fix(agent): demote non-coding skill categories to names-only — never hide skills (#44342)

Real-world failure with the original index pruning: under the default auto
posture, an agent-created ops skill in a demoted category vanished from the
prompt's skill index mid-project, and the agent silently fell back to a
stale sibling skill instead. The "discovery-only" premise didn't hold —
models do not reach for skills_list to rediscover what the index stops
showing them, and agent-created skills are the model's accumulated project
memory (runbooks, pitfalls, operating rules).

Gating pruning behind the opt-in focus mode was the wrong fix too: users
opening a worktree don't know the config exists, so the index-noise win
would effectively never ship.

Instead, the coding posture now DEMOTES non-coding categories rather than
hiding them: each demoted category renders as a single names-only line
("gaming [names only]: allthemons10-ops, mc-backup") with a footer note
explaining the omitted descriptions. Every skill name stays in the prompt,
so memory-anchored recall ("load <name>") keeps working in every mode,
while the description noise is still cut. Applies in auto/on/focus alike;
the general posture demotes nothing. Deny-list semantics unchanged —
unknown/custom categories and coding-adjacent ones keep full entries.

API renamed to match the honest semantics: hidden_skill_categories →
compact_skill_categories, build_skills_system_prompt(hidden_categories=) →
compact_categories=.

tests/agent/test_coding_context.py

@@ -368,20 +368,24 @@ class TestProfiles:
         assert cc.GENERAL_PROFILE.toolset is None
         assert cc.GENERAL_PROFILE.guidance == ""
 
-    def test_skill_pruning_scoped_to_coding_posture(self, tmp_path):
-        # Coding posture hides clearly-non-coding categories; coding-adjacent
-        # ones stay visible (deny-list semantics).
+    def test_skill_demotion_scoped_to_coding_posture(self, tmp_path):
+        # Coding posture demotes clearly-non-coding categories to names-only
+        # in the index (never hides them — agent-created skills are the
+        # model's project memory and must stay recallable by name).
+        # Coding-adjacent categories keep full entries (deny-list semantics).
         _git_init(tmp_path)
-        coding = cc.resolve_runtime_mode(platform="cli", cwd=tmp_path, config={})
-        hidden = coding.hidden_skill_categories()
-        assert "social-media" in hidden and "smart-home" in hidden
-        for kept in ("github", "devops", "software-development", "data-science"):
-            assert kept not in hidden
-        # General posture hides nothing.
-        general = cc.resolve_runtime_mode(
-            platform="telegram", cwd=tmp_path, config={}
-        )
-        assert general.hidden_skill_categories() == frozenset()
+        for raw in ("auto", "on", "focus"):
+            mode = cc.resolve_runtime_mode(
+                platform="cli", cwd=tmp_path, config={"agent": {"coding_context": raw}}
+            )
+            assert mode.is_coding is True
+            compact = mode.compact_skill_categories()
+            assert "social-media" in compact and "smart-home" in compact
+            for kept in ("github", "devops", "software-development", "data-science"):
+                assert kept not in compact
+        # General posture demotes nothing.
+        general = cc.resolve_runtime_mode(platform="telegram", cwd=tmp_path, config={})
+        assert general.compact_skill_categories() == frozenset()
 
 
 # ── detection signals ───────────────────────────────────────────────────────

tests/agent/test_prompt_builder.py

@@ -276,8 +276,14 @@ class TestBuildSkillsSystemPrompt:
         # "search" should appear only once per category
         assert result.count("- search") == 1
 
-    def test_hidden_categories_pruned_with_note(self, monkeypatch, tmp_path):
-        """Posture-driven pruning drops whole categories and discloses it."""
+    def test_compact_categories_demoted_to_names_only(self, monkeypatch, tmp_path):
+        """Posture-driven demotion keeps every skill NAME visible.
+
+        Demoted categories lose their descriptions, never their entries —
+        full pruning caused silent capability loss in a real workflow
+        (agent-created skills are the model's project memory, and models
+        don't rediscover them via skills_list once the index goes quiet).
+        """
         monkeypatch.setenv("HERMES_HOME", str(tmp_path))
         for cat, name in (("social-media", "tweet-stuff"), ("github", "pr-review")):
             d = tmp_path / "skills" / cat / name
@@ -287,14 +293,18 @@ class TestBuildSkillsSystemPrompt:
             )
 
         result = build_skills_system_prompt(
-            hidden_categories=frozenset({"social-media"})
+            compact_categories=frozenset({"social-media"})
         )
-        assert "pr-review" in result
-        assert "tweet-stuff" not in result
-        # Disclosure note so the model knows the full catalog exists.
-        assert "skills_list" in result
+        # Coding-adjacent category keeps its full entry.
+        assert "pr-review" in result and "Does pr-review things" in result
+        # Demoted category: name stays visible, description is dropped.
+        assert "tweet-stuff" in result
+        assert "Does tweet-stuff things" not in result
+        assert "social-media [names only]" in result
+        # Disclosure note explains the demotion and how to load.
+        assert "skill_view" in result
 
-    def test_hidden_categories_prune_nested_and_miss_cache_separately(
+    def test_compact_categories_demote_nested_and_miss_cache_separately(
         self, monkeypatch, tmp_path
     ):
         monkeypatch.setenv("HERMES_HOME", str(tmp_path))
@@ -303,14 +313,16 @@ class TestBuildSkillsSystemPrompt:
         (d / "SKILL.md").write_text(
             "---\nname: thread-writer\ndescription: Write threads\n---\n"
         )
-        # Nested category ("social-media/twitter") pruned via its parent.
-        pruned = build_skills_system_prompt(
-            hidden_categories=frozenset({"social-media"})
+        # Nested category ("social-media/twitter") demoted via its parent:
+        # name visible, description gone.
+        compact = build_skills_system_prompt(
+            compact_categories=frozenset({"social-media"})
         )
-        assert "thread-writer" not in pruned
-        # Unfiltered call must not be served from the filtered cache entry.
+        assert "thread-writer" in compact
+        assert "Write threads" not in compact
+        # Unfiltered call must not be served from the compacted cache entry.
         full = build_skills_system_prompt()
-        assert "thread-writer" in full
+        assert "Write threads" in full
 
     def test_excludes_incompatible_platform_skills(self, monkeypatch, tmp_path):
         """Skills with platforms: [macos] should not appear on Linux."""