Summary

Implements PR #1 of the browser-swap roadmap: a stateless FastAPI service inside the `allways` package that wraps the existing CLI swap modules with HTTP for browser orchestration. Per spec docs/swap-api/browser-swap-spec.md §6 — one new service, zero contract / DB / das-allways changes.

• HTTP wrapper at `allways/swap_api/`: `/healthz`, `/chains`, `/miners`, `/miners/best`, `/proofs/reserve`, `/proofs/confirm`, `POST /reserve`, `POST /confirm`.
• Reuses `contract_client`, `commitments`, `dendrite_lite`, `synapses`, `utils.proofs`, `utils.rate` directly — no duplicated logic.
• `POST /reserve` re-reads the live miner commitment, exact-match guards `expectedRate`, returns `409 RateChanged` on any drift (spec §4 zero-tolerance).
• Validator broadcasts go only to the contract whitelist via `discover_validators(contract_client=...)` (spec §4 — covered by `test_reserve_passes_contract_client_to_validator_discovery`).
• Added `broadcast_synapse_async` to `dendrite_lite` so FastAPI handlers don't own their event loop; sync `broadcast_synapse` now wraps the async path (CLI behavior unchanged).
• New pure helper `allways/utils/rate_selection.py` factors the CLI's eligibility filter and rate ranking out of `cli/swap_commands/swap.py` so both surfaces stay in sync.

Spec deviation

`POST /confirm` body adds `minerHotkey` alongside `requestHash`. The contract has no requestHash→miner index, and the browser already gets `minerHotkey` back from `POST /reserve`. Routes it directly into the `SwapConfirmSynapse.reservation_id` field the validators expect. `requestHash` is kept as a correlation field.

Implementation notes

• `build_app_state` reads `WS_ENDPOINT` / `NETUID` / `CONTRACT_ADDRESS` at startup; ephemeral wallet cached once via `get_ephemeral_wallet()` (spec gotcha).
• Polling cadence + quorum timeout overridable via `SWAP_API_QUORUM_TIMEOUT_S` / `SWAP_API_QUORUM_POLL_S`.
• CORS open public (`GET/POST/OPTIONS`).
• Reuses `render_and_aggregate` from `validator_rejections` with a buffer-backed `rich.Console` to keep the CLI's translated-rejection logic without console output.

Test plan

• Lint clean: `ruff format . && ruff check .`
• Unit tests: `pytest tests/swap_api/` — 15 tests, all pass
• Full repo tests: `pytest tests/` — 426 tests, all pass (no CLI regression)
• Smoke import: `python -c "from allways.swap_api.app import create_app; create_app()"` enumerates all 8 spec routes
• E2E against live dev environment — see PR Cap max fee at 5% to prevent collateral rug via fee manipulation #3 (`alw-utils`) for the curl-based suite that exercises the HTTP path end-to-end

Roadmap

This is PR #1 of 4 in docs/swap-api/pr-roadmap.md. PR #2 (`allways-ui` Swap page) and PR #3 (`alw-utils` dev-env + E2E suite) both depend on this merging first.