fix(executors): preserve tool-name casing on native Claude OAuth (#4307)

[diegosouzapw]

Closes #4307

Problem

Native Claude OAuth traffic runs through an anti-fingerprint tool-name cloak (remapToolNamesInRequest/cloakThirdPartyToolNames) that renames a tool literally named read → Read on the wire and records the reverse alias (Read → read) on a non-enumerable body._toolNameMap. The response side un-cloaks the streamed tool_use.name back to the client's original casing using that map.

Since v3.8.27 (#3941/#3968) execute() returns a JSON.parse(JSON.stringify())-round-tripped serializedBody as result.transformedBody. The round-trip drops the non-enumerable _toolNameMap, so chatCore's response-side restore sees an empty map and the cloaked Read streams verbatim to the client — corrupting the tool name (reporter: read → Read, also affects write/bash/etc.). Turning compression off does not help (it is unrelated); works direct-to-OpenRouter (cloak only fires for the native claude provider).

Fix

open-sse/executors/base.ts — after building serializedBody, re-attach the live _toolNameMap from transformedBody (non-enumerable, so it never re-serializes upstream). Mirrors the existing antigravity.ts::attachToolNameMap pattern and the #4091 capture-boundary guard.

Validation (Hard Rule #18 — TDD)

tests/unit/tool-name-case-preserve-4307.test.ts exercises the real base.ts execute() through the claude-OAuth cloak path (mocked fetch), asserting:

• precondition: the cloak fired (Read sent upstream; map not serialized on the wire);
• regression guard: result.transformedBody._toolNameMap is a Map restoring Read → read (fails RED on unfixed code, passes GREEN with the fix), and stays non-enumerable.

Related toolname/cloak/executor suites (4091/4181/oauth-cloak/passthrough/field-400) green (47/47). Lint + typecheck:core clean. base.ts file-size baseline bumped 1358 → 1387 in the same commit.

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