refactor: remove budget warning injection system (dead code)

The _get_budget_warning() method already returned None unconditionally —
the entire budget warning system was disabled. Remove all dead code:

- _BUDGET_WARNING_RE regex
- _strip_budget_warnings_from_history() function and its call site
- Both injection blocks (concurrent + sequential tool execution)
- _get_budget_warning() method
- 7 tests for the removed functions

The budget exhaustion grace call system (_budget_exhausted_injected,
_budget_grace_call) is a separate recovery mechanism and is preserved.

run_agent.py

@@ -339,10 +339,7 @@ def _paths_overlap(left: Path, right: Path) -> bool:
 
 _SURROGATE_RE = re.compile(r'[\ud800-\udfff]')
 
-_BUDGET_WARNING_RE = re.compile(
-    r"\[BUDGET(?:\s+WARNING)?:\s+Iteration\s+\d+/\d+\..*?\]",
-    re.DOTALL,
-)
+
 
 
 def _sanitize_surrogates(text: str) -> str:
@@ -463,34 +460,7 @@ def _sanitize_messages_non_ascii(messages: list) -> bool:
     return found
 
 
-def _strip_budget_warnings_from_history(messages: list) -> None:
-    """Remove budget pressure warnings from tool-result messages in-place.
 
-    Budget warnings are turn-scoped signals that must not leak into replayed
-    history.  They live in tool-result ``content`` either as a JSON key
-    (``_budget_warning``) or appended plain text.
-    """
-    for msg in messages:
-        if not isinstance(msg, dict) or msg.get("role") != "tool":
-            continue
-        content = msg.get("content")
-        if not isinstance(content, str) or "_budget_warning" not in content and "[BUDGET" not in content:
-            continue
-
-        # Try JSON first (the common case: _budget_warning key in a dict)
-        try:
-            parsed = json.loads(content)
-            if isinstance(parsed, dict) and "_budget_warning" in parsed:
-                del parsed["_budget_warning"]
-                msg["content"] = json.dumps(parsed, ensure_ascii=False)
-                continue
-        except (json.JSONDecodeError, TypeError):
-            pass
-
-        # Fallback: strip the text pattern from plain-text tool results
-        cleaned = _BUDGET_WARNING_RE.sub("", content).strip()
-        if cleaned != content:
-            msg["content"] = cleaned
 
 
 # =========================================================================
@@ -6989,24 +6959,6 @@ class AIAgent:
             turn_tool_msgs = messages[-num_tools:]
             enforce_turn_budget(turn_tool_msgs, env=get_active_env(effective_task_id))
 
-        # ── Budget pressure injection ────────────────────────────────────
-        budget_warning = self._get_budget_warning(api_call_count)
-        if budget_warning and messages and messages[-1].get("role") == "tool":
-            last_content = messages[-1]["content"]
-            try:
-                parsed = json.loads(last_content)
-                if isinstance(parsed, dict):
-                    parsed["_budget_warning"] = budget_warning
-                    messages[-1]["content"] = json.dumps(parsed, ensure_ascii=False)
-                else:
-                    messages[-1]["content"] = last_content + f"\n\n{budget_warning}"
-            except (json.JSONDecodeError, TypeError):
-                messages[-1]["content"] = last_content + f"\n\n{budget_warning}"
-            if not self.quiet_mode:
-                remaining = self.max_iterations - api_call_count
-                tier = "⚠️  WARNING" if remaining <= self.max_iterations * 0.1 else "💡 CAUTION"
-                print(f"{self.log_prefix}{tier}: {remaining} iterations remaining")
-
     def _execute_tool_calls_sequential(self, assistant_message, messages: list, effective_task_id: str, api_call_count: int = 0) -> None:
         """Execute tool calls sequentially (original behavior). Used for single calls or interactive tools."""
         for i, tool_call in enumerate(assistant_message.tool_calls, 1):
@@ -7353,36 +7305,7 @@ class AIAgent:
         if num_tools_seq > 0:
             enforce_turn_budget(messages[-num_tools_seq:], env=get_active_env(effective_task_id))
 
-        # ── Budget pressure injection ─────────────────────────────────
-        # After all tool calls in this turn are processed, check if we're
-        # approaching max_iterations. If so, inject a warning into the LAST
-        # tool result's JSON so the LLM sees it naturally when reading results.
-        budget_warning = self._get_budget_warning(api_call_count)
-        if budget_warning and messages and messages[-1].get("role") == "tool":
-            last_content = messages[-1]["content"]
-            try:
-                parsed = json.loads(last_content)
-                if isinstance(parsed, dict):
-                    parsed["_budget_warning"] = budget_warning
-                    messages[-1]["content"] = json.dumps(parsed, ensure_ascii=False)
-                else:
-                    messages[-1]["content"] = last_content + f"\n\n{budget_warning}"
-            except (json.JSONDecodeError, TypeError):
-                messages[-1]["content"] = last_content + f"\n\n{budget_warning}"
-            if not self.quiet_mode:
-                remaining = self.max_iterations - api_call_count
-                tier = "⚠️  WARNING" if remaining <= self.max_iterations * 0.1 else "💡 CAUTION"
-                print(f"{self.log_prefix}{tier}: {remaining} iterations remaining")
 
-    def _get_budget_warning(self, api_call_count: int) -> Optional[str]:
-        """Return a budget pressure string, or None if not yet needed.
-
-        Only fires once the iteration budget is fully exhausted.  No
-        intermediate warnings — those caused models to abandon complex
-        tasks prematurely.
-        """
-        # Never inject warnings during the normal run
-        return None
 
     def _emit_context_pressure(self, compaction_progress: float, compressor) -> None:
         """Notify the user that context is approaching the compaction threshold.
@@ -7675,14 +7598,6 @@ class AIAgent:
         # Initialize conversation (copy to avoid mutating the caller's list)
         messages = list(conversation_history) if conversation_history else []
 
-        # Strip budget pressure warnings from previous turns.  These are
-        # turn-scoped signals injected by _get_budget_warning() into tool
-        # result content.  If left in the replayed history, models (especially
-        # GPT-family) interpret them as still-active instructions and avoid
-        # making tool calls in ALL subsequent turns.
-        if messages:
-            _strip_budget_warnings_from_history(messages)
-        
         # Hydrate todo store from conversation history (gateway creates a fresh
         # AIAgent per message, so the in-memory store is empty -- we need to
         # recover the todo state from the most recent todo tool response in history)