feat(plugin): Phase 4 — Scribe Processes auto-surface as local skills

#755 Phase 4. Saved Scribe Processes (DRY pass, Drift Audit, …) now surface as
auto-triggered Claude Code skills instead of pull-only get_process calls.

Design correction vs the plan: stubs live in the USER's ~/.claude/skills/, NOT
plugin/skills/_instance/. The plugin is git-cloned and identical per install, so
instance-specific generated files can't ride in it; personal skills are
live-detected within the session (verified via claude-code-guide). MCP prompts
were the alternative but are pull-only (no relevance auto-surface), so skills are
the right primitive.

- backend: GET /api/plugin/processes manifest (services/plugin_context.
  build_process_manifest) — {name, slug, description} per Process; description is
  the auto-surface trigger (title + preview); slugs deduped, blanks skipped.
- plugin: scribe_sync_processes.sh writes ~/.claude/skills/scribe-proc-<slug>/
  SKILL.md (body = "call get_process(name), follow verbatim") and PRUNES stale
  scribe-proc-* stubs. Fail-open + silent; a transient fetch failure never wipes
  existing stubs. Runs as a 2nd SessionStart hook + via the /scribe:sync command.
- plugin.json 0.1.7 → 0.1.8; README updated.
- tests: build_process_manifest (render, slug dedupe, blank-title skip, preview
  truncation). Sync script's write+prune validated in isolation (plugin/** is not
  CI-covered): correct stubs created, stale pruned, unrelated skills untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_services_plugin_context.py

@@ -74,6 +74,57 @@ async def test_build_session_context_unbound_repo_emits_bind_hint():
     assert "## Active project" not in ctx
 
 
+@pytest.mark.asyncio
+async def test_build_process_manifest_renders_stub_specs():
+    items = [
+        {"id": 5, "title": "Drift Audit", "tags": [], "snippet": "Find drifted docs."},
+        {"id": 9, "title": "DRY Pass", "tags": [], "snippet": ""},
+    ]
+    with patch("scribe.services.plugin_context.knowledge_svc.query_knowledge",
+               AsyncMock(return_value=(items, 2))):
+        from scribe.services.plugin_context import build_process_manifest
+        out = await build_process_manifest(user_id=7)
+
+    assert out["total"] == 2
+    drift = out["processes"][0]
+    assert drift["id"] == 5
+    assert drift["name"] == "Drift Audit"
+    assert drift["slug"] == "drift-audit"          # kebab-cased
+    assert "Drift Audit" in drift["description"]   # auto-surface trigger
+    assert "Find drifted docs." in drift["description"]  # preview folded in
+    # No-snippet process still gets a usable description.
+    assert "DRY Pass" in out["processes"][1]["description"]
+
+
+@pytest.mark.asyncio
+async def test_build_process_manifest_dedupes_slugs_and_skips_blank_titles():
+    items = [
+        {"id": 1, "title": "My Process", "tags": [], "snippet": "a"},
+        {"id": 2, "title": "my process", "tags": [], "snippet": "b"},  # same slug
+        {"id": 3, "title": "   ", "tags": [], "snippet": "skip me"},   # blank title
+    ]
+    with patch("scribe.services.plugin_context.knowledge_svc.query_knowledge",
+               AsyncMock(return_value=(items, 3))):
+        from scribe.services.plugin_context import build_process_manifest
+        out = await build_process_manifest(user_id=7)
+
+    slugs = [p["slug"] for p in out["processes"]]
+    assert slugs == ["my-process", "my-process-2"]  # collision suffixed with id
+    assert out["total"] == 2                          # blank-title entry dropped
+
+
+@pytest.mark.asyncio
+async def test_build_process_manifest_truncates_long_preview():
+    items = [{"id": 1, "title": "Big", "tags": [], "snippet": "x" * 500}]
+    with patch("scribe.services.plugin_context.knowledge_svc.query_knowledge",
+               AsyncMock(return_value=(items, 1))):
+        from scribe.services.plugin_context import build_process_manifest
+        out = await build_process_manifest(user_id=7)
+
+    assert "…" in out["processes"][0]["description"]
+    assert "x" * 500 not in out["processes"][0]["description"]
+
+
 @pytest.mark.asyncio
 async def test_build_session_context_caps_length():
     many = [_rule(i, "x" * 200, 1) for i in range(200)]