fix(agent-framework): report dropped memory injections instead of failing silently

[inahus99]

Stacked on #1415. Both PRs touch _inject_memories, so this branch is built on that one to keep the diffs clean. It therefore shows two commits — please review only b2258f0, the second one. Once #1415 merges this will rebase down to that single commit. Happy to reorder if you'd rather take this one first.

What and why

Follow-up to the two issues noted at the end of #1415. _inject_memories had two paths that discarded memories with no signal at all, so a misbehaving context was indistinguishable from one that simply had no memories to inject.

try:
    if isinstance(messages, list):
        messages.insert(0, Message("system", [wrapped_memories]))
except Exception:
    # If messages is immutable, log a warning
    pass

1. A non-list container was skipped silently. The isinstance check sits inside the try with no else, so any other sequence type fell straight through and the memories were dropped.

2. A failing insert was swallowed. The comment says "log a warning", but the function had no logger in scope, so there was nothing to log through and the body was left as pass.

Demonstrating both against the current code:

t = (Message("user", ["Hello!"]),)
_inject_memories(Ctx(t), "User prefers Python.")
# tuple      -> len still 1 | memories dropped, nothing reported

im = Immutable([Message("user", ["Hello!"])])   # insert() raises
_inject_memories(Ctx(im), "User prefers Python.")
# immutable  -> len still 1 | exception swallowed, nothing reported

In both cases the model is silently answering without the memories it was supposed to have, and there is no way to tell from the logs — with verbose=True the middleware still reports "Memory content preview" just before, so the logs positively suggest injection succeeded.

The change

_inject_memories now takes the middleware's logger and warns on each path — one for a non-list container, carrying the type actually received, and one for an insert that raised, carrying the exception type. Neither re-raises: injection is best-effort and must not fail the chat request. That intent is now stated in the docstring, since it is the reason the exception is caught at all.

The logger is a required argument rather than optional. The function is private with exactly one call site, so there is no compatibility reason to default it, and a default of None would reintroduce the silent path this PR removes.

Tests

Three tests added: a non-list container warns with messages_type, a list whose insert raises warns with the exception type and leaves the messages untouched, and the normal existing-system-message path warns about nothing.

Because the fix changes the signature, these cannot run against the old function — the pre-fix behaviour is the manual reproduction above. Full suite: 58 passing before, 61 after.

Verified against agent-framework-core 1.13.0: mypy clean, black and flake8 report nothing on the changed lines.

No breaking changes; _inject_memories is private and its only caller is updated here.