fix(skills): surface list-modified hint on both update paths + disambiguate diff

Salvage follow-up to the cherry-picked feat/test commits:

- W1: the unpack/install update path in main.py printed the
  '~ N user-modified (kept)' notice without the new
  'hermes skills list-modified' hint that the git-pull path got.
  Mirror the hint to both sites so the count is actionable
  regardless of which update path runs.
- W2: 'hermes skills diff <name>' (bundled-vs-stock) now shares the
  verb with the gateway write-approval 'diff <id>'. The gateway
  handler's docstring + truncation message pointed users to
  '/skills diff <id>' on the CLI, which now resolves a bundled skill
  by that name instead. Point at the pending JSON file and note the
  two diff commands are distinct.
- Add an invariant test asserting every 'user-modified (kept)' notice
  in main.py carries the discovery hint (guards sibling drift).

gateway/slash_commands.py

@@ -2214,7 +2214,9 @@ class GatewaySlashCommandsMixin:
         stranded).
 
         ``diff`` output is truncated for chat bubbles — the full diff lives in
-        the CLI (``/skills diff <id>``) and the pending JSON file.
+        the pending JSON file under ``~/.hermes/pending/skills/``. (Note this is
+        the write-approval ``diff <id>``; the CLI also has an unrelated
+        ``hermes skills diff <name>`` that diffs a bundled skill vs stock.)
         """
         from gateway.run import _hermes_home
         from hermes_cli.write_approval_commands import handle_pending_subcommand
@@ -2252,12 +2254,14 @@ class GatewaySlashCommandsMixin:
                     "(Search/install are CLI-only.)")
 
         # Chat bubbles can't hold a full skill diff — truncate and point at
-        # the real review surfaces.
+        # the real review surface. (Note: `hermes skills diff <name>` is a
+        # *different* command — it diffs a bundled skill against its stock
+        # version — so we point at the pending JSON file, not that command.)
         if args and args[0].lower() == "diff" and len(out) > 3000:
             pending_id = args[1] if len(args) > 1 else "<id>"
             out = (out[:3000]
-                   + f"\n… (truncated — full diff: `/skills diff {pending_id}` "
-                     f"on the CLI, or ~/.hermes/pending/skills/{pending_id}.json)")
+                   + "\n… (truncated — full diff in "
+                     f"~/.hermes/pending/skills/{pending_id}.json)")
         return out
 
     async def _handle_fast_command(self, event: MessageEvent) -> str:

hermes_cli/main.py

@@ -6073,6 +6073,10 @@ def _update_via_zip(args):
             )
         if result.get("user_modified"):
             print(f"  ~ {len(result['user_modified'])} user-modified (kept)")
+            print(
+                "    → see them: hermes skills list-modified  "
+                "(diff/reset to resume updates)"
+            )
         if result.get("cleaned"):
             print(f"  − {len(result['cleaned'])} removed from manifest")
         if not result["copied"] and not result.get("updated"):

tests/hermes_cli/test_update_modified_notice.py

@@ -0,0 +1,50 @@
+"""Guard: every `hermes update` path that reports user-modified skills must
+also tell the user how to find them.
+
+`hermes update` keeps (does not overwrite) bundled skills the user edited and
+prints a ``~ N user-modified (kept)`` count. There are two independent update
+code paths in ``hermes_cli/main.py`` that print this notice (the git-pull path
+in ``_cmd_update_impl`` and the unpack/install path). Both must point the user
+at ``hermes skills list-modified`` so the count is actionable — otherwise,
+depending on which path a user hits, they may never learn the discovery command
+exists.
+
+This is an *invariant* test (the two sibling notices must agree), not a literal
+snapshot: it asserts the relationship "count line ⇒ discovery hint", so it
+keeps holding if the wording is reworded, as long as both sites stay in sync.
+"""
+
+import re
+from pathlib import Path
+
+import hermes_cli.main as main_mod
+
+
+_COUNT_RE = re.compile(r"user-modified \(kept\)")
+_HINT_RE = re.compile(r"hermes skills list-modified")
+
+
+def _source_lines() -> list[str]:
+    return Path(main_mod.__file__).read_text(encoding="utf-8").splitlines()
+
+
+def test_every_user_modified_notice_points_at_list_modified():
+    lines = _source_lines()
+    count_sites = [i for i, ln in enumerate(lines) if _COUNT_RE.search(ln)]
+
+    # There are at least two such notices today; the bug was that only one of
+    # them carried the discovery hint. Assert each is followed (within a small
+    # window — the count print + the hint print) by the list-modified pointer.
+    assert len(count_sites) >= 2, (
+        "expected at least two 'user-modified (kept)' notices in main.py; "
+        f"found {len(count_sites)}"
+    )
+
+    for idx in count_sites:
+        window = "\n".join(lines[idx : idx + 5])
+        assert _HINT_RE.search(window), (
+            "a 'user-modified (kept)' notice near line "
+            f"{idx + 1} of main.py does not point users at "
+            "`hermes skills list-modified` within the following lines — the "
+            "two update paths have drifted apart again:\n" + window
+        )