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/cagent/cagent.go

@@ -0,0 +1,118 @@
+// Package cagent is the cagent harness adapter.
+//
+// cagent is per-run (no persistent agent state). v1 renders a starter
+// ~/.config/cagent/default.yaml with a single default agent pointing at the
+// gateway. Import always returns an empty result.
+package cagent
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/lukaszraczylo/harness-sync/internal/adapter"
+	"github.com/lukaszraczylo/harness-sync/internal/canonical"
+
+	"gopkg.in/yaml.v3"
+)
+
+const name = "cagent"
+
+// Adapter implements adapter.Adapter for the cagent harness.
+type Adapter struct{ home string }
+
+// Option configures an Adapter.
+type Option func(*Adapter)
+
+// WithHome overrides the home directory (defaults to os.UserHomeDir).
+func WithHome(h string) Option { return func(a *Adapter) { a.home = h } }
+
+// New returns a new Adapter with the given options applied.
+func New(opts ...Option) *Adapter {
+	a := &Adapter{home: defaultHome()}
+	for _, o := range opts {
+		o(a)
+	}
+	return a
+}
+
+func defaultHome() string {
+	h, err := os.UserHomeDir()
+	if err != nil {
+		return ""
+	}
+	return h
+}
+
+// Name returns the harness identifier.
+func (a *Adapter) Name() string { return name }
+
+// Detect returns true when ~/.config/cagent/ exists.
+func (a *Adapter) Detect() bool {
+	_, err := os.Stat(filepath.Join(a.home, ".config", "cagent"))
+	return err == nil
+}
+
+// Render produces a starter default.yaml for cagent.
+func (a *Adapter) Render(b *canonical.Bundle) (*adapter.FileSet, error) {
+	fs := adapter.NewFileSet()
+	cfgPath := filepath.Join(a.home, ".config", "cagent", "default.yaml")
+
+	instructions := b.Instructions.Global
+	if override, ok := b.Instructions.PerHarness[name]; ok && override != "" {
+		instructions = override
+	}
+
+	mcps := map[string]any{}
+	for _, s := range b.MCP.Servers {
+		e := map[string]any{}
+		if s.Command != "" {
+			e["command"] = s.Command
+		}
+		args := s.Args
+		if args == nil {
+			args = []string{}
+		}
+		e["args"] = args
+		mcps[s.Name] = e
+	}
+
+	cfg := map[string]any{
+		"version": 8,
+		"metadata": map[string]any{
+			"name": "harness-sync",
+		},
+		"agents": map[string]any{
+			"default": map[string]any{
+				"model":       "gateway/" + b.Profile.Gateway.DefaultModel,
+				"instruction": instructions,
+			},
+		},
+		"models": map[string]any{
+			"gateway": map[string]any{
+				"provider": "openai", // cagent gateway via openai-compat
+				"base_url": b.Profile.Gateway.URL,
+			},
+		},
+	}
+	if len(mcps) > 0 {
+		cfg["mcps"] = mcps
+	}
+
+	body, err := yaml.Marshal(cfg)
+	if err != nil {
+		return nil, err
+	}
+
+	fs.Add(adapter.File{
+		Dest:    cfgPath,
+		Kind:    adapter.RenderedFile,
+		Content: body,
+	})
+
+	return fs, nil
+}
+
+// Import returns an empty result — cagent has no persistent state to import.
+func (a *Adapter) Import(home string) (*adapter.ImportResult, error) {
+	return &adapter.ImportResult{}, nil
+}