feat(shepherd-sdk-test): in-memory host mocks (BLEU-841)#15
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Two-part deliverable:
1. New `shepherd_sdk::host` module exposing the trait seam between
strategy logic and the wit-bindgen shims a module generates per-
cdylib:
- `ChainHost` — request(chain_id, method, params)
- `LocalStoreHost`— get / set / delete / list_keys
- `CowApiHost` — submit_order(chain_id, body)
- `LoggingHost` — log(level, message)
- `Host` — supertrait bundling all four (blanket impl
so callers only need the supertrait bound)
The traits ride on a host-neutral `HostError` (same field shape
as wit-bindgen's), with `HostErrorKind` and `LogLevel` mirroring
the WIT enums verbatim. Modules bridge their own wit-bindgen
`HostError` to the SDK's with a one-liner `From` impl on each
side; the M3 tutorial (BLEU-848) documents the adapter pattern.
2. New `shepherd-sdk-test` crate (dev-only, host-only) supplying
in-memory implementations for every trait + assertion helpers:
- `MockHost { chain, store, cow_api, logging }`
- `MockChain`: programmable `(method, params)` -> result map;
records every call with `chain_id`, `method`, `params`.
- `MockLocalStore`: HashMap-backed; `list_keys` does a prefix
scan (sorted output for stable assertions).
- `MockCowApi`: single programmable response shared across
calls; records each submission's `chain_id` + body bytes;
`last_body_as_json` helper for inline assertions.
- `MockLogging`: buffers all lines with their level; `contains`
/ `count_at` helpers.
Unconfigured calls return `HostErrorKind::Unsupported` so an
unprogrammed test fails fast instead of silently passing on a
default value.
Tests: 8 host tests on `shepherd-sdk-test` + 1 module-level doctest
locking the recommended usage pattern. Workspace + wasm32-wasip2
check still clean.
Adoption is opt-in: existing M2 modules keep their pure-function
tests for now. BLEU-848 (tutorial) will demonstrate the new
strategy-takes-Host pattern with `MockHost` end-to-end.
This was referenced Jun 17, 2026
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Summary
Two-part deliverable:
1. Host traits in `shepherd_sdk::host`
The seam between strategy logic and the per-cdylib wit-bindgen shims:
Rides on a host-neutral `HostError` (same field shape as wit-bindgen's), with `HostErrorKind` and `LogLevel` mirroring the WIT enums. Modules bridge to their own wit-bindgen `HostError` with one-liner `From` impls each direction — the BLEU-848 tutorial documents the adapter pattern.
2. `shepherd-sdk-test` crate (dev-only)
In-memory implementations + assertion helpers:
Unconfigured calls return `HostErrorKind::Unsupported` so a forgotten programming step fails the test fast rather than silently passing on a default.
Adoption
Opt-in. Existing M2 modules keep their pure-function tests for now. BLEU-848 (tutorial) demonstrates the strategy-takes-`Host` pattern with `MockHost` end-to-end.
Stacks on #14 (BLEU-843 module refactor).
Linear: BLEU-841.
Test plan