core/agent: add model-friendly hint to truncated tool results

CLAUDE.md

@@ -76,7 +76,7 @@ Async SQLAlchemy + aiosqlite. `MemoryStore`: schema init (+ lightweight SQLite `
 - **`/compact`**: soft-compact tool dumps → model summary (no tools) via the same kind dispatch → **new** session seeded with summary message. Soft-compact keeps the last **12** tool results full-size by default (`DEFAULT_RECENT_TOOL_RESULTS`); older tool payloads shrink first.
 - Events: text_delta, **reasoning_delta**, assistant_message, tool_call/result, max_rounds, **error** (`retryable`/`source`), **cancelled** (`reason`), **usage** (`TokenUsage`).
 - Usage: API `usage` from completions (stream with `include_usage`); **char≈token fallback** (~4 chars/token) when omitted; **context size** = last request ``prompt_tokens`` (API preferred); `last_turn_usage` / `session_usage` are **billed sums** (tool rounds re-send history); CLI end-of-turn + `/status`.
-- Config ``[agent]``: `system_prompt` (persona; default `DEFAULT_SYSTEM_PROMPT`; `""` omits persona), `tool_directives` (tool playbook; default `DEFAULT_TOOL_DIRECTIVES`; `""` omits playbook; both empty → no system), `max_tool_result_chars`, `parallel_tools`, `confirm_destructive`, `path_denylist`, `max_context_tokens` (default 200k est. tokens).
+- Config ``[agent]``: `system_prompt` (persona; default `DEFAULT_SYSTEM_PROMPT`; `""` omits persona), `tool_directives` (tool playbook; default `DEFAULT_TOOL_DIRECTIVES`; `""` omits playbook; both empty → no system), `max_tool_result_chars`, `parallel_tools`, `confirm_destructive`, `path_denylist`, `max_context_tokens` (default 200k est. tokens). Truncated tool results carry a model hint (`[Truncated (N chars max; M omitted). You may ask for user to increase the limit via configuration file.]`) so the model can ask the user to raise `max_tool_result_chars`; request-time compact shrinks (`hint=False`) keep the terse `...[truncated N characters]` marker.
 
 ### Tools (`tools/`)
 

src/plyngent/agent/budget.py

@@ -28,13 +28,30 @@ DEFAULT_RECENT_TOOL_RESULTS = 12
 DEFAULT_CONTEXT_MAX_CHARS = DEFAULT_CONTEXT_MAX_TOKENS * 4
 
 
-def truncate_tool_result(text: str, max_chars: int = DEFAULT_TOOL_RESULT_MAX_CHARS) -> str:
-    """Cap tool output so huge dumps do not flood model context."""
+def truncate_tool_result(
+    text: str,
+    max_chars: int = DEFAULT_TOOL_RESULT_MAX_CHARS,
+    *,
+    hint: bool = True,
+) -> str:
+    """Cap tool output so huge dumps do not flood model context.
+
+    With ``hint=True`` the suffix tells the model the result was cut and that
+    it may ask the user to raise the config limit (``max_tool_result_chars``).
+    ``hint=False`` keeps the terse marker for internal shrinks whose cap is not
+    a user-facing config knob (e.g. request-time compacting).
+    """
     if max_chars < 1:
         return text
     if len(text) <= max_chars:
         return text
     omitted = len(text) - max_chars
+    if hint:
+        return (
+            f"{text[:max_chars]}\n"
+            f"...[Truncated ({max_chars} chars max.; {omitted} chars omitted). "
+            f"You may ask for user to increase the limit via configuration file.]"
+        )
     return f"{text[:max_chars]}\n...[truncated {omitted} characters]"
 
 
@@ -103,7 +120,7 @@ def _shrink_tool(message: ToolChatMessage, max_chars: int) -> ToolChatMessage:
         return message
     return msgspec.structs.replace(
         message,
-        content=truncate_tool_result(message.content, max_chars),
+        content=truncate_tool_result(message.content, max_chars, hint=False),
     )
 
 

tests/test_agent/test_budget.py

@@ -12,8 +12,18 @@ def test_truncate_tool_result_long() -> None:
     text = "a" * 50
     out = truncate_tool_result(text, 20)
     assert out.startswith("a" * 20)
-    assert "truncated" in out
+    assert "Truncated" in out
+    assert "20" in out
     assert "30" in out
+    assert "configuration file" in out
+
+
+def test_truncate_tool_result_no_hint() -> None:
+    text = "a" * 50
+    out = truncate_tool_result(text, 20, hint=False)
+    assert out.startswith("a" * 20)
+    assert "truncated" in out
+    assert "configuration file" not in out
 
 
 def test_estimate_message_chars() -> None:

tests/test_agent/test_compact.py

@@ -41,8 +41,18 @@ def test_truncate_tool_result_long() -> None:
     text = "a" * 50
     out = truncate_tool_result(text, 20)
     assert out.startswith("a" * 20)
-    assert "truncated" in out
+    assert "Truncated" in out
+    assert "20" in out
     assert "30" in out
+    assert "configuration file" in out
+
+
+def test_truncate_tool_result_no_hint() -> None:
+    text = "a" * 50
+    out = truncate_tool_result(text, 20, hint=False)
+    assert out.startswith("a" * 20)
+    assert "truncated" in out
+    assert "configuration file" not in out
 
 
 def test_compact_shrinks_old_tool_results() -> None:

tests/test_agent/test_loop.py

@@ -848,7 +848,7 @@ async def test_tool_result_char_budget() -> None:
     tool_msgs = [m for m in messages if isinstance(m, ToolChatMessage)]
     assert len(tool_msgs) == 1
     assert tool_msgs[0].content.startswith("x" * 20)
-    assert "truncated" in tool_msgs[0].content
+    assert "Truncated" in tool_msgs[0].content
 
 
 async def test_empty_completion_raises() -> None: