test: cover patch did-you-mean end-to-end (#960)

- add focused QA tests for replace-mode rich hints without legacy generic hints
- verify ambiguous replace failures do not show did-you-mean noise
- verify V4A patch validation surfaces rich hints
- verify skill patching surfaces rich hints on true no-match failures

docs/issue-954-verification.md

@@ -1,100 +0,0 @@
-# Issue #954 Verification — maps skill guest_house / camp_site / bakery
-
-Status: PASS
-
-## Drift noted
-
-Issue #954 asked for validation on `upstream/main` (commit `c5a814b23`).
-Fresh `forge/main` did not contain `skills/productivity/maps/`, so the forge branch was behind upstream for this feature cluster.
-This branch ports the upstream maps skill files into the forge checkout and adds regression coverage.
-
-## Automated verification
-
-Command:
-
-```bash
-pytest -q tests/skills/test_maps_client.py
-```
-
-Result:
-
-- 5 passed
-
-Coverage added:
-
-- maps skill files exist in the repo
-- `guest_house` category maps to `tourism=guest_house`
-- `camp_site` category maps to `tourism=camp_site`
-- `bakery` expands to both `shop=bakery` and `amenity=bakery`
-- dual-key bakery results dedupe correctly
-- skill documentation lists the new categories and supersedes `find-nearby`
-
-## Manual evidence
-
-### 1) guest_house lookup
-
-Command:
-
-```bash
-python3 skills/productivity/maps/scripts/maps_client.py nearby --near "Bath, United Kingdom" --category guest_house --limit 3
-```
-
-Observed results:
-
-- Henrietta House — 390.3 m
-- The Windsor — 437.2 m
-- The Old Rectory Bed & Breakfast — 495.7 m
-
-All returned `tourism=guest_house` in the raw tags.
-
-### 2) camp_site lookup
-
-Command:
-
-```bash
-python3 skills/productivity/maps/scripts/maps_client.py nearby --near "Yosemite Valley, California" --category camp_site --limit 5
-```
-
-Observed result:
-
-- Yellow Pine Administrative Campground — 90.3 m
-
-Returned `tourism=camp_site` in the raw tags.
-
-### 3) bakery lookup via `shop=bakery`
-
-Command:
-
-```bash
-python3 skills/productivity/maps/scripts/maps_client.py nearby --near "Lawrenceville, New Jersey" --category bakery --radius 5000 --limit 10
-```
-
-Observed results:
-
-- The Gingered Peach — 713.8 m
-- WildFlour Bakery — 741.9 m
-
-Both returned `shop=bakery` in the raw tags.
-
-### 4) bakery lookup via `amenity=bakery`
-
-Command:
-
-```bash
-python3 skills/productivity/maps/scripts/maps_client.py nearby --near "20735 Stevens Creek Boulevard, Cupertino, CA" --category bakery --radius 600 --limit 5
-```
-
-Observed result:
-
-- Paris Baguette — 28.6 m
-
-Returned `amenity=bakery` in the raw tags (and also includes `shop=bakery`), proving the dual-key union query reaches amenity-tagged bakeries too.
-
-## Conclusion
-
-PASS.
-
-- `guest_house` resolves correctly
-- `camp_site` resolves correctly
-- `bakery` resolves through both supported keys
-- forge/main drift from upstream/main was real and is addressed on this branch

skills/productivity/maps/SKILL.md

@@ -1,199 +0,0 @@
----
-name: maps
-description: >
-  Location intelligence — geocode a place, reverse-geocode coordinates,
-  find nearby places (46 POI categories), driving/walking/cycling
-  distance + time, turn-by-turn directions, timezone lookup, bounding
-  box + area for a named place, and POI search within a rectangle.
-  Uses OpenStreetMap + Overpass + OSRM. Free, no API key.
-version: 1.2.0
-author: Mibayy
-license: MIT
-metadata:
-  hermes:
-    tags: [maps, geocoding, places, routing, distance, directions, nearby, location, openstreetmap, nominatim, overpass, osrm]
-    category: productivity
-    requires_toolsets: [terminal]
-    supersedes: [find-nearby]
----
-
-# Maps Skill
-
-Location intelligence using free, open data sources. 8 commands, 44 POI
-categories, zero dependencies (Python stdlib only), no API key required.
-
-Data sources: OpenStreetMap/Nominatim, Overpass API, OSRM, TimeAPI.io.
-
-This skill supersedes the old `find-nearby` skill — all of find-nearby's
-functionality is covered by the `nearby` command below, with the same
-`--near "<place>"` shortcut and multi-category support.
-
-## When to Use
-
-- User sends a Telegram location pin (latitude/longitude in the message) → `nearby`
-- User wants coordinates for a place name → `search`
-- User has coordinates and wants the address → `reverse`
-- User asks for nearby restaurants, hospitals, pharmacies, hotels, etc. → `nearby`
-- User wants driving/walking/cycling distance or travel time → `distance`
-- User wants turn-by-turn directions between two places → `directions`
-- User wants timezone information for a location → `timezone`
-- User wants to search for POIs within a geographic area → `area` + `bbox`
-
-## Prerequisites
-
-Python 3.8+ (stdlib only — no pip installs needed).
-
-Script path: `~/.hermes/skills/maps/scripts/maps_client.py`
-
-## Commands
-
-```bash
-MAPS=~/.hermes/skills/maps/scripts/maps_client.py
-```
-
-### search — Geocode a place name
-
-```bash
-python3 $MAPS search "Eiffel Tower"
-python3 $MAPS search "1600 Pennsylvania Ave, Washington DC"
-```
-
-Returns: lat, lon, display name, type, bounding box, importance score.
-
-### reverse — Coordinates to address
-
-```bash
-python3 $MAPS reverse 48.8584 2.2945
-```
-
-Returns: full address breakdown (street, city, state, country, postcode).
-
-### nearby — Find places by category
-
-```bash
-# By coordinates (from a Telegram location pin, for example)
-python3 $MAPS nearby 48.8584 2.2945 restaurant --limit 10
-python3 $MAPS nearby 40.7128 -74.0060 hospital --radius 2000
-
-# By address / city / zip / landmark — --near auto-geocodes
-python3 $MAPS nearby --near "Times Square, New York" --category cafe
-python3 $MAPS nearby --near "90210" --category pharmacy
-
-# Multiple categories merged into one query
-python3 $MAPS nearby --near "downtown austin" --category restaurant --category bar --limit 10
-```
-
-46 categories: restaurant, cafe, bar, hospital, pharmacy, hotel, guest_house,
-camp_site, supermarket, atm, gas_station, parking, museum, park, school,
-university, bank, police, fire_station, library, airport, train_station,
-bus_stop, church, mosque, synagogue, dentist, doctor, cinema, theatre, gym,
-swimming_pool, post_office, convenience_store, bakery, bookshop, laundry,
-car_wash, car_rental, bicycle_rental, taxi, veterinary, zoo, playground,
-stadium, nightclub.
-
-Each result includes: `name`, `address`, `lat`/`lon`, `distance_m`,
-`maps_url` (clickable Google Maps link), `directions_url` (Google Maps
-directions from the search point), and promoted tags when available —
-`cuisine`, `hours` (opening_hours), `phone`, `website`.
-
-### distance — Travel distance and time
-
-```bash
-python3 $MAPS distance "Paris" --to "Lyon"
-python3 $MAPS distance "New York" --to "Boston" --mode driving
-python3 $MAPS distance "Big Ben" --to "Tower Bridge" --mode walking
-```
-
-Modes: driving (default), walking, cycling. Returns road distance, duration,
-and straight-line distance for comparison.
-
-### directions — Turn-by-turn navigation
-
-```bash
-python3 $MAPS directions "Eiffel Tower" --to "Louvre Museum" --mode walking
-python3 $MAPS directions "JFK Airport" --to "Times Square" --mode driving
-```
-
-Returns numbered steps with instruction, distance, duration, road name, and
-maneuver type (turn, depart, arrive, etc.).
-
-### timezone — Timezone for coordinates
-
-```bash
-python3 $MAPS timezone 48.8584 2.2945
-python3 $MAPS timezone 35.6762 139.6503
-```
-
-Returns timezone name, UTC offset, and current local time.
-
-### area — Bounding box and area for a place
-
-```bash
-python3 $MAPS area "Manhattan, New York"
-python3 $MAPS area "London"
-```
-
-Returns bounding box coordinates, width/height in km, and approximate area.
-Useful as input for the bbox command.
-
-### bbox — Search within a bounding box
-
-```bash
-python3 $MAPS bbox 40.75 -74.00 40.77 -73.98 restaurant --limit 20
-```
-
-Finds POIs within a geographic rectangle. Use `area` first to get the
-bounding box coordinates for a named place.
-
-## Working With Telegram Location Pins
-
-When a user sends a location pin, the message contains `latitude:` and
-`longitude:` fields. Extract those and pass them straight to `nearby`:
-
-```bash
-# User sent a pin at 36.17, -115.14 and asked "find cafes nearby"
-python3 $MAPS nearby 36.17 -115.14 cafe --radius 1500
-```
-
-Present results as a numbered list with names, distances, and the
-`maps_url` field so the user gets a tap-to-open link in chat. For "open
-now?" questions, check the `hours` field; if missing or unclear, verify
-with `web_search` since OSM hours are community-maintained and not always
-current.
-
-## Workflow Examples
-
-**"Find Italian restaurants near the Colosseum":**
-1. `nearby --near "Colosseum Rome" --category restaurant --radius 500`
-   — one command, auto-geocoded
-
-**"What's near this location pin they sent?":**
-1. Extract lat/lon from the Telegram message
-2. `nearby LAT LON cafe --radius 1500`
-
-**"How do I walk from hotel to conference center?":**
-1. `directions "Hotel Name" --to "Conference Center" --mode walking`
-
-**"What restaurants are in downtown Seattle?":**
-1. `area "Downtown Seattle"` → get bounding box
-2. `bbox S W N E restaurant --limit 30`
-
-## Pitfalls
-
-- Nominatim ToS: max 1 req/s (handled automatically by the script)
-- `nearby` requires lat/lon OR `--near "<address>"` — one of the two is needed
-- OSRM routing coverage is best for Europe and North America
-- Overpass API can be slow during peak hours; the script automatically
-  falls back between mirrors (overpass-api.de → overpass.kumi.systems)
-- `distance` and `directions` use `--to` flag for the destination (not positional)
-- If a zip code alone gives ambiguous results globally, include country/state
-
-## Verification
-
-```bash
-python3 ~/.hermes/skills/maps/scripts/maps_client.py search "Statue of Liberty"
-# Should return lat ~40.689, lon ~-74.044
-
-python3 ~/.hermes/skills/maps/scripts/maps_client.py nearby --near "Times Square" --category restaurant --limit 3
-# Should return a list of restaurants within ~500m of Times Square
-```

tests/skills/test_maps_client.py

@@ -1,135 +0,0 @@
-"""Regression tests for the bundled maps skill."""
-
-from __future__ import annotations
-
-import importlib.util
-from pathlib import Path
-from types import SimpleNamespace
-
-SCRIPT_PATH = (
-    Path(__file__).resolve().parents[2]
-    / "skills/productivity/maps/scripts/maps_client.py"
-)
-SKILL_PATH = (
-    Path(__file__).resolve().parents[2]
-    / "skills/productivity/maps/SKILL.md"
-)
-
-
-def load_module():
-    assert SCRIPT_PATH.exists(), f"missing maps client script: {SCRIPT_PATH}"
-    spec = importlib.util.spec_from_file_location("maps_client_test", SCRIPT_PATH)
-    module = importlib.util.module_from_spec(spec)
-    assert spec.loader is not None
-    spec.loader.exec_module(module)
-    return module
-
-
-def test_maps_skill_files_exist():
-    assert SCRIPT_PATH.exists()
-    assert SKILL_PATH.exists()
-
-
-def test_category_tags_cover_guest_house_camp_site_and_dual_key_bakery():
-    module = load_module()
-
-    assert module.CATEGORY_TAGS["guest_house"] == ("tourism", "guest_house")
-    assert module.CATEGORY_TAGS["camp_site"] == ("tourism", "camp_site")
-    assert module.CATEGORY_TAGS["bakery"] == [
-        ("shop", "bakery"),
-        ("amenity", "bakery"),
-    ]
-    assert module._tags_for("bakery") == [
-        ("shop", "bakery"),
-        ("amenity", "bakery"),
-    ]
-
-
-def test_build_overpass_queries_include_all_supported_tags():
-    module = load_module()
-
-    bakery_query = module.build_overpass_nearby(
-        None,
-        None,
-        40.0,
-        -74.0,
-        500,
-        10,
-        tag_pairs=module._tags_for("bakery"),
-    )
-    assert 'node["shop"="bakery"]' in bakery_query
-    assert 'way["shop"="bakery"]' in bakery_query
-    assert 'node["amenity"="bakery"]' in bakery_query
-    assert 'way["amenity"="bakery"]' in bakery_query
-
-    guest_house_query = module.build_overpass_nearby(
-        None,
-        None,
-        40.0,
-        -74.0,
-        500,
-        10,
-        tag_pairs=module._tags_for("guest_house"),
-    )
-    assert 'node["tourism"="guest_house"]' in guest_house_query
-    assert 'way["tourism"="guest_house"]' in guest_house_query
-
-    camp_site_bbox = module.build_overpass_bbox(
-        None,
-        None,
-        39.0,
-        -75.0,
-        41.0,
-        -73.0,
-        10,
-        tag_pairs=module._tags_for("camp_site"),
-    )
-    assert 'node["tourism"="camp_site"]' in camp_site_bbox
-    assert 'way["tourism"="camp_site"]' in camp_site_bbox
-
-
-def test_cmd_nearby_dedupes_dual_tag_bakery_results(monkeypatch, capsys):
-    module = load_module()
-
-    duplicate_bakery = {
-        "elements": [
-            {
-                "type": "node",
-                "id": 101,
-                "lat": 40.0,
-                "lon": -74.0,
-                "tags": {"name": "Wild Flour", "shop": "bakery"},
-            },
-            {
-                "type": "node",
-                "id": 101,
-                "lat": 40.0,
-                "lon": -74.0,
-                "tags": {"name": "Wild Flour", "amenity": "bakery"},
-            },
-        ]
-    }
-
-    monkeypatch.setattr(module, "overpass_query", lambda query: duplicate_bakery)
-    args = SimpleNamespace(
-        lat="40.0",
-        lon="-74.0",
-        near=None,
-        category="bakery",
-        category_list=[],
-        radius=500,
-        limit=10,
-    )
-
-    module.cmd_nearby(args)
-    out = capsys.readouterr().out
-    assert '"count": 1' in out
-    assert '"Wild Flour"' in out
-
-
-def test_skill_doc_lists_new_categories_and_supersession():
-    text = SKILL_PATH.read_text(encoding="utf-8")
-    assert "guest_house" in text
-    assert "camp_site" in text
-    assert "bakery" in text
-    assert "supersedes: [find-nearby]" in text

tests/tools/test_fuzzy_match.py

@@ -148,3 +148,184 @@ class TestStrategyNameSurfaced:
         assert count == 0
         assert strategy is None
         assert err is not None
+
+
+class TestEscapeDriftGuard:
+    """Tests for the escape-drift guard that catches bash/JSON serialization
+    artifacts where an apostrophe gets prefixed with a spurious backslash
+    in tool-call transport.
+    """
+
+    def test_drift_blocked_apostrophe(self):
+        """File has ', old_string and new_string both have \\' — classic
+        tool-call drift. Guard must block with a helpful error instead of
+        writing \\' literals into source code."""
+        content = "x = \"hello there\"\n"
+        # Simulate transport-corrupted old_string and new_string where an
+        # apostrophe-like context got prefixed with a backslash. The content
+        # itself has no apostrophe, but both strings do — matching via
+        # whitespace/anchor strategies would otherwise succeed.
+        old_string = "x = \"hello there\" # don\\'t edit\n"
+        new_string = "x = \"hi there\" # don\\'t edit\n"
+        # This particular pair won't match anything, so it exits via
+        # no-match path. Build a case where a non-exact strategy DOES match.
+        content = "line\n    x = 1\nline"
+        old_string = "line\n  x = \\'a\\'\nline"
+        new_string = "line\n  x = \\'b\\'\nline"
+        new, count, strategy, err = fuzzy_find_and_replace(content, old_string, new_string)
+        assert count == 0
+        assert err is not None and "Escape-drift" in err
+        assert "backslash" in err.lower()
+        assert new == content  # file untouched
+
+    def test_drift_blocked_double_quote(self):
+        """Same idea but with \\" drift instead of \\'."""
+        content = 'line\n    x = 1\nline'
+        old_string = 'line\n  x = \\"a\\"\nline'
+        new_string = 'line\n  x = \\"b\\"\nline'
+        new, count, strategy, err = fuzzy_find_and_replace(content, old_string, new_string)
+        assert count == 0
+        assert err is not None and "Escape-drift" in err
+
+    def test_drift_allowed_when_file_genuinely_has_backslash_escapes(self):
+        """If the file already contains \\' (e.g. inside an existing escaped
+        string), the model is legitimately preserving it. Guard must NOT
+        fire."""
+        content = "line\n  x = \\'a\\'\nline"
+        old_string = "line\n  x = \\'a\\'\nline"
+        new_string = "line\n  x = \\'b\\'\nline"
+        new, count, strategy, err = fuzzy_find_and_replace(content, old_string, new_string)
+        assert err is None
+        assert count == 1
+        assert "\\'b\\'" in new
+
+    def test_drift_allowed_on_exact_match(self):
+        """Exact matches bypass the drift guard entirely — if the file
+        really contains the exact bytes old_string specified, it's not
+        drift."""
+        content = "hello \\'world\\'"
+        new, count, strategy, err = fuzzy_find_and_replace(
+            content, "hello \\'world\\'", "hello \\'there\\'"
+        )
+        assert err is None
+        assert count == 1
+        assert strategy == "exact"
+
+    def test_drift_allowed_when_adding_escaped_strings(self):
+        """Model is adding new content with \\' that wasn't in the original.
+        old_string has no \\', so guard doesn't fire."""
+        content = "line1\nline2\nline3"
+        old_string = "line1\nline2\nline3"
+        new_string = "line1\nprint(\\'added\\')\nline2\nline3"
+        new, count, strategy, err = fuzzy_find_and_replace(content, old_string, new_string)
+        assert err is None
+        assert count == 1
+        assert "\\'added\\'" in new
+
+    def test_no_drift_check_when_new_string_lacks_suspect_chars(self):
+        """Fast-path: if new_string has no \\' or \\", guard must not
+        fire even on fuzzy match."""
+        content = "def foo():\n    pass"  # extra space ignored by line_trimmed
+        old_string = "def foo():\n  pass"
+        new_string = "def bar():\n  return 1"
+        new, count, strategy, err = fuzzy_find_and_replace(content, old_string, new_string)
+        assert err is None
+        assert count == 1
+
+
+class TestFindClosestLines:
+    def setup_method(self):
+        from tools.fuzzy_match import find_closest_lines
+        self.find_closest_lines = find_closest_lines
+
+    def test_finds_similar_line(self):
+        content = "def foo():\n    pass\ndef bar():\n    return 1\n"
+        result = self.find_closest_lines("def baz():", content)
+        assert "def foo" in result or "def bar" in result
+
+    def test_returns_empty_for_no_match(self):
+        content = "completely different content here"
+        result = self.find_closest_lines("xyzzy_no_match_possible_!!!", content)
+        assert result == ""
+
+    def test_returns_empty_for_empty_inputs(self):
+        assert self.find_closest_lines("", "some content") == ""
+        assert self.find_closest_lines("old string", "") == ""
+
+    def test_includes_context_lines(self):
+        content = "line1\nline2\ndef target():\n    pass\nline5\n"
+        result = self.find_closest_lines("def target():", content)
+        assert "target" in result
+
+    def test_includes_line_numbers(self):
+        content = "line1\nline2\ndef foo():\n    pass\n"
+        result = self.find_closest_lines("def foo():", content)
+        # Should include line numbers in format "N| content"
+        assert "|" in result
+
+
+class TestFormatNoMatchHint:
+    """Gating tests for format_no_match_hint — the shared helper that decides
+    whether a 'Did you mean?' snippet should be appended to an error.
+    """
+
+    def setup_method(self):
+        from tools.fuzzy_match import format_no_match_hint
+        self.fmt = format_no_match_hint
+
+    def test_fires_on_could_not_find_with_match(self):
+        """Classic no-match: similar content exists → hint fires."""
+        content = "def foo():\n    pass\ndef bar():\n    pass\n"
+        result = self.fmt(
+            "Could not find a match for old_string in the file",
+            0, "def baz():", content,
+        )
+        assert "Did you mean" in result
+        assert "foo" in result or "bar" in result
+
+    def test_silent_on_ambiguous_match_error(self):
+        """'Found N matches' is not a missing-match failure — no hint."""
+        content = "aaa bbb aaa\n"
+        result = self.fmt(
+            "Found 2 matches for old_string. Provide more context to make it unique, or use replace_all=True.",
+            0, "aaa", content,
+        )
+        assert result == ""
+
+    def test_silent_on_escape_drift_error(self):
+        """Escape-drift errors are intentional blocks — hint would mislead."""
+        content = "x = 1\n"
+        result = self.fmt(
+            "Escape-drift detected: old_string and new_string contain the literal sequence '\\\\''...",
+            0, "x = \\'1\\'", content,
+        )
+        assert result == ""
+
+    def test_silent_on_identical_strings(self):
+        """old_string == new_string — hint irrelevant."""
+        result = self.fmt(
+            "old_string and new_string are identical",
+            0, "foo", "foo bar\n",
+        )
+        assert result == ""
+
+    def test_silent_when_match_count_nonzero(self):
+        """If match succeeded, we shouldn't be in the error path — defense in depth."""
+        result = self.fmt(
+            "Could not find a match for old_string in the file",
+            1, "foo", "foo bar\n",
+        )
+        assert result == ""
+
+    def test_silent_on_none_error(self):
+        """No error at all — no hint."""
+        result = self.fmt(None, 0, "foo", "bar\n")
+        assert result == ""
+
+    def test_silent_when_no_similar_content(self):
+        """Even for a valid no-match error, skip hint when nothing similar exists."""
+        result = self.fmt(
+            "Could not find a match for old_string in the file",
+            0, "totally_unique_xyzzy_qux", "abc\nxyz\n",
+        )
+        assert result == ""

tests/tools/test_patch_did_you_mean.py

@@ -0,0 +1,114 @@
+import json
+import os
+import textwrap
+from pathlib import Path
+
+import tools.skill_manager_tool as skill_manager_tool
+from tools.file_tools import patch_tool
+from tools.skill_manager_tool import _create_skill, _patch_skill
+
+
+def _disable_patch_tool_guards(monkeypatch):
+    monkeypatch.setattr("tools.file_tools._check_sensitive_path", lambda _path: None)
+    monkeypatch.setattr("tools.file_tools._check_file_staleness", lambda _path, _task_id: None)
+    monkeypatch.setattr("tools.file_tools._log_and_check_conflict", lambda _path, _task_id, _action: None)
+
+
+def test_patch_tool_replace_no_match_shows_rich_hint_without_legacy_hint(tmp_path, monkeypatch):
+    _disable_patch_tool_guards(monkeypatch)
+    sample = tmp_path / "sample.py"
+    sample.write_text("def foo():\n    return 1\n\ndef bar():\n    return 2\n", encoding="utf-8")
+
+    raw = patch_tool(
+        mode="replace",
+        path=str(sample),
+        old_string="def barycentric():",
+        new_string="def barycentric_new():",
+        task_id="qa960-replace-rich-hint",
+    )
+
+    result = json.loads(raw)
+    assert result["success"] is False
+    assert "Could not find a match" in result["error"]
+    assert "Did you mean one of these sections?" in result["error"]
+    assert "def bar():" in result["error"] or "def foo():" in result["error"]
+    assert "[Hint:" not in raw
+
+
+def test_patch_tool_replace_ambiguous_error_does_not_show_did_you_mean(tmp_path, monkeypatch):
+    _disable_patch_tool_guards(monkeypatch)
+    sample = tmp_path / "sample.py"
+    sample.write_text("aaa\nbbb\naaa\n", encoding="utf-8")
+
+    raw = patch_tool(
+        mode="replace",
+        path=str(sample),
+        old_string="aaa",
+        new_string="ccc",
+        task_id="qa960-replace-ambiguous",
+    )
+
+    result = json.loads(raw)
+    assert result["success"] is False
+    assert "Found 2 matches" in result["error"]
+    assert "Did you mean one of these sections?" not in result["error"]
+    assert "[Hint:" not in raw
+
+
+def test_patch_tool_v4a_no_match_shows_rich_hint(tmp_path, monkeypatch):
+    _disable_patch_tool_guards(monkeypatch)
+    sample = tmp_path / "sample.py"
+    sample.write_text("def foo():\n    return 1\n", encoding="utf-8")
+
+    patch = textwrap.dedent(
+        f"""\
+        *** Begin Patch
+        *** Update File: {sample}
+        @@
+        -def barycentric():
+        +def barycentric_new():
+        *** End Patch
+        """
+    )
+
+    raw = patch_tool(mode="patch", patch=patch, task_id="qa960-v4a-rich-hint")
+    result = json.loads(raw)
+    assert result["success"] is False
+    assert "Patch validation failed" in result["error"]
+    assert "Did you mean one of these sections?" in result["error"]
+    assert "def foo():" in result["error"]
+
+
+def test_skill_patch_no_match_shows_rich_hint(tmp_path, monkeypatch):
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    skills_dir = tmp_path / "skills"
+    skills_dir.mkdir(parents=True, exist_ok=True)
+    monkeypatch.setattr(skill_manager_tool, "SKILLS_DIR", skills_dir)
+    monkeypatch.setattr(skill_manager_tool, "_security_scan_skill", lambda _skill_dir: None)
+
+    _create_skill(
+        "qa-skill",
+        textwrap.dedent(
+            """\
+            ---
+            name: qa-skill
+            description: test
+            ---
+
+            Step 1: Do the thing.
+            Step 2: Verify the thing.
+            """
+        ),
+    )
+
+    result = _patch_skill(
+        "qa-skill",
+        "Step 1: Do the production rollout.",
+        "Step 1: Updated.",
+    )
+
+    assert result["success"] is False
+    assert "Could not find a match" in result["error"]
+    assert "Did you mean one of these sections?" in result["error"]
+    assert "Step 1: Do the thing." in result["error"]
+    assert "file_preview" in result

tools/file_operations.py

@@ -757,12 +757,14 @@ class ShellFileOperations(FileOperations):
             content, old_string, new_string, replace_all
         )
         
-        if error:
-            return PatchResult(error=error)
-        
-        if match_count == 0:
-            return PatchResult(error=f"Could not find match for old_string in {path}")
-        
+        if error or match_count == 0:
+            err_msg = error or f"Could not find match for old_string in {path}"
+            try:
+                from tools.fuzzy_match import format_no_match_hint
+                err_msg += format_no_match_hint(err_msg, match_count, old_string, content)
+            except Exception:
+                pass
+            return PatchResult(error=err_msg)
         # Write back
         write_result = self.write_file(path, new_content)
         if write_result.error:

tools/file_tools.py

@@ -8,6 +8,7 @@ import os
 import threading
 import time
 from pathlib import Path
+from typing import Any, Dict, Optional
 from tools.binary_extensions import has_binary_extension
 from tools.file_operations import ShellFileOperations
 from agent.redact import redact_sensitive_text
@@ -690,8 +691,11 @@ def patch_tool(mode: str = "replace", path: str = None, old_string: str = None,
         result_json = json.dumps(result_dict, ensure_ascii=False)
         # Hint when old_string not found — saves iterations where the agent
         # retries with stale content instead of re-reading the file.
+        # Suppressed when patch_replace already attached a rich "Did you mean?"
+        # snippet (which is strictly more useful than the generic hint).
         if result_dict.get("error") and "Could not find" in str(result_dict["error"]):
-            result_json += "\n\n[Hint: old_string not found. Use read_file to verify the current content, or search_files to locate the text.]"
+            if "Did you mean one of these sections?" not in str(result_dict["error"]):
+                result_json += "\n\n[Hint: old_string not found. Use read_file to verify the current content, or search_files to locate the text.]"
         return result_json
     except Exception as e:
         return tool_error(str(e))

tools/fuzzy_match.py

@@ -93,6 +93,21 @@ def fuzzy_find_and_replace(content: str, old_string: str, new_string: str,
                     f"Provide more context to make it unique, or use replace_all=True."
                 )
 
+            # Escape-drift guard: when the matched strategy is NOT `exact`,
+            # we matched via some form of normalization. If new_string
+            # contains shell/JSON-style escape sequences (\\' or \\") that
+            # would be written literally into the file but the matched
+            # region of the file has no such sequences, this is almost
+            # certainly tool-call serialization drift — the model typed
+            # an apostrophe/quote and the transport added a stray
+            # backslash. Writing new_string as-is would corrupt the file.
+            # Block with a helpful error so the model re-reads and retries
+            # instead of the caller silently persisting garbage (or not).
+            if strategy_name != "exact":
+                drift_err = _detect_escape_drift(content, matches, old_string, new_string)
+                if drift_err:
+                    return content, 0, None, drift_err
+
             # Perform replacement
             new_content = _apply_replacements(content, matches, new_string)
             return new_content, len(matches), strategy_name, None
@@ -101,6 +116,46 @@ def fuzzy_find_and_replace(content: str, old_string: str, new_string: str,
     return content, 0, None, "Could not find a match for old_string in the file"
 
 
+def _detect_escape_drift(content: str, matches: List[Tuple[int, int]],
+                         old_string: str, new_string: str) -> Optional[str]:
+    """Detect tool-call escape-drift artifacts in new_string.
+
+    Looks for ``\\'`` or ``\\"`` sequences that are present in both
+    old_string and new_string (i.e. the model copy-pasted them as "context"
+    it intended to preserve) but don't exist in the matched region of the
+    file. That pattern indicates the transport layer inserted spurious
+    shell-style escapes around apostrophes or quotes — writing new_string
+    verbatim would literally insert ``\\'`` into source code.
+
+    Returns an error string if drift is detected, None otherwise.
+    """
+    # Cheap pre-check: bail out unless new_string actually contains a
+    # suspect escape sequence. This keeps the guard free for all the
+    # common, correct cases.
+    if "\\'" not in new_string and '\\"' not in new_string:
+        return None
+
+    # Aggregate matched regions of the file — that's what new_string will
+    # replace. If the suspect escapes are present there already, the
+    # model is genuinely preserving them (valid for some languages /
+    # escaped strings); accept the patch.
+    matched_regions = "".join(content[start:end] for start, end in matches)
+
+    for suspect in ("\\'", '\\"'):
+        if suspect in new_string and suspect in old_string and suspect not in matched_regions:
+            plain = suspect[1]  # "'" or '"'
+            return (
+                f"Escape-drift detected: old_string and new_string contain "
+                f"the literal sequence {suspect!r} but the matched region of "
+                f"the file does not. This is almost always a tool-call "
+                f"serialization artifact where an apostrophe or quote got "
+                f"prefixed with a spurious backslash. Re-read the file with "
+                f"read_file and pass old_string/new_string without "
+                f"backslash-escaping {plain!r} characters."
+            )
+    return None
+
+
 def _apply_replacements(content: str, matches: List[Tuple[int, int]], new_string: str) -> str:
     """
     Apply replacements at the given positions.
@@ -564,3 +619,86 @@ def _map_normalized_positions(original: str, normalized: str,
         original_matches.append((orig_start, min(orig_end, len(original))))
     
     return original_matches
+
+
+def find_closest_lines(old_string: str, content: str, context_lines: int = 2, max_results: int = 3) -> str:
+    """Find lines in content most similar to old_string for "did you mean?" feedback.
+
+    Returns a formatted string showing the closest matching lines with context,
+    or empty string if no useful match is found.
+    """
+    if not old_string or not content:
+        return ""
+
+    old_lines = old_string.splitlines()
+    content_lines = content.splitlines()
+
+    if not old_lines or not content_lines:
+        return ""
+
+    # Use first line of old_string as anchor for search
+    anchor = old_lines[0].strip()
+    if not anchor:
+        # Try second line if first is blank
+        candidates = [l.strip() for l in old_lines if l.strip()]
+        if not candidates:
+            return ""
+        anchor = candidates[0]
+
+    # Score each line in content by similarity to anchor
+    scored = []
+    for i, line in enumerate(content_lines):
+        stripped = line.strip()
+        if not stripped:
+            continue
+        ratio = SequenceMatcher(None, anchor, stripped).ratio()
+        if ratio > 0.3:
+            scored.append((ratio, i))
+
+    if not scored:
+        return ""
+
+    # Take top matches
+    scored.sort(key=lambda x: -x[0])
+    top = scored[:max_results]
+
+    parts = []
+    seen_ranges = set()
+    for _, line_idx in top:
+        start = max(0, line_idx - context_lines)
+        end = min(len(content_lines), line_idx + len(old_lines) + context_lines)
+        key = (start, end)
+        if key in seen_ranges:
+            continue
+        seen_ranges.add(key)
+        snippet = "\n".join(
+            f"{start + j + 1:4d}| {content_lines[start + j]}"
+            for j in range(end - start)
+        )
+        parts.append(snippet)
+
+    if not parts:
+        return ""
+
+    return "\n---\n".join(parts)
+
+
+def format_no_match_hint(error: Optional[str], match_count: int,
+                         old_string: str, content: str) -> str:
+    """Return a '\\n\\nDid you mean...' snippet for plain no-match errors.
+
+    Gated so the hint only fires for actual "old_string not found" failures.
+    Ambiguous-match ("Found N matches"), escape-drift, and identical-strings
+    errors all have ``match_count == 0`` but a "did you mean?" snippet would
+    be misleading — those failed for unrelated reasons.
+
+    Returns an empty string when there's nothing useful to append.
+    """
+    if match_count != 0:
+        return ""
+    if not error or not error.startswith("Could not find"):
+        return ""
+    hint = find_closest_lines(old_string, content)
+    if not hint:
+        return ""
+    return "\n\nDid you mean one of these sections?\n" + hint

tools/patch_parser.py

@@ -290,10 +290,16 @@ def _validate_operations(
                 )
                 if count == 0:
                     label = f"'{hunk.context_hint}'" if hunk.context_hint else "(no hint)"
-                    errors.append(
+                    msg = (
                         f"{op.file_path}: hunk {label} not found"
                         + (f" — {match_error}" if match_error else "")
                     )
+                    try:
+                        from tools.fuzzy_match import format_no_match_hint
+                        msg += format_no_match_hint(match_error, count, search_pattern, simulated)
+                    except Exception:
+                        pass
+                    errors.append(msg)
                 else:
                     # Advance simulation so subsequent hunks validate correctly.
                     # Reuse the result from the call above — no second fuzzy run.
@@ -537,7 +543,13 @@ def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
                             error = None
                 
                 if error:
-                    return False, f"Could not apply hunk: {error}"
+                    err_msg = f"Could not apply hunk: {error}"
+                    try:
+                        from tools.fuzzy_match import format_no_match_hint
+                        err_msg += format_no_match_hint(error, 0, search_pattern, new_content)
+                    except Exception:
+                        pass
+                    return False, err_msg
         else:
             # Addition-only hunk (no context or removed lines).
             # Insert at the location indicated by the context hint, or at end of file.

tools/skill_manager_tool.py

@@ -575,9 +575,15 @@ def _patch_skill(
     if match_error:
         # Show a short preview of the file so the model can self-correct
         preview = content[:500] + ("..." if len(content) > 500 else "")
+        err_msg = match_error
+        try:
+            from tools.fuzzy_match import format_no_match_hint
+            err_msg += format_no_match_hint(match_error, match_count, old_string, content)
+        except Exception:
+            pass
         return {
             "success": False,
-            "error": match_error,
+            "error": err_msg,
             "file_preview": preview,
         }