fix(openviking): add missing /agent/{agent}/ segment to memory URI — fixes #36969

_build_memory_uri produced URIs of the form:
  viking://user/{user}/memories/{subdir}/mem_{slug}.md

The /agent/{agent}/ segment was missing, causing every agent under
the same user to write into the same flat namespace. In multi-agent
deployments agents silently overwrite each other's memories and
vector retrieval cross-pollinates results.

self._agent was already populated correctly (from OPENVIKING_AGENT
env var, default 'hermes') and sent via X-OpenViking-Agent header —
it was simply not interpolated into the URI.

Fix: add the missing segment so URIs follow the documented shape:
  viking://user/{user}/agent/{agent}/memories/{subdir}/mem_{slug}.md

Tests: 4 new regression tests in TestOpenVikingMemoryUriBuilder,
13/13 passed (9 existing + 4 new).

plugins/memory/openviking/__init__.py

@@ -627,9 +627,9 @@ class OpenVikingMemoryProvider(MemoryProvider):
             logger.warning("OpenViking session commit failed: %s", e)
 
     def _build_memory_uri(self, subdir: str) -> str:
-        """Build a viking:// memory URI under the configured user/subdir."""
+        """Build a viking:// memory URI under the configured user/agent/subdir."""
         slug = uuid.uuid4().hex[:12]
-        return f"viking://user/{self._user}/memories/{subdir}/mem_{slug}.md"
+        return f"viking://user/{self._user}/agent/{self._agent}/memories/{subdir}/mem_{slug}.md"
 
     def on_memory_write(
         self,

tests/openviking_plugin/test_openviking.py

@@ -231,3 +231,53 @@ class TestOpenVikingBrowse:
             "/api/v1/fs/ls",
             {"uri": "viking://user/hermes"},
         )]
+
+
+class TestOpenVikingMemoryUriBuilder:
+    """Regression tests for _build_memory_uri — fixes #36969.
+
+    Before the fix the URI omitted /agent/{agent}/, causing all agents
+    under the same user to share the same memory namespace.
+    """
+
+    def _make_provider(self, user="alice", agent="coder"):
+        p = OpenVikingMemoryProvider.__new__(OpenVikingMemoryProvider)
+        p._user = user
+        p._agent = agent
+        return p
+
+    def test_uri_layout_includes_agent_segment(self):
+        """URI must contain /agent/{agent}/ between user and memories."""
+        p = self._make_provider(user="alice", agent="coder")
+        uri = p._build_memory_uri("preferences")
+        assert uri.startswith("viking://user/alice/agent/coder/memories/preferences/mem_")
+        assert uri.endswith(".md")
+
+    def test_uri_uses_configured_agent_not_default(self):
+        """_agent value must be interpolated — not hardcoded to 'hermes'."""
+        p = self._make_provider(user="alice", agent="research-bot")
+        uri = p._build_memory_uri("entities")
+        assert "/agent/research-bot/" in uri
+        assert "/agent/hermes/" not in uri
+
+    def test_uri_slug_is_twelve_hex_chars_and_unique(self):
+        """Slug must be 12 hex chars and differ between calls."""
+        import re
+        p = self._make_provider()
+        uri1 = p._build_memory_uri("preferences")
+        uri2 = p._build_memory_uri("preferences")
+        slug1 = uri1.split("/mem_")[1].replace(".md", "")
+        slug2 = uri2.split("/mem_")[1].replace(".md", "")
+        assert re.fullmatch(r"[0-9a-f]{12}", slug1)
+        assert re.fullmatch(r"[0-9a-f]{12}", slug2)
+        assert slug1 != slug2
+
+    def test_uri_subdir_placed_correctly_for_all_categories(self):
+        """All five category subdirs must appear between memories/ and slug."""
+        p = self._make_provider(user="u", agent="a")
+        subdirs = ["preferences", "entities", "events", "cases", "patterns"]
+        for subdir in subdirs:
+            uri = p._build_memory_uri(subdir)
+            assert f"/memories/{subdir}/mem_" in uri, (
+                f"subdir '{subdir}' not placed correctly in URI: {uri}"
+            )