daemon: store/ — SQLite WAL schema + forward-only migrator (build step 3)

The daemon's persistent state. SQLite in WAL mode, foreign keys on,
5 s busy timeout so a writer waits rather than SQLITE_BUSY under the
RPC loop.

- store/sqlite — RAII Db/Stmt over the C API; errors returned as
  DbResult<T> (std::expected), never thrown — the RPC loop must not
  unwind. transaction() helper: BEGIN / fn / COMMIT, ROLLBACK on error.
- store/migrations/0001_initial.sql — the eight tables from the brief:
  settings, categories, queues, tasks, segments, rules, history,
  pairings. Notable choices:
    * tasks columns project onto proto TaskSummary with no computation;
      requested vs effective segments/buffer split per ADR 0010/0012;
      pause_reason column per ADR 0013.
    * segments end_byte is NOT constrained >= 0 so a whole-file
      zero-length download is one row with end_byte = -1 (ADR 0010 B3a).
    * pairings stores only token_sha256 — the plaintext token is
      returned once from session.pair and never persisted (CLAUDE.md §4).
    * indices on tasks(state), (category_id), (queue_id, queue_position),
      (created_at), (completed_at) for the "1000 tasks, download.list
      under 50 ms" DoD.
    * six built-in categories + a Main queue seeded.
- store/migrations — runs every embedded migration past PRAGMA
  user_version, each in its own transaction, forward-only. SQL files
  are embedded at build time by cmake/embed_migrations.cmake.

Test veloxd.store_migrations (ASan+UBSan and TSan clean): fresh DB ->
head, all tables present, seed rows, FK cascade (segment orphan
rejected, task delete cascades), the end_byte=-1 zero-length case,
idempotent re-run, and forward-only from every released user_version.

Also: daemon/docs/proto-requests-m1.md — P1 marked landed on lane/proto
as 1.4.0 (HandlerError/HandlerResult), to be adopted in rpc/ once that
merges to main; P2 resolved.

Not linked into the running daemon yet — the store is wired to the
dispatcher when download.add/list/get get real bodies, next.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Upd9WhG9oppieig5nRDLig

daemon/docs/proto-requests-m1.md

@@ -8,6 +8,19 @@ it needs a version note and a regen, not a silent change.
 
 ---
 
+## Status
+
+- **P1 — landed** on `lane/proto` as `contracts/` **1.4.0** (commit `5e3e215`), as the
+  `HandlerError` / `HandlerResult<T>` sketch below. Wire is byte-identical; C++-binding
+  bump only. `rpc/` adopts it (the predicted `Result<T>` → `HandlerResult<T>` swap on the
+  `on_*` overrides) **once `lane/proto` merges to `main`** — not against the unmerged
+  branch. `uds_roundtrip`'s `-32603`-collapse guard flips to `-32010` in the same change.
+- **P2 — resolved.** `session.hello.version-mismatch`'s `data.expected` is now `$any`;
+  the error-fixture compare is on `code` only, so `rpc/` echoes `kProtocolVersion` there.
+  PROTO's writeup: `contracts/proto-answers-daemon-m1.md`.
+
+---
+
 ## P1. The generated `Dispatcher` has no error channel below `-32603` — **blocking a conformant server**
 
 `velox::proto::Dispatcher`'s 39 methods each return `Result<T>` =