feat(insurance): expose read-only Archera vendor line-item discovery #91

Agent/session: cc-crossrepo-inventory, coordinated with resume-cc-audit.

Use case: cudly_archera_comparison accepts line_item_ids, but no MCP tool lists the vendor line-item UUIDs required for that argument. Main b173b02 registers only the comparison tool. Platform recommendation IDs are not vendor line-item IDs.

Proposed focused delivery: cudly_archera_line_items, explicitly read-only/open-world/non-destructive, using the existing operator-owned ARCHERA_* environment configuration and shared insurance.Client.LineItems. Arguments control only bounded local output pagination, never key, organization, plan or endpoint. Complete and validate all internal vendor pages before returning a local result page; publish total/offset/limit/next-offset metadata so omitted rows cannot be mistaken for a complete result. Provide vendor IDs, selection and a limited offer summary for the real comparison caller, with exact decimal text and nullable dimensions. Do not expose raw account/org identifiers, responses or credentials. A new fetch is not an atomic vendor snapshot; state this limit.

Prerequisite: pin only shared pkg to the same minimal published v0.0.0-20261016175124-570d168c6bc7 used by the CLI listing, retaining existing provider pins. Current pkg/providers pin is 9dae64b216d4. New comparison decoding requires selected_amount, absent from all three offers in the current synthetic MCP wire fixture. Complete that fixture from the actual documented field contract and add an actual decoder contract test without changing comparison output/goldens. Do not weaken decoding to keep outdated fixtures passing.

Reuse archeraConfig, archeraError, archeraDecimal, text cleaning and the established 512KiB result bound. Do not copy a matcher or vendor pagination implementation. Synchronize descriptor/registration, live schema/runtime bounds, actual NewServer catalog, README and bundle setting descriptions. Reuse existing in-memory MCP and intercepted transport test patterns; tool and catalog descriptions must name the available operation truthfully.

Proof: real MCP ListTools/CallTool -> actual registration/handler -> real insurance.Client -> synthetic fixed-origin transport, 101 rows/two internal pages and bounded local output pages; returned UUID can feed existing comparison filters. Late-page HTTP/decode/metadata/duplicate/size/cancellation failure returns no partial rows. Cover config/schema/runtime rejection before requests, error/log/protocol key redaction, terminal-safe text, exact long decimal/zero/null dimensions, 429/Retry-After with no retry, redirects, and startup/catalog/help doing no vendor read. Keep purchase audit behavior unchanged; listing writes no purchase audit record.

No live vendor calls, installs, purchases, enrollment, binding or implicit comparisons. Synthetic fixtures do not satisfy platform#798, which remains a human-authorized real-recording blocker. Related platform#786/#799 and paired CLI listing work.

Duplicate searches across all states for archera, line items and line-item found only completed #48, not listing. No open MCP PR exists at inspection. CONTRIBUTING feature-request instructions and current claim/assignment rules apply; there is no issue template. This issue tracks a proposed plan pending review, not implemented functionality.