[eric] deadcode: remove unused _approx_tokens

backend/apps/agents/agent_manager.py

@@ -50,7 +50,6 @@ from backend.apps.agents.tool_catalog import (
 )
 from backend.apps.agents.aux_llm import _safe_resp_text
 from backend.apps.agents.history_compaction import (
-    _approx_tokens,
     _build_history_prefix,
     _get_branch_messages,
     _summarize_message_block,

backend/apps/agents/history_compaction.py

@@ -62,14 +62,6 @@ def _build_history_prefix(messages) -> str:
     return "<prior_conversation>\n" + "\n".join(lines) + "\n</prior_conversation>"
 
 
-def _approx_tokens(text: str) -> int:
-    """Conservative chars/4 estimate. Used for the pre-send guard
-    and the compaction trigger when a precise count_tokens isn't
-    cheap (or the route isn't Anthropic). Errs slightly high so we
-    compact a touch earlier than strictly necessary."""
-    return max(1, len(text or "") // 4)
-
-
 def _summarize_message_block(messages: list) -> str:
     """Programmatic, no-LLM summary of a message slice. Mirrors the
     shape of browser_agent._summarize_messages: extracts the original

linter/config/vulture_whitelist.py

@@ -48,7 +48,6 @@ requests_delta
 # This task is tooling-only and must not edit backend source, so these stay
 # whitelisted rather than deleted. They have zero call sites today; a future
 # non-additive cleanup pass should remove the definitions and these lines.
-_approx_tokens
 _summarize_message_block
 thinking_params_for
 _resolve_model