Freeze review pass over the public API baseline #183

What

Read the whole public API baseline (tests/OpenCode.Sdk.Tests/Snapshots/PublicApi.verified.txt,
11,267 lines) once, against a checklist of things that cannot change after 1.0 without a major
version:

• Parameter names (a rename breaks named-argument callers). Example: GetShellClient(string id)
  (:1910) beside GetSessionClient(string sessionId) (:1842), GetPtyClient(string ptyId)
  (:1489) and GetIntegrationClient(string integrationId) (:463).
• Interfaces that cannot grow without breaking implementers. Example: IOpenCodeClientOptions
  (:347), which no public API accepts and OpenCodeClientOptions (:612) implements; a new
  option added to it after 1.0 breaks every implementer, and net472/netstandard2.0 have no
  default interface members.
• Public constants, which compile into consumer binaries. Example: OpenCodeRoutes (:642)
  with 121 public route-template constants.
• Enum and union growth: strict enum parsing when a newer server sends a new value, and union
  interfaces that grow and shrink with the pin.
• Public delegates and mutable options. Example: OpenCodeServerEnsureOptions.OnStart
  (:1021).
• Naming consistency across families. Example: WebsearchClient (:2015) beside
  WebSearchProvider (:11066).

Each finding gets a decision (change before the freeze, or keep and record why), and the changes
land before 1.0.0-rc.1.

Why in 1.0

The surface freezes before 1.0.0-rc.1; the API review's exit is that every surface question is
decided (docs/ROADMAP.md:87-93). A finding after the freeze costs a major version.

Evidence

• The baseline lines cited above.
• tests/OpenCode.Sdk.Tests/PublicApiBaselineTests.cs:10 covers the core assembly only; the
  Extensions baseline is part of Package API, test roster and Native AOT gates for 1.0 #51.
• Checklist sources: the .NET Framework Design Guidelines' breaking-change rules and the Azure SDK
  .NET guidelines (extend-only design).

Done when

• Every type and member in the baseline is read against the checklist, and the findings are listed
  in this issue with a decision each.
• The changes land with PublicApi.verified.txt and CHANGELOG updates before 1.0.0-rc.1.