feat: sync rules across all harnesses + agents to opencode/kilo

Add Rule as a first-class canonical kind (rules/<name>.md, loaded like
agents) and propagate it the way each harness actually loads it:

- claude-code: native ~/.claude/rules directory symlink (preserves rule
  path-scoping frontmatter); rules NOT folded into CLAUDE.md.
- opencode/kilo/zed/crush: fold rule bodies into the global AGENTS.md
  always-on instructions file (frontmatter stripped). crush has no global
  instructions file, so register the absolute AGENTS.md path in
  options.context_paths (defaults are re-prepended at load, so nothing is
  clobbered).
- goose: fold into ~/.config/goose/.goosehints.
- cagent: fold into the per-agent instruction.

Also:
- Wire markdown agents to opencode (~/.config/opencode/agents) and fix the
  kilo agents symlink: plural ~/.config/kilo/agents (singular "agent" is a
  silent no-op on current Kilo CLI).
- Add ManagesAgents/ManagesRules to HarnessCapabilities + ImportResult.Rules;
  claude-code/opencode import rules/agents round-trip.
- Centralize instruction selection in Bundle.InstructionText /
  InstructionTextWithRules (replaces per-adapter override duplication).
- init scaffolds + imports rules; README capability matrix gains
  Agents/Rules columns with native-vs-folded footnotes.

Grounded each harness's sink against official docs + config source this
session. Gate: gofmt, go vet, go test -race ./..., golangci-lint (0),
govulncheck (clean).

internal/canonical/instructions.go

@@ -0,0 +1,47 @@
+package canonical
+
+import "strings"
+
+// InstructionText returns the instruction body a harness should receive: the
+// per-harness override when one is set, otherwise the global instructions.
+func (b *Bundle) InstructionText(harness string) string {
+	if override, ok := b.Instructions.PerHarness[harness]; ok && override != "" {
+		return override
+	}
+	return b.Instructions.Global
+}
+
+// InstructionTextWithRules returns InstructionText for the harness with every
+// canonical rule body folded in. Harnesses without a native rules directory
+// (everything except claude-code/kilo) only receive rule content this way —
+// via their global instructions file. Rule frontmatter is stripped so the
+// folded output stays clean; bodies are joined in load order (deterministic).
+func (b *Bundle) InstructionTextWithRules(harness string) string {
+	base := b.InstructionText(harness)
+	var sb strings.Builder
+	sb.WriteString(base)
+	for _, r := range b.Rules {
+		body := strings.TrimSpace(stripFrontmatter(r.Body))
+		if body == "" {
+			continue
+		}
+		if sb.Len() > 0 {
+			sb.WriteString("\n\n")
+		}
+		sb.WriteString(body)
+	}
+	return sb.String()
+}
+
+// stripFrontmatter removes a leading YAML frontmatter block ("---\n…\n---") so
+// folding a rule into a plain instructions file does not leak its metadata.
+func stripFrontmatter(s string) string {
+	if !strings.HasPrefix(s, "---\n") {
+		return s
+	}
+	end := strings.Index(s[4:], "\n---")
+	if end == -1 {
+		return s
+	}
+	return strings.TrimPrefix(s[4+end+len("\n---"):], "\n")
+}

internal/canonical/instructions_test.go

@@ -0,0 +1,102 @@
+package canonical
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInstructionText(t *testing.T) {
+	t.Run("global when no override", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{Instructions: Instructions{Global: "G"}}
+		assert.Equal(t, "G", b.InstructionText("zed"))
+	})
+	t.Run("per-harness override wins", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{Instructions: Instructions{Global: "G", PerHarness: map[string]string{"zed": "Z"}}}
+		assert.Equal(t, "Z", b.InstructionText("zed"))
+	})
+	t.Run("empty override falls back to global", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{Instructions: Instructions{Global: "G", PerHarness: map[string]string{"zed": ""}}}
+		assert.Equal(t, "G", b.InstructionText("zed"))
+	})
+	t.Run("empty everything", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{}
+		assert.Equal(t, "", b.InstructionText("zed"))
+	})
+}
+
+func TestInstructionTextWithRules(t *testing.T) {
+	t.Run("folds rules after global", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{
+			Instructions: Instructions{Global: "# Global"},
+			Rules: []Rule{
+				{Name: "a", Body: "# Rule A\n\nbe concise"},
+				{Name: "b", Body: "# Rule B\n\nbe safe"},
+			},
+		}
+		got := b.InstructionTextWithRules("opencode")
+		assert.Equal(t, "# Global\n\n# Rule A\n\nbe concise\n\n# Rule B\n\nbe safe", got)
+	})
+
+	t.Run("strips rule frontmatter", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{
+			Instructions: Instructions{Global: "G"},
+			Rules: []Rule{
+				{Name: "scoped", Body: "---\nname: scoped\npaths: \"**/*.go\"\n---\n# Go\n\ngofmt"},
+			},
+		}
+		got := b.InstructionTextWithRules("opencode")
+		assert.Equal(t, "G\n\n# Go\n\ngofmt", got)
+		assert.NotContains(t, got, "paths:")
+		assert.NotContains(t, got, "---")
+	})
+
+	t.Run("no rules returns plain instruction text", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{Instructions: Instructions{Global: "G"}}
+		assert.Equal(t, "G", b.InstructionTextWithRules("opencode"))
+	})
+
+	t.Run("empty global still emits rules", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{Rules: []Rule{{Name: "a", Body: "rule body"}}}
+		assert.Equal(t, "rule body", b.InstructionTextWithRules("opencode"))
+	})
+
+	t.Run("blank rule bodies are skipped", func(t *testing.T) {
+		t.Parallel()
+		b := Bundle{
+			Instructions: Instructions{Global: "G"},
+			Rules: []Rule{
+				{Name: "empty", Body: "   \n  "},
+				{Name: "real", Body: "keep"},
+			},
+		}
+		assert.Equal(t, "G\n\nkeep", b.InstructionTextWithRules("opencode"))
+	})
+}
+
+func TestStripFrontmatter(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"no frontmatter", "# Title\nbody", "# Title\nbody"},
+		{"with frontmatter", "---\nname: x\n---\n# Title", "# Title"},
+		{"unterminated frontmatter left intact", "---\nname: x\nbody", "---\nname: x\nbody"},
+		{"empty", "", ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			assert.Equal(t, tt.want, stripFrontmatter(tt.in))
+		})
+	}
+}

internal/canonical/load.go

@@ -72,6 +72,14 @@ func LoadFS(fs fsx.FS, root string) (*Bundle, error) {
 		b.Agents = append(b.Agents, Agent(m))
 	}
 
+	rules, err := loadMarkdownDirFS(fs, filepath.Join(root, "rules"), "")
+	if err != nil {
+		return nil, err
+	}
+	for _, m := range rules {
+		b.Rules = append(b.Rules, Rule(m))
+	}
+
 	b.Instructions.PerHarness = map[string]string{}
 	body, err := readFileIfExistsFS(fs, filepath.Join(root, "instructions", "global.md"))
 	if err != nil {

internal/canonical/load_test.go

@@ -28,6 +28,10 @@ func TestLoad(t *testing.T) {
 	require.Len(t, b.Agents, 1)
 	assert.Equal(t, "sample", b.Agents[0].Name)
 
+	require.Len(t, b.Rules, 1)
+	assert.Equal(t, "sample-rule", b.Rules[0].Name)
+	assert.Contains(t, b.Rules[0].Body, "Always be concise.")
+
 	assert.Contains(t, b.Instructions.Global, "Be helpful.")
 }
 

internal/canonical/testdata/sample/rules/sample-rule.md

@@ -0,0 +1,3 @@
+# Sample Rule
+
+Always be concise.

internal/canonical/types.go

@@ -65,6 +65,16 @@ type Agent struct {
 	Path        string
 }
 
+// Rule is a topic-scoped instruction fragment (e.g. ~/.claude/rules/go.md).
+// Claude Code auto-loads a directory of these; harnesses without a native rules
+// directory receive the bodies folded into their global instructions file.
+type Rule struct {
+	Name        string
+	Description string
+	Body        string
+	Path        string
+}
+
 type Instructions struct {
 	PerHarness map[string]string
 	Global     string
@@ -77,6 +87,7 @@ type Bundle struct {
 	Profile      Profile
 	Skills       []Skill
 	Agents       []Agent
+	Rules        []Rule
 	MCP          MCPRegistry
 }