feat: Phase 9 gaps closed — ApprovalService.Decide convergence, execlog fold, execworker poller

- ApprovalService (core/app/approval.go) + ApprovalRepo (postgres adapter) with
  full decide transaction: HMAC token verify, approval flip, execution un-gate,
  session-scoped window keys (+session suffix matching GovernanceStore gate),
  nomos session flip, audit+event on failure abort. httpapi DecideApproval now
  a thin presenter delegating to the service. ListPending payload format fixed
  (json.Unmarshal not raw-wrap).
- execlog folded into postgres adapter: internal/execlog deleted, NewExecutionLog
  / ReadExecutionLog live in the db package, callers updated (mcp, httpapi).
- execworker poller over ExecutionService.DispatchQueued: advisory lock leak
  fixed (defer/recover per execution), correlation_id preserved via Finalize
  event emission (ExecRunRepo.Finalize now emits execution.{status} with
  correlation_id from the row).
- Phase 8 session export-rename completed: Store, New, and all 53 methods
  exported; cmd/nomos/ agent.go fixed to use session.PendingContinuation etc.
- Coverage gates: ExecutionService.Submit 93.1%, PolicyService.Decide 100%.
- Plans index updated, VERSION bumped to 0.36.0.

internal/adapters/postgres/execlog.go

@@ -0,0 +1,130 @@
+package db
+
+import (
+	"context"
+	"log/slog"
+	"sync"
+	"time"
+
+	"github.com/dtoro/oikos/internal/adapters/postgres/sqlcgen"
+	"github.com/dtoro/oikos/internal/observability"
+	"github.com/google/uuid"
+)
+
+// Execution log persistence + throttled event emission (folded from the
+// internal/execlog package during the hex refactor — the execution-log
+// repository lives with the other execution persistence in this adapter).
+
+// eventInterval throttles execution.output events. Chunks are persisted as
+// they arrive, but a chatty command (apt, a long build) can produce hundreds
+// per second and the SSE broker drops events for slow subscribers — flooding
+// it would push out the signal.* and approval.* events that actually need to
+// arrive. The event is only a "there is more output" ping; subscribers re-read
+// the rows.
+const eventInterval = time.Second
+
+// ExecLogSink receives output chunks as they arrive from a remote command.
+type ExecLogSink func(stream string, chunk []byte)
+
+// NewExecutionLog returns a Sink that writes chunks to execution_logs and
+// emits a throttled execution.output event, plus a Flush to call when the
+// command finishes.
+//
+// The returned Sink is safe for concurrent use: stdout and stderr are written
+// from separate goroutines.
+func NewExecutionLog(ctx context.Context, pool *Pool, execID uuid.UUID, correlationID string) (ExecLogSink, func()) {
+	var (
+		mu        sync.Mutex
+		seq       int
+		lastEvent time.Time
+		pending   bool
+	)
+
+	emit := func() {
+		if err := observability.Event(ctx, sqlcgen.New(pool), "execution.output", &execID,
+			"info", "actuator", correlationID, map[string]any{"execution_id": execID.String()}); err != nil {
+			slog.Debug("execlog: emit output event", "error", err, "execution_id", execID)
+		}
+	}
+
+	sink := func(stream string, chunk []byte) {
+		if len(chunk) == 0 {
+			return
+		}
+		mu.Lock()
+		seq++
+		n := seq
+		mu.Unlock()
+
+		// A failed log write must never fail the command: this is observability,
+		// and the authoritative output still lands in executions.result at the
+		// end. Log and carry on.
+		if _, err := pool.Exec(ctx,
+			`INSERT INTO execution_logs (execution_id, seq, stream, chunk)
+			 VALUES ($1, $2, $3, $4)`,
+			execID, n, stream, string(chunk)); err != nil {
+			slog.Debug("execlog: persist chunk", "error", err, "execution_id", execID)
+			return
+		}
+
+		mu.Lock()
+		due := time.Since(lastEvent) >= eventInterval
+		if due {
+			lastEvent = time.Now()
+			pending = false
+		} else {
+			pending = true
+		}
+		mu.Unlock()
+
+		if due {
+			emit()
+		}
+	}
+
+	// Flush emits a final event when output arrived inside the throttle window,
+	// so the last few lines of a short command are not left unannounced.
+	flush := func() {
+		mu.Lock()
+		due := pending
+		pending = false
+		mu.Unlock()
+		if due {
+			emit()
+		}
+	}
+
+	return sink, flush
+}
+
+// ExecLogChunk is one persisted slice of command output.
+type ExecLogChunk struct {
+	Seq    int       `json:"seq"`
+	Stream string    `json:"stream"`
+	Chunk  string    `json:"chunk"`
+	TS     time.Time `json:"ts"`
+}
+
+// ReadExecutionLog returns an execution's persisted output in order.
+func ReadExecutionLog(ctx context.Context, pool *Pool, execID uuid.UUID, limit int) ([]ExecLogChunk, error) {
+	if limit <= 0 {
+		limit = 1000
+	}
+	rows, err := pool.Query(ctx,
+		`SELECT seq, stream, chunk, ts FROM execution_logs
+		 WHERE execution_id = $1 ORDER BY seq LIMIT $2`, execID, limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var out []ExecLogChunk
+	for rows.Next() {
+		var c ExecLogChunk
+		if err := rows.Scan(&c.Seq, &c.Stream, &c.Chunk, &c.TS); err != nil {
+			return nil, err
+		}
+		out = append(out, c)
+	}
+	return out, rows.Err()
+}