P4b: skill noun + contrib/store (SQLite for budget/persona/skill/audit)

Merges the skill half of the persona/skill pair plus the second nested module.
(Squashed onto main from phase-4b-skill; the audit/budget/persona batteries it
was stacked on already landed via the P4 merge.)

- skill/: clean-redesign Skill noun + LEAN SkillStore (lifecycle/versions/
  schedule only) + ToRunnable + Memory default.
- contrib/store/: separate go.mod carrying modernc.org/sqlite, so the driver
  never enters the core go.sum. db.Budget()/Personas()/Skills()/Audit() back
  all four store seams (JSON-blob + indexed columns; round-trip tested).
  Includes the verified gadfly #5 fixes (AppendVersion tx+UNIQUE+error,
  Mark*ScheduledRun atomic json_set, busy_timeout, NaN guard).
- CI: builds + tests the nested module and asserts it owns the sqlite driver.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skill/memory.go

@@ -0,0 +1,169 @@
+package skill
+
+import (
+	"context"
+	"sort"
+	"sync"
+	"time"
+)
+
+// Memory is a zero-dependency in-process SkillStore — a light host or test gets
+// saved-skill persistence with no DB. Mort backs SkillStore with GORM/MySQL;
+// contrib/store adds durable SQLite.
+type Memory struct {
+	mu       sync.RWMutex
+	skills   map[string]*Skill         // by ID
+	versions map[string][]SkillVersion // by skill ID, append order
+	byVerID  map[string]SkillVersion   // by version ID
+}
+
+// NewMemory returns an empty in-memory SkillStore.
+func NewMemory() *Memory {
+	return &Memory{
+		skills:   map[string]*Skill{},
+		versions: map[string][]SkillVersion{},
+		byVerID:  map[string]SkillVersion{},
+	}
+}
+
+var _ SkillStore = (*Memory)(nil)
+
+func (m *Memory) Initialize(context.Context) error { return nil }
+
+func (m *Memory) Save(_ context.Context, s *Skill) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	cp := *s
+	m.skills[s.ID] = &cp
+	return nil
+}
+
+func (m *Memory) Get(_ context.Context, id string) (*Skill, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	s, ok := m.skills[id]
+	if !ok {
+		return nil, ErrNotFound
+	}
+	cp := *s
+	return &cp, nil
+}
+
+func (m *Memory) GetByName(_ context.Context, ownerID, name string) (*Skill, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	for _, s := range m.skills {
+		if s.OwnerID == ownerID && s.Name == name {
+			cp := *s
+			return &cp, nil
+		}
+	}
+	return nil, ErrNotFound
+}
+
+func (m *Memory) Delete(_ context.Context, id string) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	delete(m.skills, id)
+	return nil
+}
+
+func (m *Memory) listWhere(keep func(*Skill) bool) []Skill {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	out := make([]Skill, 0, len(m.skills))
+	for _, s := range m.skills {
+		if keep == nil || keep(s) {
+			out = append(out, *s)
+		}
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
+	return out
+}
+
+func (m *Memory) ListByOwner(_ context.Context, ownerID string) ([]Skill, error) {
+	return m.listWhere(func(s *Skill) bool { return s.OwnerID == ownerID }), nil
+}
+
+func (m *Memory) ListPublic(context.Context) ([]Skill, error) {
+	return m.listWhere(func(s *Skill) bool { return s.Visibility == VisibilityPublic }), nil
+}
+
+func (m *Memory) ListSharedWith(_ context.Context, memberID string) ([]Skill, error) {
+	return m.listWhere(func(s *Skill) bool {
+		if s.Visibility != VisibilityShared {
+			return false
+		}
+		for _, id := range s.SharedWith {
+			if id == memberID {
+				return true
+			}
+		}
+		return false
+	}), nil
+}
+
+func (m *Memory) ListBuiltinByName(_ context.Context, name string) (*Skill, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	for _, s := range m.skills {
+		if s.Source == SourceBuiltin && s.Name == name {
+			cp := *s
+			return &cp, nil
+		}
+	}
+	return nil, ErrNotFound
+}
+
+func (m *Memory) ListChatbotExposed(context.Context) ([]Skill, error) {
+	return m.listWhere(func(s *Skill) bool { return s.ExposeAsChatbotTool }), nil
+}
+
+func (m *Memory) ListDueScheduled(_ context.Context, now time.Time) ([]Skill, error) {
+	return m.listWhere(func(s *Skill) bool { return s.DueAt(now) }), nil
+}
+
+func (m *Memory) MarkScheduledRun(_ context.Context, skillID string, ranAt, nextAt time.Time) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	s, ok := m.skills[skillID]
+	if !ok {
+		return ErrNotFound
+	}
+	s.LastScheduledRunAt = ranAt
+	s.NextRunAt = nextAt
+	return nil
+}
+
+func (m *Memory) AppendVersion(_ context.Context, sv SkillVersion) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.versions[sv.SkillID] = append(m.versions[sv.SkillID], sv)
+	m.byVerID[sv.ID] = sv
+	return nil
+}
+
+func (m *Memory) ListVersionsBySkill(_ context.Context, skillID string, limit int) ([]SkillVersion, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	all := m.versions[skillID]
+	// newest first
+	out := make([]SkillVersion, 0, len(all))
+	for i := len(all) - 1; i >= 0; i-- {
+		out = append(out, all[i])
+		if limit > 0 && len(out) >= limit {
+			break
+		}
+	}
+	return out, nil
+}
+
+func (m *Memory) GetVersionByID(_ context.Context, versionID string) (*SkillVersion, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	sv, ok := m.byVerID[versionID]
+	if !ok {
+		return nil, ErrNotFound
+	}
+	return &sv, nil
+}