Allow configurable memory context tag in AgentCoreMemorySessionManager

[notgitika]

Context

In #191 / PR #271, the core issue was fixed: retrieved LTM is now injected before the last user message (instead of after), which resolves the assistant-prefill error on Claude 4.6+ models and improves instruction-following.

However, PR #271 also renamed the <user_context> XML tag to <retrieved_memory>. This tag rename is a breaking change for users who depend on the existing <user_context> tag in their system prompts, parsing logic, or downstream processing. That rename has been reverted to preserve backwards compatibility.

Proposal

Add a configurable context_tag parameter to AgentCoreMemorySessionManager (or AgentCoreMemoryConfig) that lets users customize the XML tag used to wrap retrieved memory context.

• Default value: user_context (preserves backwards compatibility)
• Users who prefer a more semantically accurate tag like retrieved_memory can opt in without breaking existing setups

Example API

config = AgentCoreMemoryConfig(
    memory_id="...",
    session_id="...",
    actor_id="...",
    context_tag="retrieved_memory",  # optional, defaults to "user_context"
)

This approach gives users flexibility without forcing a breaking change.

Related

• Closes the tag-rename portion of Strands session_manager: insert retrieved memory before user msg; rename <user_context> #191 (the core prefill fix from Strands session_manager: insert retrieved memory before user msg; rename <user_context> #191 is already merged via fix: insert retrieved LTM before last user message to avoid prefill error #271)