fix(agent): tools-available note on dropped-tools continuation; keep legacy stub recognized (#74990)

The dropped-tools partial-stream continuation now also states the cut was a
transport interruption and tools remain available. The pre-rewording
network-stub text stays in the compressor's synthetic-turn set so
crash-persisted nudges from older sessions are not mistaken for user turns.

agent/context_compressor.py

@@ -4192,13 +4192,15 @@ Write only the summary body. Do not include any preamble or prefix."""
         from agent.conversation_loop import (
             _CODEX_ACK_CONTINUATION_NUDGE, _CODEX_INCOMPLETE_NUDGE, _DEGENERATE_FINAL_NUDGE,
             _DROPPED_TOOLCALL_NUDGE_CONTENT, _EMPTY_TOOL_RESPONSE_NUDGE, _LENGTH_CONTINUATION_DROPPED_TOOLS_PREFIX,
-            _LENGTH_CONTINUATION_NETWORK_STUB, _LENGTH_CONTINUATION_OUTPUT_LIMIT,
+            _LEGACY_LENGTH_CONTINUATION_NETWORK_STUB, _LENGTH_CONTINUATION_NETWORK_STUB,
+            _LENGTH_CONTINUATION_OUTPUT_LIMIT,
         )
         return text in {
             COMPRESSION_CONTINUATION_USER_CONTENT, _LEGACY_COMPRESSION_CONTINUATION_USER_CONTENT,
             MAX_ITERATIONS_SUMMARY_REQUEST, _CODEX_INCOMPLETE_NUDGE, _CODEX_ACK_CONTINUATION_NUDGE,
             _DEGENERATE_FINAL_NUDGE, _DROPPED_TOOLCALL_NUDGE_CONTENT, _EMPTY_TOOL_RESPONSE_NUDGE,
-            _LENGTH_CONTINUATION_NETWORK_STUB, _LENGTH_CONTINUATION_OUTPUT_LIMIT,
+            _LENGTH_CONTINUATION_NETWORK_STUB, _LEGACY_LENGTH_CONTINUATION_NETWORK_STUB,
+            _LENGTH_CONTINUATION_OUTPUT_LIMIT,
         } or text.startswith((
             _BACKGROUND_PROCESS_NOTIFICATION_PREFIX, TODO_INJECTION_HEADER + "\n", _LENGTH_CONTINUATION_DROPPED_TOOLS_PREFIX,
         ))

agent/conversation_loop.py

@@ -892,6 +892,11 @@ _LENGTH_CONTINUATION_OUTPUT_LIMIT = (
     "[System: Your previous response was truncated by the output length limit. Continue exactly "
     "where you left off. Do not restart or repeat prior text. Finish the answer directly.]"
 )
+# Pre-#74990 wording; kept so crash-persisted nudges from older sessions are still recognized.
+_LEGACY_LENGTH_CONTINUATION_NETWORK_STUB = (
+    "[System: The previous response was cut off by a network error mid-stream. Continue exactly "
+    "where you left off. Do not restart or repeat prior text. Finish the answer directly.]"
+)
 # The dropped-tools variant interpolates tool names; matched by prefix.
 _LENGTH_CONTINUATION_DROPPED_TOOLS_PREFIX = "[System: Your previous tool call "
 
@@ -904,7 +909,8 @@ def _get_continuation_prompt(is_partial_stub: bool, dropped_tools: Optional[List
             "the stream timed out before it could be delivered. Do NOT retry the same tool call "
             "with the same large content. Instead, break the content into multiple smaller tool "
             "calls (e.g. use multiple patch calls or write smaller files). Each tool call's "
-            "arguments must be under ~8K tokens to avoid stream timeouts.]"
+            "arguments must be under ~8K tokens to avoid stream timeouts. The cut was a transport "
+            "interruption, not a capability change — your tools remain fully available.]"
         )
     return _LENGTH_CONTINUATION_NETWORK_STUB if is_partial_stub else _LENGTH_CONTINUATION_OUTPUT_LIMIT
 

tests/agent/test_partial_stream_continuation_prompt.py

@@ -0,0 +1,18 @@
+"""After a mid-stream transport cut the continuation must keep tools on the table (#74990)."""
+import pytest
+
+from agent import conversation_loop as cl
+from agent.context_compressor import ContextCompressor
+
+
+@pytest.mark.parametrize("dropped", [None, ["write_file"]])
+def test_partial_stub_continuation_says_tools_remain_available(dropped):
+    prompt = cl._get_continuation_prompt(True, dropped).lower()
+    assert "tools" in prompt and "available" in prompt
+    assert "finish the answer directly" not in prompt
+
+
+@pytest.mark.parametrize("dropped", [None, ["write_file"]])
+def test_new_and_legacy_stub_nudges_are_recognized_as_synthetic(dropped):
+    for text in (cl._get_continuation_prompt(True, dropped), cl._LEGACY_LENGTH_CONTINUATION_NETWORK_STUB):
+        assert ContextCompressor._is_synthetic_compression_user_turn({"role": "user", "content": text})