feat(testing): createComplyController seller scaffold (#701)

[bokelley]

Summary

• Adds createComplyController to @adcp/client/testing — a domain-grouped (seed / force / simulate) seller-side scaffold for AdCP's comply_test_controller tool. Returns { toolDefinition, handle, handleRaw, register } so sellers wire the tool with a single controller.register(server) call.
• Extends TestControllerStore with five seed methods (seedProduct, seedPricingOption, seedCreative, seedPlan, seedMediaBuy). Both the existing registerTestController flat-store surface and the new grouped façade now cover the full 12-scenario protocol.
• Hardened against common misuse: strict === true gate, capped seed cache, prototype-key rejection, frozen tool definition, list_scenarios bypasses the gate so capability probes always succeed, and register() warns once per controller when no gate and no env opt-out is configured.

Closes #701.

What the helper owns (so the seller doesn't)

1. Scenario dispatch — routes scenario to the correct adapter; unregistered adapters return UNKNOWN_SCENARIO.
2. Param validation — per-scenario required fields + status-enum parsing; rejections return INVALID_PARAMS.
3. Seed idempotency — same id + equivalent fixture = previous_state: "existing"; divergent fixture = INVALID_PARAMS without touching the adapter.
4. Error envelope shaping — adapters throw TestControllerError(code, msg, currentState?) or return the success shape; the helper never leaks unexpected errors.
5. Sandbox gating — optional sandboxGate with strict === true semantics, fails closed on throws, bypassed for list_scenarios.
6. MCP envelope — content + structuredContent + isError via the existing toMcpResponse.

What stays adapter-side (deliberate)

• Transition enforcement. The spec requires controllers and production to share one state machine; the helper calls into the adapter's rules rather than shipping a built-in policy that could silently diverge. The example shows the pattern with a CREATIVE_TRANSITIONS table the adapter consults.

Scope trimmed from #701 (follow-up issues filed)

• A2A transport parity — MCP only. No A2A sellers exercise the tool today.
• registerTool + outputSchema migration — repo-wide story, filed as tech-debt: migrate MCP tool registrations from deprecated tool() to registerTool() #705.
• Per-tenant ctx resolver — needs design input from a real multi-tenant case, filed as design: per-tenant resolver / ctx enrichment for createComplyController #706.
• Spec issue: ListScenariosSuccess['scenarios'] enum in the request schema doesn't include seed_* values — filed separately on adcontextprotocol/adcp.

Test plan

• 36 new unit tests in test/comply-controller.test.js covering dispatch, list_scenarios, seed idempotency (fresh / equivalent / divergent / cross-kind / cache-eviction race), sandbox gate (allow / deny / throw / truthy-non-boolean / list_scenarios bypass), fixture hardening (__proto__ / constructor / prototype / non-object types), seed cache cap, register warning de-dupe + env opt-outs, and MCP envelope shape.
• 61 existing test/server-test-controller.test.js pass unchanged (back-compat).
• Full repo suite: 0 failures (6 pre-existing skips).
• TypeScript compile clean (tsc --noEmit); lint clean on new files.
• Built-output sanity check: require('./dist/lib/testing') resolves createComplyController, SEED_SCENARIOS, createSeedFixtureCache.
• CI green.

🤖 Generated with Claude Code