Schema view doesn't expose nested object sub-fields (e.g. Open Brain metadata.share_candidate)

[rodaddy]

Problem

mcp2cli schema <server>.<tool> and the --params help render the flat MCP inputSchema from tools/list. When a tool has a nested object parameter, the sub-fields are opaque — a CLI caller can't discover them.

Concrete case (Open Brain, contract 2026-06-19.memory-tools.v5, live at http://10.71.1.21:3100/mcp):

$ mcp2cli schema open-brain.append_session_event
  "metadata": { "description": "Arbitrary JSON metadata; max 50 keys, max 100KB total" }   # opaque

But OB's metadata now carries a recognized nested field, share_candidate (boolean), which nominates an event for promotion to the shared-kb namespace — with rich usage help. A CLI caller (Rico/Claude via mcp2cli) currently has no way to discover it from mcp2cli schema; they'd have to read the OB source. The flat tool list hides it.

This is the bridge half of the new OB memory-promotion feature (open-brain #161/#172). The agents (rtech-hermes) consume OB directly over HTTP, but mcp2cli is the path Rico/Claude use, and right now that path can't see or correctly form a share_candidate nomination.

Repro

mcp2cli open-brain --help                       # append_session_event + promote_shared present (good — live discovery works)
mcp2cli schema open-brain.append_session_event  # metadata shown as opaque; no share_candidate sub-field

Proposed approaches (maintainer's call)

A. Recurse nested object fields (source-agnostic). When an inputSchema property is type: object with nested properties (standard JSON Schema) — or OB's contract dialect fields — render the sub-fields with their description/type/required. Works for any MCP server, not just OB. This is the minimal, general fix.

B. Prefer get_contract for servers that publish it (OB-aware). OB exposes get_contract with a richer per-field/per-tool help manifest (tool_contracts.append_session_event.input_schema.metadata.fields.share_candidate.description, etc.). mcp2cli could, for servers advertising that capability, render schema/help from the contract instead of the flat tools/list. Richest help, but couples mcp2cli to the OB contract dialect (fields vs properties).

A handles the general case; B gives the best help for OB specifically. They're not exclusive — A could read fields OR properties, getting most of B's benefit generically.

Acceptance

• mcp2cli schema open-brain.append_session_event shows metadata.share_candidate (boolean) with its help text.
• A --params '{"...","metadata":{"share_candidate":true}}' call round-trips correctly (already works at the transport layer; this is purely the discoverability/help gap).
• No regression for flat tools (e.g. promote_shared renders unchanged — verified it already shows table/id/reason/dry_run correctly).

Context

• Open Brain server source of truth: contract tool_contracts in open-brain repo src/contract-schemas.ts; nested help lives under metadata.fields.
• Live verification done 2026-06-19: promote_shared and append_session_event ARE discovered live (no static cache to update) — the only gap is nested-field rendering.

[rodaddy]

Pairing note: #58 (schema cache serves stale tool schema after an upstream contract bump) should be worked together with this issue. Both are schema-view fidelity for Open Brain:

• Schema view doesn't expose nested object sub-fields (e.g. Open Brain metadata.share_candidate) #55 — nested object sub-fields opaque in the schema view (e.g. metadata.share_candidate).
• Schema cache serves stale tool schema after upstream contract bump (no invalidation on version change) #58 — the schema view goes fully stale after a contract bump (verified live on OB memory-tools.v11: create_if_missing invisible until the per-client cache file was manually deleted).

A combined fix should land both: invalidate/refetch on contract_version/schema_hash change (#58) and render nested metadata.fields/properties (#55), so mcp2cli schema open-brain.append_session_event shows the current v11 tool incl. create_if_missing and the nested metadata fields in one pass.