`{}`)}
+	rec := doRequest(srv.Handler(), "POST", "/report", req, map[string]string{"Accept": "text/html"})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /report = %d, want 200", rec.Code)
+	}
+	if seen != nil {
+		t.Errorf("States() = %+v, want nil when ExternalReportRequest.States is absent", seen)
+	}
+}
+
 func TestServer_Report_BadBody(t *testing.T) {
 	p := &testProvider{
 		key:        "test",
-		definition: &CheckerDefinition{ID: "test-checker", Rules: []CheckRule{}},
+		definition: &checker.CheckerDefinition{ID: "test-checker", Rules: []checker.CheckRule{}},
 	}
 	srv := newTestServer(p)
 	req := httptest.NewRequest("POST", "/report", bytes.NewBufferString("{bad"))
@@ -502,7 +660,7 @@ func TestServer_Report_BadBody(t *testing.T) {
 func TestServer_NoDefinition_NoEvaluateEndpoint(t *testing.T) {
 	// A provider that does NOT implement CheckerDefinitionProvider
 	p := &stubProvider{key: "basic"}
-	srv := NewServer(p)
+	srv := New(p)
 	rec := doRequest(srv.Handler(), "POST", "/evaluate", nil, nil)
 	// Should 404 or 405 since /evaluate is not registered
 	if rec.Code == http.StatusOK {

checker/types.go

@@ -182,12 +182,17 @@ func (s Status) String() string {
 	}
 }
 
-// CheckState is the result of evaluating a single rule.
+// CheckState is the result of evaluating a single rule on a single subject.
+// Subject is opaque to the SDK: producers and consumers agree on its shape
+// (a hostname, a record key, a serial, …). Leave Subject empty for rules
+// that produce a single, global result.
 type CheckState struct {
-	Status  Status         `json:"status"`
-	Message string         `json:"message"`
-	Code    string         `json:"code,omitempty"`
-	Meta    map[string]any `json:"meta,omitempty"`
+	Status   Status         `json:"status"`
+	Message  string         `json:"message"`
+	RuleName string         `json:"rule,omitempty"`
+	Code     string         `json:"code,omitempty"`
+	Subject  string         `json:"subject,omitempty"`
+	Meta     map[string]any `json:"meta,omitempty"`
 }
 
 // CheckMetric represents a single metric produced by a check.
@@ -222,11 +227,20 @@ type CheckRuleInfo struct {
 	Options     *CheckerOptionsDocumentation `json:"options,omitempty"`
 }
 
-// CheckRule evaluates observations and produces a CheckState.
+// CheckRule evaluates observations and produces one or more CheckStates.
+//
+// Evaluate returns a slice so a rule iterating over multiple elements can
+// emit one state per subject (each carrying CheckState.Subject) without
+// squashing them into a single concatenated message.
+//
+// Evaluate must not return a nil or empty slice: callers expect at least
+// one state per rule. When a rule finds nothing to evaluate, return a
+// single CheckState with an appropriate status (typically StatusInfo or
+// StatusOK) describing that fact.
 type CheckRule interface {
 	Name() string
 	Description() string
-	Evaluate(ctx context.Context, obs ObservationGetter, opts CheckerOptions) CheckState
+	Evaluate(ctx context.Context, obs ObservationGetter, opts CheckerOptions) []CheckState
 }
 
 // CheckRuleWithOptions is an optional interface that rules can implement
@@ -284,32 +298,40 @@ type CheckAggregator interface {
 	Aggregate(states []CheckState) CheckState
 }
 
-// ReportContext carries both the primary observation payload and any
-// observations produced by other checkers that cover the same discovery
-// entries. Hosts build a ReportContext and hand it to reporter methods.
+// ReportContext carries the primary observation payload, any observations
+// produced by other checkers that cover the same discovery entries, and the
+// CheckStates produced by this checker's rules for the same observation.
+// Hosts build a ReportContext and hand it to reporter methods.
 //
-// The method set is deliberately tiny: a single primary payload (Data) and
-// a query for related observations by key (Related). Hosts return nil from
-// Related when there is nothing to relate; reporters must tolerate that.
+// Reporters use States() to render rule-driven sections (for example a
+// "fix these first" list) without re-deriving severity or hints from the
+// raw payload. Hosts that have not yet threaded rule output into the
+// report pipeline return nil; reporters must treat a nil or empty slice
+// as "not provided" and fall back to a data-only rendering. The same
+// nil-tolerance applies to Related(key).
 type ReportContext interface {
 	Data() json.RawMessage
 	Related(key ObservationKey) []RelatedObservation
+	States() []CheckState
 }
 
-// NewReportContext returns a ReportContext backed by a primary payload and
-// a pre-resolved map of related observations by key. The SDK's /report HTTP
-// handler uses this to wrap ExternalReportRequest contents; hosts and tests
-// can use it whenever they already have the related observations in memory.
+// NewReportContext returns a ReportContext backed by a primary payload, a
+// pre-resolved map of related observations by key, and the CheckStates
+// produced by the checker's rules on this observation. The SDK's /report
+// HTTP handler uses this to wrap ExternalReportRequest contents; hosts and
+// tests can use it whenever they already have that material in memory.
 //
-// Passing a nil or empty related map is fine; Related(key) will then return
-// nil, just like StaticReportContext.
-func NewReportContext(data json.RawMessage, related map[ObservationKey][]RelatedObservation) ReportContext {
-	return fixedReportContext{data: data, related: related}
+// Passing a nil related map or a nil states slice is fine; Related(key)
+// and States() will then return nil respectively. Use StaticReportContext
+// as a shorthand when both are absent.
+func NewReportContext(data json.RawMessage, related map[ObservationKey][]RelatedObservation, states []CheckState) ReportContext {
+	return fixedReportContext{data: data, related: related, states: states}
 }
 
-// StaticReportContext is a shorthand for NewReportContext(data, nil): a
-// ReportContext with a primary payload and no related observations.
-// Intended for tests and ad-hoc callers that have no lineage to supply.
+// StaticReportContext is a shorthand for NewReportContext(data, nil, nil):
+// a ReportContext with a primary payload, no related observations, and no
+// rule states. Intended for tests and ad-hoc callers that have no lineage
+// or rule output to supply.
 func StaticReportContext(data json.RawMessage) ReportContext {
 	return fixedReportContext{data: data}
 }
@@ -317,6 +339,7 @@ func StaticReportContext(data json.RawMessage) ReportContext {
 type fixedReportContext struct {
 	data    json.RawMessage
 	related map[ObservationKey][]RelatedObservation
+	states  []CheckState
 }
 
 func (f fixedReportContext) Data() json.RawMessage { return f.data }
@@ -326,6 +349,7 @@ func (f fixedReportContext) Related(key ObservationKey) []RelatedObservation {
 	}
 	return f.related[key]
 }
+func (f fixedReportContext) States() []CheckState { return f.states }
 
 // CheckerHTMLReporter is an optional interface that observation providers can
 // implement to render their stored data as a full HTML document (for iframe embedding).
@@ -472,13 +496,20 @@ type ExternalEvaluateResponse struct {
 // Related carries observations produced by other checkers on DiscoveryEntry
 // records originally published by the target of this report, that is, the
 // cross-checker lineage that ObservationGetter.GetRelated would expose in
-// the in-process path. The host composes it before making the HTTP request;
-// when absent, the remote checker receives a context that reports no
-// related observations (equivalent to StaticReportContext).
+// the in-process path. States carries the CheckStates the host produced by
+// evaluating this checker's rules against the same observation, letting
+// reporters render rule-driven sections (for example a "fix these first"
+// list) without re-deriving severity or hints from Data.
+//
+// The host composes both fields before making the HTTP request. When both
+// are absent, the remote checker receives a context equivalent to
+// StaticReportContext (no related observations and no states); the
+// reporter then falls back to a data-only rendering.
 type ExternalReportRequest struct {
 	Key     ObservationKey                          `json:"key"`
 	Data    json.RawMessage                         `json:"data"`
 	Related map[ObservationKey][]RelatedObservation `json:"related,omitempty"`
+	States  []CheckState                            `json:"states,omitempty"`
 }
 
 // HealthResponse is returned by GET /health on a remote checker endpoint.

checker/types_test.go

@@ -15,10 +15,24 @@
 package checker
 
 import (
+	"context"
 	"encoding/json"
+	"reflect"
 	"testing"
 )
 
+// dummyRule is a minimal CheckRule used only by tests in this package.
+type dummyRule struct {
+	name string
+	desc string
+}
+
+func (r *dummyRule) Name() string        { return r.name }
+func (r *dummyRule) Description() string { return r.desc }
+func (r *dummyRule) Evaluate(ctx context.Context, obs ObservationGetter, opts CheckerOptions) []CheckState {
+	return []CheckState{{Status: StatusOK, Message: r.name + " passed"}}
+}
+
 func TestStatus_MarshalJSON(t *testing.T) {
 	tests := []struct {
 		status Status
@@ -143,6 +157,54 @@ func TestCheckerDefinition_BuildRulesInfo(t *testing.T) {
 	}
 }
 
+// Compile-time check that fixedReportContext implements ReportContext.
+var _ ReportContext = fixedReportContext{}
+
+func TestStaticReportContext_NoExtras(t *testing.T) {
+	ctx := StaticReportContext(json.RawMessage(`{"k":"v"}`))
+	if string(ctx.Data()) != `{"k":"v"}` {
+		t.Errorf("Data() = %s, want %s", ctx.Data(), `{"k":"v"}`)
+	}
+	if ctx.Related("any") != nil {
+		t.Error("Related(any) should be nil for StaticReportContext")
+	}
+	if ctx.States() != nil {
+		t.Error("States() should be nil for StaticReportContext")
+	}
+}
+
+func TestNewReportContext_NilStates(t *testing.T) {
+	ctx := NewReportContext(json.RawMessage(`{}`), nil, nil)
+	if ctx.States() != nil {
+		t.Errorf("States() = %v, want nil", ctx.States())
+	}
+}
+
+func TestNewReportContext_PassesStates(t *testing.T) {
+	states := []CheckState{
+		{Status: StatusWarn, Message: "heads up", RuleName: "r1"},
+		{Status: StatusCrit, Message: "fix me", RuleName: "r2", Subject: "host.example"},
+	}
+	ctx := NewReportContext(json.RawMessage(`{}`), nil, states)
+	got := ctx.States()
+	if !reflect.DeepEqual(got, states) {
+		t.Errorf("States() = %+v, want %+v", got, states)
+	}
+}
+
+func TestNewReportContext_PassesRelated(t *testing.T) {
+	rel := map[ObservationKey][]RelatedObservation{
+		"other.key": {{CheckerID: "other", Key: "other.key", Ref: "r1"}},
+	}
+	ctx := NewReportContext(json.RawMessage(`{}`), rel, nil)
+	if got := ctx.Related("other.key"); len(got) != 1 || got[0].CheckerID != "other" {
+		t.Errorf("Related(other.key) = %+v, want one entry with CheckerID=other", got)
+	}
+	if ctx.Related("missing") != nil {
+		t.Error("Related(missing) should be nil")
+	}
+}
+
 func TestRegisterChecker_EmptyIDRejected(t *testing.T) {
 	resetRegistries()
 	RegisterChecker(&CheckerDefinition{ID: "", Name: "bad"})