feat: mock platform

[decrypto21]

feat: mock host foundation — MockPlatform + mock wallet + createMockHost, on the real core

Summary

A mock host that swaps the seams while running the real Rust core. Tests, CI, and product
test-suites exercise the actual truapi-server dispatcher, permission service, storage, and
statement-store logic — with the device and wallet supplied by config-driven, in-memory doubles
instead of a real phone or paired wallet. Deterministic, deviceless, scriptable.

Why "swap the seam, keep the core"

TrUAPI is one core with two seams: the platform seam (truapi-platform capability traits) and
the wallet seam (SSO + statement store). The mock replaces only those seams. Because every
request still flows through the real core, the mock is faithful by construction — it can't drift
from real host semantics the way a hand-rolled fake would.

What this delivers

truapi-platform — MockPlatform (behind the mock feature, dev-only)

• MockConfig: permission policy (AllowAll/DenyAll, device + remote), feature support, theme,
  confirmation control, chain behavior (Silent / Scripted / Closed / ConnectError), and
  MockFaults error injection.
• Implements every platform-seam trait, and records what the core asked the device to do
  (navigations, notifications, confirmations, auth-state, sent RPC) for assertions.

truapi-server — mock_wallet (behind the mock feature)

• MockWalletPlatform + MockWalletConnection: in-process, deterministic SSO pair + sign over
  the statement-store channel (sr25519 proofs, P-256 ECDH → HKDF → AES-GCM). It reuses the real
  statement-store signing helper, so it stays in lockstep with production framing. Slice-0:
  in-process-valid, not chain-valid — real on-chain signing is Headless pairing + signing hosts #264 (below).

Through-core proof — tests build the real core from the mock
(from_platform_with_config + SCALE) and assert on the wire envelopes the dispatcher emits.

truapi-host-wasm — createMockHost — an in-memory HostCallbacks (tsc-enforced complete),
a headless WASM-bridge test proving the real WASM core drives the mock across JS↔SCALE↔WASM, and
a host-wasm CI job. (The one-line createMockClient + real-browser E2E are in #261.)

Relationship to the real headless host (#264) and simulation (#36)

This is the deterministic, deviceless tier. It is complementary to
#264 (a real headless pairing/signing host: real
People-chain statement store, real mnemonic signer) — #264 has no mock, this has no real signer, and
the two do not overlap. Real-chain and real-signing capabilities are deliberately deferred to #264,
not reimplemented here. The simulation program
(sdk-team#36) builds on both: deterministic scale on
this mock, real-API runs through #264.

Status (rebased onto current #104, green)

Area	State
truapi-platform (MockPlatform)	✅ 22 unit tests
truapi-server (mock_wallet + through-core)	✅ 267 pass · 2 parked (see below)
truapi-host-wasm (createMockHost + WASM bridge)	✅ 42 tests; tsc clean; fresh WASM bundle
Workspace	✅ fmt · clippy --all-features -D warnings · test --workspace --all-features

2 through-core tests parked (#[ignore]d + flagged, not deleted): the mock wallet's
signing-response framing and preimage-submit path depend on #104 SSO internals that are still in
flight (opaque SSO ids / statement-proof routing; preimage now needs a bulletin allowance signer).
Un-park once those settle.

Scope & safety

• The mock feature is a dev-dependency only — never in the default/production build.
• No change to real host behavior or the protocol surface.

Stacked on

#104 (Rust core port). Merge order: #104 → #258 → #261. Tracked by #257.