fix(mcp): pass the retain strategy to the worker

[fhiltscher]

Summary

The MCP retain tool accepts a strategy but never delivers it to the worker, so every strategy override is silently ignored and the bank-level configuration is used instead.

build_content_dict puts the strategy into the content item, and the call passes only the contents:

content_dict, error = build_content_dict(content, context, timestamp, tags, metadata, document_id, strategy, update_mode)
...
result = await memory.submit_async_retain(
    bank_id=target_bank,
    contents=[content_dict],
    request_context=request_context,
)

submit_async_retain writes the strategy into the task payload from its own keyword argument only:

if strategy:
    task_payload["strategy"] = strategy

Nothing reads a strategy back out of the content items, so the payload has none, apply_strategy() never runs, and retain_mission, entity_labels, retain_chunk_size and entities_allow_free_form all fall back to the bank config. No error, no warning.

Both async retain registrations are affected. sync_retain, a few lines below, already does it correctly — this PR applies the same idiom:

strategy=content_dict.pop("strategy", None),

api_retain (REST) is unaffected: it groups items by item.strategy and forwards it.

Impact

Measured on a bank whose canonical_document strategy restricts record_type to state, rule, procedure via per-strategy entity_labels, importing the same three documents twice:

Import path	Facts	Types outside the strategy schema
MCP	123	4 (3 analysis, 1 decision)
REST, identical config	61	0

The illegal values are only possible because the bank-level vocabulary was in force — with the strategy's entity_labels applied, build_labels_model() turns them into a Literal[...] that structured output cannot violate.

Worth noting for triage: the dry-run extract endpoint cannot reveal this, because it strips the extracted labels from its response. The defect is only visible in the stored facts, where it looks like model non-compliance rather than lost configuration.

Test

test_retain_passes_strategy_to_the_worker asserts that submit_async_retain receives strategy as a keyword. It fails without the change; the existing TestRetainNewParams cases keep passing. tests/test_mcp_tools.py: 201 passed. ./scripts/hooks/lint.sh passes.