fix(hindsight): make hindsight_retain tool fire-and-forget

[bitfieldz]

What does this PR do?

hindsight_retain was calling client.aretain(), a thin SDK wrapper that hardcodes
retain_async=False. The tool blocks until the server finishes LLM extraction. Under load,
extraction exceeds _DEFAULT_TIMEOUT (120 s); the SDK raises a bare TimeoutError; the tool
returns {"error": "Failed to store memory: "} with an empty exception string.

_do_retain (the auto-retain path) has used aretain_batch(retain_async=True) since
a1b6d9e — the tool just never
got the same treatment. This PR brings them in line: route hindsight_retain through
aretain_batch(retain_async=True), eliminating the timeout coupling entirely. Extraction runs
server-side; results surface via recall once Reflect runs.

Success message changes from "Memory stored successfully." to "Memory queued for storage."
to reflect the queued semantics.

Related Issue

Partially addresses #14950 — resolves the retain case by eliminating the timeout dependency.
The reflect timeout described in that issue is out of scope here.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• plugins/memory/hindsight/__init__.py: replace client.aretain(**retain_kwargs) with
  client.aretain_batch(bank_id=..., items=[retain_kwargs], retain_async=True) in
  handle_tool_call("hindsight_retain"). Update success message.
• tests/plugins/memory/test_hindsight_provider.py: update five TestToolHandlers retain tests
  to assert aretain_batch.call_args.kwargs instead of aretain.call_args.kwargs.

How to Test

1. pytest tests/plugins/memory/test_hindsight_provider.py -q — 96 passed.
2. pytest tests/plugins/ -q — 539 passed. (One pre-existing flake:
   test_achievements_plugin.py::test_evaluate_all_stale_cache_serves_stale_and_refreshes_in_background
   — timing race, reproducible on clean main, unrelated.)
3. Manual: against a slow extraction backend, hindsight_retain returns
   {"result": "Memory queued for storage."} immediately; the operation appears at
   GET /v1/default/banks/<bank>/operations within ~200 ms.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs — no duplicate
• My PR contains only changes related to this fix
• I've run pytest tests/plugins/ -q — 539 passed
• I've added/updated tests for my changes
• I've tested on my platform: macOS 15 (Apple Silicon)

Documentation & Housekeeping

• Docs — N/A
• cli-config.yaml.example — N/A
• CONTRIBUTING.md / AGENTS.md — N/A
• Cross-platform — pure Python async, no platform-specific paths
• Tool schema (content, context, tags) unchanged; success string updated

Screenshots / Logs

Before:

{"error": "Failed to store memory: "}

After:

{"result": "Memory queued for storage."}

[teknium1]

Thanks for identifying the missing call-level retain_async propagation: current main still omits it in the tool path at plugins/memory/hindsight/__init__.py:1715-1724.

Problems

• The patch hard-codes retain_async=True, but retain_async is a documented user setting (plugins/memory/hindsight/README.md:91-100) and the automatic retain path preserves self._retain_async (plugins/memory/hindsight/__init__.py:1664-1686). This would make tool retains asynchronous even when the provider is configured otherwise.
• The new call remains inline. _run_hindsight_operation() calls _run_sync(...).result(...) (plugins/memory/hindsight/__init__.py:1151-1155), so it can still wait for the HTTP acknowledgement. The existing writer queue is the established in-process non-blocking mechanism (plugins/memory/hindsight/__init__.py:1690-1692).

Suggested changes

• Propagate self._retain_async; enqueue through the writer only when it is enabled, and preserve the direct synchronous/error-reporting path when disabled.
• Add tests for queued async behavior and configured synchronous behavior.

Automated hermes-sweeper review.