fix: strip leaked declare-x env dump from terminal output on macOS (#15459)

On macOS (bash 3.2 and some Homebrew bash builds) `source`ing a file that
contains `declare -x` statements prints each declaration to stdout. The
persistent-shell wrapper in tools/environments/base.py was only redirecting
stderr when sourcing the session snapshot, so ~60 lines of env vars leaked
into every terminal tool response — blowing out context and triggering
HTTP 400s on context-limited providers.

Fix: redirect both stdout and stderr when sourcing the snapshot. Linux
bash is silent here, so the redirect is harmless there; macOS no longer
leaks.

Closes #15459

Co-authored-by: Sanjays2402 <51058514+Sanjays2402@users.noreply.github.com>

tools/environments/base.py

@@ -386,9 +386,16 @@ class BaseEnvironment(ABC):
 
         parts = []
 
-        # Source snapshot (env vars from previous commands)
+        # Source snapshot (env vars from previous commands).
+        # Redirect stdout to /dev/null: on macOS (bash 3.2 and certain
+        # Homebrew bash builds) sourcing a file containing ``declare -x``
+        # can emit the declarations to stdout, leaking ~60 lines of env
+        # vars into every tool response (issue #15459).  Linux bash is
+        # silent here, but the redirect is harmless.
         if self._snapshot_ready:
-            parts.append(f"source {self._snapshot_path} 2>/dev/null || true")
+            parts.append(
+                f"source {self._snapshot_path} >/dev/null 2>&1 || true"
+            )
 
         # Preserve bare ``~`` expansion, but rewrite ``~/...`` through
         # ``$HOME`` so suffixes with spaces remain a single shell word.

tools/terminal_tool.py

@@ -1851,7 +1851,7 @@ def terminal_tool(
             # Extract output
             output = result.get("output", "")
             returncode = result.get("returncode", 0)
-            
+
             # Add helpful message for sudo failures in messaging context
             output = _handle_sudo_failure(output, env_type)