MCP floor: carry the widget-authoring tool (fork-registry delta)

[aarontrowbridge]

Important

Problem — The fork registers a widget-authoring tool natively in its tool
registry; the harness-neutral MCP tool floor does not carry an equivalent.
Every non-fork harness therefore lacks the widget-authoring affordance, and
the fork's registry change is one of only two load-bearing deltas blocking
its retirement.

Approach — Port the tool into the MCP floor as a harness-neutral tool
with the same name, schema, and semantics the fork exposes; the server-side
helper and the UI sentinel seam are already ported — only the tool shell is
missing.

Scope — in: the MCP tool (schema, execution path calling the existing
server helper, tests) · out: the fork's registry change itself (retires with
the fork), any UI changes.

Assumptions — The fork's tool definition (its registration and its
prompt file) is the reference; the MCP floor's existing 17-tool pattern is
the vehicle.

Acceptance Criteria

• The tool appears in the MCP floor's tool list with the fork-equivalent name and schema.
• A tool call drives the existing server-side widget helper end-to-end (the widget appears in the dashboard inventory).
• The MCP floor's parity test covers the tool (count and bijective-name assertions updated).
• The tool's prompt/description text is carried from the fork (its prompt file), not rewritten.

Testing Decisions

Extend the MCP floor's existing test suites (the core tests + the parity
test); no new suites.

Key Decisions

• Bare-name convention per the floor's existing rule (the host namespaces the product view).
• The tool executes against the extension-host service's widget endpoints, not the harness server.

Constraints & Invariants

• Worktree off fresh origin/main; the shared checkout's branch is never moved.
• The floor stays harness-neutral: no fork-specific imports.

Prior Art

• The fork's tool registration + prompt file (read via the remote branch origin/local/amicode).
• The MCP floor's core tools module and its parity test.
• The extension service's widget server helper (already ported).

Source

Part of the re-base leg — campaign ledger sessions/session-20260827-harness-agnostic.md, loop 28b.