docs(ai_client): rename send_result to send in 3 current docs

Doc consistency: guide_ai_client.md, guide_app_controller.md, and
the error_handling styleguide now reference the new symbol name.

Also fixes two consistency issues in error_handling.md introduced by
the mechanical rename:
1. The 'Deprecation: send -> send_result' section (lines 623-642) was
   rewritten as a 'Historical deprecation (added 2026-06-15, reverted
   2026-06-16)' note that points to the relevant track specs.
2. Line 204 (the 'Current State Audit' summary for src/ai_client.py)
   had a self-contradictory claim ('send() is the new public API;
   send() is @deprecated') after the rename. Updated to describe
   the canonical public API.

Historical archives (conductor/tracks/*/spec.md, conductor/tracks/*/plan.md,
docs/reports/*) are NOT modified - they document the 2026-06-15
public_api_migration decision and stay as historical record.

conductor/code_styleguides/error_handling.md

@@ -201,7 +201,7 @@ The 3 refactored subsystems demonstrate each pattern in context:
   removed.
 - **`src/ai_client.py`** — `_send_<vendor>_result()` returns `Result[str]`
   (8 vendors: gemini, anthropic, deepseek, minimax, gemini_cli, qwen, llama,
-  grok); `send_result()` is the new public API; `send()` is `@deprecated`.
+  grok); `send(...) -> Result[str, ErrorInfo]` is the public API.
 - **`src/rag_engine.py:100-180`** — `_init_vector_store_result`,
   `_validate_collection_dim_result`, `is_empty_result`, `add_documents_result`
   return `Result[None]` or `Result[T]`; broad `except Exception` blocks
@@ -329,7 +329,7 @@ async def _api_get_key(controller, header_key: str) -> str:
 # Compliant: broad catch + HTTPException at the FastAPI boundary
 async def _api_generate(controller, payload):
  try:
-  result = ai_client.send_result(...)
+  result = ai_client.send(...)
   return result.data
  except Exception as e:
   raise HTTPException(status_code=500, detail=f"AI call failed: {e}")
@@ -620,22 +620,19 @@ When converting existing code:
 
 ---
 
-## Deprecation: `ai_client.send()` → `ai_client.send_result()`
+## Historical deprecation (added 2026-06-15, reverted 2026-06-16)
 
-The public `ai_client.send()` is marked `@deprecated` (via
-`typing_extensions.deprecated`, the Python 3.11+ backport of
-`@warnings.deprecated`). It still works for backward compat but emits a
-`DeprecationWarning` at runtime. New code MUST use `ai_client.send_result()`.
+The public `ai_client.send()` was briefly marked `@deprecated` in favor of
+`ai_client.send_result()` on 2026-06-15 by the
+`public_api_migration_and_ui_polish_20260615` track. The decision was
+reverted on 2026-06-16 by `send_result_to_send_20260616` after the
+Tier 2 autonomous sandbox proved capable of doing the rename safely.
 
-- `send_result(...) -> Result[str, ErrorInfo]` — the new public API.
-- `send(...) -> str` — **deprecated.** Returns `str` for backward compat;
-  errors are logged to the comms log but not returned.
-- Removal timeline: `public_api_migration_20260606` follow-up track.
-
-The deprecation warning is cached per call site (Python's `__warningregistry__`)
-to avoid log spam. `tests/conftest.py` adds a `filterwarnings` entry to
-silence the warning during the transition; new tests for the new API should
-assert the warning is NOT emitted by `send_result()`.
+`ai_client.send(...) -> Result[str, ErrorInfo]` is the canonical public API.
+No deprecation is in effect. For the historical record of the brief
+deprecation cycle, see
+`conductor/tracks/public_api_migration_and_ui_polish_20260615/spec.md`
+and `conductor/tracks/send_result_to_send_20260616/spec.md`.
 
 ---