fix(claude): address tool-cloak PR review — preserve boolean schemas, null-guards, docs

Follow-up commit on PR #2943 review:

- Preserve boolean schemas in `sanitizeClaudeToolSchemas` (Gemini Code Assist,
  high severity). `additionalProperties: false` is the canonical JSON Schema
  lock-down for object tools; the previous coercion silently turned it into the
  permissive `{}`, which would invite models to hallucinate extra arguments
  during tool calling. Same rule now applies to per-property boolean schemas
  under `properties`. Placeholder strings still get the permissive `{}` slot —
  booleans get preserved verbatim.

- Defensive null guards in `cloakThirdPartyToolNames` for `tools[]` and
  `messages[]` entries that might be `null`/`undefined`. Prevents a runtime
  `TypeError` if a malformed payload reaches the cloak.

- Document `CLAUDE_DISABLE_TOOL_NAME_CLOAK` in `.env.example` and
  `docs/reference/ENVIRONMENT.md` (env/docs contract was failing in CI).

- Regression tests covering all of the above (5 boolean preservation cases,
  2 null-tolerance cases).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.env.example

@@ -683,6 +683,13 @@ GITHUB_OAUTH_CLIENT_ID=Iv1.b507a08c87ecfe98
 # Update these when providers release new CLI versions to avoid blocks.
 
 CLAUDE_USER_AGENT="claude-cli/2.1.146 (external, cli)"
+
+# Disable the deterministic tool-name cloak applied on the native Claude OAuth
+# path (executors/base.ts) — third-party-harness tool names are aliased to
+# Claude Code canonical or PascalCase forms so Anthropic does not refuse the
+# stream with a misleading 400 out-of-extra-usage placeholder. Set to true to
+# forward the original names verbatim (debugging only).
+# CLAUDE_DISABLE_TOOL_NAME_CLOAK=false
 CODEX_USER_AGENT="codex-cli/0.132.0 (Windows 10.0.26200; x64)"
 GITHUB_USER_AGENT="GitHubCopilotChat/0.45.1"
 ANTIGRAVITY_USER_AGENT="antigravity/2.0.1 linux/arm64 google-api-nodejs-client/10.3.0"