v0.18.0: MCP entity-graph CRUD, lifecycle validation, curl -o /dev/null fix

- create_entity, set_entity_state, end_relationship MCP tools
- update_entity_attributes now triggers check derivation via EnsureEntityChecks
- shared db.EnsureEntityChecks + db.ValidateTransition hooks (HTTP + MCP parity)
- curl -o /dev/null now classified read_only (was config_mutation)
- db.ErrTransitionInvalid sentinel for HTTP error-type accuracy
- SOUL.md: capability escalation, self-grounding, exploration budget rules
- Runbook: oikos check lifecycle for agent self-knowledge

internal/policy/command_test.go

@@ -102,6 +102,33 @@ func TestClassifyCommand_CurlPipeSh_ConfigMutation(t *testing.T) {
 	}
 }
 
+func TestClassifyCommand_CurlDevNull_ReadOnly(t *testing.T) {
+	// -o /dev/null is a no-op sink — the canonical GET-and-discard
+	// reachability idiom must stay read_only. Output to real paths stays
+	// config_mutation. POST/data flags after stripping still gate.
+	cases := []struct {
+		cmd string
+		cls string
+	}{
+		// read_only: GET with body discarded to /dev/null
+		{`curl -o /dev/null -w '%{http_code}' --connect-timeout 10 http://192.168.8.101:8123`, RiskReadOnly},
+		{`curl -sS -o /dev/null https://home.hubris.network`, RiskReadOnly},
+		{`curl --output /dev/null https://example.com`, RiskReadOnly},
+		{`curl -o /dev/null https://example.com`, RiskReadOnly},
+		{`curl -o/dev/null -w '%{http_code}' https://example.com`, RiskReadOnly},
+		// config_mutation: POST/data still caught after stripping devnull
+		{`curl -o /dev/null -X POST https://example.com`, RiskConfigMutation},
+		{`curl -o /dev/null -d '{"x":1}' https://example.com`, RiskConfigMutation},
+		// config_mutation: -o to real path stays config_mutation
+		{`curl -o /etc/caddy/Caddyfile http://example.com`, RiskConfigMutation},
+	}
+	for _, c := range cases {
+		if got := ClassifyCommand(c.cmd, ""); got != c.cls {
+			t.Errorf("ClassifyCommand(%q) = %q, want %q", c.cmd, got, c.cls)
+		}
+	}
+}
+
 func TestClassifyCommand_DefaultEscalatesToConfigMutation(t *testing.T) {
 	cases := []string{
 		"apt-get install -y nginx",