praxis: an empty attention list is not always an all-clear (V-540)

ECOSYSTEM-SPEC §2.6 requires list_attention to distinguish "nothing needs
attention" from "I cannot currently tell", and to say so when a source is
failed or stale. Maven said the first one unconditionally: ListAttention
decoded into []map[string]any, the word degraded appeared nowhere, and an empty
list answered "ничего не требует внимания". A Praxis with every source dead
read as calm.

Two halves, because the spec's mechanism does not exist server-side yet. The
deployed Praxis answers /api/v1/tools/attention with a bare array and no
envelope, so praxisAttention now decodes either shape and believes a degraded
array when one arrives. Until one does, an empty list triggers one read of
/api/v1/sources, and anything that is not reporting health "ok" is named
instead of the all-clear. Zero sources is the same answer: a Praxis that polls
nothing knows nothing, which is the state of this box today.

A sources read that fails is deliberately not a hedge. The attention call
succeeded, and not being able to ask about health is not evidence of a fault.

Both hedges also cover the entity-scoped digest, where a per-entity all-clear
is the more convincing of the two. New keys attention_degraded and
attention_no_sources, in acts_ru_v1.json and the floor. The fake Praxis serves
one healthy source by default, so the existing attention tests still assert an
all-clear on purpose rather than by omission.

cmd/mavend/ecosystem.go

@@ -263,18 +263,85 @@ func (c *praxisClient) getJSON(ctx context.Context, op, path string, out any) er
 	return nil
 }
 
-func (c *praxisClient) ListAttention(ctx context.Context, limit int) ([]map[string]any, error) {
-	var out []map[string]any
+// praxisAttention — an attention response in either of the two shapes Praxis
+// may send (Vikunja #540).
+//
+// ECOSYSTEM-SPEC §2.6 says the response carries `degraded: [source_ids]` when a
+// source is failed or stale, and that Maven is required to say so rather than
+// report all-clear. The deployed Praxis answers with a bare JSON array and no
+// envelope at all, so both are decoded here: an array is the items, an object is
+// the spec envelope. This lands the Maven half without waiting on the server,
+// and the sources read below is what makes the hedge work meanwhile.
+type praxisAttention struct {
+	Items    []map[string]any
+	Degraded []string
+}
+
+func (a *praxisAttention) UnmarshalJSON(data []byte) error {
+	trimmed := bytes.TrimSpace(data)
+	if len(trimmed) > 0 && trimmed[0] == '[' {
+		return json.Unmarshal(trimmed, &a.Items)
+	}
+	var env struct {
+		Items    []map[string]any `json:"items"`
+		Degraded []string         `json:"degraded"`
+	}
+	if err := json.Unmarshal(trimmed, &env); err != nil {
+		return err
+	}
+	a.Items, a.Degraded = env.Items, env.Degraded
+	return nil
+}
+
+func (c *praxisClient) ListAttention(ctx context.Context, limit int) (praxisAttention, error) {
+	var out praxisAttention
 	err := c.getJSON(ctx, "attention", fmt.Sprintf("/api/v1/tools/attention?limit=%d", limit), &out)
 	return out, err
 }
 
+// praxisSource — one polled source, as much of it as the hedge needs. The tools
+// API does not expose sources, so this decodes the plain `/api/v1/sources` rows.
+type praxisSource struct {
+	ID       string `json:"id"`
+	SourceID string `json:"source_id"`
+	Health   string `json:"health"`
+}
+
+func (s praxisSource) name() string {
+	if s.SourceID != "" {
+		return s.SourceID
+	}
+	return s.ID
+}
+
+// UnhealthySources reports which sources cannot be trusted to have reported,
+// and how many sources Praxis has at all (Vikunja #540).
+//
+// Only read when the attention list came back empty, which is the one turn where
+// an all-clear is at stake. A source whose health field is absent counts as
+// healthy: a Praxis that never reports health would otherwise make every quiet
+// turn a hedge, and an unreported field is not evidence of a fault. Everything it
+// does report other than "ok" — failed, stale, degraded, unknown — counts as
+// cannot-tell, because none of them mean the source has spoken.
+func (c *praxisClient) UnhealthySources(ctx context.Context) (bad []string, total int, err error) {
+	var out []praxisSource
+	if err := c.getJSON(ctx, "sources", "/api/v1/sources", &out); err != nil {
+		return nil, 0, err
+	}
+	for _, s := range out {
+		if s.Health != "" && s.Health != "ok" {
+			bad = append(bad, s.name())
+		}
+	}
+	return bad, len(out), nil
+}
+
 // ListAttentionForEntity is ListAttention scoped to a single canonical Nexus
 // entity, so callers already holding a resolved entity_id (e.g. after
 // resolveEntityReference) can ask "what needs attention for this entity"
 // instead of filtering the unscoped list client-side.
-func (c *praxisClient) ListAttentionForEntity(ctx context.Context, entityID string, limit int) ([]map[string]any, error) {
-	var out []map[string]any
+func (c *praxisClient) ListAttentionForEntity(ctx context.Context, entityID string, limit int) (praxisAttention, error) {
+	var out praxisAttention
 	err := c.getJSON(ctx, "attention_for_entity",
 		fmt.Sprintf("/api/v1/tools/attention?limit=%d&entity_id=%s", limit, url.QueryEscape(entityID)), &out)
 	return out, err