Ship the native Hummingbird 2 read-only server vertical slice

[DandyLyons]

Summary

Ship the native, read-only md-utils server vertical slice using Hummingbird 2.

This issue is deliberately limited to HTTP integration and application composition. Resource planning, storage, identity assessment, selection, indexing, and representation are supplied by their dedicated prerequisite issues.

Ship:

1. a MarkdownUtilitiesServer Swift library containing the generic Hummingbird adapter; and
2. an md-utils-server executable that loads configuration, composes dependencies, registers a validated EndpointPlan, and runs the application.

Responsibilities

• Register generic Hummingbird 2 collection, item, and logical-path handlers from an immutable EndpointPlan.
• Adapt the read snapshot's success, not-found, invalid-record, and identity-conflict results to HTTP.
• Implement the representative read-only books resource.
• Provide a thin executable composition root with startup configuration, logging, and lifecycle handling.
• Test route behavior in process with Hummingbird's testing support.
• Run natively on Linux without spawning the md-utils CLI.

Representative routes

• GET /books returns selected candidates according to the configured selection mode.
• GET /books/{id} returns an unambiguous primary-ID record.
• GET /_md-utils/path/** returns an exact logical-path record when fallback is enabled.

The same canonical record may appear through multiple configured resources when it conforms to multiple mdtypes. Those routes share canonical identity and revision while retaining resource-specific projection and policy.

Acceptance criteria

• Add a MarkdownUtilitiesServer library product and target.
• Add a thin md-utils-server executable composition root.
• Use Hummingbird 2 only.
• Register generic routes from the immutable plan without resource-specific generated Swift code.
• Implement collection, item, and reserved logical-path lookup handlers.
• Map structured identity collisions to 409 Conflict without selecting an arbitrary record.
• Preserve invalid rule-selected candidates with valid: false and diagnostics.
• Implement the representative read-only books vertical slice on Linux.
• Test success, not found, invalid candidates, nested paths, overlapping type membership, missing IDs, and duplicate IDs in process.
• Document startup, restart, routing, identity, validity, collision, and performance behavior.

Dependencies

Blocked by:

• Compile explicit server resources into an immutable EndpointPlan #91 — explicit resource configuration and immutable EndpointPlan;
• Build the immutable server read snapshot and generic record representation #89 — immutable read snapshot and generic record representation.

Those issues incorporate #81 identity semantics and #92 storage.

Follow-ups

• Generate OpenAPI 3.1 from the md-utils server EndpointPlan #84 — generate OpenAPI 3.1 from the same plan.
• Add REST mutations to the native md-utils server #82 — add REST mutations after the codec and store contracts are accepted.
• Add a Cloudflare Workers runtime for the md-utils server #83 — add the Cloudflare Workers runtime.

Non-goals

• Endpoint planning internals, record indexing, or projection design.
• Write operations.
• OpenAPI or Swagger output.
• Swift source generation, Swift OpenAPI Generator, or a build plugin.
• Cloudflare Workers or WebAssembly.
• SQLite or Durable Objects.
• Hot reload, authentication, authorization, or production observability.

[DandyLyons]

Implemented on PR #103 in commits 00247f3 and d3197c9. The branch adds the generic Hummingbird 2 adapter, md-utils-server composition root, .md-utils/server.yaml loading, recursive project import, stable JSON error envelopes, collision-safe 409 responses, in-process route coverage, documentation, and a dedicated Swift 6.2 Linux route smoke test. Verification: all 1,123 local Swift tests passed; MarkdownUtilitiesServer DocC built with warnings as errors; GitHub Native Server Linux and WebAssembly Core checks both passed. The PR uses Closes #77 so the issue will close when the verified branch is merged.

[DandyLyons]

Closed by merged PR #103. Merge commit: cfcb872. The native Hummingbird 2 read-only server, recursive project loader, .md-utils/server.yaml configuration, stable JSON error mapping, collision handling, Linux smoke coverage, and documentation satisfy all acceptance criteria. Verification before merge: 1,139 Swift tests passed locally; MarkdownUtilitiesServerLinuxSmoke and the md-utils-server product built successfully; GitHub Native Server Linux and WebAssembly Core checks both passed.