Slice 3: activity feed and active project (SSE + MCP tools)

Add internal/activity (thread-safe active project + bounded event feed with subscriber fan-out). Service exposes active-project/activity methods and takes the feed. New MCP tools get_active_project/set_active_project/get_activity and HTTP endpoints GET/POST /api/active-project, /api/activity, and /events (SSE). New <activity-feed> component updates live via EventSource; <repo-list> sets the active project on selection. Verified end-to-end in the running app: user actions push live events and set the active project (actor=user), all readable by Claude over MCP.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/activity/activity.go

@@ -0,0 +1,154 @@
+// Package activity holds the app's coordination state: the single active project
+// (the repo/task currently in focus) and a bounded feed of what happened — user
+// AND Claude actions. Both are in-memory (mirrored to the logs, no datastore —
+// AGENT.md §1.3) and queryable so Claude can sync on any turn boundary; new
+// events also fan out to subscribers for the browser SSE stream (§8.2). This is
+// the foundation the graceful project handoff (§8.3) builds on.
+package activity
+
+import (
+	"log/slog"
+	"sync"
+	"time"
+)
+
+// Actor is who caused an event.
+type Actor string
+
+const (
+	ActorUser   Actor = "user"
+	ActorClaude Actor = "claude"
+	ActorSystem Actor = "system"
+)
+
+// Event is one entry in the activity feed.
+type Event struct {
+	ID     int64     `json:"id"`
+	Time   time.Time `json:"time"`
+	Actor  Actor     `json:"actor"`
+	Kind   string    `json:"kind"`             // e.g. "active-project-changed"
+	Repo   string    `json:"repo,omitempty"`   // repo path, when relevant
+	Detail string    `json:"detail,omitempty"` // human-readable extra context
+}
+
+// Feed is the concurrency-safe active-project + activity store with fan-out.
+type Feed struct {
+	mu        sync.RWMutex
+	active    string // active project path ("" = none)
+	events    []Event
+	maxEvents int
+	nextID    int64
+	subs      map[chan Event]struct{}
+	log       *slog.Logger
+}
+
+// New builds a Feed keeping at most maxEvents recent events.
+func New(log *slog.Logger, maxEvents int) *Feed {
+	if maxEvents <= 0 {
+		maxEvents = 200
+	}
+	return &Feed{
+		maxEvents: maxEvents,
+		nextID:    1,
+		subs:      make(map[chan Event]struct{}),
+		log:       log,
+	}
+}
+
+// ActiveProject returns the current active project path ("" if none).
+func (f *Feed) ActiveProject() string {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+	return f.active
+}
+
+// SetActiveProject sets the active project and records an event. It is a no-op
+// (changed=false, zero Event) when path already matches, so repeated sets don't
+// spam the feed.
+func (f *Feed) SetActiveProject(actor Actor, path string) (Event, bool) {
+	f.mu.Lock()
+	if f.active == path {
+		f.mu.Unlock()
+		return Event{}, false
+	}
+	f.active = path
+	ev, subs := f.appendLocked(actor, "active-project-changed", path, "")
+	f.mu.Unlock()
+
+	publish(subs, ev)
+	return ev, true
+}
+
+// Record adds an arbitrary event to the feed.
+func (f *Feed) Record(actor Actor, kind, repo, detail string) Event {
+	f.mu.Lock()
+	ev, subs := f.appendLocked(actor, kind, repo, detail)
+	f.mu.Unlock()
+
+	publish(subs, ev)
+	return ev
+}
+
+// Events returns up to limit of the most recent events, oldest first. limit<=0
+// returns all retained events.
+func (f *Feed) Events(limit int) []Event {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+	if limit <= 0 || limit > len(f.events) {
+		limit = len(f.events)
+	}
+	out := make([]Event, limit)
+	copy(out, f.events[len(f.events)-limit:])
+	return out
+}
+
+// Subscribe returns a channel of future events and an unsubscribe func the
+// caller MUST invoke when done (e.g. via defer) to avoid leaking the channel.
+func (f *Feed) Subscribe() (<-chan Event, func()) {
+	ch := make(chan Event, 16)
+	f.mu.Lock()
+	f.subs[ch] = struct{}{}
+	f.mu.Unlock()
+
+	var once sync.Once
+	unsub := func() {
+		once.Do(func() {
+			f.mu.Lock()
+			delete(f.subs, ch)
+			f.mu.Unlock()
+			close(ch)
+		})
+	}
+	return ch, unsub
+}
+
+// appendLocked assigns id/time, appends (trimming to maxEvents), logs, and
+// returns the event plus a snapshot of subscriber channels to publish to after
+// the lock is released. Caller must hold f.mu.
+func (f *Feed) appendLocked(actor Actor, kind, repo, detail string) (Event, []chan Event) {
+	ev := Event{ID: f.nextID, Time: time.Now(), Actor: actor, Kind: kind, Repo: repo, Detail: detail}
+	f.nextID++
+	f.events = append(f.events, ev)
+	if len(f.events) > f.maxEvents {
+		f.events = f.events[len(f.events)-f.maxEvents:]
+	}
+	if f.log != nil {
+		f.log.Info("activity", "actor", actor, "kind", kind, "repo", repo, "detail", detail)
+	}
+	subs := make([]chan Event, 0, len(f.subs))
+	for ch := range f.subs {
+		subs = append(subs, ch)
+	}
+	return ev, subs
+}
+
+// publish does a non-blocking send to each subscriber; a full channel (slow
+// consumer) drops the event rather than stalling the producer.
+func publish(subs []chan Event, ev Event) {
+	for _, ch := range subs {
+		select {
+		case ch <- ev:
+		default:
+		}
+	}
+}