fix(gateway): silence background agent terminal output (#3297)

* fix(gateway): silence flush agent terminal output

quiet_mode=True only suppresses AIAgent init messages.
Tool call output still leaks to the terminal through
_safe_print → _print_fn during session reset/expiry.

Since #2670 injected live memory state into the flush prompt,
the flush agent now reliably calls memory tools — making the
output leak noticeable for the first time.

Set _print_fn to a no-op so the background flush is fully silent.

* test(gateway): add test for flush agent terminal silence + fix dotenv mock

- Add TestFlushAgentSilenced: verifies _print_fn is set to a no-op on
  the flush agent so tool output never leaks to the terminal
- Fix pre-existing test failures: replace patch('run_agent.AIAgent')
  with sys.modules mock to avoid importing run_agent (requires openai)
- Add autouse _mock_dotenv fixture so all tests in this file run
  without the dotenv package installed

* fix(display): route KawaiiSpinner output through print_fn to fully silence flush agent

The previous fix set tmp_agent._print_fn = no-op on the flush agent but
spinner output and quiet-mode cute messages bypassed _print_fn entirely:
- KawaiiSpinner captured sys.stdout at __init__ and wrote directly to it
- quiet-mode tool results used builtin print() instead of _safe_print()

Add optional print_fn parameter to KawaiiSpinner.__init__; _write routes
through it when set. Pass self._print_fn to all spinner construction sites
in run_agent.py and change the quiet-mode cute message print to _safe_print.
The existing gateway fix (tmp_agent._print_fn = lambda) now propagates
correctly through both paths.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(gateway): silence hygiene and compression background agents

Two more background AIAgent instances in the gateway were created with
quiet_mode=True but without _print_fn = no-op, causing tool output to
leak to the terminal:
- _hyg_agent (in-turn hygiene memory agent)
- tmp_agent (_compress_context path)

Apply the same _print_fn no-op pattern used for the flush agent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore(display): remove unused _last_flush_time from KawaiiSpinner

Attribute was set but never read; upstream already removed it.
Leftover from conflict resolution during rebase onto upstream/main.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Dilee <uzmpsk.dilekakbas@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

agent/display.py

@@ -231,7 +231,7 @@ class KawaiiSpinner:
         "analyzing", "computing", "synthesizing", "formulating", "brainstorming",
     ]
 
-    def __init__(self, message: str = "", spinner_type: str = 'dots'):
+    def __init__(self, message: str = "", spinner_type: str = 'dots', print_fn=None):
         self.message = message
         self.spinner_frames = self.SPINNERS.get(spinner_type, self.SPINNERS['dots'])
         self.running = False
@@ -239,12 +239,26 @@ class KawaiiSpinner:
         self.frame_idx = 0
         self.start_time = None
         self.last_line_len = 0
+        # Optional callable to route all output through (e.g. a no-op for silent
+        # background agents).  When set, bypasses self._out entirely so that
+        # agents with _print_fn overridden remain fully silent.
+        self._print_fn = print_fn
         # Capture stdout NOW, before any redirect_stdout(devnull) from
         # child agents can replace sys.stdout with a black hole.
         self._out = sys.stdout
 
     def _write(self, text: str, end: str = '\n', flush: bool = False):
-        """Write to the stdout captured at spinner creation time."""
+        """Write to the stdout captured at spinner creation time.
+
+        If a print_fn was supplied at construction, all output is routed through
+        it instead — allowing callers to silence the spinner with a no-op lambda.
+        """
+        if self._print_fn is not None:
+            try:
+                self._print_fn(text)
+            except Exception:
+                pass
+            return
         try:
             self._out.write(text + end)
             if flush: