fix(memory): port upstream's hindsight contextvars thread wrap (#92608)

Per-provider background threads (writer, daemon-start, prefetch) start
with an EMPTY contextvars Context. Under multiplex_profiles the
spawning thread carries the profile's secret scope + HERMES_HOME
override (gateway/run.py wraps the agent turn in copy_context().run),
and get_secret fails closed without it (#92608). Snapshot the
spawner's context into each thread — the exact fix upstream main
carries, ported on top of this branch's pm-migrated hindsight so the
upstream merge drops those hunks cleanly.

The shared hindsight-loop thread stays unwrapped (coroutines scheduled
via run_coroutine_threadsafe inherit the submitter's context per call).

Verified: tests/plugins/memory shows the same 7 pre-existing Windows-
host failures as the unmodified-tree baseline (symlink privilege,
hindsight_client_api thread fakes, CRLF env bytes) — no new failures
from this port. uv.lock unchanged (extras-platforms is metadata-only;
uv lock --check passes).

plugins/memory/hindsight/__init__.py

@@ -32,6 +32,7 @@ from __future__ import annotations
 
 import asyncio
 import atexit
+import contextvars
 import importlib
 import json
 import logging
@@ -1332,8 +1333,17 @@ class HindsightMemoryProvider(MemoryProvider):
         # If the previous writer exited (e.g. after a prior shutdown), reset
         # the flag so this fresh writer is allowed to drain new jobs.
         self._shutting_down.clear()
+        # Per-provider background threads start with an EMPTY contextvars
+        # Context. Under multiplex_profiles the spawning thread carries the
+        # profile's secret scope + HERMES_HOME override (gateway/run.py wraps
+        # the agent turn in copy_context().run), and get_secret fails closed
+        # without it (#92608). Snapshot the spawner's context into the thread.
+        # (The shared ``hindsight-loop`` thread needs no wrap: coroutines
+        # scheduled via run_coroutine_threadsafe inherit the submitter's
+        # context per call, so one loop can serve every profile.)
         thread = threading.Thread(
-            target=self._writer_loop,
+            target=contextvars.copy_context().run,
+            args=(self._writer_loop,),
             daemon=True,
             name="hindsight-writer",
         )
@@ -1849,7 +1859,12 @@ class HindsightMemoryProvider(MemoryProvider):
                         f.write(f"\n=== Daemon startup failed: {e} ===\n")
                         traceback.print_exc(file=f)
 
-            t = threading.Thread(target=_start_daemon, daemon=True, name="hindsight-daemon-start")
+            t = threading.Thread(
+                target=contextvars.copy_context().run,
+                args=(_start_daemon,),
+                daemon=True,
+                name="hindsight-daemon-start",
+            )
             t.start()
 
     def system_prompt_block(self) -> str:
@@ -2006,7 +2021,12 @@ class HindsightMemoryProvider(MemoryProvider):
                     self._prefetch_result = recalled.text
                     self._prefetch_count = recalled.count
 
-        self._prefetch_thread = threading.Thread(target=_run, daemon=True, name="hindsight-prefetch")
+        self._prefetch_thread = threading.Thread(
+            target=contextvars.copy_context().run,
+            args=(_run,),
+            daemon=True,
+            name="hindsight-prefetch",
+        )
         self._prefetch_thread.start()
 
     def _build_turn_messages(self, user_content: str, assistant_content: str) -> List[Dict[str, str]]: