diff --git a/backend/README.md b/backend/README.md
index 23a5227b..f9f1551b 100644
--- a/backend/README.md
+++ b/backend/README.md
@@ -8,10 +8,10 @@
 
 | Пакет | Что делает | Ключевые файлы |
 |---|---|---|
-| `cmd/tmctl` | CLI: `translate` / `status` (read-only N/M+паспорта глав+деньги, `--json`; работает ПРИ живом прогоне — store без flock) / `report` (request-log+леджер книги **+ per-run quality-report**: структурный KPI предл./нарратив-абзац, тире, cosmetic-strip/echo-rates, глоссарий-промахи, trust-gated — наблюдаемость, НЕ гейт; D39.2-T4) / `export` (**экспорт-поверхность для полигона**: final_hash→checkpoint→checks.ExportNormalize, manifest-join c pending/ghost-учётом, ConfigDrift-поле, `--plaintext`; D39.5) / `redrive` (переатака флагнутых: `--chapter/--chunk/--reason/--dry-run`, D15.3) / `manifest` (**$0-производитель персиста манифеста глав/чанков**, строка 100: нужен ДО первого прогона — дерево глав разобранной, но не запущенной книги; `--json` печатает сам документ). Денежный аргумент прогона: `--ceiling-usd` (строка 145) перекрывает книжный `ceilings.book_usd` ТОЛЬКО на этот прогон, в book.yaml не пишется, ноль/отрицательное = отказ запуска. main — тонкая обвязка: разбор/exit-коды/.env/рендеры в тестируемых функциях | `main.go`, `invocation.go`, `render.go`, `dotenv.go` |
+| `cmd/tmctl` | CLI: `translate` / `status` (read-only N/M+паспорта глав+деньги, `--json`; работает ПРИ живом прогоне — store без flock) / `report` (request-log+леджер книги **+ per-run quality-report**: структурный KPI предл./нарратив-абзац, тире, cosmetic-strip/echo-rates, глоссарий-промахи, trust-gated — наблюдаемость, НЕ гейт; D39.2-T4) / `export` (**экспорт-поверхность для полигона**: final_hash→checkpoint→checks.ExportNormalize, manifest-join c pending/ghost-учётом, ConfigDrift-поле, `--plaintext`; D39.5) / `redrive` (переатака флагнутых: `--chapter/--chunk/--reason/--dry-run`, D15.3) / `manifest` (**$0-производитель персиста манифеста глав/чанков**, строка 100: нужен ДО первого прогона — дерево глав разобранной, но не запущенной книги; `--json` печатает сам документ) / `migrate` (**$0-write-open без прогона**, строка 174: read-only команды требуют ТОЧНОГО совпадения схемы и не мигрируют, поэтому апгрейд бинаря запирал все существующие книги — платформа зовёт `status --json` перед каждым спавном, а write-команда, которая мигрировала бы, не наступала никогда. Грузит ТОЛЬКО `book.yaml` — ни цен, ни ключей на $0-пути (строка 146); restore point берёт ПОД ЛОКОМ и только когда шаг реально применяется (имя `<метка>-pre-migrate.db` — вне секундного неймспейса платного пути, строка 173); несовпадение схемы у read-only путей — типизированный отказ **exit 13** с машинным токеном `schema_mismatch found=N expected=M`). Денежный аргумент прогона: `--ceiling-usd` (строка 145) перекрывает книжный `ceilings.book_usd` ТОЛЬКО на этот прогон, в book.yaml не пишется, ноль/отрицательное = отказ запуска. main — тонкая обвязка: разбор/exit-коды/.env/рендеры в тестируемых функциях | `main.go`, `invocation.go`, `render.go`, `dotenv.go` |
 | `internal/llm` | OpenAI-совместимый транспорт + retry/backoff, **capability-слой** (budget_field/temperature/reasoning per-модель), провайдеры openai/local (no-proxy)/anthropic (DEPRECATED-референс); `failover.go` удалён паком-17 — маршрутизация лейблами живёт в config/pipeline (канал B, один хоп `chain[0]`, fail-closed) | `httpllm.go`, `capability.go`, `provider_*.go` |
 | `internal/ledger` | Цены по usage (вкл. reasoning/cache-поля), `PriceForResponse` по фактической модели | `pricing.go` |
-| `internal/store` | SQLite (modernc, CGO-free), цепочка миграций `schema_version` (⚠ ALTER-шаги v8+ не идемпотентны вопреки шапке — бэклог-строка 49а), reserve/settle+checkpoint, chunk_status, глоссарий (+подписной цикл терминолога), ruby, retrieval_state, request_log; `OpenReadOnly` — без flock/миграций/recovery для status/report/export | `ledger.go`, `migrate.go`, `glossary.go`, `store.go` |
+| `internal/store` | SQLite (modernc, CGO-free), цепочка миграций `schema_version` (⚠ ALTER-шаги v8+ не идемпотентны вопреки шапке — бэклог-строка 49а), reserve/settle+checkpoint, chunk_status, глоссарий (+подписной цикл терминолога), ruby, retrieval_state, request_log; `OpenReadOnly` — без flock/миграций/recovery для status/report/export (схема не совпала — типизированный `*store.SchemaMismatchError{Found,Expected}`, обе стороны); `Migrate` (+шов `beforeApply` под локом: restore point берётся там) — поверхность деплой-шага строки 174, `SchemaHead` — та самая `Expected`; write-open БД новее бинаря теперь ОТКАЗ, а не тихое открытие | `ledger.go`, `migrate.go`, `glossary.go`, `store.go` |
 | `internal/config` | fail-fast загрузка models/pipeline/book; **эхо-мина-гейт** `echoMineViolation`; `CheckRunnable` блокирует неисполнимое (C2/fanout/judge); **пар-слой** (D39.23): `configs/pairs/<пара>.yaml` — калибровка нарезки + коридор длины пары; **промпт-резолв КОНВЕНЦИЕЙ** `prompts/<пара>/<роль>.md` из `Book.LangPair()`+роли, **fail-loud на пару без пакета** (ja-книга не едет молча через zh-промпт), осознанное исключение — `prompt_override` на стадии | `models.go`, `pipeline.go`, `pair.go` |
 | `internal/text` | Нормализация и рун-примитивы, общие для банка/майнера/чекеров (script-agnostic слой, `lang` НЕ импортирует): `NormalizeSourceKey`/`NormalizeTargetForm` (версионированный артефакт `NormVersion()`, фолдится в снапшот), `NormalizeSource`, `TokenizeScript` (алфавит цели из данных, Mn-фолд U+0301; `TokenizeCyrillic` = ru-дефолт-обёртка), `DenseScript` — единый дом sizing-таксономии (D39.64) | `norm.go`, `runes.go`, `source.go` |
 | `internal/seed` | Схема сид-YAML книги (`File`/`Term`/`Decl`/`Alias`) — общий артефакт: майнер её ПИШЕТ (mined-дельта), банк ЧИТАЕТ (`LoadGlossarySeed`); тип общий, поэтому эмиссия не может разъехаться с загрузчиком | `seed.go` |
@@ -65,6 +65,7 @@ go run ./cmd/tmctl status --config example/book.yaml --json  # $0, N/M+пасп
 go run ./cmd/tmctl report --config example/book.yaml         # $0, quality-report (KPI/rates)
 go run ./cmd/tmctl export --config example/book.yaml         # $0, экспорт-JSON для полигона (--plaintext для человека)
 go run ./cmd/tmctl manifest --config example/book.yaml       # $0, пере-строить персист манифеста глав/чанков (--json — сам документ)
+go run ./cmd/tmctl migrate --config example/book.yaml        # $0, довести схему проекта до головы бинаря (деплой-шаг: стоп прогонов → НОВЫЙ бинарь на место → migrate ИМ по каждой книге без открытых попыток → прогоны в работу)
 go run ./cmd/tmctl translate --config example/book.yaml --ceiling-usd 0.5  # потолок ТОЛЬКО на этот прогон, book.yaml не пишется
 # live-conformance (реальные провайдеры, платно, вне CI):
 set -a; . ./.env; set +a; TM_LIVE=1 go test -tags live -run TestLive -v ./internal/pipeline/
diff --git a/backend/cmd/tmctl/main.go b/backend/cmd/tmctl/main.go
index 40c5048b..4ed4113c 100644
--- a/backend/cmd/tmctl/main.go
+++ b/backend/cmd/tmctl/main.go
@@ -1,4 +1,5 @@
-// tmctl is the TextMachine CLI: translate / report / status / export / redrive / manifest / backup.
+// tmctl is the TextMachine CLI: translate / report / status / export / redrive / manifest / backup /
+// migrate.
 // main.go — thin wiring (package №4): argument parsing — invocation.go,
 // output renderers — render.go, .env — dotenv.go; here just the
 // «parse → env → ctx → fetch → render» wiring and exit-code mapping.
@@ -45,6 +46,7 @@ const (
 	exitConfigInvalid    = 10 // the configuration will not run: unreadable, unparseable, invalid, no key
 	exitSourceUnreadable = 11 // the BOOK's source cannot be read or decoded — the one class about the text
 	exitProjectLocked    = 12 // another tmctl owns this project right now; come back later
+	exitSchemaMismatch   = 13 // this project's schema is not this binary's: run `tmctl migrate` (row 174)
 	exitRefusedOther     = 19 // a refusal class this build of tmctl has no number for
 )
 
@@ -53,6 +55,7 @@ var refusalExit = map[pipeline.RefusalClass]int{
 	pipeline.RefusalBadConfig:        exitConfigInvalid,
 	pipeline.RefusalSourceUnreadable: exitSourceUnreadable,
 	pipeline.RefusalProjectLocked:    exitProjectLocked,
+	pipeline.RefusalSchemaMismatch:   exitSchemaMismatch,
 }
 
 // exitCode maps a run() error onto the ratified shell contract (Milestone 2 / R1-FL-A):
@@ -183,10 +186,12 @@ func run() error {
 		return manifestCmd(inv.cfgPath, inv.asJSON)
 	case "backup":
 		return backupCmd(inv.cfgPath, os.Stdout)
+	case "migrate":
+		return migrateCmd(inv.cfgPath, os.Stdout)
 	case "seed-lint":
 		return seedLint(inv.seedPath)
 	default:
-		return fmt.Errorf("unknown command %q (want translate|report|status|export|redrive|manifest|backup|seed-lint)", inv.cmd)
+		return fmt.Errorf("unknown command %q (want translate|report|status|export|redrive|manifest|backup|migrate|seed-lint)", inv.cmd)
 	}
 }
 
diff --git a/backend/cmd/tmctl/migrate.go b/backend/cmd/tmctl/migrate.go
new file mode 100644
index 00000000..703b7e4c
--- /dev/null
+++ b/backend/cmd/tmctl/migrate.go
@@ -0,0 +1,108 @@
+package main
+
+// migrate.go: the $0 `tmctl migrate` verb — a project's WRITE open with no run behind it (backlog
+// row 174).
+//
+// The deadlock it breaks: the read-only commands (status, report, export, manifest) demand this
+// binary's exact schema and never migrate — only a write open applies the chain. So upgrading the
+// engine binary locks every existing book at once: the platform calls `tmctl status --json` before each
+// spawn and for the money, that call refuses the older schema, and the write command that WOULD have
+// migrated the project never comes. The deploy step is "stop the runs → put the NEW binary in place →
+// run THIS command over the books with it → let the runs start again", and a caller that meets exit 13
+// in flight can also self-heal from it.
+//
+// ⚠ WHICH books: the sweep belongs on projects with no OPEN attempt. A migrated project is above the
+// schema of every older binary, and the platform settles a finished attempt with the binary that
+// attempt was PINNED to — so migrating underneath an attempt whose settle has not happened yet would
+// trade this deadlock for a hold that can never be closed. The engine has no notion of an attempt, so
+// that rule lives in the caller's sweep (row 175); what the engine guarantees is that a project a live
+// run holds is refused rather than migrated (exit 12).
+//
+// It deliberately loads the BOOK config only. A migration touches no prompt, no provider and no price,
+// and pulling in the rest of the stack would drag its gates onto a $0 path — `prices_checked` refuses a
+// models.yaml whose prices are over 120 days old (backlog row 146), and an engine deployed onto a stand
+// with stale prices would then meet the deadlock again in exactly the shape this command exists to
+// remove. Same reason the command needs no provider key: it is an operator safety verb, like `backup`.
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"time"
+
+	"textmachine/backend/internal/config"
+	"textmachine/backend/internal/pipeline"
+	"textmachine/backend/internal/store"
+)
+
+// migrateSuffix names what the restore point below is FOR, and it is what keeps this command out of the
+// paid path's namespace. `translate`'s pre-flight guard writes backups/<stamp>.db with a stamp of
+// second precision, and BackupSQLite refuses to overwrite an existing one (backlog row 173) — so
+// sharing the name would make the very sequence this command enables (migrate, then start the run it
+// unblocked) fail inside the pre-flight guard whenever both land in the same second, turning a healthy
+// deploy into exit 1 before anything reached a provider.
+const migrateSuffix = "-pre-migrate"
+
+// migrateCmd brings the book's project database to this binary's schema and reports the transition.
+// $0: no LLM call, no network, no ledger movement — the only writes are the migration steps themselves
+// and the stale-reservation recovery every write open performs.
+//
+// Idempotent: a project already at head is opened, found current and closed — no step applied, no
+// restore point taken, no money touched.
+func migrateCmd(cfgPath string, w io.Writer) error {
+	book, err := config.LoadBook(cfgPath)
+	if err != nil {
+		// Like the pre-flight backup guard, this runs before any runner exists, so it is the first thing
+		// a broken config meets — and a refusal classified here rather than collapsed onto exit 1 is the
+		// whole of PD-196 (see pipeline/refusal.go).
+		return pipeline.RefuseConfig(err)
+	}
+	// Only ABSENT means "never run": a database this call is about to CREATE has no history to protect,
+	// and it is the one case that gets no restore point. Any other stat error read that way would skip
+	// the guard on a file that is there.
+	dbExists := true
+	if _, err := os.Stat(book.ProjectDB); err != nil {
+		if !errors.Is(err, fs.ErrNotExist) {
+			return fmt.Errorf("tmctl migrate: cannot stat the project database %s: %w", book.ProjectDB, err)
+		}
+		dbExists = false
+	}
+
+	// The restore point is taken INSIDE the project lock, and only when a step is actually going to run
+	// (store.Migrate's seam). A migration is the one $0 operation that rewrites the file holding the
+	// owner's signed bank, the checkpoints and the ledger, and the ALTER steps do not converge on a
+	// half-applied database (row 49а) — a damaged file is not something a re-run repairs. Taking it
+	// before the lock instead would copy the whole database of a project a live run owns and then refuse
+	// the migration anyway, once per retry.
+	backup := func(m store.Migration) error {
+		if !dbExists {
+			return nil
+		}
+		path, err := store.BackupSQLite(book.ProjectDB,
+			backupDirFor(book.ProjectDB), backupStamp(time.Now())+migrateSuffix)
+		if err != nil {
+			return fmt.Errorf("tmctl migrate: refusing to migrate a project it could not back up first: %w", err)
+		}
+		fmt.Fprintf(w, "pre-migrate: backed up the project DB at schema v%d to %s (integrity_check green)\n", m.From, path)
+		return nil
+	}
+
+	applied, err := store.Migrate(book.ProjectDB, backup)
+	if err != nil {
+		// The two classified open failures a caller acts on: another tmctl holds the project (come back
+		// later, exit 12) and a database NEWER than this binary (upgrade tmctl, exit 13 — a migration
+		// cannot repair that direction, so a caller looping on "migrate and retry" has to be told).
+		return pipeline.RefuseStoreOpen(err)
+	}
+	switch {
+	case !dbExists:
+		fmt.Fprintf(w, "migrate: created %s at schema v%d\n", book.ProjectDB, applied.To)
+	case applied.From == applied.To:
+		fmt.Fprintf(w, "migrate: %s already at schema v%d\n", book.ProjectDB, applied.To)
+	default:
+		fmt.Fprintf(w, "migrate: %s schema v%d -> v%d\n", book.ProjectDB, applied.From, applied.To)
+	}
+	return nil
+}
diff --git a/backend/cmd/tmctl/migrate_cli_test.go b/backend/cmd/tmctl/migrate_cli_test.go
new file mode 100644
index 00000000..8de41109
--- /dev/null
+++ b/backend/cmd/tmctl/migrate_cli_test.go
@@ -0,0 +1,398 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"database/sql"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+	"time"
+
+	"textmachine/backend/internal/pipeline"
+	"textmachine/backend/internal/store"
+)
+
+// migrate_cli_test.go is the CLI half of backlog row 174: the deploy deadlock is a SHELL fact — the
+// platform learns what happened from an exit code and a line of stderr — so the contract is exercised
+// where it is a contract. The migration mechanics themselves are pinned generically in
+// internal/store/migrate_test.go.
+
+// staleTheProjectSchema rolls the project database's recorded version back one step, which is what an
+// older engine binary left behind.
+//
+// ⚠ This fixture re-applies the newest migration on the next write open, which is fine while that step
+// is `CREATE … IF NOT EXISTS` and is NOT guaranteed for a future ALTER step (backlog row 49а). It is
+// used here because these tests are about the exit codes and the output, and the deep fixture — the
+// migration chain truncated to an older vintage — is only reachable from inside the store package,
+// where those properties are tested. If a future migration makes this fail, move the setup rather than
+// weakening the assertions.
+func staleTheProjectSchema(t *testing.T, dbPath string) int {
+	t.Helper()
+	db, err := sql.Open("sqlite", "file:"+dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	if _, err := db.Exec(`DELETE FROM schema_version WHERE version = (SELECT MAX(version) FROM schema_version)`); err != nil {
+		t.Fatal(err)
+	}
+	return schemaVersionOf(t, dbPath)
+}
+
+// schemaVersionOf reads the recorded schema version through its own connection — the state under test
+// must be asserted independently of the product code that reports it.
+func schemaVersionOf(t *testing.T, dbPath string) int {
+	t.Helper()
+	db, err := sql.Open("sqlite", "file:"+dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	var v int
+	if err := db.QueryRow(`SELECT COALESCE(MAX(version), 0) FROM schema_version`).Scan(&v); err != nil {
+		t.Fatal(err)
+	}
+	return v
+}
+
+// holdTheProject takes the project's exclusive flock the way another tmctl process would, WITHOUT
+// opening the store — because a write open would migrate the database, and the state under test is a
+// project that is both stale and held.
+func holdTheProject(t *testing.T, dbPath string) {
+	t.Helper()
+	f, err := os.OpenFile(dbPath+".lock", os.O_CREATE|os.O_RDWR, 0o644)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		_ = syscall.Flock(int(f.Fd()), syscall.LOCK_UN)
+		f.Close()
+	})
+}
+
+func projectDBOf(bookPath string) string {
+	return filepath.Join(filepath.Dir(bookPath), "cli-book.db")
+}
+
+func backupsOf(t *testing.T, dbPath string) []string {
+	t.Helper()
+	entries, err := os.ReadDir(backupDirFor(dbPath))
+	if os.IsNotExist(err) {
+		return nil
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+	var names []string
+	for _, e := range entries {
+		names = append(names, e.Name())
+	}
+	return names
+}
+
+// mockProvider answers every call with a usable draft, so a `translate` really settles money.
+func mockProvider(t *testing.T) *httptest.Server {
+	t.Helper()
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.ReadAll(r.Body)
+		fmt.Fprint(w, `{"id":"fake","model":"fake-model","choices":[{"message":{"content":"ЧЕРНОВИК ПЕРЕВОДА"},"finish_reason":"stop"}],
+			"usage":{"prompt_tokens":1000,"completion_tokens":500}}`)
+	}))
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+// TestTheDeployDeadlockIsBrokenAtTheShell drives the real binary through the exact sequence the
+// platform meets on an engine upgrade: `status --json` before a spawn refuses the older schema, and the
+// contract must make that refusal actionable — its own number inside the refusal band, and the two
+// versions machine-readable — so the caller can migrate and start the run instead of stopping the world.
+func TestTheDeployDeadlockIsBrokenAtTheShell(t *testing.T) {
+	if testing.Short() {
+		t.Skip("builds and runs the binary")
+	}
+	bin := buildTmctl(t)
+	bookPath := setupCLIProject(t, mockProvider(t).URL)
+	dbPath := projectDBOf(bookPath)
+
+	// A book an older binary left behind.
+	st, err := store.Open(dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	st.Close()
+	from := staleTheProjectSchema(t, dbPath)
+
+	var stderr bytes.Buffer
+	status := exec.Command(bin, "status", "--config", bookPath, "--json")
+	status.Stderr = &stderr
+	if got := exitCodeOf(t, status.Run()); got != exitSchemaMismatch {
+		t.Fatalf("`status --json` on an older schema exited %d, want %d", got, exitSchemaMismatch)
+	}
+	// The number says WHAT; these two say which way and how far — without them a caller cannot tell the
+	// direction a migration repairs from the one where it would loop forever.
+	want := fmt.Sprintf("schema_mismatch found=%d expected=%d", from, store.SchemaHead())
+	if !strings.Contains(stderr.String(), want) {
+		t.Fatalf("the refusal must carry %q machine-readably; got:\n%s", want, stderr.String())
+	}
+	if exitSchemaMismatch < refusalFirst || exitSchemaMismatch > refusalLast {
+		t.Fatalf("%d is outside the refusal band [%d,%d] every consumer keys on", exitSchemaMismatch, refusalFirst, refusalLast)
+	}
+
+	out, err := exec.Command(bin, "migrate", "--config", bookPath).Output()
+	if got := exitCodeOf(t, err); got != 0 {
+		t.Fatalf("`migrate` exited %d: %s", got, out)
+	}
+	if want := fmt.Sprintf("schema v%d -> v%d", from, store.SchemaHead()); !strings.Contains(string(out), want) {
+		t.Fatalf("migrate must report the transition %q; got:\n%s", want, out)
+	}
+	if got := exitCodeOf(t, exec.Command(bin, "status", "--config", bookPath, "--json").Run()); got != 0 {
+		t.Fatalf("`status --json` after the migration exited %d, want 0 — the deadlock is not broken", got)
+	}
+	// …and the run the migration unblocked actually starts. It follows within milliseconds, which is
+	// what put migrate's restore point and the paid path's pre-flight guard in the same second.
+	if run := exec.Command(bin, "translate", "--config", bookPath); exitCodeOf(t, run.Run()) != 0 {
+		t.Fatal("the run spawned right after the migration must start, not die in its pre-flight guard")
+	}
+}
+
+// TestTheMigrationRestorePointNeverCollidesWithThePaidPath is the deterministic half of the same fact:
+// both producers are handed the SAME stamp, because in the deploy sequence they really do land in the
+// same second. `store.BackupSQLite` refuses to overwrite a restore point (backlog row 173), so sharing
+// the name would make the run refuse to start with exit 1 — outside the refusal band, and after a
+// migration that already succeeded.
+func TestTheMigrationRestorePointNeverCollidesWithThePaidPath(t *testing.T) {
+	bookPath := setupCLIProject(t, "http://127.0.0.1:1")
+	dbPath := projectDBOf(bookPath)
+	st, err := store.Open(dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	st.Close()
+	staleTheProjectSchema(t, dbPath)
+
+	// PRODUCTION takes the restore point — the point of the test. Supplying the name here instead would
+	// only pin that the constant is non-empty, and the regression to catch is the call site dropping it.
+	if err := migrateCmd(bookPath, io.Discard); err != nil {
+		t.Fatal(err)
+	}
+	names := backupsOf(t, dbPath)
+	if len(names) != 1 {
+		t.Fatalf("restore points after the migration: %v, want exactly one", names)
+	}
+
+	// Strip the tag production chose and the bare second-stamp must still be free, so translate's
+	// pre-flight guard can take its own backup in the SAME second. Untagged, the two names are equal and
+	// BackupSQLite refuses to overwrite — the run the migration just unblocked would die in its
+	// pre-flight guard with exit 1. No wall clock is involved: the collision is decided by the name.
+	tagged := strings.TrimSuffix(names[0], ".db")
+	bare := strings.TrimSuffix(tagged, migrateSuffix)
+	if bare == tagged {
+		t.Fatalf("the migration's restore point %q carries no tag of its own — it is inside the paid path's namespace", names[0])
+	}
+	if _, err := store.BackupSQLite(dbPath, backupDirFor(dbPath), bare); err != nil {
+		t.Fatalf("the paid path's pre-flight backup in the SAME second must still succeed: %v", err)
+	}
+}
+
+// TestMigrateNeedsNeitherPricesNorModels: the $0 path must not carry the paid path's gates. A
+// models.yaml whose prices are older than 120 days refuses to load (backlog row 146), and if the
+// migration were built on the full config stack a stand with stale prices would meet the same deadlock
+// this command exists to remove — the read command refuses, and the one thing that could migrate
+// refuses too.
+func TestMigrateNeedsNeitherPricesNorModels(t *testing.T) {
+	bookPath := setupCLIProject(t, mockProvider(t).URL)
+	modelsPath := filepath.Join(filepath.Dir(bookPath), "models.yaml")
+	raw, err := os.ReadFile(modelsPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	stale := time.Now().UTC().AddDate(0, 0, -200).Format("2006-01-02")
+	writeCLIFile(t, modelsPath, strings.Replace(string(raw), time.Now().UTC().Format("2006-01-02"), stale, 1))
+
+	// The contrast: the read-only projection is refused by the price gate before it reads a schema.
+	if got := exitCode(status(context.Background(), bookPath, true)); got != exitConfigInvalid {
+		t.Fatalf("setup: `status` on stale prices exited %d, want %d", got, exitConfigInvalid)
+	}
+	var out bytes.Buffer
+	if err := migrateCmd(bookPath, &out); err != nil {
+		t.Fatalf("migrate must not consult prices: %v", err)
+	}
+	if !strings.Contains(out.String(), fmt.Sprintf("v%d", store.SchemaHead())) {
+		t.Fatalf("migrate must report the head it brought the project to; got %q", out.String())
+	}
+
+	// The structural version of the same claim, which also covers the provider keys the models file
+	// carries: with no models.yaml at all the migration still runs, so it cannot be consulting either.
+	if err := os.Remove(modelsPath); err != nil {
+		t.Fatal(err)
+	}
+	if got := exitCode(status(context.Background(), bookPath, true)); got != exitConfigInvalid {
+		t.Fatalf("setup: `status` without models.yaml exited %d, want %d", got, exitConfigInvalid)
+	}
+	if err := migrateCmd(bookPath, io.Discard); err != nil {
+		t.Fatalf("migrate must not load the model stack at all: %v", err)
+	}
+}
+
+// TestMigrateKeepsTheMoneyAndRepeatsAsANoOp is the money half at the command level: a real run's
+// settled spend, a reservation its process never settled, and a migration between them. `committed` is
+// what the platform's ceiling argument is computed from (PD-158) and what a settle reconciles against,
+// so it must survive the deploy step untouched; `reserved` is advisory and the write open's recovery
+// pass is entitled to zero it.
+func TestMigrateKeepsTheMoneyAndRepeatsAsANoOp(t *testing.T) {
+	bookPath := setupCLIProject(t, mockProvider(t).URL)
+	dbPath := projectDBOf(bookPath)
+	if err := translate(context.Background(), bookPath, false, pipeline.RebillConsent{}, false, 0); err != nil {
+		t.Fatalf("setup run: %v", err)
+	}
+
+	st, err := store.Open(dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	committed, _, err := st.SpentUSD("cli-book")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if committed <= 0 {
+		t.Fatalf("setup: the run must have settled money, committed=%v", committed)
+	}
+	// The reservation a killed run leaves behind.
+	if _, verdict, err := st.Reserve("cli-book", 0.25, store.Ceilings{BookUSD: 10, DayUSD: 10}); err != nil || verdict != store.ReserveOK {
+		t.Fatalf("stale reserve: %v %v", verdict, err)
+	}
+	st.Close()
+	from := staleTheProjectSchema(t, dbPath)
+
+	for i := range 2 {
+		var out bytes.Buffer
+		if err := migrateCmd(bookPath, &out); err != nil {
+			t.Fatalf("call %d: %v", i, err)
+		}
+		ro, err := store.OpenReadOnly(dbPath)
+		if err != nil {
+			t.Fatalf("call %d: the read path must work after migrating: %v", i, err)
+		}
+		gotCommitted, gotReserved, err := ro.SpentUSD("cli-book")
+		ro.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if gotCommitted != committed {
+			t.Fatalf("call %d: committed %v -> %v; a migration must not move settled money by a cent", i, committed, gotCommitted)
+		}
+		if gotReserved != 0 {
+			t.Fatalf("call %d: reserved=%v, want the recovery pass to have zeroed it", i, gotReserved)
+		}
+		// The restore point is taken for the call that MIGRATES and for no other, and it holds the
+		// database as it was BEFORE the step — a copy taken afterwards is not a restore point at all.
+		names := backupsOf(t, dbPath)
+		if len(names) != 1 {
+			t.Fatalf("call %d: restore points %v, want exactly the one the migrating call took", i, names)
+		}
+		if v := schemaVersionOf(t, filepath.Join(backupDirFor(dbPath), names[0])); v != from {
+			t.Fatalf("call %d: the restore point is at schema v%d, want the pre-migration v%d", i, v, from)
+		}
+		if i == 1 && !strings.Contains(out.String(), "already at schema") {
+			t.Fatalf("the repeat call must report a no-op; got %q", out.String())
+		}
+	}
+}
+
+func TestMigrateRefusesWithTheSameVocabularyAsEveryOtherCommand(t *testing.T) {
+	t.Run("a broken config", func(t *testing.T) {
+		bookPath := setupCLIProject(t, "http://127.0.0.1:1")
+		writeCLIFile(t, bookPath, "book_id: cli-book\n  bad indentation: [\n")
+		if got := exitCode(migrateCmd(bookPath, io.Discard)); got != exitConfigInvalid {
+			t.Fatalf("exit %d, want %d", got, exitConfigInvalid)
+		}
+	})
+
+	t.Run("a project another process holds", func(t *testing.T) {
+		// The deploy step runs while the operator believes the runs are stopped. If one is not, the
+		// answer is "come back later" — never a migration under a live writer's feet, whose reservations
+		// the recovery pass would zero. And nothing may be written for that refusal: a restore point
+		// taken before the lock would copy the whole database once per retry.
+		bookPath := setupCLIProject(t, "http://127.0.0.1:1")
+		dbPath := projectDBOf(bookPath)
+		st, err := store.Open(dbPath)
+		if err != nil {
+			t.Fatal(err)
+		}
+		st.Close()
+		staleTheProjectSchema(t, dbPath)
+		holdTheProject(t, dbPath)
+
+		if got := exitCode(migrateCmd(bookPath, io.Discard)); got != exitProjectLocked {
+			t.Fatalf("exit %d, want %d", got, exitProjectLocked)
+		}
+		if got := backupsOf(t, dbPath); len(got) != 0 {
+			t.Fatalf("a refused migration wrote %v; nothing may be written for a project it does not own", got)
+		}
+		// The retry the refusal invites reaches the lock too, instead of dying on the leftovers of the
+		// previous attempt.
+		if got := exitCode(migrateCmd(bookPath, io.Discard)); got != exitProjectLocked {
+			t.Fatalf("retry exited %d, want %d again", got, exitProjectLocked)
+		}
+	})
+
+	t.Run("a project newer than this binary", func(t *testing.T) {
+		// The direction a migration cannot repair. It must not read as success, or a caller looping
+		// "status refused → migrate → retry" would loop forever on a rolled-back binary.
+		bookPath := setupCLIProject(t, "http://127.0.0.1:1")
+		dbPath := projectDBOf(bookPath)
+		st, err := store.Open(dbPath)
+		if err != nil {
+			t.Fatal(err)
+		}
+		st.Close()
+		db, err := sql.Open("sqlite", "file:"+dbPath)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, err := db.Exec(`INSERT INTO schema_version (version) VALUES (?)`, store.SchemaHead()+7); err != nil {
+			t.Fatal(err)
+		}
+		db.Close()
+		err = migrateCmd(bookPath, io.Discard)
+		if got := exitCode(err); got != exitSchemaMismatch {
+			t.Fatalf("exit %d, want %d", got, exitSchemaMismatch)
+		}
+		if !strings.Contains(err.Error(), fmt.Sprintf("schema_mismatch found=%d expected=%d", store.SchemaHead()+7, store.SchemaHead())) {
+			t.Fatalf("the refusal must name both versions machine-readably: %v", err)
+		}
+		if got := backupsOf(t, dbPath); len(got) != 0 {
+			t.Fatalf("a refused migration wrote %v", got)
+		}
+	})
+
+	t.Run("a book that has never been run", func(t *testing.T) {
+		// The deploy sweep does not have to know which books have a database yet. Nothing is backed up:
+		// a database this call creates has no history to lose.
+		bookPath := setupCLIProject(t, "http://127.0.0.1:1")
+		var out bytes.Buffer
+		if err := migrateCmd(bookPath, &out); err != nil {
+			t.Fatal(err)
+		}
+		if !strings.Contains(out.String(), "created") {
+			t.Fatalf("migrate must say it created the project; got %q", out.String())
+		}
+		if v := schemaVersionOf(t, projectDBOf(bookPath)); v != store.SchemaHead() {
+			t.Fatalf("created at v%d, want v%d", v, store.SchemaHead())
+		}
+		if got := backupsOf(t, projectDBOf(bookPath)); len(got) != 0 {
+			t.Fatalf("a project being created was backed up: %v", got)
+		}
+	})
+}
diff --git a/backend/internal/pipeline/refusal.go b/backend/internal/pipeline/refusal.go
index 16e7da62..2d76374c 100644
--- a/backend/internal/pipeline/refusal.go
+++ b/backend/internal/pipeline/refusal.go
@@ -1,5 +1,11 @@
 package pipeline
 
+import (
+	"errors"
+
+	"textmachine/backend/internal/store"
+)
+
 // refusal.go: the shell contract's REFUSAL classes (row 165 / PD-196 of the platform).
 //
 // The defect this closes was not cosmetic. `tmctl` mapped every failure it did not recognise onto exit
@@ -27,6 +33,17 @@ const (
 	// RefusalProjectLocked is another tmctl process owning the project. Nothing is wrong with anything —
 	// the answer is to come back later.
 	RefusalProjectLocked RefusalClass = "project_locked"
+	// RefusalSchemaMismatch is a project database whose schema version is not this binary's. Nothing is
+	// wrong with the book either: the answer is `tmctl migrate` (or, in the other direction, a newer
+	// binary), and the two numbers a caller needs to tell those apart ride the message as the stable
+	// token `schema_mismatch found=<N> expected=<M>` (store.SchemaMismatchError).
+	//
+	// It is its own class because read-only opens never migrate, so an engine upgrade refuses every
+	// existing book until a write command touches it — and the platform's own pre-spawn call is one of
+	// those read-only opens, so that write command never came (the deploy deadlock, backlog row 174).
+	// A caller that can SEE this class self-heals ("caught it → migrate → retry") where it used to stop
+	// the world over what looked like a broken project.
+	RefusalSchemaMismatch RefusalClass = "schema_mismatch"
 )
 
 // Refusal is an invocation the engine turned down before doing any work of its own: nothing reached a
@@ -57,6 +74,27 @@ func RefuseConfig(err error) error {
 	return refuse(RefusalBadConfig, err)
 }
 
+// RefuseStoreOpen classifies a store-open failure. It is exported and it is the ONE place the mapping
+// lives, because two callers open a project store: openRunner below, and `tmctl migrate`, which opens
+// one with no runner at all. A second copy of this switch is how "another process holds it" and "this
+// binary does not match the schema" drift back into a single exit 1 on one of the two paths.
+//
+// An unrecognised failure is returned UNCHANGED rather than swept into the band: the band means "turned
+// down before doing any work", and a caller destroys or waits on data because of it.
+func RefuseStoreOpen(err error) error {
+	var mismatch *store.SchemaMismatchError
+	switch {
+	case err == nil:
+		return nil
+	case errors.Is(err, store.ErrLocked):
+		return refuse(RefusalProjectLocked, err)
+	case errors.As(err, &mismatch):
+		return refuse(RefusalSchemaMismatch, err)
+	default:
+		return err
+	}
+}
+
 // refuseSource classifies a failure to obtain the book's text, and it classifies almost all of them as a
 // CONFIG fault. That is deliberate, and it is the most consequential decision in this file.
 //
diff --git a/backend/internal/pipeline/refusal_test.go b/backend/internal/pipeline/refusal_test.go
new file mode 100644
index 00000000..3cd29cd2
--- /dev/null
+++ b/backend/internal/pipeline/refusal_test.go
@@ -0,0 +1,58 @@
+package pipeline
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"textmachine/backend/internal/store"
+)
+
+// refusal_test.go pins RefuseStoreOpen, the one place a store-open failure becomes a shell class. Two
+// callers share it (openRunner and `tmctl migrate`), and its arms decide what an automated caller DOES:
+// wait, migrate, or treat the project as broken.
+
+func TestRefuseStoreOpenClassifiesWhatACallerActsOn(t *testing.T) {
+	locked := fmt.Errorf("opening the project: %w", store.ErrLocked)
+	mismatch := fmt.Errorf("opening the project: %w", &store.SchemaMismatchError{Path: "/b.db", Found: 14, Expected: 15})
+
+	for _, tc := range []struct {
+		name string
+		err  error
+		want RefusalClass
+	}{
+		{"another process holds it", locked, RefusalProjectLocked},
+		{"the schema is not this binary's", mismatch, RefusalSchemaMismatch},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var refusal *Refusal
+			if !errors.As(RefuseStoreOpen(tc.err), &refusal) {
+				t.Fatalf("%v was not classified as a refusal", tc.err)
+			}
+			if refusal.Class != tc.want {
+				t.Fatalf("class %q, want %q", refusal.Class, tc.want)
+			}
+			// Both arms must survive a %w-wrap, because that is how they arrive: neither caller opens the
+			// store at the top of its own stack.
+			if !errors.Is(refusal, store.ErrLocked) && !errors.As(refusal, new(*store.SchemaMismatchError)) {
+				t.Fatal("the classification dropped the cause it was made from")
+			}
+		})
+	}
+
+	// The safety rule, and the reason the default arm is a passthrough: the refusal band means "turned
+	// down before doing ANY work", and the platform's intake acts on it — it waits instead of failing,
+	// and one number in it deletes the user's upload. A disk error during an open is not that; it must
+	// stay exit 1 (infra failure) rather than borrow a class that promises nothing happened.
+	disk := errors.New("store: open write pool: input/output error")
+	got := RefuseStoreOpen(disk)
+	if !errors.Is(got, disk) {
+		t.Fatalf("an unrecognised open failure must come back with its cause intact, got %v", got)
+	}
+	if errors.As(got, new(*Refusal)) {
+		t.Fatal("an unrecognised open failure was swept into the refusal band")
+	}
+	if RefuseStoreOpen(nil) != nil {
+		t.Fatal("a nil failure must stay nil: the classifier never invents one")
+	}
+}
diff --git a/backend/internal/pipeline/runner.go b/backend/internal/pipeline/runner.go
index fc0bf246..d145048e 100644
--- a/backend/internal/pipeline/runner.go
+++ b/backend/internal/pipeline/runner.go
@@ -262,10 +262,7 @@ func openRunner(bookPath string, logger *slog.Logger, forWrite bool) (*Runner, e
 		}
 	}
 	if err != nil {
-		if errors.Is(err, store.ErrLocked) {
-			return nil, refuse(RefusalProjectLocked, err)
-		}
-		return nil, err
+		return nil, RefuseStoreOpen(err)
 	}
 	r := &Runner{
 		Book:      book,
diff --git a/backend/internal/store/migrate.go b/backend/internal/store/migrate.go
index d8f6d8d6..746fd767 100644
--- a/backend/internal/store/migrate.go
+++ b/backend/internal/store/migrate.go
@@ -2,6 +2,7 @@ package store
 
 import (
 	"context"
+	"database/sql"
 	"fmt"
 )
 
@@ -463,32 +464,169 @@ var migrations = []string{
 //     which is membank.SpoilerLeaks over the selection's Rejected set, no schema at all. Scope amended
 //     by D39.55 (form, not intent).
 
-// migrate runs all pending migrations on the write pool, one transaction per
-// step, recording each in schema_version.
-func (s *Store) migrate(ctx context.Context) error {
-	if _, err := s.w.ExecContext(ctx, `CREATE TABLE IF NOT EXISTS schema_version (version INTEGER PRIMARY KEY)`); err != nil {
-		return fmt.Errorf("store: schema_version: %w", err)
+// SchemaHead is the schema version this binary migrates a project database to. It is the version every
+// read-only open demands (OpenReadOnly) and the version `tmctl migrate` brings a project to.
+func SchemaHead() int { return len(migrations) }
+
+// SchemaMismatchError is a project database whose recorded schema version is not this binary's. It is a
+// TYPE rather than a message because it is the one open failure a caller can repair by itself, and it
+// could not act on the difference while every failure arrived as the same text and the same exit 1.
+//
+// The engine's read-only opens never migrate — only a write open does — so upgrading the binary leaves
+// every existing book unreadable until something writes to it. The platform calls `tmctl status --json`
+// before each spawn and for the money, that call refuses the older schema, and the write command that
+// would have migrated the project never comes: the deploy deadlock of backlog row 174.
+//
+// The numbers therefore travel BOTH in the type (for a Go caller) and in the message (for the shell),
+// where they carry the stable token
+//
+//	schema_mismatch found=<N> expected=<M>
+//
+// Found < Expected is the direction `tmctl migrate` repairs — "caught it, migrated, retried" instead of
+// stopping the world. Found > Expected is a binary OLDER than the project, which no command here can fix
+// (the operator upgrades tmctl), so a caller that blindly re-ran the migration would loop forever.
+type SchemaMismatchError struct {
+	Path     string
+	Found    int
+	Expected int
+}
+
+func (e *SchemaMismatchError) Error() string {
+	repair := "the database is NEWER than this tmctl — update the binary (an old build must neither read nor write a newer schema)"
+	if e.Stale() {
+		repair = "the database is older than this tmctl — run `tmctl migrate --config <book.yaml>` (read-only opens never migrate)"
+	}
+	return fmt.Sprintf("store: schema_mismatch found=%d expected=%d path=%s — %s", e.Found, e.Expected, e.Path, repair)
+}
+
+// Stale reports whether the database is BEHIND the binary — the one direction a migration repairs.
+func (e *SchemaMismatchError) Stale() bool { return e.Found < e.Expected }
+
+// Migration is the schema transition a write open performed: From is the version the project database
+// was recorded at, To the version it is at now. From == To is a database that was already at head.
+type Migration struct {
+	From int
+	To   int
+}
+
+// Migrate applies a project database's pending migrations and reports the transition — the WRITE open
+// (exclusive flock · migration chain · stale-reservation recovery) with no run behind it, which is all
+// `tmctl migrate` is (backlog row 174). It sends nothing, spends nothing and holds the flock only for
+// as long as the migration takes.
+//
+// A database already at head is a no-op; one that does not exist is CREATED at head, exactly as the
+// first touch of a project by any other write command creates it. A database a NEWER binary wrote is
+// refused (SchemaMismatchError) before anything of this process reaches the file.
+//
+// beforeApply, when non-nil, runs INSIDE the project's exclusive lock, after the pending set is known
+// and before the first step is applied — and only when there IS a step to apply. That is where a caller
+// takes its restore point, and the placement is the whole point of the parameter: a backup taken before
+// the lock is a full copy written for a migration that a live run may then refuse (litter on every
+// retry of an exit-12), and one taken after the steps is not a restore point at all. An error from it
+// aborts the migration with nothing applied.
+func Migrate(path string, beforeApply func(Migration) error) (Migration, error) {
+	s, err := open(path, beforeApply)
+	if err != nil {
+		return Migration{}, err
+	}
+	applied := s.applied
+	if err := s.Close(); err != nil {
+		return applied, fmt.Errorf("store: close %s after migrating: %w", path, err)
+	}
+	return applied, nil
+}
+
+// schemaVersion reads the recorded schema version through db.
+//
+// A database that exists but has no schema_version TABLE — a fresh file, or a process killed between
+// creating one and committing the first migration — is version 0, which is what it is: nothing has been
+// applied. That is asked as a separate question rather than read off a failed SELECT, so a file that is
+// not a database at all still fails loudly instead of reading as an empty project.
+func schemaVersion(ctx context.Context, db *sql.DB) (int, error) {
+	var recorded int
+	if err := db.QueryRowContext(ctx,
+		`SELECT COUNT(*) FROM sqlite_master WHERE type = 'table' AND name = 'schema_version'`).Scan(&recorded); err != nil {
+		return 0, err
+	}
+	if recorded == 0 {
+		return 0, nil
 	}
 	var current int
-	if err := s.w.QueryRowContext(ctx, `SELECT COALESCE(MAX(version), 0) FROM schema_version`).Scan(&current); err != nil {
-		return fmt.Errorf("store: read version: %w", err)
+	if err := db.QueryRowContext(ctx, `SELECT COALESCE(MAX(version), 0) FROM schema_version`).Scan(&current); err != nil {
+		return 0, err
+	}
+	return current, nil
+}
+
+// migrate runs all pending migrations on the write pool, one transaction per
+// step, recording each in schema_version.
+//
+// Every phase gets its own opTimeout budget, and the caller's seam gets NONE. That is not tidiness: the
+// seam exists to take a restore point, whose cost scales with the book, and while it shared one deadline
+// with the steps a large project made the migration fail on the copy it had just paid for (see open).
+func (s *Store) migrate(path string, beforeApply func(Migration) error) error {
+	current, err := s.schemaBaseline()
+	if err != nil {
+		return err
+	}
+	// A project a NEWER binary wrote is REFUSED rather than opened. The loop below would silently do
+	// nothing with it — there is no step left to apply — and the caller would then read and, worse,
+	// WRITE a schema through code that predates it. OpenReadOnly has always refused that direction
+	// ("reading a newer schema with old code is unsafe"); the write path used to accept it, which is
+	// the more dangerous half of the same fact. It is refused here, BEFORE recoverReservations, so a
+	// refused open leaves the file exactly as it found it.
+	if current > len(migrations) {
+		return &SchemaMismatchError{Path: path, Found: current, Expected: len(migrations)}
+	}
+	// The caller's seam (Migrate): the lock is held, the pending set is known, nothing has been applied,
+	// and no deadline of this package is running — the work is the caller's and so is its bounding.
+	if beforeApply != nil && current < len(migrations) {
+		if err := beforeApply(Migration{From: current, To: len(migrations)}); err != nil {
+			return err
+		}
 	}
 	for v := current; v < len(migrations); v++ {
-		tx, err := s.w.BeginTx(ctx, nil)
-		if err != nil {
-			return fmt.Errorf("store: begin migration %d: %w", v+1, err)
-		}
-		if _, err := tx.ExecContext(ctx, migrations[v]); err != nil {
-			_ = tx.Rollback()
-			return fmt.Errorf("store: apply migration %d: %w", v+1, err)
-		}
-		if _, err := tx.ExecContext(ctx, `INSERT INTO schema_version (version) VALUES (?)`, v+1); err != nil {
-			_ = tx.Rollback()
-			return fmt.Errorf("store: record migration %d: %w", v+1, err)
-		}
-		if err := tx.Commit(); err != nil {
-			return fmt.Errorf("store: commit migration %d: %w", v+1, err)
+		if err := s.applyStep(v); err != nil {
+			return err
 		}
 	}
+	s.applied = Migration{From: current, To: len(migrations)}
+	return nil
+}
+
+// schemaBaseline makes sure the version table exists and reports what is recorded in it.
+func (s *Store) schemaBaseline() (int, error) {
+	ctx, cancel := opContext()
+	defer cancel()
+	if _, err := s.w.ExecContext(ctx, `CREATE TABLE IF NOT EXISTS schema_version (version INTEGER PRIMARY KEY)`); err != nil {
+		return 0, fmt.Errorf("store: schema_version: %w", err)
+	}
+	current, err := schemaVersion(ctx, s.w)
+	if err != nil {
+		return 0, fmt.Errorf("store: read version: %w", err)
+	}
+	return current, nil
+}
+
+// applyStep applies migrations[v] and records v+1 in ONE transaction (DDL is transactional in SQLite),
+// so a process that dies mid-step leaves the database at its previous version rather than half-applied.
+func (s *Store) applyStep(v int) error {
+	ctx, cancel := opContext()
+	defer cancel()
+	tx, err := s.w.BeginTx(ctx, nil)
+	if err != nil {
+		return fmt.Errorf("store: begin migration %d: %w", v+1, err)
+	}
+	if _, err := tx.ExecContext(ctx, migrations[v]); err != nil {
+		_ = tx.Rollback()
+		return fmt.Errorf("store: apply migration %d: %w", v+1, err)
+	}
+	if _, err := tx.ExecContext(ctx, `INSERT INTO schema_version (version) VALUES (?)`, v+1); err != nil {
+		_ = tx.Rollback()
+		return fmt.Errorf("store: record migration %d: %w", v+1, err)
+	}
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("store: commit migration %d: %w", v+1, err)
+	}
 	return nil
 }
diff --git a/backend/internal/store/migrate_test.go b/backend/internal/store/migrate_test.go
new file mode 100644
index 00000000..03a4bb3d
--- /dev/null
+++ b/backend/internal/store/migrate_test.go
@@ -0,0 +1,450 @@
+package store
+
+import (
+	"database/sql"
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+// migrate_test.go pins the mechanics `tmctl migrate` stands on (backlog row 174): a database an OLDER
+// binary wrote converges to head and unlocks the read-only path, the MONEY it holds survives the
+// conversion untouched, a database a NEWER binary wrote is refused before anything is written, and a
+// step that fails leaves nothing of itself behind.
+
+// atVersion runs fn with the migration chain TRUNCATED to v steps, so anything opened inside it sees
+// exactly the database a binary of that vintage would have written and worked with.
+//
+// The fixture truncates the chain instead of deleting rows from schema_version because those are not the
+// same thing: rolling the counter back leaves HEAD's tables in place and makes the next open re-apply
+// the newest step, which backlog row 49а says is not idempotent for an ALTER. Truncation also keeps the
+// fixture correct when a new migration lands — it never names a version or a table.
+//
+// It mutates a package-level var, which is safe because these tests do not run in parallel (nothing in
+// this package calls t.Parallel).
+func atVersion(t *testing.T, v int, fn func()) {
+	t.Helper()
+	full := migrations
+	migrations = migrations[:v]
+	defer func() { migrations = full }()
+	fn()
+}
+
+// openAtVersion creates a project database exactly as a binary with v migrations would have left it.
+func openAtVersion(t *testing.T, path string, v int) {
+	t.Helper()
+	atVersion(t, v, func() {
+		s, err := Open(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := s.Close(); err != nil {
+			t.Fatal(err)
+		}
+	})
+}
+
+// rawVersion reads MAX(schema_version) through its own connection, deliberately NOT through the
+// product's own reader: the state a migration left behind must be asserted independently of the code
+// that reports it, and this way it can also be read from a database the product is currently refusing.
+func rawVersion(t *testing.T, path string) int {
+	t.Helper()
+	db, err := sql.Open("sqlite", "file:"+path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	var v int
+	if err := db.QueryRow(`SELECT COALESCE(MAX(version), 0) FROM schema_version`).Scan(&v); err != nil {
+		t.Fatal(err)
+	}
+	return v
+}
+
+func TestMigrateBringsAnOlderProjectToHeadAndUnlocksTheReadPath(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+	openAtVersion(t, path, head-1)
+
+	// The deadlock itself: the read-only projections the platform calls before every spawn refuse a
+	// database an older binary wrote, and they never migrate it.
+	_, err := OpenReadOnly(path)
+	var mismatch *SchemaMismatchError
+	if !errors.As(err, &mismatch) {
+		t.Fatalf("a read-only open of an older schema must return the typed refusal, got %v", err)
+	}
+	if mismatch.Found != head-1 || mismatch.Expected != head || !mismatch.Stale() {
+		t.Fatalf("found=%d expected=%d stale=%v, want %d/%d/true", mismatch.Found, mismatch.Expected, mismatch.Stale(), head-1, head)
+	}
+
+	applied, err := Migrate(path, nil)
+	if err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+	if applied.From != head-1 || applied.To != head {
+		t.Fatalf("transition %+v, want v%d -> v%d", applied, head-1, head)
+	}
+	if got := rawVersion(t, path); got != head {
+		t.Fatalf("schema is at v%d after migrating, want v%d", got, head)
+	}
+	ro, err := OpenReadOnly(path)
+	if err != nil {
+		t.Fatalf("the read-only path must work after a migration: %v", err)
+	}
+	ro.Close()
+}
+
+func TestMigrateIsANoOpOnAProjectAlreadyAtHead(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+	openAtVersion(t, path, head)
+
+	for i := range 2 {
+		applied, err := Migrate(path, nil)
+		if err != nil {
+			t.Fatalf("call %d: %v", i, err)
+		}
+		if applied.From != head || applied.To != head {
+			t.Fatalf("call %d: transition %+v, want a no-op at v%d", i, applied, head)
+		}
+	}
+}
+
+func TestMigrateCreatesAProjectThatWasNeverRun(t *testing.T) {
+	// The deploy sweep runs over every book, including one that has been accepted but never translated.
+	// Creating it at head is what every other write open already does on first touch, and it keeps the
+	// sweep uniform instead of making the caller ask which books exist yet.
+	path := filepath.Join(t.TempDir(), "fresh.db")
+	applied, err := Migrate(path, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if applied.From != 0 || applied.To != SchemaHead() {
+		t.Fatalf("transition %+v, want v0 -> v%d", applied, SchemaHead())
+	}
+	ro, err := OpenReadOnly(path)
+	if err != nil {
+		t.Fatalf("a created project must be readable at head: %v", err)
+	}
+	ro.Close()
+}
+
+// TestMigrateKeepsCommittedMoneyAndZeroesOnlyTheStaleReservation is the money test.
+//
+// It is the one property the platform's ratified ceiling formula rests on (PD-158: the argument is
+// committed + increment, WITHOUT reserved, precisely because a write open zeroes leftover reservations
+// and a read-only status does not). A migration is a write open, so it performs that recovery — and it
+// must move `committed` by not one cent while doing it, or every ceiling computed from a status taken
+// after a deploy would be wrong.
+func TestMigrateKeepsCommittedMoneyAndZeroesOnlyTheStaleReservation(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+	caps := Ceilings{BookUSD: 10, DayUSD: 10}
+
+	// A book an older binary ran: one settled call, and one reservation whose process died before it
+	// settled — exactly the state a crashed or killed run leaves behind.
+	atVersion(t, head-1, func() {
+		s, err := Open(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer s.Close()
+		job := mustSnapshotAndJob(t, s)
+		res, verdict, err := s.Reserve("book", 0.10, caps)
+		if err != nil || verdict != ReserveOK {
+			t.Fatalf("reserve: %v %v", verdict, err)
+		}
+		cp := Checkpoint{RequestHash: "h1", JobID: job.ID, Stage: "draft", Role: "translator",
+			ModelRequested: "m", ModelActual: "m", ResponseText: "текст", UsageJSON: "{}", CostUSD: 0.04}
+		if err := s.SettleWithCheckpoint(res, 0.04, cp, nil); err != nil {
+			t.Fatal(err)
+		}
+		if _, verdict, err = s.Reserve("book", 0.25, caps); err != nil || verdict != ReserveOK {
+			t.Fatalf("stale reserve: %v %v", verdict, err)
+		}
+		committed, reserved, err := s.SpentUSD("book")
+		if err != nil || committed != 0.04 || reserved != 0.25 {
+			t.Fatalf("fixture: committed=%v reserved=%v err=%v", committed, reserved, err)
+		}
+	})
+
+	if _, err := Migrate(path, nil); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+
+	// Twice: the second call is the idempotency half — a deploy sweep that runs over a book it already
+	// migrated must not move money either.
+	for i := range 2 {
+		if i == 1 {
+			if _, err := Migrate(path, nil); err != nil {
+				t.Fatalf("repeat migrate: %v", err)
+			}
+		}
+		ro, err := OpenReadOnly(path)
+		if err != nil {
+			t.Fatalf("call %d: %v", i, err)
+		}
+		committed, reserved, err := ro.SpentUSD("book")
+		ro.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if committed != 0.04 {
+			t.Fatalf("call %d: committed moved to %v — a migration must not touch settled money", i, committed)
+		}
+		if reserved != 0 {
+			t.Fatalf("call %d: reserved=%v, want 0 — the write open owes the recovery pass", i, reserved)
+		}
+	}
+	if got := rawVersion(t, path); got != head {
+		t.Fatalf("schema v%d after migrating, want v%d", got, head)
+	}
+	// The checkpoint the money is anchored to is still there: `committed == SUM(checkpoints)` is the
+	// invariant the platform settles from, so a migration that kept the number and lost the row would
+	// pass the assertion above and still have broken the book.
+	ro, err := OpenReadOnly(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ro.Close()
+	cp, err := ro.GetCheckpoint("h1")
+	if err != nil || cp == nil || cp.CostUSD != 0.04 {
+		t.Fatalf("checkpoint after migration: %+v err=%v", cp, err)
+	}
+}
+
+// TestOpenRefusesAProjectNewerThanTheBinary: the write path used to accept a database it could not
+// understand and would then have written through pre-dating code. It is refused in both open modes, and
+// the refusal happens BEFORE the recovery pass — a live reservation still standing afterwards is the
+// proof that nothing of the refused process reached the file.
+func TestOpenRefusesAProjectNewerThanTheBinary(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+	s, err := Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, verdict, err := s.Reserve("book", 0.25, Ceilings{BookUSD: 10, DayUSD: 10}); err != nil || verdict != ReserveOK {
+		t.Fatalf("reserve: %v %v", verdict, err)
+	}
+	s.Close()
+
+	db, err := sql.Open("sqlite", "file:"+path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.Exec(`INSERT INTO schema_version (version) VALUES (?)`, head+7); err != nil {
+		t.Fatal(err)
+	}
+	db.Close()
+
+	for name, open := range map[string]func(string) (*Store, error){"write": Open, "read-only": OpenReadOnly} {
+		st, err := open(path)
+		if err == nil {
+			st.Close()
+			t.Fatalf("%s open of a newer schema must be refused", name)
+		}
+		var mismatch *SchemaMismatchError
+		if !errors.As(err, &mismatch) {
+			t.Fatalf("%s open: %v, want a typed SchemaMismatchError", name, err)
+		}
+		if mismatch.Found != head+7 || mismatch.Expected != head || mismatch.Stale() {
+			t.Fatalf("%s open: found=%d expected=%d stale=%v", name, mismatch.Found, mismatch.Expected, mismatch.Stale())
+		}
+	}
+	if _, err := Migrate(path, nil); !errors.As(err, new(*SchemaMismatchError)) {
+		t.Fatalf("migrate of a newer schema must be refused with the typed error, got %v", err)
+	}
+
+	// Nothing was written: the reservation the fixture left standing is still standing, so the recovery
+	// pass never ran on a schema this binary does not know.
+	ro, err := sql.Open("sqlite", "file:"+path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ro.Close()
+	var reserved float64
+	if err := ro.QueryRow(`SELECT COALESCE(SUM(reserved_usd), 0) FROM spend WHERE book_id = 'book'`).Scan(&reserved); err != nil {
+		t.Fatal(err)
+	}
+	if reserved != 0.25 {
+		t.Fatalf("reserved=%v after three refused opens, want the fixture's 0.25 untouched", reserved)
+	}
+}
+
+// TestAFailedMigrationStepLeavesTheDatabaseAtItsPreviousVersion answers, by execution, the question
+// `tmctl migrate` raises: is APPLYING a step atomic? It is — DDL is transactional in SQLite and the
+// version row is inserted in the SAME transaction as the step — so a process that dies mid-migration
+// leaves a database at its previous version rather than a half-applied one whose ALTER steps (row 49а)
+// will not converge on the next try. The migration bodies themselves are untouched by this pack.
+func TestAFailedMigrationStepLeavesTheDatabaseAtItsPreviousVersion(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+
+	// A step whose FIRST statement succeeds and whose second does not: if application were not atomic,
+	// `probe` would outlive the failure. Restored with defer, so a panic inside Open cannot leave the
+	// package-level chain rewritten for whatever runs next.
+	full := migrations
+	defer func() { migrations = full }()
+	migrations = append(append([]string(nil), migrations...), `CREATE TABLE probe (x INTEGER); THIS IS NOT SQL;`)
+	s, err := Open(path)
+	if err == nil {
+		s.Close()
+		t.Fatal("a migration step that does not execute must fail the open")
+	}
+
+	if got := rawVersion(t, path); got != head {
+		t.Fatalf("schema recorded v%d after a failed step, want the previous v%d", got, head)
+	}
+	db, err := sql.Open("sqlite", "file:"+path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	var probes int
+	if err := db.QueryRow(`SELECT COUNT(*) FROM sqlite_master WHERE type = 'table' AND name = 'probe'`).Scan(&probes); err != nil {
+		t.Fatal(err)
+	}
+	if probes != 0 {
+		t.Fatal("the failed step's first statement survived: applying a migration is not atomic")
+	}
+}
+
+// TestADatabaseWithNothingAppliedIsAVersionAndNotAnError: a file that exists but has no
+// schema_version table — a process killed between creating one and committing the first migration —
+// used to fail the read path with prose and exit 1, i.e. as an unrepairable project. It is version 0:
+// the SAME typed refusal as any other mismatch, so the same "caught it → migrate → retry" repairs it.
+func TestADatabaseWithNothingAppliedIsAVersionAndNotAnError(t *testing.T) {
+	dir := t.TempDir()
+	empty := filepath.Join(dir, "empty.db")
+	if err := os.WriteFile(empty, nil, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	_, err := OpenReadOnly(empty)
+	var mismatch *SchemaMismatchError
+	if !errors.As(err, &mismatch) {
+		t.Fatalf("a database with nothing applied must be the typed refusal, got %v", err)
+	}
+	if mismatch.Found != 0 || mismatch.Expected != SchemaHead() || !mismatch.Stale() {
+		t.Fatalf("found=%d expected=%d stale=%v, want 0/%d/true", mismatch.Found, mismatch.Expected, mismatch.Stale(), SchemaHead())
+	}
+	if _, err := Migrate(empty, nil); err != nil {
+		t.Fatalf("and a migration must repair it: %v", err)
+	}
+	ro, err := OpenReadOnly(empty)
+	if err != nil {
+		t.Fatalf("read path after the repair: %v", err)
+	}
+	ro.Close()
+
+	// A file that is not a database at all must NOT read as "version 0, migrate me".
+	junk := filepath.Join(dir, "junk.db")
+	if err := os.WriteFile(junk, []byte("this is not a database, it is a text file"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := OpenReadOnly(junk); err == nil || errors.As(err, &mismatch) {
+		t.Fatalf("a corrupt file must fail loudly and NOT as a schema mismatch, got %v", err)
+	}
+}
+
+// TestTheMigrationSeamRunsUnderTheLockAndOnlyWhenAStepWillRun pins the placement `tmctl migrate` takes
+// its restore point in. The three properties are what make a backup a backup: it runs BEFORE the first
+// step (a copy taken afterwards is not a restore point), only when there IS a step (else a repeat call
+// litters, and its second-precision stamp collides), and inside the lock (else a project a live run
+// owns is copied in full for a migration that is refused anyway — once per retry).
+func TestTheMigrationSeamRunsUnderTheLockAndOnlyWhenAStepWillRun(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+	openAtVersion(t, path, head-1)
+
+	var seen []Migration
+	versionAtHook := -1
+	applied, err := Migrate(path, func(m Migration) error {
+		seen = append(seen, m)
+		versionAtHook = rawVersion(t, path)
+		// The lock is ours while the hook runs: a second opener must be turned away, which is what
+		// makes "back up here" different from "back up before calling".
+		if s, err := Open(path); !errors.Is(err, ErrLocked) {
+			if err == nil {
+				s.Close()
+			}
+			t.Errorf("the seam must run INSIDE the project lock; a concurrent open got %v", err)
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(seen) != 1 || seen[0] != (Migration{From: head - 1, To: head}) {
+		t.Fatalf("the seam saw %+v, want exactly one v%d -> v%d", seen, head-1, head)
+	}
+	if versionAtHook != head-1 {
+		t.Fatalf("the database was at v%d when the seam ran, want the PRE-migration v%d", versionAtHook, head-1)
+	}
+	if applied.From != head-1 || applied.To != head {
+		t.Fatalf("transition %+v", applied)
+	}
+
+	// Nothing left to apply → the seam does not run at all.
+	seen = nil
+	if _, err := Migrate(path, func(m Migration) error { seen = append(seen, m); return nil }); err != nil {
+		t.Fatal(err)
+	}
+	if len(seen) != 0 {
+		t.Fatalf("the seam ran %d time(s) on a project already at head", len(seen))
+	}
+}
+
+// TestTheSeamIsNotChargedToTheStoreOperationBudget: the seam's work is the CALLER's (a restore point
+// whose cost scales with the book), and opTimeout bounds operations that are O(1) in the size of the
+// book. While the two shared one deadline, a large project failed the migration on the copy it had just
+// paid for — «context deadline exceeded» on the first step, exit 1 outside the refusal band, and a
+// retry that copied the whole database again (round-2 review, reproduced on 2.6 GB).
+//
+// The budget is shrunk instead of the seam sleeping ten real seconds: same property, no dead time in
+// the battery. It is restored on the way out and nothing here runs in parallel.
+func TestTheSeamIsNotChargedToTheStoreOperationBudget(t *testing.T) {
+	head := SchemaHead()
+	defer func(original time.Duration) { opTimeout = original }(opTimeout)
+	opTimeout = 150 * time.Millisecond
+
+	path := filepath.Join(t.TempDir(), "book.db")
+	openAtVersion(t, path, head-1)
+
+	applied, err := Migrate(path, func(Migration) error {
+		time.Sleep(3 * opTimeout) // a restore point on a book far larger than the budget
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("a slow seam must not fail the migration it protects: %v", err)
+	}
+	if applied.From != head-1 || applied.To != head {
+		t.Fatalf("transition %+v, want v%d -> v%d", applied, head-1, head)
+	}
+	if got := rawVersion(t, path); got != head {
+		t.Fatalf("schema at v%d, want v%d", got, head)
+	}
+}
+
+// TestASeamFailureAbortsTheMigrationWithNothingApplied: a caller that cannot take its restore point is
+// telling the engine not to migrate — the answer is to stop with the database exactly as it was, not to
+// proceed unprotected.
+func TestASeamFailureAbortsTheMigrationWithNothingApplied(t *testing.T) {
+	head := SchemaHead()
+	path := filepath.Join(t.TempDir(), "book.db")
+	openAtVersion(t, path, head-1)
+
+	refuse := errors.New("no room for a restore point")
+	if _, err := Migrate(path, func(Migration) error { return refuse }); !errors.Is(err, refuse) {
+		t.Fatalf("the seam's error must abort the migration, got %v", err)
+	}
+	if got := rawVersion(t, path); got != head-1 {
+		t.Fatalf("schema moved to v%d after a refused seam, want v%d", got, head-1)
+	}
+	// And the lock is released, so the next attempt is not locked out by the failed one.
+	if _, err := Migrate(path, nil); err != nil {
+		t.Fatalf("a retry after a refused seam: %v", err)
+	}
+}
diff --git a/backend/internal/store/store.go b/backend/internal/store/store.go
index 2357c52b..60fa6f51 100644
--- a/backend/internal/store/store.go
+++ b/backend/internal/store/store.go
@@ -29,13 +29,24 @@ import (
 // opTimeout bounds every store operation: SQLite is a local file and
 // effectively never blocks; the cap keeps a wedged filesystem from hanging a
 // pipeline goroutine forever.
-const opTimeout = 10 * time.Second
+//
+// It is a PER-OPERATION budget and only holds while every operation under it is O(1) in the size of the
+// book — which is what the migration chain and the recovery pass are (metadata-only DDL and one UPDATE).
+// A caller's own work must therefore never be charged to it; see the seam in migrate.
+//
+// A var, not a const, so a test can shrink it: the property "the seam is not charged to this budget" is
+// otherwise only testable by sleeping ten real seconds in the battery.
+var opTimeout = 10 * time.Second
 
 // Store is one project database.
 type Store struct {
 	w    *sql.DB // single-connection write pool; all mutations go through it
 	r    *sql.DB // read pool
 	lock *os.File
+	// applied is the schema transition this open performed — the zero value on a read-only open, which
+	// never migrates. It is recorded because a write open is the only thing that MAY migrate, so it is
+	// also the only thing that knows what it migrated (`tmctl migrate` reports it, row 174).
+	applied Migration
 }
 
 // Open opens (or creates) the project database at path, applies pending
@@ -45,7 +56,11 @@ type Store struct {
 // owns the project file" is enforced here, not assumed. Without the lock a
 // concurrent `tmctl report` during a translation would zero a running process's live
 // reservations via the recovery pass and blind its ceilings (review finding).
-func Open(path string) (*Store, error) {
+func Open(path string) (*Store, error) { return open(path, nil) }
+
+// open is Open with the migration seam exposed: beforeApply, when non-nil, runs after the lock is held
+// and the pending set is known, and before the first step is applied. See Migrate.
+func open(path string, beforeApply func(Migration) error) (*Store, error) {
 	lock, err := acquireLock(path + ".lock")
 	if err != nil {
 		return nil, err
@@ -80,12 +95,18 @@ func Open(path string) (*Store, error) {
 	r.SetMaxOpenConns(4)
 
 	s := &Store{w: w, r: r, lock: lock}
-	ctx, cancel := context.WithTimeout(context.Background(), opTimeout)
-	defer cancel()
-	if err := s.migrate(ctx); err != nil {
+	// Each phase takes its OWN budget rather than sharing one across the whole open. The migration is
+	// the only phase that can host caller work of unbounded size (the seam below), and a single shared
+	// deadline made that work eat the budget of the steps it was called to protect: on a large project
+	// the restore point finished and the first step then failed «context deadline exceeded» — an exit 1
+	// outside the refusal band, after an expensive write, with every retry copying the database again
+	// (round-2 review, reproduced on a 2.6 GB project).
+	if err := s.migrate(path, beforeApply); err != nil {
 		s.Close()
 		return nil, err
 	}
+	ctx, cancel := opContext()
+	defer cancel()
 	if err := s.recoverReservations(ctx); err != nil {
 		s.Close()
 		return nil, err
@@ -104,9 +125,9 @@ func Open(path string) (*Store, error) {
 //
 // Guarantees: connections are strictly read-only (PRAGMA query_only=1 — an accidental
 // write fails loudly rather than corrupting a live writer's state); a missing DB is a loud
-// error (we don't create an empty one); a schema older than the binary is a loud error "run a
-// write command" (only the writer applies migrations). A known, honest boundary:
-// after a run crashes, reserved_usd stays non-zero until the next WRITE command
+// error (we don't create an empty one); a schema this binary does not match is a TYPED refusal naming
+// `tmctl migrate` (only a write open applies migrations — see SchemaMismatchError). A known, honest
+// boundary: after a run crashes, reserved_usd stays non-zero until the next WRITE command
 // (the recovery pass runs only there) — status will show this leftover as reserved.
 func OpenReadOnly(path string) (*Store, error) {
 	if _, err := os.Stat(path); err != nil {
@@ -128,20 +149,18 @@ func OpenReadOnly(path string) (*Store, error) {
 	s := &Store{w: r, r: r, lock: nil}
 	ctx, cancel := context.WithTimeout(context.Background(), opTimeout)
 	defer cancel()
-	var current int
-	if err := s.r.QueryRowContext(ctx, `SELECT COALESCE(MAX(version), 0) FROM schema_version`).Scan(&current); err != nil {
+	current, err := schemaVersion(ctx, s.r)
+	if err != nil {
 		s.Close()
-		return nil, fmt.Errorf("store: read schema version of %s (empty/corrupt database?): %w", path, err)
+		return nil, fmt.Errorf("store: read schema version of %s (not a database?): %w", path, err)
 	}
-	if current < len(migrations) {
+	// A version this binary does not match is a TYPED refusal, in both directions: the caller's repair
+	// differs ("migrate this project" versus "upgrade this binary"), and while both arrived as prose and
+	// exit 1 an automated caller could act on neither — which is what turned a binary upgrade into a
+	// deadlock across every existing book (row 174, SchemaMismatchError).
+	if current != len(migrations) {
 		s.Close()
-		return nil, fmt.Errorf("store: %s is at schema v%d, this binary expects v%d — run a write command (`tmctl translate`/`redrive`) to migrate first (read-only open never migrates)",
-			path, current, len(migrations))
-	}
-	if current > len(migrations) {
-		s.Close()
-		return nil, fmt.Errorf("store: %s is at schema v%d, NEWER than this binary's v%d — update tmctl (reading a newer schema with old code is unsafe)",
-			path, current, len(migrations))
+		return nil, &SchemaMismatchError{Path: path, Found: current, Expected: len(migrations)}
 	}
 	return s, nil
 }