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/zed/zed.go

@@ -0,0 +1,102 @@
+// Package zed is the Zed editor harness adapter.
+//
+// Zed uses ~/.config/zed/settings.json with many user-managed keys.
+// We MERGE only "agent" and "context_servers"; all other keys are preserved.
+// MCP servers become context_servers entries with source: "custom".
+package zed
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/lukaszraczylo/harness-sync/internal/adapter"
+	"github.com/lukaszraczylo/harness-sync/internal/adapter/common"
+	"github.com/lukaszraczylo/harness-sync/internal/canonical"
+)
+
+const name = "zed"
+
+// Adapter implements adapter.Adapter for the Zed 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/zed/ exists.
+func (a *Adapter) Detect() bool {
+	_, err := os.Stat(filepath.Join(a.home, ".config", "zed"))
+	return err == nil
+}
+
+// Render produces the FileSet that applies the canonical bundle to Zed.
+// settings.json is MERGED to preserve all user-managed Zed configuration.
+// Only "agent" (default_model) and "context_servers" (MCP) are overlaid.
+func (a *Adapter) Render(b *canonical.Bundle) (*adapter.FileSet, error) {
+	fs := adapter.NewFileSet()
+	cfgPath := filepath.Join(a.home, ".config", "zed", "settings.json")
+	existing, _ := os.ReadFile(cfgPath)
+
+	overlay := map[string]any{
+		"context_servers": common.BuildMCPMapStyled(&b.MCP, common.MCPZedStyle),
+	}
+
+	if dm := b.Profile.Gateway.DefaultModel; dm != "" {
+		provider, model := splitProviderModel(dm)
+		overlay["agent"] = map[string]any{
+			"default_model": map[string]any{
+				"provider": provider,
+				"model":    model,
+			},
+		}
+	}
+
+	merged, err := common.MergeJSONKeys(existing, overlay)
+	if err != nil {
+		return nil, err
+	}
+	fs.Add(adapter.File{
+		Dest:    cfgPath,
+		Kind:    adapter.RenderedFile,
+		Content: merged,
+	})
+
+	return fs, nil
+}
+
+// Import reads context_servers from Zed settings.json back to MCP servers.
+func (a *Adapter) Import(home string) (*adapter.ImportResult, error) {
+	return importFrom(home)
+}
+
+// splitProviderModel splits "provider/model" at the first slash.
+// If no slash, provider is "anthropic".
+func splitProviderModel(s string) (string, string) {
+	if idx := strings.IndexByte(s, '/'); idx >= 0 {
+		return s[:idx], s[idx+1:]
+	}
+	return "anthropic", s
+}