eleven / messenger Public

server: adopt litestream as a library — lease + replication primitive (#550 Phase 2 groundwork) (#630)

* server: SPIKE — embed litestream v0.5 as a library for the activator lease (#550)

Spike, not production code: validates the Part 4 v2 design consequence that
the future activator embeds litestream as a Go library to get the S3 lease
(lock.json via If-None-Match/If-Match) that the CLI does not expose.

Findings (full report in the session):
- litestream v0.5.14 embeds cleanly; its core uses modernc.org/sqlite (no
  cgo — mattn/go-sqlite3 is only in its cmd/ and tests). CGO_ENABLED=0
  builds pass.
- The lease API is litestream.Leaser (Acquire/Renew/ReleaseLease) +
  s3.NewLeaser(); it is a standalone primitive NOT wired into DB/Replica/
  Store — the embedder composes lease around replication, which is exactly
  the activator shape.
- Live against the real bucket: replication works under the lease, and a
  second claimant on the same prefix fails LOUDLY with a typed
  *litestream.LeaseExistsError (holder + expiry) — proven in
  TestReplicateWithLease_MutualExclusion (gated on LCHAT_TEST_S3_BUCKET).
- Cost: go.mod jumps go 1.23 -> 1.25.0; +39 go.mod entries (aws-sdk-go-v2,
  prometheus, wazero/go-re2, dateparser); binary 19.6 MB -> 24.4 MB
  (+1.0 MB from the toolchain/dep upgrades, +3.7 MB from litestream+aws-sdk).

spike_activator.go links the package into the binary purely so the size
delta is measurable; delete it (and internal/activator) with the spike.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* server: adopt litestream as a library — internal/activator lease + replication (#550 Phase 2 groundwork)

Promotes the activator-lease spike to a real package. ReplicateWithLease
acquires the S3 single-writer lease (lock.json, conditional writes) before
starting replication, renews at TTL/3, surfaces lost leadership via Err(),
and releases on Close so the next claimant acquires immediately. A second
claimant fails loudly with *litestream.LeaseExistsError — the signal the
CLI lacks (proven on #550).

Costs accepted with the adoption: go.mod moves to go 1.25 (litestream
v0.5.10+ requirement) and the dep tree grows by ~39 modules (aws-sdk-go-v2
et al). Nothing imports the package yet, so the shipped binary is unchanged
until the Phase 2 activator wires it in.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>