## Summary - `S3.list_refs/3` now issues per-ref GETs concurrently via `Task.async_stream` (default `max_concurrency: 32`) - `S3.put_pack/5` uploads `.pack` and `.idx` concurrently via `Task.async` + `Task.await_many` - Both wrapped in `:telemetry.span/3` under the new `[:ex_git_objectstore, :storage, _]` namespace so the improvement is observable in production - Tuning knobs (`list_refs_concurrency`, `list_refs_timeout`, `put_pack_timeout`) live in the S3 config map — no Anvil-side changes required, defaults are sensible Closes #25 ## Impact - **Protocol advertisement on ref-heavy repos: ~25s → ~1s.** A repo with 50 branches + 200 tags used to trigger 250 sequential 100ms GETs on every clone/fetch/push. Now parallel, bounded by `max_concurrency: 32`. - **Pack upload latency halved** on every push that produces a pack. ## Partial-write semantics (put_pack) If one of the two concurrent PUTs succeeds and the other fails, the successful object is left in place and the function returns `{:error, reason}`. A `.pack` without a matching `.idx` is unreachable through any lookup path, so GC/fsck reclaims it. Retries with the same `pack_sha` overwrite the orphan. Documented in the moduledoc alongside the existing CAS note. ## Telemetry Two new events (S3 backend only for now; Filesystem/Memory may adopt in a follow-up): | Event | Measurements (stop) | Metadata | |---|---|---| | `[:ex_git_objectstore, :storage, :list_refs, _]` | `:duration`, `:ref_count` | `:ref_prefix`, `:backend` | | `[:ex_git_objectstore, :storage, :put_pack, _]` | `:duration`, `:pack_size`, `:idx_size` | `:pack_sha`, `:backend` | Full event list is documented in the `ExGitObjectstore.Telemetry` moduledoc. ## Test plan - [x] Existing 1001-ref pagination test extended with sort assertion - [x] Low-concurrency smoke test (`list_refs_concurrency: 1`) verifies the config path - [x] Concurrent `put_pack` round-trip with 128KB pack + 32KB idx - [x] Error propagation test using a nonexistent bucket - [x] Telemetry assertions for both events (backend metadata, size measurements, ref_count) - [x] 595 total tests pass (566 non-S3 + 29 S3), `mix dialyzer` clean, `mix format --check-formatted` clean ## Out of scope (follow-ups) - Filesystem/Memory backend telemetry (uniform coverage) - Retry/backoff for transient S3 errors - Range-based pack reads (`NOTE(C7)` in `object_resolver.ex`) - hackney connection pool tuning docs