[Bug][Storage] Sessions created before the JSONL→SQLite cutover disappear from the UI after updating — legacy JSONL transcripts are never imported

[cat0825]

What happened

After updating Maka to the build where SQLite became the sole operational
session store, every session created before the cutover disappeared from the
UI. The session list only shows sessions created after the update.

The old data is not deleted — the legacy transcript files are still on
disk, byte-for-byte intact. The new storage layer simply never reads them.

Evidence (data layer, from a real upgrade on macOS)

1. Legacy transcript file still exists, intact:
   ~/Library/Application Support/Maka/workspaces/default/sessions/b156d249-dbd1-4ddb-ae16-a801a9fe9526/session.jsonl
   — schemaVersion: 1, opens with a legacy-header record, then user/turn
   message records. (In the affected install it contains a full turn: user
   message, turn_state, token_usage, system_note.)

2. But the session is absent from the new SQLite store:
   runtime.sqlite → session_messages returns 0 rows for that
   session_id; the id appears in neither session_metadata nor
   session_catalog_projection. The UI therefore has nothing to list.

3. Schema migrations ran on first launch, but imported nothing:
   operational_schema_migrations (runtime|9, session_metadata|21, …) all
   applied at 1785904471629, which is exactly the first launch after the
   update. The migration machinery ran; no legacy-session import was part of
   it.

Root cause (source layer)

• refactor(storage): make SQLite the sole operational authority #1994 refactor(storage): make SQLite the sole operational authority
  made SQLite the only session store. Its README documents that several
  legacy file stores are not imported (e.g. pre-existing Electron
  safeStorage credential files "are not imported; affected users must
  re-authenticate"), but for session transcripts it removes the JSONL path
  without adding a one-time JSONL→SQLite importer.
• fix(scripts): drop session-bundle imports deleted with the JSONL session tree #2029 fix(scripts): drop session-bundle imports deleted with the JSONL session tree explicitly deletes the remaining JSONL-session import
  code rather than replacing it with a migration.
• In the shipped 0.1.5 bundle (dist/main/), grepping for jsonl finds no
  session-transcript reading code at all — the new store only reads SQLite.
• Startup (app-lifecycle.ts) calls backfillSessionProjects, but that only
  backfills project grouping for sessions that already exist in SQLite; it
  never scans sessions/b156d249-dbd1-4ddb-ae16-a801a9fe9526/session.jsonl.
• The only remaining JSONL handling is packages/core/src/foreign-session.ts
  / packages/storage/src/foreign-session-store.ts (importing Claude Code
  / Codex external transcripts) — not Maka's own legacy transcripts.

So the upgrade path is: JSONL tree → (nothing) → SQLite. Silent invisibility
of intact user data.

Expected behavior

On upgrade, legacy schemaVersion: 1 JSONL sessions should be migrated into
SQLite (session_metadata + session_messages) so they stay visible — or at
minimum surfaced with an explicit import path / notice. Intact data must not
become silently invisible.

Suggested fix (any of)

1. One-time importer at first launch after cutover: scan
   sessions/*/session.jsonl, parse legacy-header + message records,
   insert into session_metadata / session_messages, and mark the
   migration done (schema-version bump or a durable one-time flag) so it runs
   exactly once and is idempotent.
2. If full transcript import is too risky, import at least the session
   metadata + last message so the session appears in the list and can be
   opened/exported.
3. Add a "import legacy sessions" action / notice for installs that still
   carry a sessions/ tree.

Repro / verification commands (maintainers)

# 1. Legacy transcript still on disk, intact
ls "~/Library/Application Support/Maka/workspaces/default/sessions/"
head -1 "~/Library/Application Support/Maka/workspaces/default/sessions/b156d249-dbd1-4ddb-ae16-a801a9fe9526/session.jsonl"

# 2. But the new store does not contain it
sqlite3 "~/Library/Application Support/Maka/workspaces/default/runtime.sqlite" \
  "SELECT COUNT(*) FROM session_messages WHERE session_id='b156d249-dbd1-4ddb-ae16-a801a9fe9526';"      # → 0
sqlite3 "~/Library/Application Support/Maka/workspaces/default/runtime.sqlite" \
  "SELECT COUNT(*) FROM session_metadata WHERE session_id='b156d249-dbd1-4ddb-ae16-a801a9fe9526';"      # → 0

# 3. Migrations ran on first launch, none imported the legacy tree
sqlite3 "~/Library/Application Support/Maka/workspaces/default/runtime.sqlite" \
  "SELECT * FROM operational_schema_migrations;"                        # all applied_at ≈ first launch after update

Environment

• Maka version: 0.1.5 (desktop, CFBundleShortVersionString = 0.1.5; also
  reproduced from source at upstream/main HEAD 07c1e680)
• OS: macOS, Apple Silicon (arm64)
• Updated via auto-updater from an earlier 0.1.x build

Related

• refactor(storage): make SQLite the sole operational authority #1994 — SQLite as sole operational authority (cutover)
• fix(scripts): drop session-bundle imports deleted with the JSONL session tree #2029 — dropped JSONL session-tree imports
• feat(storage): migrate all session metadata to SQLite #1370 / feat(storage): add SQLite session metadata foundation #1371 / feat(storage): make SQLite the default session metadata store #1372 / feat(storage): complete SQLite session metadata migration #1373 — earlier SQLite session-metadata migration
  work (metadata only; message transcripts stayed in JSONL until refactor(storage): make SQLite the sole operational authority #1994)