fix(cli): add missing _log.debug call to session export/import/tell DatabaseError handlers

Add _log.debug("session export failed", exc_info=True),
_log.debug("session import failed", exc_info=True), and
_log.debug("session tell failed", exc_info=True) to the DatabaseError
handlers in export_session, import_session, and tell commands respectively.

This brings these handlers into consistency with the existing create, list,
show, and delete handlers which already include the _log.debug call for
diagnostic tracebacks when --log-level debug is used.

Also adds three new BDD scenarios and step implementations that verify
_log.debug is called in each of the three handlers, ensuring the pattern
is tested and cannot regress.

ISSUES CLOSED: #2788

features/session_cli_coverage_boost.feature

@@ -166,6 +166,11 @@ Feature: Session CLI Coverage Boost
     Then session coverage boost the exit code is 1
     And session coverage boost the output contains "Database unavailable"
 
+  Scenario: export command DatabaseError handler emits debug log
+    Given session coverage boost a mock service that raises DatabaseError on export
+    When session coverage boost I invoke the export command to stdout with log capture
+    Then session coverage boost the debug log "session export failed" was emitted
+
   # ---------------------------------------------------------------
   # import command
   # ---------------------------------------------------------------
@@ -202,6 +207,12 @@ Feature: Session CLI Coverage Boost
     Then session coverage boost the exit code is 1
     And session coverage boost the output contains "Database unavailable"
 
+  Scenario: import command DatabaseError handler emits debug log
+    Given session coverage boost a mock service that raises DatabaseError on import
+    And session coverage boost a temporary import file with valid JSON
+    When session coverage boost I invoke the import command expecting database error with log capture
+    Then session coverage boost the debug log "session import failed" was emitted
+
   # ---------------------------------------------------------------
   # tell command
   # ---------------------------------------------------------------
@@ -236,6 +247,11 @@ Feature: Session CLI Coverage Boost
     Then session coverage boost the exit code is 1
     And session coverage boost the output contains "Database unavailable"
 
+  Scenario: tell command DatabaseError handler emits debug log
+    Given session coverage boost a mock service that raises DatabaseError on append
+    When session coverage boost I invoke the tell command without stream with log capture
+    Then session coverage boost the debug log "session tell failed" was emitted
+
   # ---------------------------------------------------------------
   # show command with long message content truncation
   # ---------------------------------------------------------------

features/steps/session_cli_coverage_boost_steps.py

@@ -643,6 +643,53 @@ def step_tell_db_error(context):
     _patch_service(context, svc)
 
 
+# ---------------------------------------------------------------------------
+# Debug log verification steps (for _log.debug call consistency checks)
+# ---------------------------------------------------------------------------
+
+
+@when("session coverage boost I invoke the export command to stdout with log capture")
+def step_invoke_export_stdout_log_capture(context):
+
+    with patch("cleveragents.cli.commands.session._log") as mock_log:
+        context.result = _runner.invoke(session_app, ["export", _ULID1])
+        context.scvbst_mock_log = mock_log
+
+
+@when(
+    "session coverage boost I invoke the import command expecting database error with log capture"
+)
+def step_invoke_import_db_error_log_capture(context):
+    with patch("cleveragents.cli.commands.session._log") as mock_log:
+        context.result = _runner.invoke(
+            session_app,
+            ["import", "--input", str(context.scvbst_import_path)],
+        )
+        context.scvbst_mock_log = mock_log
+
+
+@when(
+    "session coverage boost I invoke the tell command without stream with log capture"
+)
+def step_invoke_tell_no_stream_log_capture(context):
+    with patch("cleveragents.cli.commands.session._log") as mock_log:
+        context.result = _runner.invoke(
+            session_app,
+            ["tell", "--session", _ULID1, "Hello world"],
+        )
+        context.scvbst_mock_log = mock_log
+
+
+@then('session coverage boost the debug log "{message}" was emitted')
+def step_assert_debug_log_emitted(context, message):
+    mock_log = context.scvbst_mock_log
+    calls = mock_log.debug.call_args_list
+    messages = [str(c.args[0]) if c.args else "" for c in calls]
+    assert any(message in m for m in messages), (
+        f"Expected _log.debug called with '{message}'. Actual debug calls: {calls}"
+    )
+
+
 # ---------------------------------------------------------------------------
 # Shared assertions
 # ---------------------------------------------------------------------------

src/cleveragents/cli/commands/session.py

@@ -622,6 +622,7 @@ def export_session(
         console.print(f"[red]Export error:[/red] {exc}")
         raise typer.Exit(1) from exc
     except DatabaseError as exc:
+        _log.debug("session export failed", exc_info=True)
         console.print(
             f"[red]Error:[/red] Database unavailable: {exc}\n"
             "Hint: run 'agents init' to initialise the database."
@@ -672,6 +673,7 @@ def import_session(
         console.print(f"[red]Import error:[/red] {exc}")
         raise typer.Exit(1) from exc
     except DatabaseError as exc:
+        _log.debug("session import failed", exc_info=True)
         console.print(
             f"[red]Error:[/red] Database unavailable: {exc}\n"
             "Hint: run 'agents init' to initialise the database."
@@ -746,6 +748,7 @@ def tell(
         console.print(f"[red]Session not found:[/red] {session_id}")
         raise typer.Exit(1) from exc
     except DatabaseError as exc:
+        _log.debug("session tell failed", exc_info=True)
         console.print(
             f"[red]Error:[/red] Database unavailable: {exc}\n"
             "Hint: run 'agents init' to initialise the database."