feat(codemode): add OpenAPI tool adapter

[rekram1-node]

Adds OpenAPI.fromSpec (exported as @opencode-ai/codemode/openapi): a basic OpenAPI 3.x document -> codemode tool subtree adapter, one tool per operation. The host places the subtree under a key in its tools tree; that key is the model-visible namespace.

Design

• Auth is never model-visible. The adapter reads each operation's effective security (root default, operation override, security: [] / empty {} alternative = unauthenticated), picks the first satisfiable OR alternative (AND within one), and injects credentials from a host auth.resolve callback into the carrier the scheme declares. undefined from the resolver tries the next alternative; a failure aborts the call so an expired refresh token cannot fall through to unauthenticated.
• Transport is an Effect service. Generated tools require HttpClient.HttpClient (effect/unstable/http) in R; hosts provide FetchHttpClient.layer or a custom/test layer. No new dependencies; the spec is a parsed document (hosts parse JSON/YAML themselves).
• fromSpec is sync and total: returns { tools, skipped }. Operations it cannot represent (non-JSON request bodies, non-absolute server URLs) land in skipped with a reason instead of becoming broken tools.
• Schemas: inputs group parameters by location (path/query/headers/body); outputs come from the first success (2xx/2XX) JSON response, no-content success -> null; #/components/schemas/* refs are shared as $defs so signatures expand referenced types. Reserved header parameters (Accept/Content-Type/Authorization) are ignored per the spec. Non-2xx responses become safe catchable tool failures carrying status + size-capped body summary.
• Hardening: path parameters are URL-encoded with ./../empty rejected (URL retargeting), required query/header/body inputs fail before auth/network, operation names avoid CodeMode-blocked members, and record lookups keyed by spec/model-controlled names guard against prototype-inherited values.
• Also extends the signature renderer with allOf (union members parenthesized) and teaches Services<Tools> to infer R from index-signature tool records.

Deliberately out of scope for a basic converter: YAML parsing, server URL templates/variables, path/operation-level server overrides, cookie parameters, multipart/binary bodies, and default-response schemas.

Verification

• bun typecheck and bun test from packages/codemode (243 pass; 19 adapter tests covering auth semantics, carriers, resolver failure vs unavailability, unauthenticated alternatives, response-schema selection, naming sanitization/dedup/blocking, header precedence, required query/header preflight, path traversal rejection, and skipped reporting)
• Reviewed by parallel focused agents (bugs, scope, comments, inlining, tests, Effect/API); findings addressed or explicitly descoped