REPL: prefer OpenAPI paths in completer and split lookup logic

[Copilot]

Summary

REPL route autocomplete now prefers OpenAPI path templates (when available) instead of registry-derived paths, so completions reflect canonical spec routes like /example/hello/{name}. The completer logic was also decomposed into focused lookup helpers to make behavior explicit and easier to evolve.

• Route source selection

  • Added OpenAPI-first route source resolution with registry fallback.
  • Preserves existing behavior when no OpenAPI paths are present.

• Completer decomposition

  • Split createCompleter() into dedicated helpers for:
    • .scenario completions
    • route-builder method completions
    • route string completions
    • route source resolution

• Coverage + docs

  • Added a regression test proving OpenAPI path completion is preferred over registry path aliases.
  • Updated REPL docs to state that Tab completion uses OpenAPI templates when loaded.

const completer = createCompleter(
  registry,
  undefined,
  { paths: { "/example/hello/{name}": { get: {} } } },
);

const [completions] = await callCompleter(completer, 'client.get("/example/h');
// completions => ["/example/hello/{name}"]

Original Prompt

1. The completer in the REPL currently relies on registry to get a list of valid routes. If an OpenAPI document is available, it should rely on that instead.

2. Break up the createCompleter() function -- delegate each lookup to a smaller function.

3. The completer should know about the prefix "/example/hello/{name}" not "/hello/name".

Manual acceptance tests

• With an OpenAPI document loaded, typing client.get("/example/h in REPL and pressing Tab suggests /example/hello/{name}.
• With an OpenAPI document loaded, typing route("/example/h and pressing Tab suggests /example/hello/{name}.
• Without OpenAPI paths, route completion still uses registry routes (existing behavior).
• Typing route("/pets"). still suggests RouteBuilder methods (method(, query(, send(, etc.).
• .scenario completion still suggests index exports and file-prefix/function combinations as before.

Tasks

• Refactored createCompleter() into focused helper functions for each completion domain.
• Added OpenAPI-first route lookup (openApiDocument.paths), with registry fallback.
• Updated startRepl() completer wiring to pass the OpenAPI document into createCompleter().
• Added REPL unit test asserting OpenAPI path-template completion precedence.
• Updated REPL docs and added a patch changeset entry.