feat: agent-capability gate for coupled features — typed StatusError + Supports probe/cache + netstorage add gate (option-1)

- agentapi: non-2xx GETs now surface as typed *StatusError (same text); features.go
  adds Feature/SupportState/SupportCache (route probe, TTL 5m, Yes/No cached,
  Unknown never cached or refused) + Client.Supports
- web: handleNetStorageAdd refuses up front (412, code agent_outdated, Hungarian
  message) when the agent predates /netstorage/verify-status (= pre-0.81 add
  semantics); gate runs BEFORE the single-flight claim; SupportUnknown passes
  through to the existing agent-error paths
- netAddSupport page-render helper lands here; its template consumer follows
- tests: T1 gate refusal (job never starts, slot free), T2 unchanged happy path +
  warm-cache negative assertion, T3 indeterminate never 'too old', T4
  classification incl. the string-match trap, T6 TTL, wire-level 404-typing;
  red-proofs RP1-RP4 run and reverted

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

controller/internal/agentapi/client.go

@@ -26,6 +26,8 @@ type Client struct {
 	baseURL string
 	token   string
 	hc      *http.Client
+	// features caches capability-probe verdicts for Supports (features.go).
+	features SupportCache
 }
 
 // MountInfo mirrors the agent's GET /storage mount entry (doc 03 §6).
@@ -853,6 +855,18 @@ func (c *Client) HostMetrics(ctx context.Context) (HostMetricsResponse, error) {
 	return out, nil
 }
 
+// StatusError is a non-2xx agent HTTP status surfaced as a TYPED error (same text the old
+// fmt.Errorf produced). errors.As-able — the capability probe (features.go) keys on Code 404 to
+// distinguish "this agent predates the route" from every other failure. Never match the string.
+type StatusError struct {
+	Path string
+	Code int
+}
+
+func (e *StatusError) Error() string {
+	return fmt.Sprintf("agentapi: GET %s: HTTP %d", e.Path, e.Code)
+}
+
 // get issues an authenticated GET and unwraps the {ok,data,error} envelope.
 func (c *Client) get(ctx context.Context, path string) (json.RawMessage, error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+path, nil)
@@ -867,7 +881,7 @@ func (c *Client) get(ctx context.Context, path string) (json.RawMessage, error)
 	defer resp.Body.Close()
 	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
 	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("agentapi: GET %s: HTTP %d", path, resp.StatusCode)
+		return nil, &StatusError{Path: path, Code: resp.StatusCode}
 	}
 	var env apiResponse
 	if err := json.Unmarshal(raw, &env); err != nil {

controller/internal/agentapi/features.go

@@ -0,0 +1,126 @@
+package agentapi
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// Agent-capability probing (the publish-train backstop). A controller release that depends on
+// coupled agent behavior must not fail mid-pipeline against an older agent — it detects support up
+// front and refuses honestly. Detection is a ROUTE PROBE: a route that shipped together with the
+// coupled semantics either answers (2xx ⇒ supported) or 404s (older agent). Transport errors and
+// 5xx are INDETERMINATE — an agent problem is never claimed as "too old".
+
+// Feature names one coupled controller↔agent capability.
+type Feature string
+
+// FeatureNetstorageVerify is the NAS verify-before-commit add semantics (agent v0.81.0): the
+// coupled add behavior shipped together with GET /netstorage/verify-status, so that route IS the
+// capability signal.
+const FeatureNetstorageVerify Feature = "netstorage_verify"
+
+// SupportState is a probe verdict. The zero value is SupportUnknown (fail-open: unknown never
+// refuses — the existing agent-error paths speak honestly when the agent is down).
+type SupportState int
+
+const (
+	// SupportUnknown — the probe could not decide (transport error, timeout, auth, 5xx).
+	SupportUnknown SupportState = iota
+	// SupportYes — the agent answered 2xx on the feature's probe route.
+	SupportYes
+	// SupportNo — the agent answered 404: it predates the route, and with it the coupled semantics.
+	SupportNo
+)
+
+// SupportProber is the minimal agent surface a probe needs. *Client satisfies it, and so does the
+// web layer's netAgent seam — tests inject fakes there.
+type SupportProber interface {
+	NetVerifyStatus(ctx context.Context) (NetVerifyStatus, error)
+}
+
+// featureProbes maps each coupled feature to its route probe.
+//
+// CONVENTION (publish-train rules doc, felhom.eu/documentation/runbooks/publish-train-rules.md):
+// every future coupled feature adds a row here plus a Supports gate call at its entry point, and
+// declares MinAgent in its CHANGELOG header. When the agent someday reports an explicit version in
+// its envelope, Supports should prefer that version comparison over route probing — that
+// enhancement is roadmap, not built yet.
+var featureProbes = map[Feature]func(ctx context.Context, p SupportProber) error{
+	FeatureNetstorageVerify: func(ctx context.Context, p SupportProber) error {
+		_, err := p.NetVerifyStatus(ctx)
+		return err
+	},
+}
+
+// supportTTL bounds how long a probe verdict (either polarity) is trusted. An agent updated
+// mid-window flips within this — no invalidation plumbing by design.
+const supportTTL = 5 * time.Minute
+
+type supportEntry struct {
+	state SupportState
+	at    time.Time
+}
+
+// SupportCache caches per-feature probe verdicts. Yes and No are cached for supportTTL; Unknown is
+// NEVER cached (a down agent re-probes on the next call, so recovery is immediate). The zero value
+// is ready to use.
+type SupportCache struct {
+	mu      sync.Mutex
+	now     func() time.Time // test seam; nil → time.Now
+	entries map[Feature]supportEntry
+}
+
+// Supports reports whether the agent behind p provides feature f, answering from the cache inside
+// the TTL window and probing otherwise. The probe runs OUTSIDE the lock — concurrent misses may
+// double-probe (harmless: the probe is one cheap GET).
+func (sc *SupportCache) Supports(ctx context.Context, p SupportProber, f Feature) SupportState {
+	probe, ok := featureProbes[f]
+	if !ok {
+		return SupportUnknown // unregistered feature — never refuse on a table gap
+	}
+	sc.mu.Lock()
+	nowFn := sc.now
+	if nowFn == nil {
+		nowFn = time.Now
+	}
+	if e, hit := sc.entries[f]; hit && nowFn().Sub(e.at) < supportTTL {
+		sc.mu.Unlock()
+		return e.state
+	}
+	sc.mu.Unlock()
+
+	state := classifySupportErr(probe(ctx, p))
+	if state != SupportUnknown {
+		sc.mu.Lock()
+		if sc.entries == nil {
+			sc.entries = map[Feature]supportEntry{}
+		}
+		sc.entries[f] = supportEntry{state: state, at: nowFn()}
+		sc.mu.Unlock()
+	}
+	return state
+}
+
+// Supports probes (cached, TTL 5m, both polarities) whether the connected agent provides the
+// feature. 2xx ⇒ Yes. 404 ⇒ No. Anything else ⇒ Unknown (never "too old"). The web layer drives
+// the same machinery through its netAgent seam (Server.netFeatures) so tests can fake the probe.
+func (c *Client) Supports(ctx context.Context, f Feature) SupportState {
+	return c.features.Supports(ctx, c, f)
+}
+
+// classifySupportErr maps a probe outcome to a SupportState. ONLY a typed HTTP 404 means
+// "unsupported" — every other error (transport, timeout, 401, 5xx, envelope problems) is Unknown,
+// so a merely-down agent is never reported as outdated. Typed errors only; never string-match.
+func classifySupportErr(err error) SupportState {
+	if err == nil {
+		return SupportYes
+	}
+	var se *StatusError
+	if errors.As(err, &se) && se.Code == http.StatusNotFound {
+		return SupportNo
+	}
+	return SupportUnknown
+}

controller/internal/agentapi/features_test.go

@@ -0,0 +1,164 @@
+package agentapi
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+)
+
+// fakeProber scripts the capability probe (the SupportProber seam) and counts calls.
+type fakeProber struct {
+	err   error
+	calls int
+}
+
+func (f *fakeProber) NetVerifyStatus(context.Context) (NetVerifyStatus, error) {
+	f.calls++
+	return NetVerifyStatus{Phase: "none"}, f.err
+}
+
+// --- T4: probe classification — ONLY a typed 404 means "too old" -------------------------------
+// Companion red-proof (the classification trap): mutate classifySupportErr to string-match
+// "HTTP 404" → the "plain error with 404 text" case classifies No → FAIL. A second mutant treating
+// ANY error as SupportNo fails every Unknown case here (and T3 in web).
+func TestSupports_Classification(t *testing.T) {
+	cases := []struct {
+		name string
+		err  error
+		want SupportState
+	}{
+		{"2xx (nil error)", nil, SupportYes},
+		{"typed 404", &StatusError{Path: "/netstorage/verify-status", Code: http.StatusNotFound}, SupportNo},
+		{"typed 404 wrapped", fmt.Errorf("probe: %w", &StatusError{Path: "/x", Code: 404}), SupportNo},
+		{"typed 401", &StatusError{Path: "/x", Code: http.StatusUnauthorized}, SupportUnknown},
+		{"typed 500", &StatusError{Path: "/x", Code: http.StatusInternalServerError}, SupportUnknown},
+		{"typed 502", &StatusError{Path: "/x", Code: http.StatusBadGateway}, SupportUnknown},
+		{"connection refused", errors.New("dial tcp 10.0.0.9:8443: connect: connection refused"), SupportUnknown},
+		{"timeout", context.DeadlineExceeded, SupportUnknown},
+		// The string-matching trap: the OLD untyped error text carries "HTTP 404" but is NOT a
+		// *StatusError — a classifier that matches the message would wrongly say "too old".
+		{"plain error with 404 text", errors.New("agentapi: GET /netstorage/verify-status: HTTP 404"), SupportUnknown},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			sc := &SupportCache{}
+			got := sc.Supports(context.Background(), &fakeProber{err: tc.err}, FeatureNetstorageVerify)
+			if got != tc.want {
+				t.Errorf("Supports(%v) = %v, want %v", tc.err, got, tc.want)
+			}
+		})
+	}
+}
+
+// Unknown feature names must never refuse (a table gap fails open).
+func TestSupports_UnknownFeature(t *testing.T) {
+	sc := &SupportCache{}
+	p := &fakeProber{}
+	if got := sc.Supports(context.Background(), p, Feature("no_such_feature")); got != SupportUnknown {
+		t.Errorf("unknown feature = %v, want SupportUnknown", got)
+	}
+	if p.calls != 0 {
+		t.Errorf("unknown feature must not probe (calls=%d)", p.calls)
+	}
+}
+
+// --- T6: cache TTL — both polarities cached; Unknown NEVER cached ------------------------------
+// Companion red-proof: drop the TTL expiry check (treat every entry as fresh) → the
+// "re-probes after TTL" assertion fails. Dropping the cache entirely → the warm-cache negative
+// assertion (calls stays 1) fails (T2's red-proof shape).
+func TestSupports_CacheTTL(t *testing.T) {
+	t.Run("positive cached, re-probes after TTL", func(t *testing.T) {
+		now := time.Date(2026, 7, 11, 12, 0, 0, 0, time.UTC)
+		sc := &SupportCache{now: func() time.Time { return now }}
+		p := &fakeProber{} // nil err → Yes
+		if got := sc.Supports(context.Background(), p, FeatureNetstorageVerify); got != SupportYes {
+			t.Fatalf("first = %v, want Yes", got)
+		}
+		if got := sc.Supports(context.Background(), p, FeatureNetstorageVerify); got != SupportYes {
+			t.Fatalf("warm = %v, want Yes", got)
+		}
+		if p.calls != 1 { // the NEGATIVE assertion: a warm cache must NOT re-probe
+			t.Errorf("probe calls on a warm cache = %d, want 1", p.calls)
+		}
+		now = now.Add(supportTTL + time.Second)
+		if got := sc.Supports(context.Background(), p, FeatureNetstorageVerify); got != SupportYes {
+			t.Fatalf("post-TTL = %v, want Yes", got)
+		}
+		if p.calls != 2 {
+			t.Errorf("probe calls after TTL expiry = %d, want 2 (must re-fire)", p.calls)
+		}
+	})
+	t.Run("negative cached too", func(t *testing.T) {
+		now := time.Date(2026, 7, 11, 12, 0, 0, 0, time.UTC)
+		sc := &SupportCache{now: func() time.Time { return now }}
+		p := &fakeProber{err: &StatusError{Path: "/x", Code: 404}}
+		for i := 0; i < 2; i++ {
+			if got := sc.Supports(context.Background(), p, FeatureNetstorageVerify); got != SupportNo {
+				t.Fatalf("call %d = %v, want No", i, got)
+			}
+		}
+		if p.calls != 1 {
+			t.Errorf("negative verdict not cached (calls=%d, want 1)", p.calls)
+		}
+	})
+	t.Run("unknown never cached", func(t *testing.T) {
+		sc := &SupportCache{}
+		p := &fakeProber{err: errors.New("connection refused")}
+		for i := 0; i < 2; i++ {
+			if got := sc.Supports(context.Background(), p, FeatureNetstorageVerify); got != SupportUnknown {
+				t.Fatalf("call %d = %v, want Unknown", i, got)
+			}
+		}
+		if p.calls != 2 {
+			t.Errorf("Unknown must re-probe every call (calls=%d, want 2)", p.calls)
+		}
+	})
+}
+
+// --- 1.1 wire-level: a real HTTP 404 through Client.get IS the typed StatusError ----------------
+// This pins the verify-first finding: an agent without the route (≤0.80's plain mux 404) reaches
+// classifySupportErr as *StatusError{404}, end-to-end through the pinned-TLS client.
+func TestClient_404IsTypedAndSupportsSaysNo(t *testing.T) {
+	mux := http.NewServeMux() // NO /netstorage/verify-status route — the ≤0.80 shape
+	srv := httptest.NewTLSServer(mux)
+	defer srv.Close()
+	fp := sha256.Sum256(srv.Certificate().Raw)
+	c, err := New(strings.TrimPrefix(srv.URL, "https://"), "test-token", hex.EncodeToString(fp[:]))
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+	_, verr := c.NetVerifyStatus(context.Background())
+	var se *StatusError
+	if !errors.As(verr, &se) || se.Code != http.StatusNotFound {
+		t.Fatalf("404 must surface as *StatusError{404}, got %T: %v", verr, verr)
+	}
+	if got := c.Supports(context.Background(), FeatureNetstorageVerify); got != SupportNo {
+		t.Errorf("Supports on a routeless agent = %v, want SupportNo", got)
+	}
+}
+
+// The supported shape: the route answers the envelope → Supports says Yes.
+func TestClient_SupportsYesOnLiveRoute(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/netstorage/verify-status", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"ok":true,"data":{"phase":"none"}}`)) // the no-job envelope
+	})
+	srv := httptest.NewTLSServer(mux)
+	defer srv.Close()
+	fp := sha256.Sum256(srv.Certificate().Raw)
+	c, err := New(strings.TrimPrefix(srv.URL, "https://"), "test-token", hex.EncodeToString(fp[:]))
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+	if got := c.Supports(context.Background(), FeatureNetstorageVerify); got != SupportYes {
+		t.Errorf("Supports on a live route = %v, want SupportYes", got)
+	}
+}

controller/internal/web/netstorage_gate_test.go

@@ -0,0 +1,168 @@
+package web
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/agentapi"
+)
+
+// Capability-gate tests (agent-outdated backstop): the probe runs through the SAME netAgent seam
+// as the orchestration — fakeNetAgent's NetVerifyStatus doubles as the probed route.
+
+// counts reads the fake's recorded call counters under its lock.
+func (f *fakeNetAgent) counts() (adds, verifyCalls int) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.addCalls, f.verifyPoll
+}
+
+// setAddRes swaps the scripted add result between requests (under the fake's lock).
+func (f *fakeNetAgent) setAddRes(res agentapi.NetStorageAddResult) {
+	f.mu.Lock()
+	f.addRes = res
+	f.mu.Unlock()
+}
+
+// postNetAdd drives the REAL handler (the pipeline a user triggers) with a valid body.
+func postNetAdd(t *testing.T, s *Server, name string) *httptest.ResponseRecorder {
+	t.Helper()
+	body := `{"name":"` + name + `","protocol":"nfs","server":"10.0.0.5","export":"/srv/` + name + `"}`
+	r := httptest.NewRequest(http.MethodPost, "/api/storage/netstorage/add", strings.NewReader(body))
+	w := httptest.NewRecorder()
+	s.handleNetStorageAdd(w, r)
+	return w
+}
+
+// --- T1 (Scenario A): old agent ⇒ sync refusal; the job NEVER starts ---------------------------
+// Companion red-proof: remove the gate call in handleNetStorageAdd → the job starts against the
+// old add semantics → the "never started" + zero-add-calls assertions fail.
+func TestNetAddGate_OldAgent_RefusedUpFront(t *testing.T) {
+	s := testServer(t)
+	// The ≤0.80 shape: the probed route 404s (typed — the wire path is pinned in agentapi tests).
+	agent := &fakeNetAgent{
+		addRes:    okAddRes("media"),
+		verifyErr: &agentapi.StatusError{Path: "/netstorage/verify-status", Code: http.StatusNotFound},
+	}
+	s.netAgentFn = func() (netAgent, error) { return agent, nil }
+	s.netProbeFn = func(context.Context, string) probeOutcome { t.Error("probe must never run on a gated add"); return probeOutcome{} }
+
+	w := postNetAdd(t, s, "media")
+	if w.Code != http.StatusPreconditionFailed {
+		t.Fatalf("gate: got %d want 412 (%s)", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), `"code":"agent_outdated"`) {
+		t.Errorf("refusal must carry the machine code agent_outdated: %s", w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "Az ügynök frissítése szükséges ehhez a funkcióhoz") {
+		t.Errorf("refusal must carry the §Part-3 Hungarian message: %s", w.Body.String())
+	}
+	// The orchestration was NEVER started and no agent add/remove ran.
+	if j := s.netAdd.snapshot(); j != nil {
+		t.Errorf("job slot must stay empty on a gated add, got %+v", j)
+	}
+	adds, _ := agent.counts()
+	if adds != 0 {
+		t.Errorf("agent add calls = %d, want 0", adds)
+	}
+	if got := agent.removed(); len(got) != 0 {
+		t.Errorf("no rollback should ever run (removes=%v)", got)
+	}
+	if got := networkPathCount(s); got != 0 {
+		t.Errorf("nothing may register on a gated add (got %d)", got)
+	}
+	// The single-flight slot was NEVER claimed — it must still be acquirable.
+	if !s.netAdd.acquire(&netAddJob{Name: "slot-check"}) {
+		t.Error("single-flight slot was consumed by the refused add")
+	}
+	s.netAdd.release()
+}
+
+// --- T2 (Scenario B): current agent ⇒ pre-gate behavior + ONE probe per cache window ------------
+// Companion red-proof: drop the cache in SupportCache.Supports (always probe) → the warm-cache
+// negative assertion (verify calls stays 1) fails with 2.
+func TestNetAddGate_CurrentAgent_UnchangedAndProbeCached(t *testing.T) {
+	s := testServer(t)
+	// Pre-verify-shaped OK result (Verify != "started"): the orchestrator skips the verify poll, so
+	// the fake's NetVerifyStatus count measures the GATE PROBE alone.
+	res1 := okAddRes("m1")
+	res1.Verify, res1.JobID = "", ""
+	agent := &fakeNetAgent{addRes: res1, verify: agentapi.NetVerifyStatus{Phase: "none"}}
+	s.netAgentFn = func() (netAgent, error) { return agent, nil }
+	s.netProbeFn = func(context.Context, string) probeOutcome { return probeOutcome{OK: true} }
+
+	// Add #1 — identical end-to-end shape to the pre-gate happy path (C1's contract).
+	w := postNetAdd(t, s, "m1")
+	if w.Code != http.StatusOK || !strings.Contains(w.Body.String(), `"started":true`) {
+		t.Fatalf("add #1: got %d %s, want 200 started", w.Code, w.Body.String())
+	}
+	if job := waitNetAdd(t, s); job.Phase != netAddPhaseDone {
+		t.Fatalf("add #1 phase = %s (category=%s detail=%s), want done", job.Phase, job.Category, job.Detail)
+	}
+	if got := networkPathCount(s); got != 1 {
+		t.Fatalf("registered paths after add #1 = %d, want 1", got)
+	}
+	if got := agent.removed(); len(got) != 0 {
+		t.Fatalf("happy path must not roll back: %v", got)
+	}
+
+	// Add #2 inside the TTL window — the probe must answer from the cache.
+	res2 := okAddRes("m2")
+	res2.Verify, res2.JobID = "", ""
+	agent.setAddRes(res2)
+	w = postNetAdd(t, s, "m2")
+	if w.Code != http.StatusOK {
+		t.Fatalf("add #2: got %d (%s)", w.Code, w.Body.String())
+	}
+	if job := waitNetAdd(t, s); job.Phase != netAddPhaseDone || job.Name != "m2" {
+		t.Fatalf("add #2 job = %+v, want done/m2", job)
+	}
+	adds, verifyCalls := agent.counts()
+	if adds != 2 {
+		t.Errorf("agent add calls = %d, want 2", adds)
+	}
+	if verifyCalls != 1 { // the NEGATIVE assertion: no probe increment on a warm cache
+		t.Errorf("probe (verify-status) calls across two adds = %d, want exactly 1 (cached)", verifyCalls)
+	}
+}
+
+// --- T3 (Scenario C): probe indeterminate ⇒ NEVER "too old"; the existing error paths speak -----
+// Companion red-proof (the classification trap): mutate classifySupportErr to return SupportNo on
+// ANY error → both subtests fail with the false 412 agent_outdated refusal.
+func TestNetAddGate_ProbeIndeterminate_PassesThrough(t *testing.T) {
+	cases := map[string]error{
+		"transport error": errors.New("dial tcp 10.0.0.9:8443: connect: connection refused"),
+		"http 5xx":        &agentapi.StatusError{Path: "/netstorage/verify-status", Code: http.StatusBadGateway},
+	}
+	for name, perr := range cases {
+		t.Run(name, func(t *testing.T) {
+			s := testServer(t)
+			agent := &fakeNetAgent{
+				verifyErr: perr,
+				addErr:    errors.New("agentapi: POST /netstorage/add: connection refused"),
+			}
+			s.netAgentFn = func() (netAgent, error) { return agent, nil }
+
+			w := postNetAdd(t, s, "media")
+			// The gate must NOT refuse: the add is accepted and fails through the EXISTING
+			// agent-error path with its honest message.
+			if w.Code != http.StatusOK {
+				t.Fatalf("indeterminate probe must pass the gate: got %d (%s)", w.Code, w.Body.String())
+			}
+			if strings.Contains(w.Body.String(), "agent_outdated") || strings.Contains(w.Body.String(), "frissítés") {
+				t.Fatalf("a down agent must never be called outdated: %s", w.Body.String())
+			}
+			job := waitNetAdd(t, s)
+			if job.Phase != netAddPhaseFailed || job.Category != "agent_error" {
+				t.Errorf("job = %s/%s, want failed/agent_error (the existing path)", job.Phase, job.Category)
+			}
+			if got := networkPathCount(s); got != 0 {
+				t.Errorf("nothing may register (got %d)", got)
+			}
+		})
+	}
+}

controller/internal/web/netstorage_handlers.go

@@ -22,6 +22,31 @@ import (
 // agent applies the +100000 host offset; this is the in-guest id the share is mapped to.
 const defaultMediaUID = 1000
 
+// netAddOutdatedMsg is the sync add-time refusal (machine code "agent_outdated") when the agent
+// predates the coupled verify-before-commit add semantics (pre-v0.81.0).
+const netAddOutdatedMsg = "Az ügynök frissítése szükséges ehhez a funkcióhoz — a frissítés megérkezése után próbáld újra."
+
+// netAddSupport evaluates the coupled-feature probe for the settings-page render with a SHORT
+// budget — a down agent must not stall the page (the cache usually answers instantly). Returns the
+// template vocabulary: "yes" | "no" | "unknown"; only "no" swaps the add form for the banner —
+// flaky states belong to the add-time handling.
+func (s *Server) netAddSupport() string {
+	agent, err := s.netAgentForAdd()
+	if err != nil {
+		return "unknown"
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	switch s.netFeatures.Supports(ctx, agent, agentapi.FeatureNetstorageVerify) {
+	case agentapi.SupportYes:
+		return "yes"
+	case agentapi.SupportNo:
+		return "no"
+	default:
+		return "unknown"
+	}
+}
+
 // networkStorageItem is the UI row: the registered descriptor + live per-share health from the agent.
 // Orphan marks an agent-configured share with NO registry entry (a crash-window leftover — Scenario
 // F's visible closure): the row renders with ONLY the remove action.
@@ -91,6 +116,16 @@ func (s *Server) handleNetStorageAdd(w http.ResponseWriter, r *http.Request) {
 		writeDiskJSON(w, http.StatusServiceUnavailable, false, err.Error(), nil)
 		return
 	}
+	// Capability gate (the publish-train backstop): the coupled add semantics shipped with agent
+	// v0.81.0 together with GET /netstorage/verify-status — on an older agent, refuse up front
+	// instead of failing mid-pipeline in `verifying` with a misleading rollback. Runs BEFORE the
+	// single-flight claim (a refused add must not consume the slot). SupportUnknown passes: a down
+	// agent speaks through the existing agent-error paths, never as "too old".
+	if s.netFeatures.Supports(r.Context(), agent, agentapi.FeatureNetstorageVerify) == agentapi.SupportNo {
+		s.logger.Printf("[WARN] [web] netstorage add %q refused: agent predates %s (probe 404)", name, agentapi.FeatureNetstorageVerify)
+		writeDiskJSON(w, http.StatusPreconditionFailed, false, netAddOutdatedMsg, map[string]any{"code": "agent_outdated"})
+		return
+	}
 	label := strings.TrimSpace(req.Label)
 	if label == "" {
 		label = "Hálózati tárhely: " + name

controller/internal/web/server.go

@@ -74,6 +74,9 @@ type Server struct {
 	netAgentFn func() (netAgent, error)
 	netProbeFn func(ctx context.Context, dir string) probeOutcome
 	netListFn  func(ctx context.Context) ([]agentapi.NetworkMountStatus, error)
+	// netFeatures caches the agent-capability probe (agentapi features.go) for the coupled NAS add
+	// semantics — the add gate + the settings-page banner read it. Zero value ready.
+	netFeatures agentapi.SupportCache
 
 	// Asset syncer for Hub-managed assets (optional)
 	assetsSyncer *assets.Syncer