fix: disable experimental API betas by default, reduce side query token usage, standardize Headers type (#281)

* fix: disable experimental API betas by default to prevent 500 errors

Tool search (defer_loading), global cache scope, and context management
betas require internal Anthropic server-side support. External accounts
receive 500 Internal Server Error when these are sent.

Set CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=true by default in the CLI
entrypoint. Users with internal access can opt back in with =false.

Also includes: cache key stability fixes (Sonnet 1M latch, system-before-
messages key ordering, resume fingerprint isMeta skip), sideQuery default
cleanup, and /dream command.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: standardize API headers to Headers type and enable tengu feature flags by default

* fix: address PR review — dream lock, MCP betas guard, redundant Partial

- Call recordConsolidation() programmatically in /dream instead of
  delegating to model prompt (unreliable)
- Add CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS guard to MCP entrypoint
  (was only in CLI entrypoint, causing 500s in MCP server mode)
- Remove redundant ? markers from SecretValueSource Partial<{}> type

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/api/openaiShim.ts

@@ -41,6 +41,13 @@ import {
 import { sanitizeSchemaForOpenAICompat } from '../../utils/schemaSanitizer.js'
 import { redactSecretValueForDisplay } from '../../utils/providerProfile.js'
 
+type SecretValueSource = Partial<{
+  OPENAI_API_KEY: string
+  CODEX_API_KEY: string
+  GEMINI_API_KEY: string
+  GOOGLE_API_KEY: string
+}>
+
 const GITHUB_MODELS_DEFAULT_BASE = 'https://models.github.ai/inference'
 const GITHUB_API_VERSION = '2022-11-28'
 const GITHUB_429_MAX_RETRIES = 3
@@ -750,7 +757,7 @@ class OpenAIShimMessages {
           ? ` or place a Codex auth.json at ${credentials.authPath}`
           : ''
         const safeModel =
-          redactSecretValueForDisplay(request.requestedModel, process.env) ??
+          redactSecretValueForDisplay(request.requestedModel, process.env as SecretValueSource) ??
           'the requested model'
         throw new Error(
           `Codex auth is required for ${safeModel}. Set CODEX_API_KEY${authHint}.`,
@@ -941,13 +948,13 @@ class OpenAIShimMessages {
         response.status,
         errorResponse,
         `OpenAI API error ${response.status}: ${errorBody}${rateHint}`,
-        response.headers as unknown as Record<string, string>,
+        response.headers as unknown as Headers,
       )
     }
 
     throw APIError.generate(
       500, undefined, 'OpenAI shim: request loop exited unexpectedly',
-      {} as Record<string, string>,
+      new Headers(),
     )
   }