feat(config): make tool output truncation limits configurable

Port from anomalyco/opencode#23770: expose a new `tool_output` config
section so users can tune the hardcoded truncation caps that apply to
terminal output and read_file pagination.

Three knobs under `tool_output`:
- max_bytes (default 50_000) — terminal stdout/stderr cap
- max_lines (default 2000) — read_file pagination cap
- max_line_length (default 2000) — per-line cap in line-numbered view

All three keep their existing hardcoded values as defaults, so behaviour
is unchanged when the section is absent. Power users on big-context
models can raise them; small-context local models can lower them.

Implementation:
- New `tools/tool_output_limits.py` reads the section with defensive
  fallback (missing/invalid values → defaults, never raises).
- `tools/terminal_tool.py` MAX_OUTPUT_CHARS now comes from
  get_max_bytes().
- `tools/file_operations.py` normalize_read_pagination() and
  _add_line_numbers() now pull the limits at call time.
- `hermes_cli/config.py` DEFAULT_CONFIG gains the `tool_output` section
  so `hermes setup` writes defaults into fresh configs.
- Docs page `user-guide/configuration.md` gains a "Tool Output
  Truncation Limits" section with large-context and small-context
  example configs.

Tests (18 new in tests/tools/test_tool_output_limits.py):
- Default resolution with missing / malformed / non-dict config.
- Full and partial user overrides.
- Coercion of bad values (None, negative, wrong type, str int).
- Shortcut accessors delegate correctly.
- DEFAULT_CONFIG exposes the section with the right defaults.
- Integration: normalize_read_pagination clamps to the configured
  max_lines.

tests/tools/test_tool_output_limits.py

@@ -0,0 +1,152 @@
+"""Tests for tools.tool_output_limits.
+
+Covers:
+1. Default values when no config is provided.
+2. Config override picks up user-supplied max_bytes / max_lines /
+   max_line_length.
+3. Malformed values (None, negative, wrong type) fall back to defaults
+   rather than raising.
+4. Integration: the helpers return what the terminal_tool and
+   file_operations call paths will actually consume.
+
+Port-tracking: anomalyco/opencode PR #23770
+(feat(truncate): allow configuring tool output truncation limits).
+"""
+
+from __future__ import annotations
+
+from unittest.mock import patch
+
+import pytest
+
+from tools import tool_output_limits as tol
+
+
+class TestDefaults:
+    def test_defaults_match_previous_hardcoded_values(self):
+        assert tol.DEFAULT_MAX_BYTES == 50_000
+        assert tol.DEFAULT_MAX_LINES == 2000
+        assert tol.DEFAULT_MAX_LINE_LENGTH == 2000
+
+    def test_get_limits_returns_defaults_when_config_missing(self):
+        with patch("hermes_cli.config.load_config", return_value={}):
+            limits = tol.get_tool_output_limits()
+        assert limits == {
+            "max_bytes": tol.DEFAULT_MAX_BYTES,
+            "max_lines": tol.DEFAULT_MAX_LINES,
+            "max_line_length": tol.DEFAULT_MAX_LINE_LENGTH,
+        }
+
+    def test_get_limits_returns_defaults_when_config_not_a_dict(self):
+        # load_config should always return a dict but be defensive anyway.
+        with patch("hermes_cli.config.load_config", return_value="not a dict"):
+            limits = tol.get_tool_output_limits()
+        assert limits["max_bytes"] == tol.DEFAULT_MAX_BYTES
+
+    def test_get_limits_returns_defaults_when_load_config_raises(self):
+        def _boom():
+            raise RuntimeError("boom")
+
+        with patch("hermes_cli.config.load_config", side_effect=_boom):
+            limits = tol.get_tool_output_limits()
+        assert limits["max_lines"] == tol.DEFAULT_MAX_LINES
+
+
+class TestOverrides:
+    def test_user_config_overrides_all_three(self):
+        cfg = {
+            "tool_output": {
+                "max_bytes": 100_000,
+                "max_lines": 5000,
+                "max_line_length": 4096,
+            }
+        }
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            limits = tol.get_tool_output_limits()
+        assert limits == {
+            "max_bytes": 100_000,
+            "max_lines": 5000,
+            "max_line_length": 4096,
+        }
+
+    def test_partial_override_preserves_other_defaults(self):
+        cfg = {"tool_output": {"max_bytes": 200_000}}
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            limits = tol.get_tool_output_limits()
+        assert limits["max_bytes"] == 200_000
+        assert limits["max_lines"] == tol.DEFAULT_MAX_LINES
+        assert limits["max_line_length"] == tol.DEFAULT_MAX_LINE_LENGTH
+
+    def test_section_not_a_dict_falls_back(self):
+        cfg = {"tool_output": "nonsense"}
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            limits = tol.get_tool_output_limits()
+        assert limits["max_bytes"] == tol.DEFAULT_MAX_BYTES
+
+
+class TestCoercion:
+    @pytest.mark.parametrize("bad", [None, "not a number", -1, 0, [], {}])
+    def test_invalid_values_fall_back_to_defaults(self, bad):
+        cfg = {"tool_output": {"max_bytes": bad, "max_lines": bad, "max_line_length": bad}}
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            limits = tol.get_tool_output_limits()
+        assert limits["max_bytes"] == tol.DEFAULT_MAX_BYTES
+        assert limits["max_lines"] == tol.DEFAULT_MAX_LINES
+        assert limits["max_line_length"] == tol.DEFAULT_MAX_LINE_LENGTH
+
+    def test_string_integer_is_coerced(self):
+        cfg = {"tool_output": {"max_bytes": "75000"}}
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            limits = tol.get_tool_output_limits()
+        assert limits["max_bytes"] == 75_000
+
+
+class TestShortcuts:
+    def test_individual_accessors_delegate_to_get_tool_output_limits(self):
+        cfg = {
+            "tool_output": {
+                "max_bytes": 111,
+                "max_lines": 222,
+                "max_line_length": 333,
+            }
+        }
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            assert tol.get_max_bytes() == 111
+            assert tol.get_max_lines() == 222
+            assert tol.get_max_line_length() == 333
+
+
+class TestDefaultConfigHasSection:
+    """The DEFAULT_CONFIG in hermes_cli.config must expose tool_output so
+    that ``hermes setup`` and default installs stay in sync with the
+    helpers here."""
+
+    def test_default_config_contains_tool_output_section(self):
+        from hermes_cli.config import DEFAULT_CONFIG
+        assert "tool_output" in DEFAULT_CONFIG
+        section = DEFAULT_CONFIG["tool_output"]
+        assert isinstance(section, dict)
+        assert section["max_bytes"] == tol.DEFAULT_MAX_BYTES
+        assert section["max_lines"] == tol.DEFAULT_MAX_LINES
+        assert section["max_line_length"] == tol.DEFAULT_MAX_LINE_LENGTH
+
+
+class TestIntegrationReadPagination:
+    """normalize_read_pagination uses get_max_lines() — verify the plumbing."""
+
+    def test_pagination_limit_clamped_by_config_value(self):
+        from tools.file_operations import normalize_read_pagination
+        cfg = {"tool_output": {"max_lines": 50}}
+        with patch("hermes_cli.config.load_config", return_value=cfg):
+            offset, limit = normalize_read_pagination(offset=1, limit=1000)
+        # limit should have been clamped to 50 (the configured max_lines)
+        assert limit == 50
+        assert offset == 1
+
+    def test_pagination_default_when_config_missing(self):
+        from tools.file_operations import normalize_read_pagination
+        with patch("hermes_cli.config.load_config", return_value={}):
+            offset, limit = normalize_read_pagination(offset=10, limit=100000)
+        # Clamped to default MAX_LINES (2000).
+        assert limit == tol.DEFAULT_MAX_LINES
+        assert offset == 10