diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a828c3..c290bac 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@
 
 ---
 
+## [v0.50.13] Fix session_search in WebUI sessions — inject SessionDB into AIAgent (PR #356)
+
+- **`session_search` now works in WebUI sessions** (`api/streaming.py`): The agent's `session_search` tool returned "Session database not available" for all WebUI sessions. The CLI and gateway code paths both initialize a `SessionDB` instance and pass it via `session_db=` to `AIAgent.__init__()`, but the WebUI streaming path was missing this step. `_run_agent_streaming` now initializes `SessionDB()` before constructing the agent and passes it in. A `try/except` wrapper makes the init non-fatal — if `hermes_state` is unavailable (older installs, test environments), a `WARNING` is printed and `session_db=None` is passed instead, preserving the prior behavior gracefully.
+  - 7 new tests in `tests/test_sprint42.py`; 822 tests total (up from 815)
+
 ## [v0.50.12] Profile .env isolation — prevent API key leakage on profile switch (fixes #351)
 
 - **API keys no longer leak between profiles on switch** (`api/profiles.py`): `_reload_dotenv()` now tracks which env vars were loaded from the active profile's `.env` and clears them before loading the next profile. Previously, switching from a profile with `OPENAI_API_KEY=X` to a profile without that key left `X` in `os.environ` for the duration of the process — effectively leaking credentials across the profile boundary. A module-level `_loaded_profile_env_keys: set[str]` tracks loaded keys; it is cleared and repopulated on every `_reload_dotenv()` call.
diff --git a/api/streaming.py b/api/streaming.py
index c080794..620edc9 100644
--- a/api/streaming.py
+++ b/api/streaming.py
@@ -186,6 +186,14 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
             _AIAgent = _get_ai_agent()
             if _AIAgent is None:
                 raise ImportError("AIAgent not available -- check that hermes-agent is on sys.path")
+
+            # Initialize SessionDB so session_search works in WebUI sessions
+            _session_db = None
+            try:
+                from hermes_state import SessionDB
+                _session_db = SessionDB()
+            except Exception as _db_err:
+                print(f"[webui] WARNING: SessionDB init failed — session_search will be unavailable: {_db_err}", flush=True)
             resolved_model, resolved_provider, resolved_base_url = resolve_model_provider(model)
 
             # Resolve API key via Hermes runtime provider (matches gateway behaviour).
@@ -235,6 +243,7 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
                 enabled_toolsets=_toolsets,
                 fallback_model=_fallback_resolved,
                 session_id=session_id,
+                session_db=_session_db,
                 stream_delta_callback=on_token,
                 tool_progress_callback=on_tool,
             )
diff --git a/tests/test_sprint42.py b/tests/test_sprint42.py
new file mode 100644
index 0000000..b618084
--- /dev/null
+++ b/tests/test_sprint42.py
@@ -0,0 +1,107 @@
+"""
+Sprint 42 Tests: SessionDB injection into AIAgent for WebUI sessions (PR #356).
+
+Covers:
+- streaming.py: SessionDB is initialized inside _run_agent_streaming (import present)
+- streaming.py: try/except guards SessionDB init so failures are non-fatal
+- streaming.py: session_db= kwarg is passed to AIAgent constructor
+- streaming.py: SessionDB init failure prints a WARNING (not silently swallowed)
+- streaming.py: SessionDB init is placed before AIAgent construction
+"""
+import ast
+import pathlib
+import re
+import unittest
+
+REPO_ROOT = pathlib.Path(__file__).parent.parent
+STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text()
+
+
+class TestSessionDBInjection(unittest.TestCase):
+    """Verify SessionDB is initialized and passed to AIAgent in streaming.py."""
+
+    def test_hermes_state_import_present(self):
+        """SessionDB must be imported from hermes_state inside _run_agent_streaming."""
+        self.assertIn(
+            "from hermes_state import SessionDB",
+            STREAMING_PY,
+            "SessionDB import missing from streaming.py (PR #356)",
+        )
+
+    def test_session_db_kwarg_passed_to_agent(self):
+        """session_db= must be passed to the AIAgent constructor call."""
+        self.assertIn(
+            "session_db=_session_db",
+            STREAMING_PY,
+            "session_db kwarg not passed to AIAgent (PR #356)",
+        )
+
+    def test_sessiondb_init_in_try_except(self):
+        """SessionDB() init must be wrapped in try/except for non-fatal failure handling."""
+        # Check that the try/except pattern surrounding SessionDB() is present
+        pattern = r"try:\s*\n\s*from hermes_state import SessionDB\s*\n\s*_session_db\s*=\s*SessionDB\(\)"
+        self.assertRegex(
+            STREAMING_PY,
+            pattern,
+            "SessionDB() init must be inside a try block for non-fatal error handling (PR #356)",
+        )
+
+    def test_sessiondb_failure_logs_warning(self):
+        """A failure initializing SessionDB must print a WARNING (not silently drop the error)."""
+        self.assertIn(
+            "WARNING: SessionDB init failed",
+            STREAMING_PY,
+            "SessionDB init failure must log a WARNING message (PR #356)",
+        )
+
+    def test_session_db_initialized_before_agent_construction(self):
+        """SessionDB initialization must appear before the AIAgent(...) constructor call."""
+        db_pos = STREAMING_PY.find("from hermes_state import SessionDB")
+        agent_pos = STREAMING_PY.find("session_db=_session_db")
+        self.assertGreater(
+            agent_pos,
+            db_pos,
+            "SessionDB init must appear before AIAgent construction (PR #356)",
+        )
+
+    def test_session_db_default_is_none(self):
+        """_session_db must be initialized to None before the try block (safe default)."""
+        # Pattern: _session_db = None followed (eventually) by the try/SessionDB block
+        pattern = r"_session_db\s*=\s*None\s*\n\s*try:"
+        self.assertRegex(
+            STREAMING_PY,
+            pattern,
+            "_session_db must default to None before try/except block (PR #356)",
+        )
+
+
+class TestSessionDBAST(unittest.TestCase):
+    """AST-level checks: verify the try/except is not inside _ENV_LOCK (deadlock guard)."""
+
+    def setUp(self):
+        self.tree = ast.parse(STREAMING_PY)
+
+    def test_sessiondb_try_not_inside_env_lock(self):
+        """The try block that wraps SessionDB init must NOT be inside a 'with _ENV_LOCK:' block.
+
+        Putting a try/except inside _ENV_LOCK is the deadlock pattern caught by test_sprint34.
+        The SessionDB try/except is outside the lock scope, which is correct.
+        """
+        # Find all 'with _ENV_LOCK:' nodes; check none of their bodies contain
+        # a Try node that also contains 'from hermes_state import SessionDB'
+        for node in ast.walk(self.tree):
+            if not isinstance(node, ast.With):
+                continue
+            names = [getattr(item.context_expr, "id", "") for item in node.items]
+            if "_ENV_LOCK" not in names:
+                continue
+            # Walk the with-body for Try nodes
+            for stmt in node.body:
+                if isinstance(stmt, ast.Try):
+                    # Check if this try imports hermes_state
+                    src = ast.unparse(stmt)
+                    self.assertNotIn(
+                        "hermes_state",
+                        src,
+                        "SessionDB try/except must NOT be inside _ENV_LOCK body (deadlock risk)",
+                    )