fix(parser): align zed shelley capabilities

Provider capabilities are used as a contract for what normalized content a provider can actually emit. Shelley currently records token totals from messages but does not emit aggregate usage events, and Zed filters child threads before relationship fields can surface.

Keep the declarations conservative so the facade does not advertise unsupported content features while the providers continue to preserve the parser behavior they actually expose today.

Author: mariusvniekerk

internal/parser/shelley_provider.go

@@ -436,7 +436,6 @@ func shelleyProviderCapabilities() Capabilities {
 			ToolCalls:            CapabilitySupported,
 			ToolResults:          CapabilitySupported,
 			PerMessageTokenUsage: CapabilitySupported,
-			AggregateUsageEvents: CapabilitySupported,
 			Model:                CapabilitySupported,
 		},
 	}

internal/parser/zed_provider.go

@@ -438,7 +438,6 @@ func zedProviderCapabilities() Capabilities {
 			FirstMessage:         CapabilitySupported,
 			SessionName:          CapabilitySupported,
 			Cwd:                  CapabilitySupported,
-			Relationships:        CapabilitySupported,
 			Thinking:             CapabilitySupported,
 			ToolCalls:            CapabilitySupported,
 			ToolResults:          CapabilitySupported,

internal/parser/zed_shelley_provider_test.go

@@ -16,6 +16,9 @@ func TestZedProviderFactoryReplacesLegacyAdapter(t *testing.T) {
 	require.True(t, ok)
 	_, legacyFactory := factory.(legacyProviderFactory)
 	assert.False(t, legacyFactory)
+	caps := factory.Capabilities()
+	assert.Equal(t, CapabilityUnsupported, caps.Content.Relationships)
+	assert.Equal(t, CapabilitySupported, caps.Content.AggregateUsageEvents)
 
 	provider, ok := NewProvider(AgentZed, ProviderConfig{
 		Roots:   []string{t.TempDir()},
@@ -213,6 +216,9 @@ func TestShelleyProviderFactoryReplacesLegacyAdapter(t *testing.T) {
 	require.True(t, ok)
 	_, legacyFactory := factory.(legacyProviderFactory)
 	assert.False(t, legacyFactory)
+	caps := factory.Capabilities()
+	assert.Equal(t, CapabilitySupported, caps.Content.Relationships)
+	assert.Equal(t, CapabilityUnsupported, caps.Content.AggregateUsageEvents)
 
 	provider, ok := NewProvider(AgentShelley, ProviderConfig{
 		Roots:   []string{t.TempDir()},