feat(skills): size limits for agent writes + fuzzy matching for patch (#4414)

* feat(skills): add content size limits for agent-created skills

Agent writes via skill_manage (create/edit/patch/write_file) are now
constrained to prevent unbounded growth:

- SKILL.md and supporting files: 100,000 character limit
- Supporting files: additional 1 MiB byte limit
- Patches on oversized hand-placed skills that reduce the size are
  allowed (shrink path), but patches that grow beyond the limit are
  rejected

Hand-placed skills and hub-installed skills have NO hard limit —
they load and function normally regardless of size. Hub installs
get a warning in the log if SKILL.md exceeds 100k chars.

This mirrors the memory system's char_limit pattern. Without this,
the agent auto-grows skills indefinitely through iterative patches
(hermes-agent-dev reached 197k chars / 72k tokens — 40x larger than
the largest skill in the entire skills.sh ecosystem).

Constants: MAX_SKILL_CONTENT_CHARS (100k), MAX_SKILL_FILE_BYTES (1MiB)
Tests: 14 new tests covering all write paths and edge cases

* feat(skills): add fuzzy matching to skill patch

_patch_skill now uses the same 8-strategy fuzzy matching engine
(tools/fuzzy_match.py) as the file patch tool. Handles whitespace
normalization, indentation differences, escape sequences, and
block-anchor matching. Eliminates exact-match failures when agents
patch skills with minor formatting mismatches.

tests/tools/test_skill_improvements.py

@@ -0,0 +1,174 @@
+"""Tests for skill fuzzy patching via tools.fuzzy_match."""
+
+import json
+import os
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from tools.skill_manager_tool import (
+    _create_skill,
+    _patch_skill,
+    _write_file,
+    skill_manage,
+)
+
+
+SKILL_CONTENT = """\
+---
+name: test-skill
+description: A test skill for unit testing.
+---
+
+# Test Skill
+
+Step 1: Do the thing.
+Step 2: Do another thing.
+Step 3: Final step.
+"""
+
+
+# ---------------------------------------------------------------------------
+# Fuzzy patching
+# ---------------------------------------------------------------------------
+
+
+class TestFuzzyPatchSkill:
+    @pytest.fixture(autouse=True)
+    def setup_skills(self, tmp_path, monkeypatch):
+        skills_dir = tmp_path / "skills"
+        skills_dir.mkdir()
+        monkeypatch.setattr("tools.skill_manager_tool.SKILLS_DIR", skills_dir)
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+        self.skills_dir = skills_dir
+
+    def test_exact_match_still_works(self):
+        _create_skill("test-skill", SKILL_CONTENT)
+        result = _patch_skill("test-skill", "Step 1: Do the thing.", "Step 1: Done!")
+        assert result["success"] is True
+        content = (self.skills_dir / "test-skill" / "SKILL.md").read_text()
+        assert "Step 1: Done!" in content
+
+    def test_whitespace_trimmed_match(self):
+        """Patch with extra leading whitespace should still find the target."""
+        skill = """\
+---
+name: ws-skill
+description: Whitespace test
+---
+
+# Commands
+
+    def hello():
+        print("hi")
+"""
+        _create_skill("ws-skill", skill)
+        # Agent sends patch with no leading whitespace (common LLM behaviour)
+        result = _patch_skill("ws-skill", "def hello():\n    print(\"hi\")", "def hello():\n    print(\"hello world\")")
+        assert result["success"] is True
+        content = (self.skills_dir / "ws-skill" / "SKILL.md").read_text()
+        assert 'print("hello world")' in content
+
+    def test_indentation_flexible_match(self):
+        """Patch where only indentation differs should succeed."""
+        skill = """\
+---
+name: indent-skill
+description: Indentation test
+---
+
+# Steps
+
+  1. First step
+  2. Second step
+  3. Third step
+"""
+        _create_skill("indent-skill", skill)
+        # Agent sends with different indentation
+        result = _patch_skill(
+            "indent-skill",
+            "1. First step\n2. Second step",
+            "1. Updated first\n2. Updated second"
+        )
+        assert result["success"] is True
+        content = (self.skills_dir / "indent-skill" / "SKILL.md").read_text()
+        assert "Updated first" in content
+
+    def test_multiple_matches_blocked_without_replace_all(self):
+        """Multiple fuzzy matches should return an error without replace_all."""
+        skill = """\
+---
+name: dup-skill
+description: Duplicate test
+---
+
+# Steps
+
+word word word
+"""
+        _create_skill("dup-skill", skill)
+        result = _patch_skill("dup-skill", "word", "replaced")
+        assert result["success"] is False
+        assert "match" in result["error"].lower()
+
+    def test_replace_all_with_fuzzy(self):
+        skill = """\
+---
+name: dup-skill
+description: Duplicate test
+---
+
+# Steps
+
+word word word
+"""
+        _create_skill("dup-skill", skill)
+        result = _patch_skill("dup-skill", "word", "replaced", replace_all=True)
+        assert result["success"] is True
+        content = (self.skills_dir / "dup-skill" / "SKILL.md").read_text()
+        assert "word" not in content
+        assert "replaced" in content
+
+    def test_no_match_returns_preview(self):
+        _create_skill("test-skill", SKILL_CONTENT)
+        result = _patch_skill("test-skill", "this does not exist anywhere", "replacement")
+        assert result["success"] is False
+        assert "file_preview" in result
+
+    def test_fuzzy_patch_on_supporting_file(self):
+        """Fuzzy matching should also work on supporting files."""
+        _create_skill("test-skill", SKILL_CONTENT)
+        ref_content = "    function hello() {\n        console.log('hi');\n    }"
+        _write_file("test-skill", "references/code.js", ref_content)
+        # Patch with stripped indentation
+        result = _patch_skill(
+            "test-skill",
+            "function hello() {\nconsole.log('hi');\n}",
+            "function hello() {\nconsole.log('hello world');\n}",
+            file_path="references/code.js"
+        )
+        assert result["success"] is True
+        content = (self.skills_dir / "test-skill" / "references" / "code.js").read_text()
+        assert "hello world" in content
+
+    def test_patch_preserves_frontmatter_validation(self):
+        """Fuzzy matching should still run frontmatter validation on SKILL.md."""
+        _create_skill("test-skill", SKILL_CONTENT)
+        # Try to destroy the frontmatter via patch
+        result = _patch_skill("test-skill", "---\nname: test-skill", "BROKEN")
+        assert result["success"] is False
+        assert "structure" in result["error"].lower() or "frontmatter" in result["error"].lower()
+
+    def test_skill_manage_patch_uses_fuzzy(self):
+        """The dispatcher should route to the fuzzy-matching patch."""
+        _create_skill("test-skill", SKILL_CONTENT)
+        raw = skill_manage(
+            action="patch",
+            name="test-skill",
+            old_string="  Step 1: Do the thing.",  # extra leading space
+            new_string="Step 1: Updated.",
+        )
+        result = json.loads(raw)
+        # Should succeed via line-trimmed or indentation-flexible matching
+        assert result["success"] is True