feat(backend): SQLite storage layer + CDC pipeline

.gitignore

@@ -17,6 +17,15 @@ vendor/
 /backend/backend
 agent-orchestrator.yaml
 
+# Backend runtime data artifacts (SQLite store + WAL, CDC event log).
+# Created at AO_DATA_DIR (outside the repo by default); ignored here so a
+# data dir pointed at the tree never gets committed.
+*.db
+*.db-shm
+*.db-wal
+session-events.jsonl
+session-events.jsonl.*
+
 # Environment
 .env
 .env.*

backend/cdc_wiring.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"log/slog"
+
+	"github.com/aoagents/agent-orchestrator/backend/internal/cdc"
+	"github.com/aoagents/agent-orchestrator/backend/internal/storage/sqlite"
+)
+
+// cdcPipeline owns the running CDC poller and the broadcaster the SSE transport
+// subscribes to. The DB triggers write change_log; the poller tails it and fans
+// each new event out through the broadcaster. Durable catch-up is the client's
+// job (it reads change_log from its own Last-Event-ID), so the poller only
+// pushes live events and re-seeks to head on restart.
+type cdcPipeline struct {
+	Broadcaster *cdc.Broadcaster
+	done        <-chan struct{}
+}
+
+// startCDC seeks the poller to the current head and starts its loop. It stops
+// when ctx is cancelled; Stop waits for it to drain.
+func startCDC(ctx context.Context, store *sqlite.Store, logger *slog.Logger) (*cdcPipeline, error) {
+	bcast := cdc.NewBroadcaster()
+	poller := cdc.NewPoller(cdcSource{store}, bcast, cdc.PollerConfig{Logger: logger})
+	if err := poller.SeekToHead(ctx); err != nil {
+		return nil, err
+	}
+	return &cdcPipeline{Broadcaster: bcast, done: poller.Start(ctx)}, nil
+}
+
+// Stop waits for the poller goroutine to exit (the caller must have cancelled the
+// ctx passed to startCDC).
+func (p *cdcPipeline) Stop() error {
+	<-p.done
+	return nil
+}
+
+// cdcSource adapts *sqlite.Store's change_log reads to cdc.Source.
+type cdcSource struct{ store *sqlite.Store }
+
+func (s cdcSource) EventsAfter(ctx context.Context, after int64, limit int) ([]cdc.Event, error) {
+	rows, err := s.store.ReadChangeLogAfter(ctx, after, limit)
+	if err != nil {
+		return nil, err
+	}
+	out := make([]cdc.Event, len(rows))
+	for i, r := range rows {
+		out[i] = cdc.Event{
+			Seq:       r.Seq,
+			ProjectID: r.ProjectID,
+			SessionID: r.SessionID,
+			Type:      cdc.EventType(r.EventType),
+			Payload:   json.RawMessage(r.Payload),
+			CreatedAt: r.CreatedAt,
+		}
+	}
+	return out, nil
+}
+
+func (s cdcSource) LatestSeq(ctx context.Context) (int64, error) {
+	return s.store.MaxChangeLogSeq(ctx)
+}

backend/go.mod

@@ -1,5 +1,25 @@
 module github.com/aoagents/agent-orchestrator/backend
 
-go 1.22
+go 1.25.7
 
-require github.com/go-chi/chi/v5 v5.1.0
+require (
+	github.com/go-chi/chi/v5 v5.1.0
+	github.com/pressly/goose/v3 v3.27.1
+	modernc.org/sqlite v1.51.0
+)
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/mattn/go-isatty v0.0.21 // indirect
+	github.com/mfridman/interpolate v0.0.2 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	github.com/sethvargo/go-retry v0.3.0 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
+	golang.org/x/sync v0.20.0 // indirect
+	golang.org/x/sys v0.43.0 // indirect
+	modernc.org/libc v1.72.3 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
+)

backend/go.sum

@@ -1,2 +1,68 @@
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backend/internal/cdc/broadcast.go

@@ -0,0 +1,66 @@
+package cdc
+
+import (
+	"log/slog"
+	"sync"
+)
+
+// Broadcaster is the in-process fan-out the poller feeds. Subscribers (the
+// WS/SSE transport, wired in the frontend task) register a callback; every
+// polled Event is delivered to all current subscribers. It is the single seam
+// between the CDC poller and live delivery, so the transport can be built and
+// swapped without touching the poller.
+type Broadcaster struct {
+	mu     sync.RWMutex
+	nextID int
+	subs   map[int]func(Event)
+	logger *slog.Logger
+}
+
+// NewBroadcaster returns an empty Broadcaster ready for subscriptions.
+func NewBroadcaster() *Broadcaster {
+	return &Broadcaster{subs: map[int]func(Event){}, logger: slog.Default()}
+}
+
+// Subscribe registers fn and returns an unsubscribe function. fn is called
+// synchronously from the poller loop, so it must not block; a transport that
+// needs buffering should push onto its own channel inside fn.
+func (b *Broadcaster) Subscribe(fn func(Event)) (unsubscribe func()) {
+	b.mu.Lock()
+	id := b.nextID
+	b.nextID++
+	b.subs[id] = fn
+	b.mu.Unlock()
+	return func() {
+		b.mu.Lock()
+		delete(b.subs, id)
+		b.mu.Unlock()
+	}
+}
+
+// SubscriberCount reports the number of current subscribers.
+func (b *Broadcaster) SubscriberCount() int {
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	return len(b.subs)
+}
+
+// Publish delivers e to every current subscriber. A panicking subscriber is
+// recovered and logged so one bad callback can't kill the poller goroutine or
+// starve the other subscribers.
+func (b *Broadcaster) Publish(e Event) {
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	for _, fn := range b.subs {
+		b.deliver(fn, e)
+	}
+}
+
+func (b *Broadcaster) deliver(fn func(Event), e Event) {
+	defer func() {
+		if r := recover(); r != nil {
+			b.logger.Error("cdc broadcaster: subscriber panicked", "seq", e.Seq, "panic", r)
+		}
+	}()
+	fn(e)
+}