feat: Phase 8 — nomos packages extracted into internal/nomos/{turngate,retrycap,messagequeue,assent,session}

Mechanical extraction of nomos internal components into plain-Go subpackages
per the hexagonal plan (ADR 0016 §3.1 rule 3):
  turngate/   — per-session turn serialization (plan 2026-08-03 F1)
  retrycap/   — per-turn run retry cap (maxRunRetries=3)
  messagequeue/ — operator-message queue for busy-turn re-entry (F2)
  assent/     — chat-assent detection (isAssent, isTypedConfirmation,
                ExtractPendingApprovals), decoupled from agent via
                []string input instead of persistedCall
  session/    — store (chat sessions, plan execution, DB persistence),
                migration runner + local emitEvent to break adapter
                dependency

internal/migrate/ — shared migration runner extracted from postgres pool,
                    used by both the oikos postgres adapter and session tests.

session package export-rename finishing touches remain; the four smaller
packages compile with passing tests. Depguard rules and ADR-0016 leaf-note
update deferred to a followup. VERSION 0.35.1.

internal/migrate/migrate.go

@@ -0,0 +1,119 @@
+// Package migrate applies the embedded forward-only SQL migrations
+// (migrations/*.up.sql). It is shared infrastructure: the oikos postgres
+// adapter runs it at pool startup, and nomos's session tests use it to
+// build throwaway databases — nomos must not import the adapters, so the
+// runner lives here, one level above both (ADR 0016 rule 3).
+package migrate
+
+import (
+	"context"
+	"fmt"
+	"io/fs"
+	"log/slog"
+	"sort"
+	"strings"
+
+	"github.com/dtoro/oikos/migrations"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// migrationLockKey is the advisory-lock key serializing migration runs —
+// two concurrent migrators must not interleave DDL.
+const migrationLockKey = 0x01c05e5
+
+// PgxPool is the surface Apply needs: acquire a dedicated connection for
+// the lock-held run.
+type PgxPool interface {
+	Acquire(ctx context.Context) (*pgxpool.Conn, error)
+}
+
+// Apply runs all embedded forward migrations in order, on one connection
+// holding a session advisory lock. Uses the schema_migrations table to
+// track applied versions.
+func Apply(ctx context.Context, pool PgxPool) error {
+	conn, err := pool.Acquire(ctx)
+	if err != nil {
+		return fmt.Errorf("acquire migration conn: %w", err)
+	}
+	defer conn.Release()
+
+	if _, err := conn.Exec(ctx, "SELECT pg_advisory_lock($1)", migrationLockKey); err != nil {
+		return fmt.Errorf("acquire migration lock: %w", err)
+	}
+	defer func() {
+		if _, err := conn.Exec(context.WithoutCancel(ctx), "SELECT pg_advisory_unlock($1)", migrationLockKey); err != nil {
+			slog.Warn("migrate: release lock failed", "error", err)
+		}
+	}()
+
+	// Create tracking table if not exists
+	_, err = conn.Exec(ctx, `
+		CREATE TABLE IF NOT EXISTS schema_migrations (
+			version INT PRIMARY KEY,
+			applied_at TIMESTAMPTZ NOT NULL DEFAULT now()
+		)
+	`)
+	if err != nil {
+		return fmt.Errorf("create schema_migrations: %w", err)
+	}
+
+	// List migration files
+	entries, err := fs.ReadDir(migrations.FS, ".")
+	if err != nil {
+		return fmt.Errorf("read migration fs: %w", err)
+	}
+
+	var files []string
+	for _, e := range entries {
+		if !e.IsDir() && strings.HasSuffix(e.Name(), ".up.sql") {
+			files = append(files, e.Name())
+		}
+	}
+	sort.Strings(files)
+
+	for _, fname := range files {
+		// Extract version number (001, 002, etc.)
+		var version int
+		if _, err := fmt.Sscanf(fname, "%03d", &version); err != nil {
+			continue
+		}
+
+		// Check if already applied
+		var applied int
+		err := conn.QueryRow(ctx,
+			"SELECT COUNT(*) FROM schema_migrations WHERE version = $1", version).Scan(&applied)
+		if err != nil {
+			return fmt.Errorf("check migration %d: %w", version, err)
+		}
+		if applied > 0 {
+			continue
+		}
+
+		// Read and execute migration — split into individual statements
+		// because TimescaleDB CAGGs and some DDL can't run inside a transaction,
+		// and pgx's multi-statement Exec wraps them implicitly.
+		content, err := migrations.FS.ReadFile(fname)
+		if err != nil {
+			return fmt.Errorf("read %s: %w", fname, err)
+		}
+
+		stmts := SplitSQL(string(content))
+		for i, stmt := range stmts {
+			stmt = strings.TrimSpace(stmt)
+			if stmt == "" {
+				continue
+			}
+			_, err := conn.Exec(ctx, stmt)
+			if err != nil {
+				return fmt.Errorf("exec migration %s stmt %d: %w", fname, i+1, err)
+			}
+		}
+		_, err = conn.Exec(ctx, "INSERT INTO schema_migrations (version) VALUES ($1)", version)
+		if err != nil {
+			return fmt.Errorf("record migration %d: %w", version, err)
+		}
+		slog.Info("migration applied", "file", fname, "version", version, "statements", len(stmts))
+	}
+
+	return nil
+}