fix(cli): handle --format color in session delete as Rich output

The delete command's output branch used `fmt == OutputFormat.RICH` which
caused --format color to emit a JSON envelope instead of Rich panels.
Align with all other session commands by checking
`fmt not in (OutputFormat.RICH, OutputFormat.COLOR)` for machine-readable
paths. Add BDD scenario and step for --format color to close the coverage gap.

ISSUES CLOSED: #6457

features/session_cli.feature

@@ -119,6 +119,12 @@ Feature: Session CLI commands
     And the session CLI output should be valid JSON
     And the session CLI JSON envelope message should be "Session deleted"
 
+  Scenario: Delete session with --format color emits Rich output
+    Given there is a mocked session to delete
+    When I run session CLI delete with --yes and --format color
+    Then the session CLI delete should succeed
+    And the session CLI output should contain "deleted"
+
   Scenario: Delete non-existent session
     When I run session CLI delete with a non-existent ID
     Then the session CLI should exit with error

features/steps/session_cli_steps.py

@@ -428,6 +428,13 @@ def step_delete_yes_json(context: Context) -> None:
     )
 
 
+@when("I run session CLI delete with --yes and --format color")
+def step_delete_yes_color(context: Context) -> None:
+    context.result = context.runner.invoke(
+        session_app, ["delete", context.session_id, "--yes", "--format", "color"]
+    )
+
+
 @when("I run session CLI delete with a non-existent ID")
 def step_delete_nonexistent(context: Context) -> None:
     context.mock_service.get.side_effect = SessionNotFoundError("Session not found")

src/cleveragents/cli/commands/session.py

@@ -717,9 +717,21 @@ def delete(
 
         service.delete(session_id)
 
-        # Rich output: render Deletion Summary and Cleanup panels
-        if fmt == OutputFormat.RICH:
-            # Deletion Summary panel
+        if fmt not in (OutputFormat.RICH, OutputFormat.COLOR):
+            # Machine-readable formats: emit a structured JSON/YAML envelope per spec
+            # (docs/specification.md §"agents session delete" line ~1959)
+            typer.echo(
+                format_output(
+                    {"session_id": session_id},
+                    fmt.value,
+                    command=_command_label(
+                        "delete", session_id, "--yes", "--format", fmt.value
+                    ),
+                    messages=[{"level": "ok", "text": "Session deleted"}],
+                )
+            )
+        else:
+            # Rich/Color output: render Deletion Summary and Cleanup panels
             summary_table = Table.grid(padding=(0, 1))
             summary_table.add_column(style="cyan bold", justify="left")
             summary_table.add_column(style="white", justify="left")
@@ -746,19 +758,6 @@ def delete(
             console.print(Panel(cleanup_table, title="Cleanup", border_style="blue"))
             console.print()
             console.print("[green]✓ OK[/green] Session deleted")
-        else:
-            # Non-rich formats: emit a structured JSON/YAML envelope per spec
-            # (docs/specification.md §"agents session delete" line ~1959)
-            typer.echo(
-                format_output(
-                    {"session_id": session_id},
-                    fmt.value,
-                    command=_command_label(
-                        "delete", session_id, "--yes", "--format", fmt.value
-                    ),
-                    messages=[{"level": "ok", "text": "Session deleted"}],
-                )
-            )
 
     except SessionNotFoundError as exc:
         console.print(f"[red]Session not found:[/red] {session_id}")