fix: require authenticated principal for task management tools

[numarasSigmaSoftware]

Closes #1132 (F-03)

Summary

list_tasks, get_task, and complete_task checked identity.tenant but not identity.principal_id. Because the localhost tenant fallback resolves a tenant even for requests with no auth token, the existing guard was silently bypassed — an unauthenticated caller could read task state and advance or complete workflow steps on behalf of any tenant.

Changes

src/core/tools/task_management.py

Added identity.is_authenticated check immediately after the existing tenant check in all three functions, preserving the existing error order: tenant resolution fails first, then authentication, then DB access.
Unauthenticated callers now receive AdCPAuthenticationError before any DB access occurs.
Scope is intentionally limited to these three task-mutating operations. The localhost tenant fallback for read-only tools such as get_products is unchanged.
tests/unit/test_task_management_auth.py (new)

6 rejection cases: unauthenticated callers (no principal_id, no identity) across all three tools.
3 regression cases confirming authenticated callers pass through normally.

Note on architecture compliance

While reviewing the auth fix I noticed a pre-existing violation worth flagging: task_management.py imports Context from fastmcp.server.context at module level and accepts it as a parameter in all three functions. This is the pattern the transport-boundary guards are designed to prevent — business logic functions should accept ResolvedIdentity, not Context.

The structural guard in test_transport_agnostic_impl.py does not catch this because it only scans functions whose names end in _impl. These three functions are named list_tasks, get_task, and complete_task, so the AST sweep never inspects them.

This is not introduced by this PR. I'm not fixing it here to keep the scope of the auth change narrow, but I think it warrants a follow-up issue so it doesn't get lost. The fix would be:

Rename to _list_tasks_impl, _get_task_impl, _complete_task_impl
Remove the context: Context | None parameter from each
Move identity resolution from context into the MCP/A2A wrapper layer, consistent with every other tool in src/core/tools/
Happy to open that issue separately if useful.

[KonstantinMirin]

I think this a great catch regarding the architecture compliance - I suggest adding them ti the structural guard and allowlist and file a follow-up refactoring issue.

[numarasSigmaSoftware]

Thanks! I will do it for sure!

[KonstantinMirin]

Good work. The is_authenticated check is the right fix for the right gap.

One outstanding item: you mentioned you'd file a follow-up issue for the task_management.py architecture refactor (functions accept Context directly instead of using the _impl + transport wrapper pattern). Please file that before we merge so it's tracked. The debt is pre-existing, but we want it in the issue tracker.