tool, mavend: Hexis owns the tier of a Hexis capability (V-523)

read_only was the whole decision on the Hexis act path, which flattened three
answers into two. A capability that wipes the thing it names got the same
single spoken "да" as one that restarts a service, and requires_confirmation —
which the Hexis contract calls server-derived and never settable by a caller —
was read by nobody. docs/ecosystem.md §17.3 says confirmation follows risk.

RiskOfCapability reads Hexis's risk, read_only and requires_confirmation and
returns one of the three tiers internal/tool already had. It takes plain values
rather than a Capability, so internal/tool keeps no dependency on the Hexis
client. RiskOf keeps deriving, because a shell row the owner ticked on /tools
has no upstream to ask.

Every disagreement between the three fields goes up, never down: safe and
mutating is a contradiction and takes the confirm, an unrecognised tier takes
the confirm, and requires_confirmation may only raise. Same default as an
unrecognised dispatch shape — argue your way down, never up.

The irreversible refusal was a Go literal in two places and is now one deck
entry, act_needs_authed_surface. It lost four words to the persona ceiling.

internal/tool/risk_test.go

@@ -79,3 +79,33 @@ func TestExecConfirmsAnUnreadableRow(t *testing.T) {
 		t.Errorf("%v; want ErrNeedsConfirm", err)
 	}
 }
+
+// Hexis owns the tier of a Hexis capability, so this reads rather than derives
+// (Vikunja #523). The cases that matter are the ones where the three fields
+// disagree, or where the tier is a word this package has never seen: every one
+// of those goes up to a confirm, never down to running freely.
+func TestRiskOfCapabilityReadsHexis(t *testing.T) {
+	for _, c := range []struct {
+		name    string
+		risk    string
+		ro      bool
+		confirm bool
+		want    Risk
+	}{
+		{"hexis says irreversible", "irreversible", false, true, TierIrreversible},
+		{"case and space do not change the tier", "  Irreversible ", false, true, TierIrreversible},
+		{"hexis says destructive", "destructive", false, true, TierDestructive},
+		{"a read hexis calls safe", "safe", true, false, TierSafe},
+		{"safe but mutating is a contradiction", "safe", false, false, TierDestructive},
+		{"safe but wants a confirm is a contradiction", "safe", true, true, TierDestructive},
+		{"no tier, read-only, no confirm", "", true, false, TierSafe},
+		{"no tier and mutating", "", false, false, TierDestructive},
+		{"no tier but hexis wants a confirm", "", true, true, TierDestructive},
+		{"a word we have never seen", "spicy", true, false, TierDestructive},
+	} {
+		if got := RiskOfCapability(c.risk, c.ro, c.confirm); got != c.want {
+			t.Errorf("%s: RiskOfCapability(%q, ro=%v, confirm=%v) = %q; want %q",
+				c.name, c.risk, c.ro, c.confirm, got, c.want)
+		}
+	}
+}