feat(session-persistence-sqlite): preserve interrupted turns on load, don't truncate

Mirror the JSONL backend's crash-recovery contract change: load() now PRESERVES
the real events of an interrupted final turn (a turn can be huge — truncating it
would destroy work) and durably CLOSES the orphaned turn with synthetic boundary
events (step/end if open, then turn/end {interrupted}) inside one transaction
that also deletes any torn tail row. load() is therefore mutating; the deferred
truncation-repair on the next append is gone. Replaces cutAtLastTurnEnd with
scanRows (longest preserved prefix + torn-tail offset). Updates the sqlite tests
and README to the preserve-and-close semantics; the shared runPersistenceContract
suite now holds both backends to identical interrupted-turn behavior.

packages/session-persistence-sqlite/README.md

@@ -1,6 +1,6 @@
 # @deepseek-ai/dsh-session-persistence-sqlite
 
-A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([ADR 0018](../../docs/adr/0018-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, crash-tail-on-load), expressed over `node:sqlite` rows instead of file bytes.
+A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([ADR 0018](../../docs/adr/0018-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, interrupted-turn close on load), expressed over `node:sqlite` rows instead of file bytes.
 
 > **TODO:** this backend talks to `node:sqlite` directly. If a cordis database service (`cordis/db` / a `@cordisjs` SQL driver plugin) is adopted, route through that instead of holding a raw `DatabaseSync` here — the contract surface (`SessionPersistence`) would not change, only the storage driver.
 
@@ -12,9 +12,9 @@ The repo targets Node ≥ 24 (the root `engines` field), which includes the stab
 
 ## Contract semantics over rows
 
-- **Append = a transaction.** `append` runs `BEGIN`/`COMMIT` around the batch: it runs any deferred crash-tail repair, materializes the `sessions` row (if still lazy), and INSERTs every event, asserting the contiguous-seq contract first (the first event's `seq` must equal the stored next-seq). A mid-batch failure (a UNIQUE violation on a duplicated seq) rolls back entirely, so the stored log and the in-memory cursor stay consistent.
+- **Append = a transaction.** `append` runs `BEGIN`/`COMMIT` around the batch: it materializes the `sessions` row (if still lazy) and INSERTs every event, asserting the contiguous-seq contract first (the first event's `seq` must equal the stored next-seq). A mid-batch failure (a UNIQUE violation on a duplicated seq) rolls back entirely, so the stored log and the in-memory cursor stay consistent. (`load()` already balanced the stored log, so `append` never has to repair a crash tail.)
 - **Lazy materialization.** `create()` records intent in memory only — no row is written until the first `append`. A created-but-never-appended session has no `sessions` row, so it is absent from `has()`/`list()` (which report exactly the sessions that have a row).
-- **Crash-tail-on-load.** `load()` reads every stored event ordered by `seq` and returns only the prefix through the **last complete `turn/end`** (the `SessionPersistence.load` contract), computed from the `seq`/`type` columns so a malformed `data` in the uncommitted tail is never parsed. A batch that landed without its closing `turn/end` (a process killed mid-turn) is an uncommitted tail: `load()` stays non-mutating w.r.t. the event log and records a repair point; the **next `append`** physically DELETEs the orphaned rows inside its transaction (the one-time truncation-repair, matching the JSONL backend and the abstract contract). A `seq` gap inside the committed region makes the session unloadable. A session materialized by a partial first turn (all-tail, zero committed events) keeps its metadata row and stays present in `has()`/`list()` — the same as the JSONL backend, whose file likewise survives a first append that never reached `turn/end`.
+- **Interrupted-turn close on load.** `load()` reads every stored event ordered by `seq` and finds the longest seq-contiguous, parseable prefix — INCLUDING the real events of an interrupted final turn after the last `turn/end` (the loop only flushes at `turn/end`, so a process killed mid-turn leaves real, fully-written rows past it). A single turn can be huge in a long-horizon task, so those events are **preserved, never truncated**: `load()` CLOSES the orphaned turn by durably appending the minimal synthetic boundary events (a `step/end` if a step was open, then a `turn/end` carrying `{ kind: 'interrupted' }`), inside one transaction that also DELETEs any never-fully-written torn tail row. `load()` is therefore mutating — after it the stored rows are balanced and the cursor is truthful, so the next `append` continues cleanly. The boundary (last `turn/end`, torn-tail detection) is computed from the `seq`/`type` columns so a malformed `data` in a torn tail row is never parsed (discarded, not unloadable). A parse error or `seq` gap inside the committed region (at or before the last real `turn/end`) makes the session unloadable. A session whose only turn never closed keeps its metadata row and stays present in `has()`/`list()` — the same as the JSONL backend, whose file likewise survives a first append that never reached `turn/end`.
 
 ## Configuration (schemastery)