Summary

Stacked on #35108. Reworks the form when conditional-visibility contract, which was previously under-specified and partly broken (a when targeting a boolean or number field could never match because value was string-only and compared with ===).

Schema (Form.When)

• when is now always an array (When[]), evaluated as AND.
• value is string | number | boolean, matching the referenced field's type.
• Ops stay minimal: eq / neq. Extensions (in, etc.) can be added later without breaking the shape.

Semantics (documented on the schema and enforced in core)

• Against a multiselect answer, eq means "selection includes value", neq means "does not include".
• An unanswered referenced field makes the condition false for both ops (kills the old accident where neq activated fields whose parent was untouched).
• Inactive fields cannot be answered — replies containing answers for inactive fields fail with Form.InvalidAnswerError. Combined with unanswered⇒false, inactivity cascades through chains (hiding B falsifies every condition referencing B) with no recursive evaluation needed.
• required continues to apply only while a field is active.

Create-time validation (new Form.InvalidFormError)

Invalid when definitions are rejected at create/ask instead of silently never matching, so the authoring caller (usually an LLM tool call) sees an actionable error:

• when.key must reference an earlier field (also rules out cycles)
• duplicate field keys are rejected
• value type must match the referenced field's type
• when the referenced field has closed options, value must be one of them

The server handler maps Form.InvalidFormError to the existing InvalidRequestError (400) — no new protocol errors or routes.

Verification

• bun typecheck in packages/schema, packages/core, packages/protocol, packages/server, packages/client, packages/sdk/js, packages/opencode
• bun test test/form.test.ts in packages/core — 7 pass (4 new: gating + inactive rejection, multiselect inclusion, unanswered/cascade semantics, creation validation)
• bun test test/event-manifest.test.ts in packages/schema
• bun test + bun run check:generated in packages/client
• HttpApi exerciser form scenarios 6/6