fix(adapters): ground native schemas, merge-not-replace, add goose/cagent/zed

- common/mcp.go: MCPStyle enum + BuildMCPMapStyled for claude/crush/opencode/zed dialects
- common/jsonmerge.go: MergeJSONKeys (JSON-first, JSONC fallback) preserves user keys;
  fix: try plain json.Unmarshal before StripJSONComments to avoid mangling URLs with //
- common/yamlmerge.go: MergeYAMLKeys for YAML configs (goose)
- common/blocks.go: add ProvidersAsMap for opencode map-shaped provider key
- claudecode: merge settings.json (preserves hooks/permissions/env); MCPClaudeStyle (no type field)
- crush: fix mcp key (was mcpServers); MCPCrushStyle entries include type field; merge crush.json; fix import key mcp
- kilo: drop providers key (kilo has none); MCPOpencodeStyle (local/remote); merge kilo.json
- opencode: fix provider (singular map) + model (not default_model); MCPOpencodeStyle; merge jsonc; fix import key mcp
- goose: new adapter — YAML merge, extensions map, splitProviderModel, import reconstructs MCP from extensions
- cagent: new adapter — renders starter default.yaml, import returns empty
- zed: new adapter — merge settings.json, context_servers (MCPZedStyle) + agent.default_model
- docs: append Grounded harness schemas section to design spec

internal/adapters/opencode/opencode_test.go

@@ -34,12 +34,81 @@ func TestOpencodeRender(t *testing.T) {
 	assert.Equal(t, adapter.RenderedFile, seen[cfgDest].Kind)
 	var parsed map[string]any
 	require.NoError(t, json.Unmarshal(seen[cfgDest].Content, &parsed))
+	// Correct key is "provider" (singular map), not "providers" (slice).
+	assert.Contains(t, parsed, "provider")
+	assert.NotContains(t, parsed, "providers")
+	// Correct key is "model", not "default_model".
+	assert.Contains(t, parsed, "model")
+	assert.NotContains(t, parsed, "default_model")
+	// No "mcpServers" — opencode uses "mcp".
+	assert.NotContains(t, parsed, "mcpServers")
 
 	agentsDest := filepath.Join(home, ".config", "opencode", "AGENTS.md")
 	assert.Equal(t, adapter.RenderedFile, seen[agentsDest].Kind)
 	assert.Contains(t, string(seen[agentsDest].Content), "# global")
 }
 
+func TestOpencodeRenderWithMCP(t *testing.T) {
+	home := t.TempDir()
+	ad := New(WithHome(home))
+	b := &canonical.Bundle{
+		Profile: canonical.Profile{
+			Gateway: canonical.Gateway{DefaultModel: "sonnet"},
+		},
+		MCP: canonical.MCPRegistry{Servers: []canonical.MCPServer{
+			{Name: "fp", Command: "/bin/fp"},
+		}},
+	}
+	fs, err := ad.Render(b)
+	require.NoError(t, err)
+	seen := map[string]adapter.File{}
+	fs.ForEach(func(f adapter.File) { seen[f.Dest] = f })
+
+	cfgDest := filepath.Join(home, ".config", "opencode", "opencode.jsonc")
+	var parsed map[string]any
+	require.NoError(t, json.Unmarshal(seen[cfgDest].Content, &parsed))
+	mcp := parsed["mcp"].(map[string]any)
+	fp := mcp["fp"].(map[string]any)
+	// MCPOpencodeStyle: type local, command as array, enabled true.
+	assert.Equal(t, "local", fp["type"])
+	assert.Equal(t, true, fp["enabled"])
+	cmd, _ := fp["command"].([]any)
+	assert.Equal(t, "/bin/fp", cmd[0])
+}
+
+func TestOpencodeRenderMergesExistingKeys(t *testing.T) {
+	home := t.TempDir()
+	base := filepath.Join(home, ".config", "opencode")
+	require.NoError(t, os.MkdirAll(base, 0o750))
+
+	existing := map[string]any{
+		"$schema": "https://opencode.schema/v1",
+		"agent":   map[string]any{"maxTokens": 8192},
+	}
+	body, _ := json.Marshal(existing)
+	require.NoError(t, os.WriteFile(filepath.Join(base, "opencode.jsonc"), body, 0o600))
+
+	ad := New(WithHome(home))
+	b := &canonical.Bundle{
+		Profile: canonical.Profile{
+			Gateway: canonical.Gateway{DefaultModel: "sonnet"},
+		},
+	}
+	fs, err := ad.Render(b)
+	require.NoError(t, err)
+	seen := map[string]adapter.File{}
+	fs.ForEach(func(f adapter.File) { seen[f.Dest] = f })
+
+	cfgDest := filepath.Join(base, "opencode.jsonc")
+	var parsed map[string]any
+	require.NoError(t, json.Unmarshal(seen[cfgDest].Content, &parsed))
+	// User keys preserved.
+	assert.Equal(t, "https://opencode.schema/v1", parsed["$schema"])
+	assert.Contains(t, parsed, "agent")
+	// Managed keys overlaid.
+	assert.Contains(t, parsed, "model")
+	assert.Contains(t, parsed, "provider")
+}
 func TestOpencodeImportStripsComments(t *testing.T) {
 	home := t.TempDir()
 	base := filepath.Join(home, ".config", "opencode")